Northern White-Cedar
Suggested Citation:
Villemaire-Côté, Olivier; Kenefic, Laura S.; Michigiizhigookwe Clark, Robin; Allogio, Jeanette; Capolla, Béatrice; Ruel, Jean-Claude. 2026. Northern white-cedar (Thuja occidentalis). In: McNulty, Steven; Callaham, Mac A., Jr., project co-leads. Silvics of North America. U.S. Department of Agriculture, Forest Service; Natural Resources Canada, Canadian Forest Service; National Forestry Commission of Mexico, collaborators. Washington, DC: U.S. Department of Agriculture, Forest Service. https://doi.org/10.2737/sna.thuja.occidentalis.
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| Distribution and Environmental Associations |
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| Regeneration and Management |
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| Genetics |
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| Insects and Diseases |
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| Wildland Fire |
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- Steven McNulty, Project Lead (USDA Forest Service)
- Mac A. Callaham, Jr., Program Manager (USDA Forest Service)
- Rachel Cook, Principal Investigator (North Carolina State University)
- Emma Gates, U.S. Project Coordinator (Three Vowels, LLC)
- Sébastien Meunier, Canada Project Coordinator (Canadian Forest Service)
- Cynthia F. Moser, Managing Editor (Three Vowels, LLC)
- Michael Gavazzi, Content Coordinator (U.S. Forest Service)
- Brody Hall, Business Administrator (North Carolina State University)
Northern white-cedar (Thuja occidentalis) is a long-lived, medium-sized, shade-tolerant evergreen tree that grows in mixed and pure stands in the northern United States and southern Canada, from the Great Lakes to the Atlantic coast. It has scale-like foliage in flat sprays and outer bark of thin, brown vertical strips (figs. 1, 2). A poor competitor, northern white-cedar is often a minor species in mixed stands but abundant in swamps and seeps and on cliffs and abandoned pastureland. Growth can be rapid in full light on uplands (Villemaire-Côté et al., 2017) but is typically slow, with trees originating as advance regeneration and experiencing multiple releases (Fraver et al., 2020; Ruel et al., 2014). Regeneration occurs sexually from seeds and asexually from layers. Seed germination and survival are best on moisture-holding substrates including mineral soil and decayed deadwood (Cornett et al., 2000a; Larouche et al., 2011). Though tolerant of periodic high water, northern white-cedar cannot withstand prolonged inundation (Chimner and Hart, 1996; Schulz et al., 2024) and tends to grow on elevated microsites in swamps (Allogio et al., 2021; Chimner and Hart, 1996).
Natural disturbances in northern white-cedar forests are primarily small scale and trees can live over 400 (infrequently 1,000) years (Larson and Kelly, 1991). Trees have sectored architecture (linkages between specific roots and branches) that allows them to persist with damage or decay, for example, following mortality of portions of the root system and connected aerial parts (Larson et al., 1994). Though decay prone when living, the wood is decay resistant after death (Bouslimi et al., 2013). Trees are valuable for wildlife, providing cavities, snags, bark for nesting material, dense canopies for protection from deep snow (e.g., deer wintering areas), and vitamin-rich foliage. Heavy browsing by white-tailed deer (Odocoileus virginianus) and snowshoe hares (Lepus americanus) has led to widespread recruitment failures (Aldous, 1952; Patton et al., 2021).
Northern white-cedar trees are sacred and elder relatives to many Indigenous peoples who use them in ceremonies and for items like canoes and textiles (Clark et al., 2022). The name arborvitae (tree of life) was given by Europeans after Indigenous people taught them its medicinal properties (Durzan, 2009). Since European colonial settlement, the wood has been commonly used for shingles, fenceposts, and other items requiring rot resistance. The trees tend to have long, dense crowns when open grown and are planted for windbreaks and snow fences in agriculture and privacy screens and ornamentals in urban-suburban settings.
Figure 1—(A) Northern white-cedar tree. U.S. Forest Service photo by Laura Kenefic. (B) Northern white-cedar foliage and cones. Courtesy photo by Victoria Hunter.
Distribution
The current distribution of northern white-cedar extends from the Atlantic coast in Nova Scotia and Maine to Manitoba and Minnesota in the Great Lakes region (fig. 3). The southern edge of its contiguous range crosses central New York and central Michigan, with isolated populations along the Appalachian Mountains as far south as North Carolina. The boundaries of northern white-cedar’s range have been attributed to fire in the north and west (Greller, 2000; Heinrichs, 2009; Jules et al., 2018; Rayfield et al., 2020), agriculture and urban development in the west and south (Radeloff et al., 2005; Rhemtulla et al., 2009; Zenner and Almendinger, 2012), and high temperatures in the south (Kincaid, 2017). In Michigan, some peatlands originated as long as 8,500 years ago and appear to have been continuously occupied by northern white-cedar since that time (Ott and Chimner, 2016). Within this range, abundance of northern white-cedar has been greatly reduced since before European colonial settlement, with declines in both northern white-cedar forest land area and amount of northern white-cedar in mixed-species stands (Danneyrolles et al., 2017; Zenner and Almendinger, 2012). These changes in abundance have been attributed to land clearing for agriculture and development, preferential browsing by white-tailed deer and snowshoe hares, and unintended forest-type conversion after harvesting (Clark et al., 2024; Cornett et al., 2000b; Danneyrolles et al., 2017).
Northern white-cedar is widely planted as an ornamental in urban-suburban settings, for privacy screens, and as windbreaks and snow fences in agricultural landscapes in North America, Europe, and Asia (Storm and Kenefic, 2022). There are numerous cultivars suitable for planting far outside the native range of the species (Kenefic et al., in press).
Figure 3—Modeled distribution and habitat quality for northern white-cedar under current climate conditions. U.S. Forest Service cartography by Matthew P. Peters
As temperatures continue to rise and the timing, intensity, and patterns of precipitation change, declines in suitable northern white-cedar habitat are projected along the central and southern boundary of its range by the end of the century (fig. 4) (Handler et al., 2014a; Handler et al., 2014b; Janowiak et al., 2014; Janowiak et al., 2018), with disjunct populations in the Appalachian Mountains susceptible to extirpation (Kincaid, 2016). Suitable habitat is projected to shift north and west into boreal Canada (Prasad et al., 2020a; Prasad et al., 2020b). Much of this habitat is predicted to be low to medium quality, with limited potential for unassisted migration (Prasad et al., 2024) (fig. 5). In the far north, northern white-cedar populations are limited more by precipitation and fire than by cold; these effects could be exacerbated by changing environmental conditions (Housset et al., 2015; Paul et al., 2014; Rayfield et al., 2020). However, northern white-cedar peatlands have been documented as stable systems, persisting through close to 2,000 to more than 8,500 years of change, likely aided by the longevity of northern white-cedar trees and their ability to regenerate asexually through layering (Ott and Chimner, 2016). Similarly, research suggests that marginal populations of northern white-cedar along the northern extent of their range may be maintained through layering of existing trees where sexual regeneration is limited (Paul et al., 2014).
Figure 4—Maps showing future habitat suitability for northern white-cedar projected under (A) a moderate emissions scenario and (B) a high emissions scenario. U.S. Forest Service cartography by Matthew P. Peters.
Figure 5—Maps showing migration potential for northern white-cedar projected under (A) a moderate emissions scenario and (B) a high emissions scenario. U.S. Forest Service cartography by Matthew P. Peters.
Environmental Associations
Average annual temperatures across the contiguous range of northern white-cedar have been reported to span from about 10 °C (50 °F) at the southern boundary in the Lake States to 4 °C (39 °F) at the northern boundary in Quebec (Johnston, 1990; Paul et al., 2014); modeled current minimum mean is 0.1 °C (32 °F) (table 1). In marginal populations in Manitoba, average annual temperatures can be as low as 1 °C (34 °F) (Grotte et al., 2012), and up to 16 °C (61 °F) in discontinuous populations in the southern Appalachians (Johnston, 1990).
Precipitation throughout most of northern white-cedar’s range is typically 760 to 1030 mm year -1 (30 to 40 inches year -1) (table 1) with a general trend of higher precipitation totals in the south and lower totals in the north (Johnston, 1990). Average annual precipitation in the northern range limits can be 400 mm (16 inches) or less (Grotte et al., 2012), while the southern Appalachians can have over 1580 mm year-1 (62 inches year-1) (table 1).
Northern white-cedar is a temperate and boreal forest species that grows in the Northern Forest and Eastern Temperate Forest ecological regions. Marginal populations at the northern limit of the range are located in the Hudson Plain ecological region (U.S. Environmental Protection Agency, 2024). Elevation ranges from near sea level to more than 300 m (1,000 feet) at the eastern edge of the species’ range and from about 300 to 600 m (1,000 to 2,000 feet) in parts of New England; average elevation is 300 m (1,000 feet) in the Lake States (Grotte, 2007; Johnston and Booker, 1983).
Under both moderate and high emissions scenarios, mean annual temperature and precipitation are generally expected to increase in northern white-cedar’s range (table 1). With few exceptions, mean annual temperature is predicted to increase by about 1 to 2 °C (2 to 3 °F) and mean annual precipitation by less than 100 mm (4 inches). Maximum mean annual precipitation, however, is predicted to increase far more: from 1580 mm (62 inches) to 2900 and 5990 mm (114 and 240 inches) under moderate and high emissions scenarios, respectively. Minimum elevation in northern white-cedar’s modeled range could decrease slightly from 20 m (50 feet) to 10 m (40 feet) under both emissions scenarios. Maximum elevation, however, could increase more than threefold, from 860 m (2,830 feet) to 2970 m (9,740 feet) and 3030 m (9,950 feet) under moderate and high emissions scenarios, respectively.
Table 1—Temperature, precipitation, and elevation ranges for northern white-cedar in North America modeled for 1991–2020 and two future climate scenarios for 2070–2099
Summary statistics (current modeled, 1991–2020) | Mean annual temperature in °C (°F) | Mean annual precipitation in millimeters (inches) | Elevation in meters (feet) |
Minimum | 0.1 (32) | 400 (16) | 20 (50) |
Lower 25 percent | 2.5 (37) | 760 (30) | 230 (760) |
Median | 4.0 (39) | 880 (34) | 320 (1,050) |
Mean | 4.1 (39) | 890 (35) | 310 (1,020) |
Upper 25 percent | 5.6 (42) | 1030 (40) | 390 (1,290) |
Maximum | 10.0 (50) | 1580 (62) | 860 (2,830) |
Summary statistics under a moderate emissions scenario (2070–2099) | Mean annual temperature in °C (°F) | Mean annual precipitation in millimeters (inches) | Elevation in meters (feet) |
Minimum | 0.3 (33) | 430 (17) | 10 (40) |
Lower 25 percent | 3.8 (39) | 830 (32) | 260 (860) |
Median | 5.1 (41) | 940 (37) | 360 (1,160) |
Mean | 5.3 (41) | 960 (38) | 440 (1,450) |
Upper 25 percent | 6.6 (44) | 1100 (48) | 440 (1,450) |
Maximum | 11.4 (53) | 2900 (114) | 2970 (9,740) |
Summary statistics under a high emissions scenario (2070–2099) | Mean annual temperature in °C (°F) | Mean annual precipitation in millimeters (inches) | Elevation in meters (feet) |
Minimum | -0.6 (31) | 480 (19) | 10 (40) |
Lower 25 percent | 4.1 (39) | 840 (33) | 280 (930) |
Median | 5.7 (42) | 980 (38) | 380 (1,260) |
Mean | 5.6 (42) | 990 (39) | 470 (1,540) |
Upper 25 percent | 7.2 (45) | 1130 (44) | 500 (1,640) |
Maximum | 12.4 (54) | 5990 (240) | 3030 (9,950) |
Northern white-cedar grows on a wide range of soils that provide reliable moisture, including moderately decomposed to well-decomposed organic soils on lowlands, mineral soils over glacial till or bedrock on uplands, and pockets of duff in crevices on cliffs and bluffs (Storm and Kenefic, 2022) (fig. 6). Soils tend to be cool and moist with drainage ranging from very poor to well drained, though survival and growth are better where nutrient-rich ground water flows below or rises to the surface (Heinselman, 1963). Northern white-cedar trees can tolerate high levels of soil calcium, giving them a competitive advantage on calcareous escarpments and other calcium-rich sites; the species grows fastest on well-drained, calcium-rich mineral soils of limestone origin (Villemaire-Côté et al., 2017; but see Hofmeyer et al., 2009). However, northern white-cedar tends to be more abundant on poorly drained organic soils (Johnston and Booker, 1983) because of site-related differences in competition (Johnston, 1980), fire frequency (Heinselman, 1973), and land use history (Boucher et al., 2006; Dupuis et al., 2011).
On lowlands, northern white-cedar is common in rich conifer swamps (forested wetlands, fens) (Kost et al., 2007) and peat ridges in bog and fen complexes (Heinselman, 1970). These sites typically have moderately decomposed to well-decomposed and mostly woody organic material (peat), usually ranging in depth from 0.3 to 1.8 m (1.0 to 6.0 feet) (Heinselman, 1963), though ranges from 0.4 to 3.25 m (1.3 to 10.7 feet) have also been reported (Ott and Chimner, 2016). Peat depth rarely exceeds 2 m (6.6 feet) or, exceptionally, 7.3 m (24 feet) (Heinselman, 1963). On uplands, northern white-cedar is common on abandoned pasturelands, limestone and dolostone cliffs, and sandstone bluffs. Soils there tend to be moist and well drained (Curtis, 1944) but otherwise highly variable, including calcareous clay (Curtis, 1946), shallow loam over limestone bedrock (Nelson, 1951), and thin sandy to loamy organic soil over glacial deposits (Kost et al., 2007). Northern white-cedar is also common on gentle lower slopes in the transition zone between uplands and lowlands (Gawlor and Cutko, 2010).
Though soil pH in stands with northern white-cedar can be as low as 4.2 (Habeck, 1958), this species is less abundant and grows poorly on acidic soils (Conway, 1949; Heinselman, 1963). Soils supporting northern white-cedar generally have pH values ranging from somewhat acidic to slightly alkaline. Published reports from various sites show soils supporting northern white-cedar with pH of 4.6 to 7.4, with pH trending higher in upland sites (Conway, 1949; Curtis, 1946; Habeck, 1958; Petraborg, 1969; Reuling et al., 2019).
Figure 6—(A) Northern white-cedar on a rocky summit. U.S. Forest Service photo by Laura Kenefic. (B) Organic soils in a lowland stand of northern white-cedar. Courtesy photo by Olivier Villemaire-Côté.
Sexual Reproduction
Northern white-cedar trees are monoecious and wind pollinated (Caulkins, 1967). Male (staminate) and female (pistillate) flowers (strobili) are borne on separate twigs or branchlets (Martin, 1950). Male flowers are reddish and located near the base of the shoot; female flowers are green or purple-tinged and located on short terminal branches (USDA Forest Service, 1948). Fertilized cones change from green to light brown as they ripen; they are oblong in shape and 8 to 15 mm (0.3 to 0.6 inch) long (Brand and Schopmeyer, 2008; Martin, 1950). Each cone has four or five pairs of scales, of which the middle two or three pairs are fertile; each fertile scale contains two seeds (Briand et al., 1992a).
Flower buds form in the fall, expand from mid- or late April to early May the following spring, and disperse pollen from late April to early June in the Great Lakes region and northern New England (Ahlgren, 1957; Nelson, 1951). Pollinated conelets (immature cones) begin growing rapidly in late June; ovulate (seed) cones are fully grown by mid-August, ripen from August to September, and open in mid-September to late October (Godman, 1958; Johnston, 1990). The time between cone ripening and opening is 7 to 10 days (USDA Forest Service, 1948). Northern white-cedar can begin producing cones in as few as 6 years under normal conditions (Curtis, 1946), though gibberellic acid and a long photoperiod have been used to induce cone production within 3 months of germination in nursery settings (Fraser, 1971).
Shoot and radial growth of seedlings generally lasts from May to August or September (Ahlgren, 1957; Johnston, 1990). Northern white-cedar has indeterminate growth for its main stem and first-order branches (Briand et al., 1992b).
Northern white-cedar seeds are brown and 4.5 to 6.5 mm (0.18 to 0.25 inch) long, with lateral wings nearly as wide as the embryo (Briand et al., 1992a). Production of large quantities of seed can begin at less than 10 years of age (Curtis, 1944) but typically begins after 20 to 30 years and peaks after 75 years (Grenier, 1995; Rudolf, 1949; Schaffer, 1996). An average-sized tree can produce about 9 L (0.25 bushel) of cones (Maki, 1931), yielding 42,500 to 142,000 cleaned seeds (Caulkins, 1967; Heit and Eliason, 1940; Watson, 1936). Cleaned seeds average 716,500 to 893,500·kg-1 (325,000 to 405,200·pound-1) (Heit and Eliason, 1940; Toumey and Stevens, 1928). The proportion of empty seeds can be high (Heit and Eliason, 1940; Schopmeyer, 1974), though researchers found that 86 percent from saplings less than 20 years old on cliff and swamp sites appeared fully developed (Briand et al., 1992a). Data from Michigan suggest that larger seed crops with greater proportions of full seeds are produced by northern white-cedar trees in mesic forests compared to those in swamps (Caulkins, 1967); however, that finding is inconsistent with an Ontario study that found similar seed crops from trees on cliffs and swamps, though differences in number of seeds per cone were observed among trees within sites (Briand et al., 1992a).
Northern white-cedar trees tend to produce good or better seed crops at intervals of 3 to 5 years (Grenier, 1995), though deviations from this pattern have been observed. For example, good or better crops were produced every 1 to 3 years over a 26-year period (1949 to 1974) in Wisconsin, with medium crops or failures in intervening years (Godman and Mattson, 1976). Reports suggest that good or better northern white-cedar seed crops can be predicted by similar-sized red maple (Acer rubrum) seed crops the preceding spring (Godman and Mattson, 1976). The number of northern white-cedar cone buds in the dormant season is also predictive, as a low number of buds indicates that a poor cone crop will follow in the fall (Brand and Schopmeyer, 2008).
Seed dispersal can begin as early as August but more commonly begins in September, with most seeds released by November (Ahlgren, 1957; Godman, 1958; Schopmeyer, 1974). Seeds are primarily wind disseminated (Nelson, 1951). Seeds have been observed traveling 60 m (200 feet) from parent trees (Asselin et al., 2001), though stand density and tree height affect seeding distance. Dispersal leading to adequate stocking is generally found within 12 to 15 m (40 to 50 feet) of parent trees (Nelson, 1951). Northern white-cedar is also known to naturally shed branchlets (cladoptosis) that may be seed bearing (Briand et al., 1992b). Numerous authors have reported that red squirrels (Sciurus vulgaris) clip branchlets with cones (Curtis, 1946; Klugh, 1927; Nelson, 1951), thus potentially contributing to dispersal. Northern white-cedar has no soil seedbank (Caulkins, 1967; Frank and Safford, 1970).
Extreme variation in northern white-cedar seed viability and quality has been reported, but research suggests an average germination rate of 42 percent for unstratified seed lots (Heit and Eliason, 1940). Stratification is shown to enhance germination rate, though several methods are described in the literature: 5 °C (41 °F) for 60 days in a moist medium (Barton, 1930), 0 to 10 °C (32 to 50 °F) (USDA Forest Service, 1948) or 1 to 5 °C (34 to 41 °F) for 30 to 60 days (Schopmeyer, 1974), and soaking for 24 to 48 hours and stratification at 2 °C (36 °F) for 7 to 60 days (Brand and Schopmeyer, 2008). Commercial seed lots have been reported to have germinability of 72 percent (Larouche et al., 2011), and cold-stored seed lots can have a germination rate of 80 percent when well-filled, healthy-appearing seeds are selected (Nelson, 1951). In comparison, field-run seeds are reported to have germinability ranging from 4 percent (Nelson, 1951) to 80 percent (Curtis, 1944). In-field seeding of 250 seeds m-2 (23.2·foot-2) on upland cedar stands led to an increase of 0.5 seedling m-2 (0.05·foot-2) after 1 to 2 years (Larouche et al., 2011). Seedling density was higher under partially open canopy than closed canopies or 25-m (82-foot) gaps (Larouche et al., 2011).
Northern white-cedar seeds remain viable on the forest floor for only up to 1 year (Caulkins, 1967; Frank and Safford, 1970). Those stored in sealed containers at about 2 to 4 °C (36 to 39 °F) with no more than 5 to 8 percent moisture content can last 5 years without losing viability (Grenier, 1995; Heit and Eliason, 1940). Northern white-cedar is commonly stored in seedbanks, including the National Seed Tree Center (Canada), the National Laboratory for Genetic Resource Preservation (United States), and the Province of Quebec.
Seed germination normally begins in May or June—but can occur in late July or early August—in the year following dispersal. Laboratory experiments determined that the lower threshold for northern white-cedar seed germination is between 14 and 18 °C (57 and 64 °F), with germination rates peaking in a laboratory setting at 24 to 26 °C (75 to 78 °F) (Nelson, 1951). Limited data from Michigan swamps demonstrate that mean substrate temperatures during the germination season of June and July range from 10 to 16 °C (50 to 60 °F), with deadwood substrates 13.1 to 15.6 °C (55.5 to 60.3 °F) and forest floor substrates 11.5 to 13.9 °C (52.7 to 57.7 °F) (Nelson, 1951). Germination is epigeal, with cotyledons rising above the ground (Johnston, 1990).
Northern white-cedar is small-seeded (Heit and Eliason, 1940), and new germinants have limited resources and are slow growing with shallow roots (Curtis, 1944; Curtis, 1946; Maki, 1931). Though northern white-cedar exhibits plasticity in rooting habit (Matthes-Sears and Larson, 1995), the few taproots that seedlings form in better aerated, upland soils are temporary and shed within a few years (Curtis, 1946). Roots are therefore primarily lateral. Seeds can germinate on a range of substrates, though seedbeds of highly decayed logs and stumps are favorable and thick or slow-decomposing litter is unfavorable (Cornett et al., 1997; Curtis, 1959; Holcombe, 1976; Scott and Murphy, 1987) (fig. 7C). Compared to other potential seedbeds, decayed wood tends to have more consistent moisture and higher temperatures associated with higher rates of northern white-cedar seedling establishment (Caulkins, 1967). Decayed wood substrates also accumulate less litter than other substrates and are easier for roots to penetrate (Cornett et al., 1997; Cornett et al., 2000b).
Mounds (often composed of buried deadwood) are preferred microtopographic positions, primarily on lowland sites but also on upland sites (Allogio et al., 2021; Kangas et al., 2016; Saucier et al., 2018). On lowland sites, mounds provide elevated safe sites in areas with a high water table (fig. 7A); on uplands, the primary benefit of mounds is likely reduced litter accumulation (Saucier et al., 2018). Both seedling density and growth are positively correlated with pH within an acidic to slightly alkaline range (Kell, 2009; Nelson, 1951; Reuling et al., 2019); seedling abundance is reportedly greatest where the upper 10 cm (4 inches) of soil has a pH of 6.6 to 7.2 (Petraborg, 1969).
Seedling establishment also occurs on exposed mineral soil (Larouche et al., 2011). Northern white-cedar seedlings establish well where passive scarification by harvesting equipment exposes mineral soil or deadwood (Larouche et al., 2011; Saucier et al., 2018). Seedling establishment on exposed mineral soil can be double that on an undisturbed forest floor (Larouche et al., 2011). A heavy cover of slash hinders seedling establishment, but a light cover providing low shade and protection from browsing can be favorable (Verme and Johnston, 1986). Though fire is fatal for northern white-cedar seedlings (Bergeron and Dubuc, 1989; Frelich and Reich, 1995), establishment can be prolific in the absence of competing vegetation following burning under certain conditions. Extensive regeneration can occur if seeds from trees in adjacent stands, or from residual trees in wet areas within burned stands, fall on favorable microsites, such as shaded microsites where fires were severe enough to expose mesic mineral soil on cool slopes (Apfelbaum et al., 2017) or to improve seedbed in swamps (Verme and Johnston, 1986). Where precipitation is limited, exposed mineral soil may not retain sufficient water for northern white-cedar germinants to survive (Cornett et al., 2000b).
Mortality of northern white-cedar seedlings can be extremely high, with studies showing mortality rates of up to 96 percent in the first 3 years (Scott and Murphy, 1987). Small northern white-cedar seedlings have low root-to-shoot ratios (Bender et al., 1987) and low drought tolerance (Cornett et al., 2000b; Larouche et al., 2011). Drought and desiccation are thought to be the most common causes of new germinant mortality, particularly on upland (mesic) sites (Cornett et al., 2000b; Larouche et al., 2011).This can occur on lowlands in harvest gaps if increased sunlight reaching the forest floor dries the rooting substrate, causing mortality of small seedlings (Hunter, 2025; Maki, 1931). Once established, seedlings have intermediate tolerance to drought (Schulz et al., 2024). Established seedlings also have intermediate tolerance to flooding. Greenhouse experiments with large northern white-cedar seedlings (averaging 80 cm [31 inches] tall) found that prolonged flooding reduced growth (after 31 days) and caused foliage browning (25 percent of foliage affected after 21 days) but that seedlings could recuperate.
Smothering by sphagnum moss or logging slash, cutting or girdling by small mammals such as snowshoe hares and red-backed voles (Myodes rutilus), and browsing by white-tailed deer also account for considerable seedling mortality (Cornett et al., 2000a; Curtis, 1946; Heitzman et al., 1997; Larouche and Ruel, 2015; Verme and Johnston, 1986; Villemaire-Côté et al., 2017). Browsing impacts are often apparent on seedlings and saplings 0.3 to 3 m tall (Villemaire-Côté et al., 2017). Small seedlings (less than 30 cm [1 foot]) are also affected, but impact can be difficult to determine if they are completely consumed and therefore overlooked in browsing surveys (Reuling et al., 2019; Villemaire-Côté et al., 2022).
Asexual Reproduction
Vegetative reproduction of northern white-cedar can occur naturally through layering or through clonal propagation in laboratory, greenhouse, and field environments. Layers naturally form when low-hanging branches, branches of windthrown trees, or branches and stems of seedlings and saplings weighed down by snow and ice contact the forest floor and form roots from adventitious buds (fig. 7B). Over time, the connecting tissue between newly rooted and originating stems may decay, separating the layer from its parent tree (Wason, 2022).
Methods for clonal propagation with cuttings and tissue culture have been developed for ornamental cultivars due to their importance in urban-suburban landscapes worldwide (e.g., Szasz Len et al., 2015). Cuttings are a common means of vegetative propagation, while in vitro techniques can produce hundreds of individuals per embryo (Harry et al., 1987) with axillary bud development utilizing growth hormones (Nour et al., 1993). Tissues in some cultivars are most generative when taken near the end of the growing season (Zontikov et al., 2016). Fungal and pest infections are common issues in clonal reproduction, requiring the use of sterilization techniques and attention to growing mediums (Nour and Thorpe, 1993). While there have been some reports of branch cuttings rooting after being buried in moss on the forest floor (Curtis, 1946; Harlow, 1928), this is uncommon.
Layering can happen repeatedly on a single parent tree and its layers, resulting in a dozen or more new individuals that can survive independently (Kenefic et al., 2020; Wason, 2022). Seedlings can reportedly produce layers as early as 5 years old (Nelson, 1951). Most northern white-cedar reproduction in swamps is believed to be from layers (Caulkins, 1967; Curtis, 1946; Nelson, 1951; Scott and Murphy, 1987). Layering is also common in old-growth stands (Apfelbaum et al., 2017) and those at the northern margins of the species’ range (Paul et al., 2014). Layers cannot be reliably identified in the field unless connected to their parent tree (sometimes discernable by excavating portions of the stem below the surface). Lowland sites where germinants struggle to compete with fast-growing sphagnum and a dense herbaceous community may favor regeneration by layering (Maki, 1931). Furthermore, layering in the forest is more likely to occur when stems and branches are resting in moss than on decayed deadwood or exposed organic soil substrates (Curtis, 1946; Nelson, 1951).
Compared to seedlings, layers have a slightly greater photosynthetic acclimation capacity, leading to greater resilience to changes in light levels associated with disturbance, though the effect may not last long after establishment (Man et al., 2013). Such differences likely disappear over time, notably as the link between layers and parent tree decays. Field observations suggest that layers are more shade tolerant than seedlings (Curtis, 1946), but this is likely due to layers having higher survival rates because of their more developed root systems rather than actual differences in shade tolerance (Man et al., 2013).
Figure 7—(A) Pit and mound microtopography in northern white-cedar swamps providing safe sites for regeneration above the high water table. U.S. Forest Service photo by Laura Kenefic. (B) Layers formed when a northern white-cedar sapling rooted in a moss-covered forest floor (note that the aboveground portions of layers often look the same as seed-origin stems). U.S. Forest Service photo by Laura Kenefic. (C) Northern white-cedar growing on decayed deadwood, an important regeneration substrate for the species (note that newly germinated northern white-cedar seedlings like those shown here do not develop characteristic scale-like foliage for the first few years). Courtesy photo by Olivier Villemaire-Côté.
Northern white-cedar is found in pure and mixed stands across its range, with distinct habitat types that vary by region. Habitat and related forest cover typing systems identify potential tree species composition based on soils, topography, and hydrology. In the Lake States and New England, northern white-cedar forms the majority of stocking in the northern white-cedar forest type (Society of American Foresters Type 37) (Johnston, 1980). It is an associated species in the following forest types (forest type number in parentheses): balsam fir (5), black spruce (12), black spruce-tamarack (13), eastern white pine (21), eastern hemlock (23), eastern hemlock-yellow birch (24), red spruce-yellow birch (30), red spruce (32), red spruce-balsam fir (33), paper birch-red spruce-balsam fir (35), tamarack (38), black ash-American elm-red maple (39), and red maple (108). These fall within both the northern conifer (i.e., eastern spruce-fir) and northern hardwood associations (Burns, 1983).
Habitat type names in Canada differ among Provinces. In Ontario, northern white-cedar is found mostly in the conifer lowland Provincial forest type. It is also present in the conifer upland, mixedwood, tolerant hardwood, and red and white pine forest types (Ontario Ministry of Natural Resources and Forestry, 2022a). Its presence is marginal in other forest types. In Quebec, northern white-cedar can be found in the following forest types: fir-yellow birch (MS1), peat cedar-fir (RC3), old field white spruce or cedar (RB1), fir-cedar (RS1), fir-red spruce (RS5), black ash-fir (MF1), yellow birch-fir and sugar maple (MJ1), and yellow birch-fir (MJ2) (Grondin and Gosselin, 2013). In New Brunswick, northern white-cedar is present in all seven ecoregions, but its abundance is low in the Central Uplands (3) (New Brunswick Department of Natural Resources, 2007). The other ecoregions of New Brunswick are Highlands (1), Northern Uplands (2), Fundy Coast (4), Valley Lowlands (5), Eastern Lowlands (6), and Grand Lake (7).
Plant associates vary across habitat types (e.g., swamps, seeps, old fields, cliffs, and bluffs) but commonly include trees such as balsam fir (Abies balsamea), tamarack (Larix laricina), eastern white pine (Pinus strobus), black ash (Fraxinus nigra), red maple, spruce (Picea spp.), birch (Betula spp.), and aspen (Populus spp.) as well as shrubs such as alder (Alnus spp.), holly (Ilex spp.), honeysuckle (Lonicera spp.), mountain maple (Acer spicatum), blueberry (Vaccinium spp.), and blackberry (Rubus spp.) (Storm and Kenefic, 2022). Mosses and liverworts are abundant in northern white-cedar swamps and include Sphagnum species, feather mosses (order Hypnales), brown mosses (family Amblystegiaceae), and Bazzania species. Several rare and sensitive orchids, such as fairy slipper (Calypso spp.), ram’s head lady’s slipper (Cypripedium arietinum), showy lady’s slipper (Cypripedium reginae), and roundleaf orchid (Amerorchis rotundifolia), can be found in northern white-cedar stands (Epstein, 2017; Gawler and Cutko, 2010).
Northern white-cedar is shade tolerant. It is also tolerant of both low and high soil moisture, allowing growth in upland and lowland sites. Spring flooding has a negative effect on northern white-cedar trees as it delays the start of the growing season (Denneler et al., 2010). Mortality can occur if road building or beavers (Castor canadensis) impound water (Chimner et al., 2017; Ferrell et al., 2007). Northern white-cedar has moderate salinity tolerance (Foster et al., 1978; Sucoff, 1975). It is common on old fields (abandoned pasturelands) in New England and Quebec, where its tolerance of limestone and dolomite bedrock (where present) and to trampling by livestock are believed to have provided a competitive advantage (de Blois and Bouchard, 1995). Northern white-cedar has a low tolerance to fire, with recurring or stand-replacing fires potentially excluding northern white-cedar by killing both regeneration and mature trees (Bergeron and Dubuc, 1989; Frelich and Reich, 1995); this has been associated with its distribution around water bodies in fire-adapted sites (Ouarmim et al., 2016).
Northern white-cedar stands may contain one or multiple cohorts depending on disturbance severity and frequency (Heitzman et al., 1997). Stand-replacing disturbances such as wildfire, clearcutting, or clearing and abandoning pastureland (Curtis, 1946; Curtis, 1959; de Blois and Bouchard, 1995; Johnston, 1980) can result in even-aged stands of northern white-cedar if a seed source is available and neither competition nor browsing pressure is high (Heitzman et al., 1997). High-intensity wind disturbance events have also resulted in nearly even-aged stands, with northern white-cedar later replacing early successional species such as jack pine (Pinus banksiana), red pine (Pinus resinosa), black spruce (Picea mariana), and aspen through a process of accelerated succession (Anoszko et al., 2022).
Uneven-aged northern white-cedar stands are generally associated with later successional stages and are found mainly in swamps or other moist sites (Heinselman, 1973). These can develop where northern white-cedar regenerates by seed or layers beneath a canopy and are released by small-scale disturbances that create canopy openings (e.g., partial harvesting or windthrow) (Fraver et al., 2020). Uneven-aged stands also develop where northern white-cedar gradually succeeds associates that are not as shade tolerant or long lived, such as balsam poplar (Populus balsamifera), tamarack, eastern white and jack pine, or black spruce (Apfelbaum et al., 2017; Frelich and Reich, 1995; Johnston, 1980). In systems where fire is the dominant disturbance, transition to northern white-cedar dominance tends to increase with time since fire (Bergeron, 2000; Frelich and Reich, 1995), with northern white-cedar gradually colonizing burned areas and even forming even-aged monotypic stands in some instances (Frelich and Reich, 1995). Establishment after stand-replacing disturbance typically takes place during the first 10 to 50 years but may take up to 100 years (Heitzman et al., 1997). After partial disturbance, establishment gradually increases over at least 30 years (Villemaire-Côté et al., 2022).
Mature height ranges from 10 to 20 m (35 to 65 feet), and crown width 2.8 to 6.2 m (9 to 20 feet) (Weiskittel et al., 2010). Maximum diameter at breast height (DBH) ranges from 60 to 90 cm (24 to 36 inches) (Hardin et al., 2001) and can occasionally exceed 120 cm (45 inches) (Curtis, 1946). Lifespan reaches 400 years on most sites, and more than 900 or 1,000 years on cliffs and bluffs, respectively (Archambault and Bergeron, 1992; Larson and Kelly, 1991).
Seedlings often grow slowly, but this is partly related to the shaded understory conditions under which they commonly develop. Individual seedling monitoring demonstrated a mean annual height growth of 0.5 to 4.0 cm (0.2 to 1.6 inches) from shaded to full sun conditions for seedlings less than 120 cm (47 inches) tall (Villemaire-Côté et al., 2024). A dendrochronological study found an average annual height increment of 8.0 cm (3.1 inches) over the first 4 m (13 feet) in height (Hofmeyer et al., 2010). This may be an overestimation of average growth given the survivor bias associated with dendrochronological analyses. Planted seedlings up to about 40 cm (15.7 inches) tall reportedly grew close to 20 cm (7.9 inches) in height per year in forest gaps (Larouche et al., 2011) and over 60 cm year-1 (23.6 inches year-1) in fertile conditions with 50 percent incident light (Villemaire-Côté et al., 2023).
Studies have used planted northern white-cedar to assess relationships between incident radiation and growth of established seedlings. Greater height, diameter, and branch growth of planted seedlings was observed under 50 percent sunlight than in full sun conditions (Villemaire-Côté et al., 2023), likely because northern white-cedar seedlings do not acclimate well to full light conditions (Man et al., 2013). Yet another study found shoot and root biomass growth to be greatest in full sun, with height growth greater under 45 percent sunlight (Logan, 1969). Additionally, height growth of planted seedlings was greater in 625-m2 (0.15-acre) gaps than in areas where 25 or 50 percent of stand basal area had been harvested using single tree selection and shelterwood establishment cuts, respectively (Larouche et al., 2011). Seedling establishment, on the other hand, was best in more shaded conditions (i.e., where basal area removal was 25 percent). Partial overstory shade provides protection from water stress and herbaceous competition.
Northern white-cedar trees have slow growth in the shade (Fraver et al., 2020; Hofmeyer et al., 2010) and moderate growth in partial shade to full sun (Larouche et al., 2011; Villemaire-Côté et al., 2017). Northern white-cedar trees from across central and northern Maine took an average of 42, 96, and 140 years to reach sapling (2.5 cm [1 inch]), poletimber (12.7 cm [5 inches]), and sawtimber (22.9 cm [9 inches]) DBH, respectively, and 170 years to reach shingle stock (38.1 cm [15 inches]) stump diameter (Hofmeyer et al., 2010). Regressions from dendrochronological work in Maine suggest 81 years to reach 10 cm (3.9 inches) DBH (Fraver et al., 2020).
Diameter increment of saplings was found to be 0.85, 0.94, and 1.63 cm (0.33, 0.37, and 0.64 inch) over 10 years for trees with small (1.3 to 4.6 cm [0.5 to 1.8 inches]), medium (4.7 to 8.0 cm [1.9 to 3.1 inches]), and large (8.1 to 11.4 cm [3.2 to 4.5 inches]) DBH, respectively (Larouche et al., 2010). Unsuppressed planted northern white-cedar in Quebec took an average of 27 years to reach 15 cm (5.9 inches) root collar diameter (Villemaire-Côté et al., 2017). Growth rates reported from cliff trees are some of the lowest recorded for any plant, with an average lifetime productivity as low as 0.26 g year-1 (0.009 ounce year-1) for trees over 500 years (Larson and Kelly, 1991).
Aboveground biomass was found to be 159 t ha-1 (71 tons acre-1) in a Minnesota northern white-cedar swamp, and annual production was 10.1 t ha-1 (4.5 tons acre-1) (Reiners, 1972). A study in Maine calculated a 13 dm3 (0.5 foot3) stemwood volume increment at a projected leaf area of 100 m2 (1076.4 feet2) (Hofmeyer et al., 2010). This suggests a stand with a projected leaf area index of 4 would annually produce 5.2 m3 ha-1 (74.3 feet3 acre-1) of stemwood.
Site index curves have been developed in the United States by Carmean et al. (1989) and in Quebec by Pothier and Savard (1998) and presented in Boulfroy et al. (2012). They were geographically refined for Quebec in Laflèche et al. (2013). A study in central and northern Maine found site index for northern white-cedar ranging from 9.6 to 12.3 m (31.5 to 40.4 feet) depending on site class (Hofmeyer et al., 2009). Stands on organic soil had lower site index, and site index increased with drainage (Hofmeyer et al., 2009).
Management with Natural Regeneration
Given the diversity of stand structures associated with northern white-cedar, even-aged and multi-aged silvicultural systems (i.e., with one or two or more age classes, respectively) have been recommended (e.g., Boulfroy et al., 2012; Heitzman et al., 1999). Though northern white-cedar establishment sometimes occurs in the open, it usually takes place beneath a partial canopy. Partial shade remains a protective factor that helps regeneration establish and survive by reducing water stress (Larouche et al., 2011; Saucier et al., 2018), especially in the absence of a substrate with good moisture retention (Allogio et al., 2021; Kern et al., 2021). Partial shade also helps reduce competing vegetation (Larouche et al., 2011). Furthermore, complete overstory removal precludes retention of seed trees as insurance against a regeneration or recruitment failure. For these reasons, multi-aged silvicultural systems are usually recommended for northern white-cedar in both cedar-dominated and mixed-species stands (Boulfroy et al., 2012). This recommendation is consistent with the gap-phase dynamics that characterize old-growth stands containing northern white-cedar (Fraver et al., 2020).
Even-aged systems that establish and release advance regeneration may be applicable in situations with low browsing pressure (Benzie, 1963; Hannah, 2004). Given northern white-cedar’s growth rates, longer rotation periods have been suggested for even-aged management, as a means of ensuring timber production while maintaining habitat values, especially in areas with moderate to high browsing pressure. However, even-aged systems that fail to establish advance regeneration prior to overstory removal, or that create openings too large to ensure natural seeding and partial shade for competition control during regeneration establishment (e.g., clearcutting and seed tree methods), have proven unreliable for northern white-cedar and are not recommended in recent silvicultural guides (Boulfroy et al., 2012).
Prescribed burns could favor northern white-cedar regeneration where a seed source is available nearby and dense slash inhibits regeneration, because leaf litter and thick mosses limit establishment (Cornett et al., 2000b; Verme and Johnston, 1986). However, this method is not advised where there are residual northern white-cedar trees (Kenefic et al., in press). Mechanical scarification and soil mounding have been suggested to increase northern white-cedar establishment on upland sites if no advance regeneration is present (Lanasa and Zuidema, 1991; Larouche et al., 2011), though care should be taken to protect the shallow root systems of residual trees from physical damage during site preparation. Regardless, site preparation must balance benefits of substrate manipulation with negative impact on advance regeneration, if present; decayed deadwood and microtopography (on wet sites) must be protected (Allogio et al., 2021; Fraver et al., 2020).
Management with Planted Regeneration
Planted stands of northern white-cedar in forests are uncommon outside of a restoration or assisted migration scenario. Planting in gaps about 1.5 tree heights wide resulted in good initial survival and growth (Larouche et al., 2011). Seedlings planted in partial shade (50 percent full sunlight) initially grew faster in height and diameter than those planted in full sunlight (Villemaire-Côté et al., 2023). Older planted stands indicate variable results, depending on the level of competition control, but tend to show high survival (Villemaire-Côté et al., 2017). Northern white-cedar responds well to tending treatments so that, in the most successful cases, stems in planted stands can reach pole size (11.4 cm [4.5 inches]) in less than 20 years (Villemaire-Côté et al., 2017). For enrichment planting, large containerized seedlings (40 to 50 cm [15 to 20 inches] tall) are recommended to limit the negative impact of competition following partial cuts (Bourque et al., 2022). Direct seeding has not proven to be very effective; manual seeding of 250 seeds m-2 (23.2·foot-2) in upland northern white-cedar stands led to an increase over natural seeding of only 0.5 seedling m-2 (0.05·foot-2) after 1 to 2 years (Larouche et al., 2011). In lowland stands such as swamps (forested wetlands) and seeps, planting on elevated microsites (mounds) is important for survival. An experimental planting of northern white-cedar seedlings on pits, flats, and mounds in Maine revealed survival of 12, 62, and 80 percent, respectively, after two growing seasons (Allogio et al., 2021).
Northern white-cedar seedlings planted on exposed mineral soil showed slightly larger root collar diameter than those planted on undisturbed soil (Larouche et al., 2011). However, as microtopography can influence survival, it is important that site preparation efforts preserve natural microtopography or, in the case of degraded wetlands, create favorable microtopography if lacking. On wetlands, planting on mounds has shown better growth and survival than on flat areas, as mounds act as safe sites against flooding (Kangas et al., 2016).
Tending or Intermediate Management
Northern white-cedar is often outcompeted by its companion tree species. While northern white-cedar can regenerate in the presence of abundant competing vegetation, seedling abundance decreases with increasing competition (Chimner and Hart, 1996; Kneeshaw and Bergeron, 1996; Larouche et al., 2011; Verme and Johnston, 1986). Where shrubs or hardwoods are competing with northern white-cedar in the regenerating stratum, competition control has been recommended 5 to 10 years after harvest to increase growth (Benzie, 1963). Northern white-cedar seems to be sensitive to glyphosate; its application leads to decreased growth, so mechanical vegetation control is preferred (Noland et al., 2017). Mechanical removal of competitors (i.e., weeding or cleaning) tends to increase northern white-cedar growth rates in planted stands (Villemaire-Côté et al., 2017) and has been found to increase growth by more than 30 percent over a period of 5 years in naturally regenerated lowland stands (Benzie, 1963).
Tending is generally not needed for northern white-cedar survival, as it can remain in suppressed or intermediate canopy positions for decades and react positively to canopy opening (Fraver et al., 2020; Hofmeyer et al., 2010; Ruel et al., 2014). Where growing with other species for which precommercial thinning is desired, northern white-cedar can be treated as invisible (excluded from treatment; i.e., neither felled nor released) or released at the same spacing as its associates, depending on its relative abundance and priority (Boulfroy et al., 2012). Mechanical release of seedlings or saplings through cleaning or weeding has been recommended to accelerate growth above browsing height (Boulfroy et al., 2012) and has been shown to be efficient in a context of planting (Villemaire-Côté et al., 2017). Faster growth at the seedling and sapling stage can reduce the likelihood of browsing damage and increase the likelihood of recruitment to taller size classes in a context where browsing pressure is high (Villemaire-Côté et al., 2022).
Response to thinning northern white-cedar in lowlands has been variable, depending on site quality, residual stand density, and stand age (Foltz and Johnston, 1968; Roe, 1947). Thinning from below in a 45-year-old stand led to basal area of 21.4 m2 ha-1 (93 feet2 acre-1) after 8 years compared to 5.3 m2 ha-1 (23 feet2 acre-1) in an unthinned stand, while the same treatment applied to a 60-year-old stand on a poorly drained site showed no response (Roe, 1947). A second thinning can be applied to reach a density 20.5 m2 ha-1 (90 feet2 acre-1) or less without compromising growth, and successive thinnings from below can be used to maintain diameter growth (Foltz and Johnston, 1968). In a study of partial cutting in mixedwood stands in Quebec, smaller trees responded better than larger trees, but larger trees initially grew faster and maintained their advantage (Ruel et al., 2014). Furthermore, the growth response of individual trees was better at lower residual densities, though windthrow risk increases for shallow-rooted species like northern white-cedar as harvest intensity increases, particularly on poorly drained or exposed sites or when root decay is present (Ruel, 2000; Ruel, 2020).
In mixed-species stands where northern white-cedar is not the dominant species, a multiple-treatment approach to thinning may be appropriate (Boulfroy et al., 2012) (see the section Management with Natural Regeneration: Silvicultural Options and Considerations for more detail). If the silvical properties of the dominant species (e.g., growth rate, longevity, windfirmness) differ from those of northern white-cedar, a silvicultural prescription that specifies a different residual density or spacing for northern white-cedar than other species in the stand can be used. In addition, given northern white-cedar’s slow growth and longevity, it may not have reached financial or biological maturity when shorter lived associates are ready for a regeneration harvest. In this case, thinning northern white-cedar microstands while conducting a regeneration harvest of other species elsewhere in the stand may be desirable. This approach can be operationalized as part of an irregular shelterwood system (Lussier and Meek, 2014).
Northern white-cedar trees grown at high densities or under closed canopies tend to have small branches that naturally shed. Manual pruning is not regarded as necessary.
Not applicable.
The slow decay rate of northern white-cedar wood after tree mortality suggests that salvage is possible, but there is no information on operations of this type in the published literature. The ability of northern white-cedar trees to continue to live if partially rooted (i.e., if trees are windthrown but not snapped) and the important role of asexual reproduction through branch layering for regeneration (Scott and Murphy, 1987; Wason, 2022) suggest that harvesting fallen trees may negatively impact natural regeneration processes. Furthermore, harvesting dead northern white-cedar trees would reduce habitat for wildlife that use the trees for foraging or nesting (e.g., red squirrels) (Riege, 1991) and diminish the recruitment of decayed deadwood and formation of mound microtopography, both of which have been found beneficial for northern white-cedar seedling germination and survival (Allogio et al., 2021; Cornett et al., 2000b; Kangas et al., 2016; Larouche et al., 2011; Saucier et al., 2018). For these reasons, salvage harvesting is not recommended.
Thuja occidentalis has no recognized subspecies. Limited research suggests populations from different site types and climatic regions are morphologically or physiologically differentiated (Champagne et al., 2021; Jokela and Cyr, 1977), but genetic studies have not supported the presence of genetic ecotypes (Matthes-Sears et al., 1991). Over 100 cultivars are used as ornamentals across and beyond northern white-cedar’s natural range (Kenefic et al., in press).
Genetic Variation
Northern white-cedar has low to moderate genetic diversity when compared to other conifers (Pandey and Rajora, 2012a; Perry et al., 1990). Gene flow among populations is limited by selfing, inbreeding, and seed dispersal distance (Pandey and Rajora, 2012b). However, populations appear to have low differentiation, suggesting that gene flow is high enough to prevent diversifying evolutionary processes (Perry et al., 1990; Xu et al., 2018). Peripheral populations have more within-population spatial genetic structure (Sp) and higher gene flow distance (σg) (Sp = 0.023, σg = 135 m [443 feet]) than core populations (Sp = 0.014, σg = 109 m [358 feet]) (Pandey and Rajora, 2012b). Increase in inbreeding coefficient and heterozygote deficiency is seen in the marginal (Fis = 0.244, PHW=0.0042) and discontinuous range (Fis = 0.166, PHW=0.0042) (Xu et al., 2012). Despite high levels of self-fertilization and high survival of selfed embryos, mature northern white-cedar stands do not appear to be inbred, implying that individuals issued from inbreeding present a selective disadvantage (Perry and Knowles, 1990; Perry et al., 1990; Xu et al., 2012).
Expected heterozygosity (He) varies broadly across the range of northern white-cedar. Using isozyme (allozyme) markers detected via electrophoresis, He ranges from 0.113 to 0.141 in young old-field stands mostly of asexual origin in Quebec (Lamy et al., 1999). Using these same methods, He ranged from 0.146 to 0.327 for three populations in mixed forests in Ontario (Perry and Knowles, 1990) and 0.077 to 0.109 for six populations in Ontario (Perry et al., 1990). At the northern edge of the range in Quebec, He determined using microsatellite markers averaged between 0.712 and 0.826 (Xu et al., 2012) and between 0.574 and 0.624 for two island populations (Xu et al., 2013). High levels of genetic substructuring and an excess of homozygotes were identified in areas where populations are isolated and reproduce mainly by layering (Lamy et al., 1999).
The percentage of polymorphic loci averages determined via isozyme (allozyme) markers also varies broadly, at 54 percent from young old-field stands (Lamy et al., 1999), 37 percent for six populations in mixed forests in Ontario (Perry et al., 1990), and 18 percent for three cliff and three lowland northern white-cedar-dominated stands in Ontario (Matthes-Sears et al., 1991).
Using simple sequence repeat (SSR) microsatellite markers, the average number of alleles per locus (allelic diversity) ranged from 5.50 to 5.75 (Xu et al., 2013) and 4.94 to 6.38 (Xu et al., 2018) at the northern limit of northern white-cedar’s range. When comparing isolated stands on islands and in fragmented fire refuges to those in the mainland continuous zone, genetic differentiation of sites increased from island sites (Fst = 0.015) to mainland (Fst = 0.023) to fragmented fire refuge sites (Fst = 0.052) (Xu et al., 2018). A decrease in allelic richness from mainland (AR = 5.59) to island (AR = 5.42) to fragmented fire refuges (AR = 5.06) was observed, suggesting that allelic richness is more sensitive to population size than other factors (Xu et al., 2018). Mainland stands are sources of gene flow for isolated stands, and the retention of a few small patches of northern white-cedar is not sufficient to conserve genetic diversity over the landscape (Xu et al., 2018). Retaining sizable areas of intact forest in heavily harvested landscapes can be beneficial for the conservation of northern white-cedar genetic diversity.
Hybridization of northern white-cedar with western redcedar (Thuja plicata) has been described but not confirmed with genetic analysis (Zieliński et al., 2019). This phenomenon could happen when the two species are cultivated in close proximity, because their natural ranges do not overlap.
No seed transfer guidance specific to northern white-cedar is available. However, guidelines for black spruce (Pike and Haase, 2024), as well as nonspecies-specific recommendations, can be applied to northern white-cedar. Considering current and projected changes in temperature and precipitation, it is possible to plant seeds one to two USDA Plant Hardiness Zones farther north than their harvest location (USDA Natural Resources Conservation Service, n.d.). The U.S. Forest Service recommends seed transfer to sites with a mean annual temperature 1.5 to 2.2 °C (2.7 to 4.0 °F) warmer than the collection site (Pike and Haase, 2024). Ontario produces maps to advise for seed transfer in the Province from local and U.S. sources (Ontario Ministry of Natural Resources and Forestry, 2022b).
Breeding of northern white-cedar remains limited as it is not a highly productive planted species (Villemaire-Côté et al., 2017). It has so far been produced at a large scale only for horticultural uses. Small productions for industrial planting exist, notably in Quebec. Breeding programs seem limited to second-generation seed orchards, and no proper selection or improvement is known to have occurred. Favorable traits could include high levels of defense compounds against herbivory (Champagne et al., 2021) as well as rapid initial seedling height growth to increase the likelihood of escaping herbivory and increased apical dominance to reduce forking (Villemaire-Côté et al., 2017). Planting objectives are shifting from solely production focused toward other objectives such as adaptation and biodiversity, and northern white-cedar breeding programs are shifting accordingly.
Genomic Resources for Forest Tree Species
A number of genomic resources exist, including reconstructions of evolutionary history (Li et al., 2021) and microsatellite information (Xu et al., 2013).
See preceding section.
Arborvitae leafminers (Argyresthia spp., Coleotechnites thujaella) are native insect pests of northern white-cedar leaves and twigs (table 2). Arborvitae leafminers were found on northern white-cedar more than 150 years ago (Packard, 1871), but frequency and severity of leafminer damage were not well understood until recently (Fraver et al., 2024). Damage is now recognized as more common than previously thought, though it can be variable. For example, in Ontario, the extent of light to severe defoliation was near 16 600 ha (41,000 acres) in 2023 (Ontario Ministry of Natural Resources and Forestry, 2024). Similarly, the area affected by a leafminer outbreak in Minnesota varied from 0 to more than 4850 ha (12,000 acres) annually between 2016 and 2020 (Minnesota Department of Natural Resources, 2019; Minnesota Department of Natural Resources, 2020; Minnesota Department of Natural Resources, 2021). Knowledge of leafminer impacts on northern white-cedar remains geographically segmented; for instance, its abundance in Ontario is well documented, but Quebec, adjacent and with very similar climate, has no known leafminer inventories.
Carpenter ants (Camponotus spp.) are common in stems of northern white-cedar infected by fungi (Boulet, 2007).
Several pests are known to affect northern white-cedar in nursery and landscape settings, though they are rarely observed in forests. These include the arborvitae aphid (Cinara tujafilina), bagworm (family Psychidae), Fletcher scale (Parthenolecanium fletcheri), juniper scale (Carulaspis juniperi), and spruce spider mite (Oligonychus ununguis), all of which attack the twigs and foliage. The arborvitae weevil (Phyllobius intrusus) feeds on foliage and roots. The cedar longhorn beetle (Callidiellum rufipenne) and cedar tree borer (Semanotus ligneus) are known to infest the wood of nursery stock and, less commonly, weakened trees in the forest (Kenefic et al., in press; Rose et al., 2000).
Northern white-cedar is prone to infection by root- and butt-rot fungi including redheart rot (Stereum sanguinolentum), red-brown butt rot (Coniophora puteana and Phaeolus schweinitzii), and stringy butt rot (Odontia bicolor, Perenniporia subacida, and Scytinostroma galactinum). These decay fungi penetrate wounds on the bole, branches, or forks caused by heavy snow, ice, logging damage, or pruning (Hofmeyer et al., 2009). In a study across Maine, 80 percent of outwardly sound northern white-cedar trees selected for stem analysis had decay. Outwardly sound northern white-cedar had higher proportions of their basal area decayed on well-drained mineral soils than on poorly drained soils, with as high as 15 percent on well-drained soils to as low as 6 percent on organic soils. Incidence of logging damage was thought to be a factor in site differences in proportion of basal area decayed (i.e., more historical logging and thus more logging damage on better drained sites). Wood decay is more prevalent in earlywood than in latewood (Bouslimi et al., 2014). Blight fungi, particularly Phomopsis juniperovora, are mainly observed on the young shoots of cultivars.
Table 2—Significant insects and diseases of northern white-cedar by tree structure and relative impact
Degree of impacta | Roots | Bole (bark, phloem, and xylem) | Foliage, shoot, and twig | Flowers, fruit, and seeds |
Greatest | N/A | N/A | Arborvitae leafminer (Argyresthia spp., Coleotechnites thujaella) | N/A |
Moderate | Redheart rot (Stereum sanguinolentum)
Red-brown butt rot (Coniophora puteana, Phaeolus schweinitzii)
Stringy butt rot (Odontia bicolor, Perenniporia subacida, Scytinostroma galactinum) | Redheart rot
Red-brown butt rot
Stringy butt rot |
| N/A |
Low | Arborvitae weevil (Phyllobius intrusus) | Cedar longhorn beetle (Callidiellum rufipenne)
Cedar tree borer (Semanotus ligneus) | Arborvitae aphid (Cinara tujafilina)
Bagworm (family Psychidae)
Fletcher scale (Parthenolecanium fletcheri)
Juniper scale (Carulaspis juniperi)
Spruce spider mite (Oligonychus ununguis)
Arborvitae weevil
Blight fungi (e.g., Phomopsis juniperovora) | N/A |
N/A: not applicable.
a Note that northern white-cedar trees very commonly live for decades or centuries with extensive decay and that fungal infection should not be regarded as directly affecting survival, though product potential can be greatly impacted by rot.
Arborvitae leafminers cause mortality of foliage and twigs (fig. 8). Mined leaves wither and turn brown, leading to growth decline that is mostly observable the year following leaf mining (Silver, 1957). It can sometimes lead to mortality, though trees are often able to recover by producing new foliage, even after up to 80 percent foliage loss.
Northern white-cedar can continue living and growing for decades to centuries with moderate to extensive decay (fig. 9). The probability of internal decay increases with increasing tree size (Fraver et al., 2020). Old trees are often affected by red-brown butt rot and stringy butt rot (Basham, 1991; Boulet, 2007). Decay causes decreases in modulus of rupture and bending modulus of elasticity in northern white-cedar wood (Bouslimi et al., 2014).
Blight fungi can kill young shoots of northern white-cedar. For trees under 4 years old, reduction of shoot biomass can be up to 50 percent, impacting establishment of regenerating stands (Callan, 2024).
Figure 8—(A, B) Arborvitae leafminer damage and (C) larva in northern white-cedar foliage. Courtesy photos by Neil Thompson.
Figure 9—Mature northern white-cedar showing decay. Northern white-cedar trees are prone to decay when living and many stems are hollow with exposed wood and wildlife excavations. The trees’ radially sectored architecture allows them to persist despite damage and decay. U.S. Forest Service photo by Laura Kenefic.
Not applicable.
Care should be taken to avoid damage to northern white-cedar roots, boles, and branches during harvesting, as these can act as entry ports for decay fungi (Hofmeyer et al., 2009; Vasiliauskas, 2001).
Wildland fire is not common in northern white-cedar forests, and trees of this species are not tolerant of fire (Asselin et al., 2001; Bergeron and Charron, 1994; Bergeron and Dubuc, 1989; Caulkins, 1967; Curtis, 1946; Frelich and Reich, 1995; Grotte et al., 2012; Heinselman, 1973).
Northern white-cedar has thin bark and oily leaves that are vulnerable to fire, and its shallow roots have little protection (Caulkins, 1967; Curtis, 1946). Mature trees and seedlings are often killed by fire (Bergeron and Charron, 1994; Frelich and Reich, 1995; Miller 1990). Mature northern white-cedar can persist in fire-prone landscapes where fire leaves unburned patches, such as in wet areas (Bergeron and Charron, 1994; Frelich and Reich, 1995). It has also been observed that older trees with high sparse crowns offer less ladder fuel for crown fires (Agee and Skinner, 2005). The trees can sometimes survive large injuries because of their radially sectored architecture (Bergeron and Charron, 1994; Frelich and Reich, 1995; Larson et al., 1994). However, frequent and high-severity fires can exclude northern white-cedar from a landscape (Bergeron and Charron, 1994; Frelich and Reich, 1995; Heinselman, 1973). In areas with a history of fire, northern white-cedar trees tend to be most abundant near fire breaks and natural features that are resistant to fire, such as lake shores and rocky bluffs (Bergeron and Charron, 1994; Grotte et al., 2012; Heinselman, 1973).
Northern white-cedar can regenerate after fire if seed trees are present in nearby unburned areas and competition and herbivory are limited, likely when the fire exposes a moist seedbed and eliminates competition (Verme and Johnston, 1986). Yet northern white-cedar is generally slow to reestablish after stand-replacing fires because it lacks serotinous cones, the ability to stump sprout, or other fire adaptations (Asselin et al., 2001). Colonization is dependent on seed dispersal from nearby trees. Due to the short dispersal distance of northern white-cedar seeds (maximum 60 m [200 feet]), the abundance of northern white-cedar regeneration in burned gaps tends to decline sharply with distance from intact forest. Recolonization can be further delayed if the fire destroys deadwood on the forest floor, reducing the availability of adequate germination sites for northern white-cedar seeds (Bergeron and Dubuc, 1989). Northern white-cedar is often among the last tree species to return after a fire, and it may take decades for a new northern white-cedar cohort to establish (Bergeron and Charron, 1994; Frelich and Reich, 1995).
With future climate-driven changes, projected increases in frequency, intensity, and size of wildland fires are expected to negatively impact northern white-cedar (Bouchard et al., 2019; Boulanger et al., 2022).
Prescribed fire is not recommended in stands with existing northern white-cedar regeneration due to the high likelihood of mortality; fire can severely damage or kill northern white-cedar (Miller, 1990). Where northern white-cedar trees and regeneration are lacking, prescribed burning has been used for site preparation, whereby slash is removed to create a more favorable seedbed, notably in clearcuts (Verme and Johnston, 1986). However, the benefits of slash, including microclimate-moderating shade and protection from browsing, are reduced. Positive outcomes for northern white-cedar regeneration have been observed following prescribed burning after clearcutting, but reestablishment can take decades (Bergeron, 2000), and browsing remains a constraining factor throughout its range (Patton et al., 2021).
In northern white-cedar’s range, droughts occur periodically and are predicted to become more common due to climate-driven changes in precipitation and temperature regimes (Handler et al., 2014a; Handler et al., 2014b; Janowiak et al., 2014; Janowiak et al., 2018). Topographic position and hydrology affect severity and frequency of drought, with droughts more common in upland than lowland (e.g., swamp) northern white-cedar stands (Maki, 1931).
Current and predicted future drought regime varies across northern white-cedar’s range. Near the central and southern extent of northern white-cedar's range, for example, winter precipitation falling more often as rain, associated reductions in snowpack and spring snowmelt, and warmer mean annual temperatures (see table 1) may increase the likelihood and impacts of drought in the future (Housset et al., 2015; Kincaid, 2016; Tardif and Bergeron, 1997). Nevertheless, northern white-cedar stands located at the northern range limit may be more likely to experience drought than elsewhere because mean annual precipitation is already relatively low (e.g., less than 500 mm [20 inches]) (Grotte et al., 2012; Housett et al., 2015).
Northern white-cedar has been ranked as somewhat tolerant to intolerant of drought (Coble et al., 2017). Newly germinated seedlings are especially sensitive to drought because of the species’ high shoot-to-root ratio and shallow root systems (Bender et al., 1987; Curtis, 1944; Curtis, 1946; Maki, 1931). Depending on the seasonal timing, length, and severity of drought, young seedlings can be highly vulnerable to drought-induced mortality (Larouche et al., 2011; van Kampen et al., 2022). This is true even in lowland stands, where seedlings that germinated in the early summer on moss or elevated microsites (e.g., mounds or buttresses of larger trees) are subject to desiccation during late-season droughts when the surface substrate dries out (Maki, 1931). Moisture-holding substrates like decayed deadwood are important for seedling survival (Caulkins, 1967; Cornett et al., 2000b).
A greenhouse experiment in which northern white-cedar seedlings about 0.8 m (2.5 feet) tall were exposed to droughts of up to 53 days showed increasing mortality with increasing drought length, but there were no lag effects on mortality the following year (Schulz et al., 2024). Nevertheless, seedling biomass decreased with decreasing water availability (Champagne et al., 2021; Schulz et al., 2024). Seedlings in the greenhouse experiment exhibited reduced height and (to a lesser extent) diameter growth after 24 and 53 days of drought, respectively, but recovered both height and diameter within a year. The largely indeterminate shoot growth habit of northern white-cedar (Briand et al., 1992a) likely helped reduce negative effects of short-term water limitation on seedling growth through shoot growth resumption after stress relief (Schulz et al., 2024; van Kampen et al., 2022).
The stem growth of mature northern white-cedar has been observed to be affected by June drought and elevated temperatures, especially on xeric sites, indicating the more severe water-stress conditions associated with xeric sites (Tardif and Bergeron, 1997). These factors can interact in affecting northern white-cedar growth (Housset et al., 2015). Elevated summer temperature during the preceding year can also cause temporary drought stress (Housset et al., 2015). This effect appears greater for larger trees, indicating their higher evapotranspiration.
Lowland and upland northern white-cedar populations exhibit the same drought tolerance (Collier and Boyer, 1989), suggesting no ecotypic differentiation as has previously been proposed. Some geographic provenances show increased growth allocation to roots following periods of reduced water availability (Champagne et al., 2021). Reduced water availability also increases phenolic concentration in shoots (Champagne et al., 2021).
During severe droughts on cliff-edge habitat, northern white-cedar saplings show reductions in net photosynthesis and stomatal conductance (Matthes-Sears and Larson, 1990). Yet northern white-cedar trees at least 2 years old exhibit radially sectored architecture that helps the trees maintain uptake of spatially heterogeneous substrate moisture (Larson et al., 1994). This characteristic may increase survival in water-limited conditions.
Seedlings and mature northern white-cedar trees exhibit shoot osmotic adjustment following exposure to water stress, though decreased transpiration rate appears to be a more important drought tolerance mechanism (Collier and Boyer, 1989; Edwards and Dixon, 1995a). Prior exposure to drought stress increases tolerance to subsequent droughts, expressed through higher leaf relative water content and water potential, and lower transpiration rates (Edwards and Dixon, 1995b). This lower transpiration is maintained following the relief of water stress.
The browning of foliage typical of drought damage is not to be confused with cladoptosis, where older branchlets naturally shed (Briand et al., 1992a), frost desiccation (moisture loss through foliage while the root system is frozen), or damage from pests such as leafminers.
A growth chamber experiment with 4-year-old northern white-cedar revealed that high temperatures can accentuate the negative effects of drought on leaf gas exchange and whole-plant carbon balance (Zhao et al., 2013). This interaction between temperature and drought resulted in seedlings becoming carbon deficient at a higher soil moisture content. Whether this contributed to drought-induced mortality was unclear; the authors were unable to determine whether hydraulic failure or interaction between water stress and carbon deficiency caused the seedlings to die.
Regeneration methods that retain partial canopy cover (e.g., variants of selection or irregular shelterwood cutting) have been suggested for northern white-cedar (Boulfroy et al., 2012; Bourque et al., 2022; Larouche et al., 2011). Relative to methods that create a more open canopy, these treatments provide partial shade that helps maintain lower temperatures, higher humidity, and more soil and deadwood moisture (Breigenzer et al., 2023; Larouche et al., 2011). This understory environment is more mesic than that found in stands in which the overstory has been removed and may result in less evapotranspiration, lower seedling water stress, and less drought-induced northern white-cedar seedling mortality.
Northern white-cedar is also influenced by other agents including flooding, wind, snow and ice, and herbivory. Although the species is well adapted to small-scale wind disturbance and can recover from moderate flooding and browsing, persistent browsing and altered hydrology can result in regeneration failure or mortality.
There is no specific flood regime in northern white-cedar’s range, though flooding can occur, especially when precipitation is unusually high and in the spring after heavy snow accumulation. Trees located near a body of water or in swamps are more susceptible to flooding (Denneler et al., 2010), and water impoundment from road building or beaver activity can flood lowland stands (Chimner et al., 2017).
White-tailed deer are highly selective for northern white-cedar in their winter diet (Cornett et al., 2000a; Heitzman et al., 1997; Larouche and Ruel, 2015). White-tailed deer are overabundant across much of the range of northern white-cedar (Côté et al., 2004) and their populations are projected to expand northward (Weiskopf et al., 2019). This is expected to increase the overlap between the two species at the northern limit of northern white-cedar’s current range, where the trees currently experience little browsing pressure (Larouche and Ruel, 2015). White-tailed deer also aggregate in deer yards over the winter, seeking the shelter and food that northern white-cedar trees provide and leading to very high local browsing pressure (Morrison et al., 2003; Verme and Johnston, 1986).
Snowshoe hares and moose (Alces alces) also browse northern white-cedar (Villemaire-Côté et al., 2017). Squirrels clip ends of northern white-cedar branches bearing cones and eat or cache them in middens (Riege, 1991) (fig. 10).
Wind is an important natural disturbance agent in northern white-cedar-dominated stands, causing frequent small- to moderate-scale canopy openings by breaking and uprooting individual and small groups of trees (Fraver et al., 2020; Pregitzer, 1991). Windthrow is generally a small-scale disturbance in northern white-cedar stands, though large areas of blowdown do occur (Pregitzer, 1991).
Snow and ice buildup can cause northern white-cedar trees to lean or break and to topple over when root systems are loose or weakened (Caulkins, 1967).
Newly germinated northern white-cedar is extremely sensitive to flooding. On lowland sites, seedling abundance is higher on flats and mounds than in pits, where survival of planted seedlings was observed to be as low as 12 percent over two growing seasons (Allogio et al., 2021). Northern white-cedar seedlings show good stress resistance and growth recovery following moderate flood events. Over a single growing season, seedlings were found to have 78 percent survival regardless of flood duration (3 to 15 weeks) (Keller et al., 2023). However, after two growing seasons, fewer than 50 percent of seedlings survived flooding events of more than 12 days (Schulz et al., 2024). Seedling height growth has been reported to be reduced after 11 (Schulz et al., 2024) to 42 (Keller et al., 2023) days of flooding. Seedling diameter growth was either not impacted (Keller et al., 2023) or minimally impacted by flooding, though only short-duration flooding (8 to 11 days) allowed full diameter recovery within 1 year (Schulz et al., 2024). At the beginning of the growing season, radial growth can be negatively affected by high levels of precipitation during the previous fall, especially on poorly drained sites (Vanderschoot, 2024). Mortality of mature trees can occur if road building or beavers impound water, creating prolonged flooding conditions (Chimner et al., 2017). Wet and dry seed sources appear to have the same flood tolerance, suggesting no ecotypic differentiation (Collier and Boyer, 1989).
Browsing of northern white-cedar seedlings varies among trees and sites such that some individuals are minimally impacted, while others are completely consumed (Reuling et al., 2019; Villemaire-Côté et al., 2022). Northern white-cedar has low apical dominance, and browsing can lead to forking and loss of a clear leader (Villemaire-Côté et al., 2017; Villemaire-Côté et al., 2023). Northern white-cedar can survive in a prostrate and browsed state under high-intensity browsing for multiple decades (Villemaire-Côté et al., 2017). Over 2 years, artificial browsing of up to 50 percent of live foliage on northern white-cedar 50 to 150 cm (1.6 to 4.9 feet) tall led to aboveground growth compensation; total height was not affected, and diameter and branch growth were only negatively affected by high-intensity (50 percent) browsing (Villemaire-Côté et al., 2023). Shorter seedlings (about 30 cm) from which only apical shoots were removed did not fully compensate for total aboveground biomass (Champagne et al., 2021). A study of 6 consecutive years of artificial browsing (25 and 50 percent of foliage removed each year) on northern white-cedar trees that were 2 m tall in young, closed stands revealed that clipped trees prioritized branch growth over diameter and height growth, as browsed trees produced 40 percent more foliage mass than unbrowsed trees (Aldous, 1952).
Nevertheless, white-tailed deer browsing is a major constraint to northern white-cedar seedling survival, growth, and recruitment and has been associated with regeneration and recruitment failures across much of northern white-cedar’s range (Cornett et al., 2000a; Heitzman et al., 1997; Larouche and Ruel, 2015; Reuling et al., 2019). Snowshoe hare browsing is also known to greatly affect northern white-cedar regeneration, though more sporadically and locally than deer (Verme and Johnston, 1986; Villemaire-Côté et al., 2017; Villemaire-Côté et al., 2022; Villemaire-Côté et al., 2024). Browsing by moose can also be locally damaging, though this species does not preferentially browse northern white-cedar (Peek et al., 1976; Villemaire-Côté et al., 2017). The extent of the damage caused by squirrels clipping ends of northern white-cedar branches bearing cones is not known (Riege, 1991).
Vulnerability to browsing damage is generally up to 3 m in height, at which point enough foliage is considered outside browsing reach to ensure survival (Villemaire-Côté et al., 2017). This height can be reached anywhere between 9 and 75 years (Hofmeyer et al., 2010; Villemaire-Côté et al., 2017). Slow growth, notably under closed canopies, extends the duration of browsing vulnerability. Deer browsing pressure tends to be recurrent over time because of high winter range fidelity (Lesage et al., 2000; Verme, 1973).
Removal of deer browsing pressure can lead to a measurable increase in northern white-cedar regeneration abundance in canopy gaps within 10 years (Villemaire-Côté et al., 2022). Following partial cutting, northern white-cedar regeneration survival can be considerably impacted by browsing; in New Brunswick, the 2-year survival of regenerating northern white-cedar was less than 30 percent with browsing and more than 95 percent without (Villemaire-Côté et al., 2024).
Windthrow is common in northern white-cedar stands (Pregitzer, 1991). Natural development and maintenance of multi-aged structures in old-growth and late successional northern white-cedar forests have been attributed to partial disturbances from wind (Fraver et al., 2020; Frelich and Reich, 1995). Northern white-cedar's shade tolerance, ability to persist for decades in a shaded understory (Fraver et al., 2020; Ruel et al., 2014), and capacity to respond to release even at advanced ages (e.g., after nearly 200 years) (Hofmeyer et al., 2010) allow it to perpetuate itself in the absence of browsing under a natural disturbance regime driven by wind (Pregitzer, 1991). Northern white-cedar trees commonly establish sexually or asexually (via layering) beneath an existing overstory and ascend to the canopy through one or many release events resulting from wind-caused mortality of overtopping trees (Fraver et al., 2020; Hofmeyer et al., 2010; Ruel et al., 2014).
Relative to northern white-cedar trees in dense stands, those in harvest gaps are more prone to windthrow (Pregitzer, 1991). In mixed-species expanding gap irregular shelterwood stands in Maine, for example, northern white-cedar retention trees in gaps had higher wind-related mortality over 25 years than associated species (Carter et al., 2017). At the landscape level, large-scale wind events can cause extensive areas of northern white-cedar to blow down (Pregitzer, 1991), though this is relatively uncommon. Furthermore, mortality from large-scale wind events is influenced by stage of stand development and tree size, with northern white-cedar less susceptible to mortality than taller, early successional species; for instance, northern white-cedar mortality averaged 12 percent while the mean for all species was 42 percent following a large-scale wind event in 90- to 200-year-old southern boreal forests (Rich et al., 2007).
Tipping or partial uprooting of windthrown northern white-cedar trees is common and may bring branches into contact with the forest floor, enabling layering if the parent tree survives and is not heavily browsed (Nelson, 1951; Pregitzer, 1991). Asexual reproduction through layering is facilitated by windthrown trees’ contact with moist substrates such as moss. Sexual reproduction also benefits from seedling regeneration safe sites provided by moisture-holding, elevated microsites associated with decaying deadwood from wind-broken and uprooted trees.
Snow and ice buildup can bring branches or seedling and sapling stems into contact with soil, leading to layering (Curtis, 1946). Late spring frosts can kill 1- to 2-year-old seedlings and newly flushed tissues of mature trees (Curtis, 1946; Man et al., 2009).
Drought stress can increase the negative impact of browsing on northern white-cedar seedling growth (Champagne et al., 2021). Northern white-cedar seedlings growing under 50 percent incident light have more capacity to compensate for browsing damage than those under full sun, likely because of their high susceptibility to water stress caused by the high irradiance, daytime temperatures, and vapor pressure deficits under full light conditions (Man et al., 2013; Villemaire-Côté et al., 2023). Alternatively, by decreasing its photosynthetic capacity and reserves, browsing can considerably decrease regenerating northern white-cedar's vigor and ability to resist other disturbances.
Though northern white-cedar composition is maintained or increased by release of established regeneration and trees in wind-created canopy openings, wind followed by one or more fires reduces abundance of northern white-cedar by killing seedlings and trees (Anoszko et al., 2022).
In stands where northern white-cedar is mixed with species affected by spruce budworm (Choristoneura fumiferana) such as balsam fir or spruce, spruce budworm-killed standing dead trees gradually break and uproot, leading to expanding windthrows that can blow over or release standing northern white-cedar (Villemaire-Côté et al., 2022) and increase northern white-cedar regeneration (Fraver et al., 2020; Hofmeyer et al., 2010; Ruel et al., 2014).
The tendency for seedlings to layer following snow and ice accumulation can further slow the recruitment of seedlings to the canopy and increase the duration of vulnerability to browsing (Wason, 2022).
On lowland sites, mounds can help reduce the effect of flooding on northern white-cedar regeneration and thus increase seedling survival and abundance (Allogio et al., 2021). Silvicultural decisions that maintain and increase the abundance of decayed deadwood are therefore recommended. Managers must consider the risk that harvests in lowland sites may raise the water table, potentially decreasing the role of mounds as safe regeneration microsites (Jutras et al., 2013). Partial harvests that retain a portion of the canopy may mitigate this risk. It is recommended that road-building activities take hydrologic functioning into account. For example, culverts could be used to pass the water through the road, or a porous roadbed that allows water to flow beneath the road could prevent erosion by culvert-channelized water (Chimner, 2022; Chimner et al., 2014).
Regeneration and recruitment failures have been observed for decades across much of northern white-cedar’s range and are in large part due to deer browsing (Cornett et al., 2000a; Heitzman et al., 1997; Larouche and Ruel, 2015). Deer browsing is most problematic in areas where deer aggregate during winter months, as they select stands for both cover and food (Morrison et al., 2003). Potential solutions to protect northern white-cedar from overbrowsing include fencing, single-tree protectors, and deer population control. More generally, good monitoring of herbivore populations can help identify windows of opportunity for northern white-cedar regeneration (Villemaire-Côté et al., 2017; Villemaire-Côté et al., 2022). A number of management actions have been suggested to minimize browsing, including growing northern white-cedar with other species to confer associational resistance (Champagne et al., 2020; Herfindal et al., 2015), precommercial thinning (cleaning or weeding) to accelerate growth above browsing height (Boulfroy et al., 2012; Villemaire-Côté et al., 2017), and leaving some logging slash after harvesting to create physical barriers to deer (Verme and Johnston, 1986). Though promising, these approaches are largely unproven and merit further investigation.
Northern white-cedar is susceptible to windthrow when left as a retention tree in large gaps, such as those created in expanding gap irregular shelterwood stands (Carter et al., 2017). Research in mixedwood stands in Maine in which northern white-cedar trees were left as reserves in 0.1- to 0.6-ha (0.3- to 1.5-acre) gaps found that northern white-cedar was the species most at risk of wind-related mortality; 15 percent of trees were uprooted or broken by wind in the first 20 years (Carter et al., 2017). More generally, windthrow risk increases for shallow-rooted species like northern white-cedar as harvest intensity increases, particularly on poorly drained or exposed sites or when root decay is present (Ruel, 2000; Ruel, 2020).
Windthrown northern white-cedar trees that have not fully uprooted can reproduce by layering if living branches are in contact with a moist substrate; leaving some or all of these trees during post-blowdown harvesting or salvage operations may facilitate regeneration.
Figure 10—(A) Deer browsing (ripped) and (B) hare browsing (clipped) of northern white-cedar; (C) distinctive browse line in northern white-cedar stands, below which browsing mammals have consumed all palatable vegetation. Courtesy photos by Olivier Villemaire-Côté.
Goods
Northern white-cedar wood's lightweight and decay-resistant qualities make it a desired species for outdoor uses with direct exposure to water and soils (Grossman and Potter-Witter, 1990; Storm and Kenefic, 2022). Commercial northern white-cedar wood products include fenceposts, shakes and shingles, logs for cabins and homes, appearance-grade lumber, paneling, outdoor furniture, canoe ribs, gunwales, footbridges, recreation trails, and decks. Wood processing residues are utilized in mulch production, which is valued in gardening and landscaping applications. Smaller-scale wood uses have included pails and tubs, lagging (i.e., for shoring walls in excavations and mines), railroad ties, fishing floats, and duck-hunting decoys (Storm and Kenefic, 2022).
Northern white-cedar foliage contains antiviral and antibiotic chemicals that are distilled into oils used worldwide in medicines, cleaning products, cosmetics, and insect repellants (Erichsen-Brown, 1989; Hakobjanyan et al., 2025). Boughs and cones are used to create decorative wreaths, potpourri, and sachets. Boughs, boles, and bark are used by many Indigenous peoples for building lodges, canoes, and tools, for medicine, and in ceremonies (Clark et al., 2022; Kern, 2022; Moerman, 1998). Shredded northern white-cedar bark is also used for starting fires.
Ecosystem Services
Northern white-cedar supports biodiversity as a long-lived species (Archambault and Bergeron, 1992) with unique growth forms adding structural complexity to forests (Weiskittel et al., 2010). Because northern white-cedar wood tends to decay when living (Hofmeyer et al., 2009) and resist rotting after death, long-lasting cedar snags and coarse woody material (Garber et al., 2005; Russell and Weiskittel, 2012) provide cavity and downed log habitats. Northern white-cedar is an important component of old-growth conifer stands (Allogio et al., 2021; Kost et al., 2007; Wesely et al., 2018) that provide key habitat for both common and rare plant species (Anderson and Leopold, 2002; Smith, 2017; Storm and Kenefic, 2022). Northern white-cedar stands provide habitat for many wildlife species (Bryan, 2007). In particular, wood warblers (Phylloscopus sibilatrix) nest in northern white-cedar stands during the summer breeding season (Doepker and Ozoga, 1991) and red squirrels, northern flying squirrels (Glaucomys sabrinus), and black bears (Ursus americanus) commonly use northern white-cedar bark as nesting material (Patterson, 2008; Storm and Kenefic, 2022). Northern white-cedar is also a host for larvae of numerous moth and butterfly species (Storm and Kenefic, 2022).
With its extreme longevity (more than 400 years) and wood very slow to decay, northern white-cedar can be expected to offer long carbon residence times. In the Great Lakes region, northern white-cedar peatlands have been shown to be important carbon pools, containing an average of 80 kg carbon·m-2 (16 pounds carbon·foot-2) (Ott and Chimner, 2016). The peat was found to be derived primarily from wood, with an average thickness of 1.12 m (3.7 feet) and the high bulk density of 0.16 g cm-3 (10 pounds foot-3). These peatlands originated 1,970 to 8,590 years ago and have apparently continuous occupation by northern white-cedar. The long-term carbon accumulation rates ranged from 6.4 g m-2 year-1 (0.02 ounce foot-2 year-1) to 39.7 g m-2 year-1 (0.13 ounce foot-2 year-1), with an average of 17.5 g m-2 year-1 (0.06 ounce foot-2 year-1).
The biodiversity within northern white-cedar stands attracts birdwatchers and other outdoor enthusiasts (Storm and Kenefic, 2022). Lowland northern white-cedar stands and bordering uplands are important locations for people hunting white-tailed deer, snowshoe hares, and grouse (e.g., Bonasa umbellus).
Northern white-cedar is a major component of wildlife wintering complexes in northern climates. These northern white-cedar stands provide thermal shelter, snow interception, and winter forage, supporting deer survival during winter months in locations near the northern limit of their range (Dumont et al., 2005; Lesage et al., 2000; Moen, 1976). Northern white-cedar swamps (forested wetlands) are among the most diverse ecosystems in the Great Lakes and play an essential role in carbon sequestration and storage (Ott and Chimner, 2016), water filtering, and other hydrologic functions (Chimner et al., 2017).
Northern white-cedar is often used in windbreaks in fields and farmsteads (Burridge and Porter, 2023; Ontario Extension, 1995). Its dense foliage and long-lived full crown when grown in full sunlight are desirable characteristics when used as a natural windbreak.
Northern white-cedar is commonly planted as an ornamental in urban-suburban settings both inside and outside its native range, including overseas. It is reportedly suitable for USDA Plant Hardiness Zones 2 through 7 (USDA Natural Resources Conservation Service, n.d.). Many tree and shrub-like cultivars are used in landscaping and hedgerows for their dense, evergreen foliage (University of Minnesota Urban Forestry Outreach and Research Nursery and Lab, 2024). Northern white-cedar is thus often identified as among the most abundant urban tree species in Canadian cities (Hutt-Taylor and Ziter, 2022; Sousa-Silva et al., 2023). Northern white-cedar is commonly planted in cemeteries and as a privacy screen along urban-suburban property lines.
Forests in Cities
Not applicable.
Northern white-cedar regeneration and growth may be inhibited by road salt pollution along major highways (Janssen et al., 2024).
Trees in Planted Urban Landscapes
Saplings and trees may experience stunted growth as a result of atypical temperature gradients and moisture deficits in highly developed areas, where temperatures are higher near the base of the tree and moisture is limited (Kycheryavyj et al., 2021). Deer will sometimes browse northern white-cedar trees planted in urban-suburban settings (Walter et al., 2011), causing distinctive defoliation of the lower approximately 2 to 3 m (6.5 to 10 feet) of the tree. Physical barriers or chemical repellents can be used to prevent browsing damage.
Whether growing in hedgerows or as individuals, northern white-cedar trees provide shade and privacy and contribute to urban-suburban biodiversity by providing bird, insect, and wildlife habitat (Storm and Kenefic, 2022).
Baseline genetic data are needed to assess genetic structure and local adaptation in northern white-cedar, which will inform adaptive forest management such as assisted migration.
Information is lacking about genotypes with herbivory resistance and how local site conditions such as soil nutrition affect palatability.
There is a lack of knowledge on dynamics and growth potential of northern white-cedar in even-aged, planted stands in a production forestry context. Wood quality of faster grown northern white-cedar, notably in terms of rot resistance, is also unknown.
There is uncertainty about the effects of changing environmental conditions on the frequency, intensity, and interaction of disturbances such as drought and fire, and how these factors and their influences on northern white-cedar seedlings and mature trees vary across the species’ range.
More information is needed to understand the impacts of changing environmental conditions on the abundance and distribution of the insects and herbivores that damage northern white-cedar trees and forests.
Further research on harvesting technology and operations in managed lowland northern white-cedar forests (e.g., swamps) is warranted, particularly in light of increasing challenges associated with shorter and less predictable periods of frozen ground.
More information is needed on how to favor northern white-cedar regeneration, recruitment, and retention through management, in order to overcome problems with overbrowsing and replacement by competitors after harvest.
Agee, J.K.; Skinner, C.N. 2005. Basic principles of forest fuel reduction treatments. Forest Ecology and Management. 211(1–2): 83–96. https://doi.org/10.1016/j.foreco.2005.01.034.
Ahlgren, C. 1957. Phenological observations of nineteen native tree species in northeastern Minnesota. Ecology. 38(4): 622–628. https://doi.org/10.2307/1943128.
Aldous, S.E. 1952. Deer browse clipping study in the Lake States region. The Journal of Wildlife Management. 16(4): 401–409. https://doi.org/https:/doi.org/10.2307/3797487.
Allogio, J.A.; Fraver, S.; Kenefic, L.S.; Wason, J.W.; Berrill, J.P. 2021. Microsite requirements for successful regeneration in lowland northern white-cedar (Thuja occidentalis L.) forests. Forest Ecology and Management. 499: 119639. https:/doi.org/10.1016/j.foreco.2021.
Anderson, K.L.; Leopold, D.J. 2002. The role of canopy gaps in maintaining vascular plant diversity at a forested wetland in New York State. Journal of the Torrey Botanical Society. 129(3): 238–250. https://doi.org/10.2307/3088774.
Anoszko, E.; Frelich, L.E.; Rich, R.L.; Reich, P.B. 2022. Wind and fire: rapid shifts in tree community composition following multiple disturbances in the southern boreal forest. Ecosphere. 13(3). https://doi.org/10.1002/ecs2.3952.
Apfelbaum, S.I.; Haney, A.; Wang, F.; Burris, J.; Carlson, J. 2017. Old-growth southern boreal forest stability and response to a stand-replacing wildfire. Natural Areas Journal. 37(4): 474–488. https://doi.org/10.3375/043.037.0404.
Archambault, S.; Bergeron, Y. 1992. Discovery of a living 900-year-old northern white cedar, Thuja occidentalis, in northwestern Quebec. Canadian Field Naturalist. 106(2): 192–195. https://doi.org/10.5962/p.356928.
Asselin, H.; Fortin, M.J.; Bergeron, Y. 2001. Spatial distribution of late-successional coniferous species regeneration following disturbance in southwestern Québec boreal forest. Forest Ecology and Management. 140(1): 29–37. https://doi.org/10.1016/S0378-1127(00)00273-5.
Barton, L.V. 1930. Hastening the germination of some coniferous seeds. American Journal of Botany. 17(1): 88–115. https://doi.org/10.1002/j.1537-2197.1930.tb09535.x.
Basham, J.T. 1991. Stem decay in living trees in Ontario’s forests: a users’ compendium and guide. Inf. Rep. O-X-408. Sault Ste. Marie, ON: Canadian Forest Service, Great Lakes Forest Research Centre. 64 p.
Bender, L.; Harry, I.S.; Yeung, E.C.; Thorpe, T.A. 1987. Root histology, and nutrient uptake and translocation in tissue culture plantlets and seedlings of Thuja occidentalis L. Trees. 1: 232–237. https://doi.org/10.1007/BF01816821.
Benzie, J.W. 1963. Cutting methods in mixed conifer swamps, Upper Michigan. Res. Pap. LS-4. St. Paul, MN: U.S. Department of Agriculture, Forest Service, Lake States Forest Experiment Station. 24 p.
Bergeron, Y. 2000. Species and stand dynamics in the mixed woods of Québec’s southern boreal forest. Ecology. 81(6): 1500–1516. https://doi.org/10.1890/0012-9658(2000)081[1500:SASDIT]2.0.CO;2.
Bergeron, Y.; Charron, D. 1994. Postfire stand dynamics in a southern boreal forest (Québec): a dendroecological approach. Ecoscience. 1(2): 173–184. https://doi.org/https://doi.org/10.1080/11956860.1994.11682241.
Bergeron, Y.; Dubuc, M. 1989. Succession in the southern part of the Canadian boreal forest. Vegetatio. 79: 51–63. https://doi.org/10.1007/BF00044848.
Boisvert‐Marsh, L.; Pedlar, J.H.; de Blois, S.; Le Squin, A.; Lawrence, K.; McKenney, D.W.; [et al.]. 2022. Migration‐based simulations for Canadian trees show limited tracking of suitable climate under climate change. Diversity and Distributions. 28(11): 2330–2348. https://doi.org/10.1111/ddi.13630.
Bouchard, M.; Aquilué, N.; Périé, C.; Lambert, M.C. 2019. Tree species persistence under warming conditions: a key driver of forest response to climate change. Forest Ecology and Management. 442: 96–104. https://doi.org/10.1016/j.foreco.2019.03.040.
Boucher, Y.; Arseneault, D.; Sirois, L. 2006. Logging-induced change (1930-2002) of a preindustrial landscape at the northern range limit of northern hardwoods, eastern Canada. Canadian Journal of Forest Resources. 36(2): 505–517. https://doi.org/10.1139/x05-252.
Boulanger, Y.; Pascal, J.; Bouchard, M; D’Orangeville, L.; Périé, C.; Girardin, M.P. 2022. Multi-model projections of tree species performance in Quebec, Canada under future climate change. Global Change Biology. 28(5): 1884–1902. https://doi.org/10.1111/gcb.16014.
Boulet, B. 2007. Défauts et indices de la carie des arbres. 2nd ed. Québec City, QC: Les Publications du Québec. 317 p.
Boulfroy, E.; Forget, E.; Hofmeyer, P.V.; Kenefic, L.; Larouche, C.; Lessard, G.; [et al.]. 2012. Silvicultural guide for northern white-cedar. Gen. Tech. Rep. NRS-98. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 74 p. https://doi.org/10.2737/NRS-GTR-98.
Bourque, C.; Dumais, D.; Ruel, J.C.; Larouche, C; Raymond, P. 2022. How do advance regeneration and planted seedlings of Thuja occidentalis and Picea rubens acclimate under a first irregular shelterwood cut? Canadian Journal of Forest Research. 52(11). https://doi.org/10.1139/cjfr-2022-0072.
Bouslimi, B.; Koubaa, A.; Bergeron, Y. 2013. Variation of brown rot decay in eastern white cedar (Thuja occidentalis L.). BioRes. 8(3): 4735–4755. https://doi.org/10.15376/biores.8.3.4735-4755.
Bouslimi, B.; Koubaa, A.: Bergeron, Y. 2014. Effects of biodegradation by brown-rot decay on selected wood properties in eastern white cedar (Thuja occidentalis L.). International Biodeterioration & Biodegradation. 87: 87–98. https://doi.org/10.1016/j.ibiod.2013.11.006.
Brand, G.J.; Schopmeyer, C.S. 2008. Thuja L. In: Bonner, F.T.; Karrfalt, R.P., eds. The woody plant seed manual. Agric. Handb. 727. Washington, DC: U.S. Department of Agriculture, Forest Service: 1108–1112.
Breigenzer, P.; Fraver, S.; Gallagher, M.; Kenefic, L.; Lane, E.; Neely, J.; [et al.]. 2023. Forest structure drives fine scale variation in microclimate and fuel moisture. Webinar. 2 November 2023. North Atlantic Fire Science Exchange. https://www.firesciencenorthatlantic.org/post/webinar-forest-structure-drives-fine-scale-variation-in-microclimate-and-fuel-moisture (accessed 11 November 2025).
Briand, C.H.; Posluszny, U.; Larson, D.W. 1992a. Comparative seed morphology of Thuja occidentalis (eastern white cedar) from upland and lowland sites. Canadian Journal of Botany. 70(2): 434–438. https://doi.org/10.1139/b92-056.
Briand, C.H.; Posluszny, U.; Larson, D.W. 1992b. Differential axis architecture in Thuja occidentalis (eastern white cedar). Canadian Journal of Botany. 70(2): 340–348. https://doi.org/10.1139/b92-045.
Bryan, R.B. 2007. Focus species forestry: a guide to integrating timber and biodiversity management in Maine. 3rd ed. Falmouth, ME: Maine Audubon. 92 p.
Burns, R.M., tech. comp. 1983. Silvicultural systems for the major forest types of the United States. Agric. Handb. 445. Washington, DC: U.S. Department of Agriculture, Forest Service. 191 p.
Burridge, J.A.; Porter, S. 2023. The thin green line: windbreak advice. University of Illinois Extension, Plant Clinic Fact Sheets. https://extension.illinois.edu/plant-clinic/fact-sheets (accessed 3 March 2023).
Callan, B.E. 2024. Cedar leaf blight. In: Brandt, J.P.; Daigle, B.I.; St.-Germain, J.L.; Skinner, A.C.; Callan, B.C.; Nealis, V.G., eds. Trees, insects, mites, and diseases of Canada’s forests. Ottawa, ON: Natural Resources Canada, Canadian Forest Service. 1 p.
Carmean, W.H.; Hahn, J.T.; Jacobs, R.D. 1989. Site index curves for forest tree species in the eastern United States. Gen. Tech. Rep. NC-128. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 42 p.
Carter, D.R.; Seymour, R.S.; Fraver, S.; Weiskittel, A.R. 2017. Reserve tree mortality in two expanding-gap silvicultural systems 20 years after establishment in the Acadian forest of Maine, USA. Forest Ecology and Management. 389: 149–157. https://doi.org/10.1016/j.foreco.2016.12.031.
Caulkins, H.L., Jr. 1967. The ecology and reproduction of northern white-cedar. Dissertations and Theses (Ph.D. and Master's). Ann Arbor, MI: University of Michigan. 70 p. M.S. thesis.
Champagne, E.; Moore, B.D.; Côté, S.D.; Tremblay, J.P. 2020. Intraspecific variation in nutritional traits of neighbouring plants generates a continuum of associational effects. Journal of Vegetation Science. 31(5): 920–933. https://doi.org/10.1111/jvs.12914.
Champagne, E.; Turgeon, R.; Munson, A.D.; Raymond, P. 2021. Seedling response to simulated browsing and reduced water availability: insights for assisted migration plantations. Forests. 12(10): 1396. https://doi.org/10.3390/f12101396.
Chimner, R.A. 2022. Northern white-cedar swamp restoration. In: Storm, G.; Kenefic, L.S., eds. Northern white-cedar: the tree of life. East Lansing, MI: Michigan State University Press: 108–113.
Chimner, R.A.; Clark, R.; Webster, C.; Kenefic, L.; Kern, K. 2022. Assessing northern white-cedar (Thuja occidentalis L.) regeneration after forest harvesting across northern Michigan. 2021-2022 Annual Report. Houghton, MI: Michigan Technological University. 62 p.
Chimner, R.A.; Cooper, D.J.; Wurster, F.C.; Rochefort, L. 2017. An overview of peatland restoration in North America: Where are we after 25 years? Peatland restoration in North America. Restoration Ecology. 25(2): 283–292. https://doi.org/10.1111/rec.12434.
Chimner, R.A.; Hart, J.B. 1996. Hydrology and microtopography effects on northern white-cedar regeneration in Michigan’s Upper Peninsula. Canadian Journal of Forest Research. 26(3): 389–393. https://doi.org/10.1139/x26-043.
Chimner, R.A.; Schwartz, R.; Stensing, J.; Dahlman, R.; Krystosek, D. 2014. Northeast Minnesota white cedar plant community restoration: phases I&II. Final Tech Rep. Houghton, MI: Environment and Natural Resources Trust Fund. 71 p.
Clark, R.M.; Reo, N.J.; Hudson-Niigaanwewiidan, J.E.; Waawaashkeshikwe Collins-Downwind, L.E.; Waabhskaa, A. 2022. Gathering Giizhik in a changing landscape. Ecology and Society. 27(4): 29. https://doi.org/10.5751/ES-13605-270429.
Clark, R.M.; Webster, C.R.; Kenefic, L.S.; Kern, C.C.; Chimner, R.A. 2024. Characterizing northern white-cedar communities in harvested and unharvested lowland forests of Michigan, USA. Wetlands Ecology and Management. 32: 327–353. https://doi.org/10.1007/s11273-024-09979-y.
Coble, A.P.; Vadeboncoeur, M.A.; Berry, Z.C.; Jennings, K. 2017. Are northeastern U.S. forests vulnerable to extreme drought? Ecological Processes. 6(1): 34. https://doi.org/ 10.1186/s13717-017-0100-x.
Collier, D.E.; Boyer, M.G. 1989. The water relations of Thuja occidentalis L. from two sites of contrasting moisture availability. Botanical Gazette. 150(4): 445–448. https://doi.org/10.1086/337790.
Conway, V. 1949. The bogs of central Minnesota. Ecological Monographs. 19(2): 173–206. https://doi.org/10.2307/1948637.
Cornett, M.W.; Frelich, L.E.; Puettmann, K.J.; Reich, P.B. 2000b. Conservation implications of browsing by Odocoileus virginianus in remnant upland Thuja occidentalis forests. Biological Conservation. 93(3): 359–369. https://doi.org/10.1016/S0006-3207(99)00129-9.
Cornett, M.W.; Reich, P.B.; Puettmann, K.J. 1997. Canopy feedbacks and microtopography regulate conifer seedling distribution in two Minnesota conifer-deciduous forests. Ecoscience. 4(3): 353–364. https://doi.org/10.1080/11956860.1997.11682414.
Cornett, M.W.; Reich, P.B.; Puettmann, K.J.; Frelich, L.E. 2000a. Seedbed and moisture availability determine safe sites for early Thuja occidentalis (Cupressaceae) regeneration. American Journal of Botany. 87(12): 1807–1814. https://doi.org/10.2307/2656833.
Côté, S.D.; Rooney, T.P.; Tremblay, J.P.; Dussault, C.; Waller, D.M. 2004. Ecological impacts of deer overabundance. Annual Review of Ecology, Evolution, and Systematics. 35: 113–147. https://doi.org/10.1146/annurev.ecolsys.35.021103.105725.
Curtis, J.D. 1944. Northern white cedar on upland soils in Maine. Journal of Forestry. 42(10): 756–759. https://doi.org/10.1093/jof/42.10.756.
Curtis, J.D. 1946. Preliminary observations on northern white cedar in Maine. Ecology. 27(1): 23–36. https://doi.org/10.2307/1931014.
Curtis, J.T. 1959. The vegetation of Wisconsin: an ordination of plant communities. Madison, WI: University of Wisconsin Press. 704 p.
Danneyrolles, V.; Dupuis, S.; Arseneault, D.; Terrail, R.; Leroyer, M.; de Römer, A.; [et al.]. 2017. Eastern white cedar long-term dynamics in eastern Canada: implications for restoration in the context of ecosystem-based management. Forest Ecology and Management. 400: 502–510. https://doi.org/10.1016/j.foreco.2017.06.024.
de Blois, S.; Bouchard, A. 1995. Dynamics of Thuja occidentalis in an agricultural landscape of southern Quebec. Journal of Vegetation Science. 6(4): 531–542. https://doi.org/10.2307/3236352.
Denneler, B., Bergeron, Y.; Bégin, Y. 2010. Flooding effect on tree-ring formation of riparian eastern white-cedar (Thuja occidentalis L.), northwestern Québec, Canada. Tree-Ring Research. 66(1): 3–17. https://doi.org/10.3959/2008-11.1.
Doepker, R.V.; Ozoga, J.J. 1991. Wildlife values of northern white-cedar. Northern White Cedar in Michigan Workshop. Res. Rep. 512. East Lansing, MI: Michigan State University Agricultural Experiment Station. 122 p.
Dumais, D.; Raymond, P.; Champagne, E. 2025. Translocated southern seedlings perform as well as local provenances: insights from an ecophysiological monitoring under varying cutting modalities. New Forests. 56(20): 1–25. https://doi.org/10.1007/s11056-024-10089-z.
Dumont, A.; Ouellet, J.P.; Crête, M.; Huot, J. 2005. Winter foraging strategy of white-tailed deer at the northern limit of its range. Ecoscience. 12(4): 476–484. https://doi.org/10.2980/i1195-6860-12-4-476.
Dupuis, S.; Arseneault, D.; Sirois, L. 2011. Change from pre-settlement to present-day forest composition reconstructed from early land survey records in eastern Québec, Canada. Journal of Vegetation Science. 22(3): 564–575. https://doi.org/10.1111/j.1654-1103.2011.01282.x.
Durzan, D.J. 2009. Arginine, scurvy and Cartier’s ‘tree of life.’ Journal of Ethnobiology and Ethnomedicine. 5: 5. https://doi.org/10.1186/1746-4269-5-5.
Edwards, D.R.; Dixon, M.A. 1995a. Mechanisms of drought response in Thuja occidentalis L. I. Water stress conditioning and osmotic adjustment. Tree Physiology. 15(2): 121–127. https://doi.org/10.1093/treephys/15.2.121.
Edwards, D.R.; Dixon, M.A. 1995b. Mechanisms of drought response in Thuja occidentalis L. II. Postconditioning water stress and stress relief. Tree Physiology. 15(2): 129–133. https://doi.org/10.1093/treephys/15.2.129.
Epstein, E.E. 2017. Natural communities, aquatic features, and selected habitats of Wisconsin. In: The ecological landscapes of Wisconsin: an assessment of ecological resources and a guide to planning sustainable management. Madison, WI: Wisconsin Department of Natural Resources: H1–H293.
Erichsen-Brown, C. 1989. Medicinal and other uses of North American plants: a historical survey with special reference to the eastern Indian tribes. Mineola, NY: Dover Publications. 544 p.
Ferrell, G.M.; Strickland, A.G.; Spruill, T.B. 2007. Effects of canals and roads on hydrologic conditions and health of Atlantic white cedar at Emily and Richardson Preyer Buckridge Coastal Reserve, North Carolina, 2003-2006. Scientific Investigations Report 2007-5163. 175 p. https://doi.org/10.3133/sir20075163.
Foltz, B.W.; Johnston, W.F. 1968. Gross basal area growth of northern white-cedar is independent of stand density over a wide range. Res. Note NC-61. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 4 p.
Foster, A.C.; Maun, M.A.; Webb, D.P. 1978. Effects of road salt on eastern white cedar (Thuja occidentalis). Inf. Rep. O-X-277. Sault Ste. Marie, ON: Canadian Forest Service, Great Lakes Forest Research Centre. 25 p.
Frank, R.M.; Safford, L.O. 1970. Lack of viables in the forest floor after clearcutting. Journal of Forestry. 68(12): 776–778. https://doi.org/10.1093/jof/68.12.776.
Fraser, D.A. 1971. Interaction of gibberellic acid and photoperiod on reproductive and vegetative growth of white cedar seedlings (Thuja occidentalis L.). Proceedings of the 12th meeting of Committee on Forest Tree Breeding in Canada, 1970, pt. 2. Ottawa, ON: Canadian Forestry Service: 15–20.
Fraver, S.; Bosely-Smith, C.; Seirup, C.; Guiterman, C.H.; Schmeelk, T.; Teets, A.; [et al.]. 2024. Dendrochronological reconstruction of arborvitae leafminer (Argyresthia spp.) outbreaks on northern white-cedar (Thuja occidentalis) in Maine, USA. Canadian Journal of Forest Research. 54(4): 479–485. https://doi.org/10.1139/cjfr-2023-0193.
Fraver, S.; Kenefic, L.S.; Cutko, A.R.; White, A.S. 2020. Natural disturbance and stand structure of old-growth northern white-cedar (Thuja occidentalis) forests, northern Maine, USA. Forest Ecology and Management. 456: 117680. https://doi.org/10.1016/j.foreco.2019.117680.
Frelich, L.E.; Reich, P.B. 1995. Spatial patterns and succession in a Minnesota southern‐boreal forest. Ecological Monographs. 65(3): 325–346. https://doi.org/10.2307/2937063.
Garber, S.M.; Brown, J.P.; Wilson, D.S.; Maguire, D.A.; Heath, L.S. 2005. Snag longevity under alternative silvicultural regimes in mixed-species forests of central Maine. Canadian Journal of Forest Research. 35: 787–796. https://doi.org/10.1139/x05-021.
Gawler, S.; Cutko, A. 2010. Natural landscapes of Maine: a guide to natural communities and ecosystems. Augusta, ME: Maine Natural Areas Program, Maine Department of Conservation. 347 p.
Godman, R.M. 1958. Silvical characteristics of northern white-cedar (Thuja occidentalis). St. Paul, MN: U.S. Department of Agriculture, Forest Service, Lake States Forest Experiment Station. 17 p.
Godman, R.M.; Mattson, G.A. 1976. Seed crops and regeneration problems of 19 species in northeastern Wisconsin. Res. Pap. NC-123. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 5 p.
Greller, A.M. 2000. Vegetation in the floristic regions of North and Central America. In: Lentz, D., ed. Imperfect balance: landscape transformations in the pre-Columbian Americas. New York, NY: Columbia University Press: 39–87.
Grenier, J. 1995. Petit manuel des semences forestières au Québec. 4th ed. Québec City, QC: Gouvernement du Québec, Ministère des Ressources naturelles. 72 p.
Grondin, P.; Gosselin, J. 2013. La dynamique des peuplements et les végétations potentielles. In: Le guide sylvicole du Québec. Québec City, QC: Les Publications du Québec: 297–393.
Grossman, G.H.; Potter-Witter, K. 1990. Michigan's cedar resource: timber supply, value, and related employment. In: Lantagne, D.O., ed. Proceedings of the northern white-cedar in Michigan workshop. Res. Rep. 512. Sault Ste. Marie, MI: Department of Forestry, Michigan State University, Agricultural Experiment Station: 31–43.
Grotte, K. 2007. Old-growth northern white-cedar (Thuja occidentalis L.) stands in the mid-boreal lowlands of Manitoba. Winnipeg, MB: University of Winnipeg. 49 p. Honors thesis.
Grotte, K.L.; Heinrichs, D.K.; Tardif, J.C. 2012. Old-growth characteristics of disjunct Thuja occidentalis stands at their northwestern distribution limit, central Canada. Natural Areas Journal. 32(3): 270–282. https://doi.org/10.3375/043.032.0304.
Habeck, J.R. 1958. White cedar ecotypes in Wisconsin. Ecology. 39(3): 457–463. https://doi.org/10.2307/1931754.
Hakobjanyan, A.; Karapetyan, A.; Mairapetyan, S.; Ghahramanyan, A.; Yeghiazaryan, A.; Mayrapetyan, K. 2025. Medicinal potential of Thuja occidentalis and its essential oil. Bioactive Compounds in Health and Disease. 8(5): 166–176. https://doi.org/10.31989/bchd.v8i5.1626.
Handler, S.; Duveneck, M.J.; Iverson, L.; Peters, E.; Scheller, R.M.; Wythers, K.R.; [et al.]. 2014a. Michigan forest ecosystem vulnerability assessment and synthesis: a report from the Northwoods Climate Change Response Framework project. Gen. Tech. Rep. NRS-129. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 229 p.
Handler, S.; Duveneck, M.J.; Iverson, L.; Peters, E.; Scheller, R.M.; Wythers, K.R.; [et al.]. 2014b. Minnesota forest ecosystem vulnerability assessment and synthesis: a report from the Northwoods Climate Change Response Framework project. Gen. Tech. Rep. NRS-133. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 228 p.
Hannah, P.R. 2004. Stand structures and height growth patterns in northern white cedar stands on wet sites in Vermont. Northern Journal of Applied Forestry. 21(4): 173–179. https://doi.org/10.1093/njaf/21.4.173.
Hardin, J.W.; Leopold, D.J.; White, F.M. 2001. Textbook of dendrology. 9th ed. New York, NY: McGraw-Hill. 544 p.
Harlow, W.M. 1928. Reproduction of Adirondack white cedar by natural cuttings. Journal of Forestry. 26: 244.
Harry, I.S.; Thompson, M.R.; Lu, C.-Y.; Thorpe, T.A. 1987. In vitro plantlet formation from embryonic explants of eastern white cedar (Thuja occidentalis L.). Tree Physiology. 3(3): 273–283. https://doi.org/10.1093/treephys/3.3.273.
Heinrichs, D.K. 2009. Ecology of northern white-cedar (Thuja occidentalis L.) stands at their northwestern limit of distribution in Manitoba, Canada. Winnipeg, MB: University of Manitoba. 121 p. M.S. thesis.
Heinselman, M.L. 1963. Forest sites, bog processes, and peatland types in the Glacial Lake Agassiz region, Minnesota. Ecological Monographs. 33(4): 327–374. https://doi.org/10.2307/1950750.
Heinselman, M.L. 1970. Landscape evolution, peatland types, and the environment in the Lake Agassiz peatland natural area, Minnesota. Ecological Monographs. 40(2): 235–261. https://doi.org/10.2307/1942297.
Heinselman, M.L. 1973. Fire in the virgin forests of the Boundary Waters Canoe Area, Minnesota. Quaternary Research. 3(3): 329–382. https://doi.org/10.1016/0033-5894(73)90003-3.
Heit, C.E.; Eliason, E.J. 1940. Coniferous seed tree testing and factors affecting germination and seed quality. Tech. Bull. 255. Geneva, NY: Cornell University, New York State Agricultural Experiment Station. 45 p.
Heitzman, E.; Pregitzer, K.S.; Miller, R.O. 1997. Origin and early development of northern white-cedar stands in northern Michigan. Canadian Journal of Forest Research. 27(12): 1953–1961. https://doi.org/10.1139/cjfr-27-12-1953.
Heitzman, E.; Pregitzer, K.S.; Miller, R.O.; Lanasa, M.; Zuidema, M. 1999. Establishment and development of northern white-cedar following strip clearcutting. Forest Ecology and Management. 123(2–3): 97–104. https://doi.org/10.1016/S0378-1127(99)00025-0.
Herfindal, I.; Tremblay, J.P.; Hester, A.J.; Lande, U.S.; Wam, H.K. 2015. Associational relationships at multiple spatial scales affect forest damage by moose. Forest Ecology and Management. 348: 97–107. https://doi.org/10.1016/j.foreco.2015.03.045.
Hofmeyer, P.V.; Kenefic, L.S.; Seymour, R.S. 2010. Historical stem development of northern white-cedar (Thuja occidentalis L.) in Maine. Northern Journal of Applied Forestry. 27(3): 92–96. https://doi.org/10.1093/njaf/27.3.92.
Hofmeyer, P.V.; Seymour, R.S.; Kenefic, L.S. 2009. Influence of soil site class on growth and decay of northern white-cedar and two associates in Maine. Northern Journal of Applied Forestry. 26(2): 68–75. https://doi.org/10.1093/njaf/26.2.68.
Holcombe, J.W. 1976. The bryophyte flora of Thuja seedbed logs in a northern white-cedar swamp. The Michigan Botanist. 15: 173–181.
Housset, J.M.; Girardin, M.P.; Baconnet, M.; Carcaillet, C.; Bergeron, Y. 2015. Unexpected warming-induced growth decline in Thuja occidentalis at its northern limits in North America. Journal of Biogeography. 42(7): 1233–1245. https://doi.org/10.1111/jbi.12508.
Hunter, V. 2025. Environmental and silvicultural factors associated with northern white-cedar (Thuja occidentalis) seedling regeneration in harvested lowlands. Houghton, MI: Michigan Technological University. 46 p. M.S. thesis.
Hutt-Taylor, K.; Ziter, C.D. 2022. Private trees contribute uniquely to urban forest diversity, structure and service-based traits. Urban Forestry & Urban Greening. 78: 127760. https://doi.org/10.1016/j.ufug.2022.127760.
Janowiak, M.K.; D’Amato, A.W.; Swanston, C.W.; Iverson, L.; Thompson, F.R.; Dijak, W.D.; [et al.]. 2018. New England and northern New York forest ecosystem vulnerability assessment and synthesis: a report from the New England Climate Change Response Framework project. Gen. Tech. Rep. NRS-173. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 234 p.
Janowiak, M.K.; Iverson, L.R.; Mladenoff, D.J.; Peters, E.; Wythers, K.R.; Xi, W.; [et al.]. 2014. Forest ecosystem vulnerability assessment and synthesis for northern Wisconsin and western Upper Michigan: a report from the Northwoods Climate Change Response Framework project. Gen. Tech. Rep. NRS-136. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 247 p.
Janssen, E.; Johnson, S.A.; Reed, N.; Dickerson, P.; Whelan, C.J.; Molano-Flores, B. 2024. Impacts of road salt on seed germination of Thuja occidentalis found in natural communities adjacent to the Illinois Tollway in northeastern IL, USA. Botany. 102(8): 340–348. https://doi.org/10.1139/cjb-2023-0137.
Johnston, W.F. 1980. Northern white-cedar. In: Eyre, F.H., ed. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters: 23–24.
Johnston, W.F. 1990. Thuja occidentalis L. Northern white-cedar. In: Burns, R.M.; Honkala, B.H., tech. coords. Silvics of North America, vol. 1: Conifers. Agric. Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest Service: 580–589.
Johnston, W.F.; Booker, R.G. 1983. Northern white-cedar. In: Burns, R.M., tech. comp. Silvicultural systems for the major forest types of the United States. Agric. Handb. 445. Washington, DC: U.S. Department of Agriculture, Forest Service: 105–108.
Jokela, J.J.; Cyr, C.L. 1977. Performance of northern white-cedar in central Illinois. In: Proceedings of the 13th Lake States forest tree improvement conference. Gen. Tech. Rep. NC-50. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station: 100–106.
Jules, A.N.; Asselin, H.; Bergeron, Y.; Ali, A.A. 2018. Are marginal balsam fir and eastern white cedar stands relics from once more extensive populations in north-eastern North America? The Holocene. 28(10): 1672–1679. https://doi.org/10.1177/0959683618782.
Jutras, S.; Boileau, E.; Séto, M.; Prévost, M.; Huot, M. 2013. La remontée de la nappe phréatique. In: Le guide sylvicole du Québec, Tome 1 - Les fondements biologiques de la sylviculture. Québec City, QC: Les Publications du Québec: 789–799.
Kangas, L.C.; Schwartz, R.; Pennington, M.R.; Webster, C.R.; Chimner, R.A. 2016. Artificial microtopography and herbivory protection facilitates wetland tree (Thuja occidentalis L.) survival and growth in created wetlands. New Forests. 47(1): 73–86. https://doi.org/10.1007/s11056-015-9483-7.
Kell, J. 2009. Soil-site influences on northern white-cedar (Thuja occidentalis, L.) stem quality and growth. Orono, ME: University of Maine. 75 p. M.S. thesis.
Keller, G.J.; Slesak, R.A.; Bronson, D.; Windmuller-Campione, M.A.; McGraw, A. 2023. Effects of flood duration on seedling survival and growth of potential replacement species in black ash (Fraxinus nigra Marshall) forests threatened by emerald ash borer. Trees, Forests and People. 11: 100367. https://doi.org/10.1016/j.tfp.2022.100367.
Kenefic, L.; Villemaire-Côté, O.; Allogio, J.; Ruel, J.-C.; Clark, R.M. [In press]. Northern white-cedar. Guidebook for selecting tree and shrub species for agroforestry in the United States, vol. 1: Species profiles. Washington, DC: U.S. Department of Agriculture, Forest Service.
Kenefic, L.S.; Kabrick, J.M.; Knapp, B.O.; Raymond, P.; Clark, K.L.; D’Amato, A.W.; [et al.]. 2021. Mixedwood silviculture in North America: the science and art of managing for complex, multi-species temperate forests. Canadian Journal of Forest Research. 51(7): 921–934. https://doi.org/10.1139/cjfr-2020-0410.
Kenefic, L.S.; Kizha, A.; Fraver, S.; Roth, A.; Wason, J.; Kanoti, K. 2020. Silviculture and operations in northern white-cedar lowlands. In: Anderson, S.M.; Fergusson, M., eds. Cooperative Forestry Research Unit 2019 annual report. Orono, ME: University of Maine: 27–30.
Kern, C.C. 2022. Cedar is Ojibwe life. In: Storm, G.; Kenefic, L.S., eds. Northern white-cedar: the tree of life. East Lansing, MI: Michigan State University Press: 19–23.
Kern, C.C.; Waskiewicz, J.D.; Frelich, L.; Muñoz Delgado, B.L.; Kenefic, L.S.; Clark, K.L.; Kabrick, J.M. 2021. Understanding compositional stability in mixed wood forests of eastern North America. Canadian Journal of Forest Research. 51(7): 897–909. https://doi.org/10.1139/cjfr-2020-0492.
Kincaid, J.A. 2016. Structure and dendroecology of Thuja occidentalis in disjunct stands south of its contiguous range in the central Appalachian Mountains, USA. Forest Ecosystem. 3(1): 25. https://doi.org/10.1186/s40663-016-0085-4.
Kincaid, J.A. 2017. The effects of climate on radial growth of disjunct northern white cedar (Thuja occidentalis L.) in Virginia. Virginia Journal of Science. 68(3). https://doi.org/10.25778/WGGY-JY81.
Klugh, A.B. 1927. Ecology of the red squirrel. Journal of Mammalogy. 8(1): 1–32. https://doi.org/10.2307/1373393.
Kneeshaw, D.D.; Bergeron, Y. 1996. Ecological factors affecting the abundance of advance regeneration in Quebec’s southwestern boreal forest. Canadian Journal of Forest Research. 26(5): 888–898. https://doi.org/10.1139/x26-097.
Kost, M.A.; Albert, D.A.; Cohen, J.G.; Slaughter, B.S.; Schillo, R.K.; Weber, C.R.; Chapman, K.A. 2007. Natural communities of Michigan: classification and description. Michigan State University Report 2007-21. Lansing, MI: Michigan Natural Features Inventory. 317 p.
Kycheryavyj, V.; Popovych, V. 2023. Esthetic assessment of the ornamental forms of northern white cedar (Thuja occidentalis L.) and their use in garden and park compositions. Journal of Agricultural Sciences, Belgrade. 68(3): 315–328. https://doi.org/10.2298/JAS2303315K.
Laflèche, V.; Bernier, S.; Saucier, J.P.; Gagné, C. 2013. Indices de qualité de station des principales essences commerciales en fonction des types écologiques du Québec méridional. Québec City, QC: Ministère des Ressources naturelles du Québec, Direction des inventaires forestiers. 115 p.
Lamy, S.; Bouchard, A.; Simon, J.P. 1999. Genetic structure, variability, and mating system in eastern white cedar (Thuja occidentalis) populations of recent origin in an agricultural landscape in southern Quebec. Canadian Journal of Forest Research. 29(9): 1383–1392. https://doi.org/10.1139/x99-107.
Lanasa, M.; Zuidema, M. 1991. Site preparation for northern white cedar. CEDAR Action Group Note 2. East Lansing, MI: Michigan State University. 6 p.
Larouche, C.; Kenefic, L.S.; Ruel, J.C. 2010. Northern white-cedar regeneration dynamics on the Penobscot Experimental Forest in Maine: 40-year results. Northern Journal of Applied Forestry. 27(1): 5–12. https://doi.org/10.1093/njaf/27.1.5.
Larouche, C.; Ruel, J.C. 2015. Development of northern white-cedar regeneration following partial cutting, with and without deer. Forests. 6(2): 344–359. https://doi.org/10.3390/f6020344.
Larouche, C.; Ruel, J.C.; Lussier, J.M. 2011. Factors affecting northern white-cedar (Thuja occidentalis) seedling establishment and early growth in mixed wood stands. Canadian Journal of Forest Research. 41(3): 568–582. https://doi.org/10.1139/X10-233.
Larson, D.W.; Doubt, J.; Matthes-Sears, U. 1994. Radially sectored hydraulic pathways in the xylem of Thuja occidentalis as revealed by the use of dyes. International Journal of Plant Sciences. 155(5): 569–582. https://doi.org/10.1086/297195.
Larson, D.W.; Kelly, P.E. 1991. The extent of old-growth Thuja occidentalis on cliffs of the Niagara escarpment. Canadian Journal of Botany. 69(7): 1628–1636. https://doi.org/10.1139/b91-206.
Lesage, L.; Crête, M.; Huot, J.; Dumont, A.; Ouellet, J.P. 2000. Seasonal home range size and philopatry in two northern white-tailed deer populations. Canadian Journal of Zoology. 78(11): 1930–1940. https://doi.org/10.1139/z00-117.
Li, J.; Zhang, Y.; Ruhsam, M.; Milne, R.I.; Wang, Y.; Wu, D.; [et al.]. 2022. Seeing through the hedge: phylogenomics of Thuja (Cupressaceae) reveals prominent incomplete lineage sorting and ancient introgression for Tertiary relict flora. Cladistics. 38(2): 187–203. https://doi.org/10.1111/cla.12491.
Logan, K.T. 1969. Growth of tree seedlings as affected by light intensity. IV. Black spruce, white spruce, balsam fir, and eastern white cedar. Canadian Forest Service Publication 1256. Chalk River, ON: Government of Canada, Department of Fisheries and Forestry. 12 p.
Lumis, G.; Johnson, A.G. 1980. Transplanting method influences survival and growth of bare-root coniferous nursery stock. Arboriculture & Urban Forestry. 6(10): 261–268. https://10.48044/jauf.1980.062.
Lussier, J.M.; Meek, P. 2014. Managing heterogeneous stands using multiple-treatment irregular shelterwood method. Journal of Forestry. 112(3): 287–295. https://doi.org/10.5849/jof.13-041.
Maki, T.E. 1931. Some factors affecting the growth and reproduction of Thuja occidentalis in swamps of Minnesota. St. Paul, MN: University of Minnesota. 60 p. M.S. thesis.
Man, R.; Kayahara, G.J.; Dang, Q.L.; Rice, J.A. 2009. A case of severe frost damage prior to budbreak in young conifers in northeastern Ontario: Consequence of climate change? The Forestry Chronicle. 8(3): 453–462. https://doi.org/10.5558/tfc85453-3.
Man, R.; Lu, P.; Parker, W.C.; Kayahara, G.J.; Dang, Q.L. 2013. Light-use efficiency and photosynthetic capacity of northern white-cedar (Thuja occidentalis L.) cuttings originated from layering and seed. Northern Journal of Applied Forest Ecology. 30(2): 53–57. https://doi.org/https://doi.org/10.5849/njaf.12-010.
Martin, P.C. 1950. A morphological comparison of biota and Thuja. Proceedings of the Pennsylvania Academy of Science. 24: 65–112. http://www.jstor.org/stable/44109440 (accessed 28 May 2026).
Matthes-Sears, U.; Larson, D.W. 1990. Environmental controls of carbon uptake in two woody species with contrasting distributions at the edge of cliffs. Canadian Journal of Botany. 68(11): 2371–2380. https://doi.org/10.1139/b90-302.
Matthes-Sears, U.; Larson, D.W. 1995. Rooting characteristics of trees in rock: a study of Thuja occidentalis on cliff faces. International Journal of Plant Sciences. 156(5): 679–686. https://doi.org/10.1086/297290.
Matthes‐Sears, U.; Stewart, S.C.; Larson, D.W. 1991. Sources of allozymic variation in Thuja occidentalis in southern Ontario, Canada. Silvae Genetica. 40(3–4): 100–105.
Michigan Department of Natural Resources. 2025. MICedar project: lowland cedar mastication map. Sault Ste. Marie, MI. https://www.michigandnr.com/ftp/forestry/tsreports/Maps/WUP%20Cult/Mi%20Cedar/45184040.pdf (accessed 9 November 2025).
Miller, R.O. 1990. Ecology and management of northern white-cedar. Presented at the Regenerating Conifer Cover in Deer Yards workshop. North Bay, ON. 13 p.
Minnesota Department of Natural Resources. 2019. Minnesota 2018 forest health annual report. St. Paul, MN: Minnesota Department of Natural Resources, Division of Forestry, Forest Health Unit. 51 p.
Minnesota Department of Natural Resources. 2020. Minnesota 2019 forest health annual report. St. Paul, MN. Minnesota Department of Natural Resources, Division of Forestry, Forest Health Unit. 44 p.
Minnesota Department of Natural Resources. 2021. Minnesota 2020 forest health annual report. St. Paul, MN: Minnesota Department of Natural Resources, Division of Forestry, Forest Health Unit. 43 p.
Moen, A.N. 1976. Energy conservation by white-tailed deer in the winter. Ecology. 57(1): 192–198. https://doi.org/10.2307/1936411.
Moerman, D.E. 1998. Native American ethnobotany. Portland, OR: Timber Press. 927 p.
Morrison, S.F.; Forbes, G.J.; Young, S.J.; Lusk, S. 2003. Within-yard habitat use by white-tailed deer at varying winter severity. Forest Ecology and Management. 172(2–3): 173–182. https://doi.org/10.1016/S0378-1127(01)00809-X.
Nelson, T.C. 1951. A reproduction study of northern white cedar including results of investigations under federal aid in wildlife restoration project Michigan 49-R. Lansing, MI: Department of Conservation, Game Division. 108 p.
New Brunswick Department of Natural Resources. 2007. Our landscape heritage: the story of ecological land classification in New Brunswick. Fredericton, NB: New Brunswick Department of Natural Resources. 359 p.
Noland, T.L.; Man, R.; Irvine, M. 2017. Glyphosate tolerance of eastern white cedar: third year results. Forestry Chronicle. 93(2): 190–193. https://doi.org/10.5558/tfc2017-025.
Nour, K.A.; Thorpe, T.A. 1993. In vitro shoot multiplication of eastern white cedar (Thuja occidentalis). In Vitro Cellular & Developmental Biology – Plant. 29 (2): 65–71. https://doi.org/10.1007/BF02632254.
Nour, K.A.; Yeung, E.C.; Thorpe, T.A. 1993. Shoot bud histogenesis from mature embryos and shoots of eastern white cedar (Thuja occidentalis L.) cultured in vitro. International Journal of Plant Sciences. 154(3): 378–385. https://doi.org/10.1086/297119.
Ontario Extension. 1995. Designing and caring for windbreaks. Publ. 50515. Toronto, ON: LandOwner Resource Centre and Faculty of Forestry, University of Toronto. 6 p.
Ontario Ministry of Natural Resources and Forestry. 2022a. The forest resources of Ontario 2021. Sault Ste. Marie, ON. https://public.tableau.com/app/profile/larlo/viz/TheForestResourcesofOntario2021/Landbase (accessed 31 March 2025).
Ontario Ministry of Natural Resources and Forestry. 2022b. Seed transfer policy spatial direction. Sault Ste. Marie, ON. https://public.tableau.com/app/profile/larlo/viz/SeedSourceOntario/Intro (accessed 21 February 2025).
Ontario Ministry of Natural Resources and Forestry. 2024. Forest health conditions in Ontario 2023. Peterborough, ON: Ontario Ministry of Natural Resources and Forestry, Science and Research Branch. 125 p. https://www.ontario.ca/files/2024-05/mnrf-srb-forest-health-conditions-report-2023-2024-05-09.pdf (accessed 21 February 2025).
Ott, C.A.; Chimner, R.A. 2016. Long-term peat accumulation in temperate forested peatlands (Thuja occidentalis swamps) in the Great Lakes region of North America. Mires and Peat. 18(1): 1–9. https://doi.org/10.19189/MaP.2015.OMB.182.
Ouarmim, S.; Paradis, L.; Asselin, H.; Bergeron, Y.; Ali, A.; Hély, C. 2016. Burning potential of fire refuges in the boreal mixedwood forest. Forests. 7(10): 246. https://doi.org/10.3390/f7100246.
Packard, A.S. 1871. First report on the injurious and beneficial insects of the State of Massachusetts. Boston, MA: Secretary of the Massachusetts Board of Agriculture. 4 p.
Pandey, M.; Rajora, O.P. 2012a. Genetic diversity and differentiation of core vs peripheral populations of eastern white cedar, Thuja occidentalis (Cupressaceae). American Journal of Botany. 99(4). https://doi.org/10.3732/ajb.1100116.
Pandey, M.; Rajora, O.P. 2012b. Higher fine-scale genetic structure in peripheral than in core populations of a long-lived and mixed-mating conifer - eastern white cedar (Thuja occidentalis L.). BMC Evolutionary Biology. 12(48). https://bmcecolevol.biomedcentral.com/articles/10.1186/1471-2148-12-48 (accessed 28 May 2026).
Patterson, J.E.H. 2008. Forest fragmentation effects and the cavity nest material requirements of northern flying squirrels and red squirrels in a fragmented secondary hardwood forest region of Ontario, Canada. Doctoral and Master theses prior to ETD mandate (pre-2009). Toronto, ON: University of Toronto. 98 p. M.S. thesis.
Patton, S.R.; Russell, M.B.; Windmuller-Campione, M.A.; Frelich, L.E. 2021. White-tailed deer herbivory impacts on tree seedling and sapling abundance in the Lake States region of the USA. Annals of Forest Science. 78(4): 91. https://doi.org/10.1007/s13595-021-01108-6.
Paul, V.; Bergeron, Y.; Tremblay, F. 2014. Does climate control the northern range limit of eastern white cedar (Thuja occidentalis L.)? Plant Ecology. 215(2): 181–194. https://doi.org/10.1007/s11258-013-0288-5.
Peek, J.M.; Urich, D.L.; Mackie, R.J. 1976. Moose habitat selection and relationships to forest management in northeastern Minnesota. Wildlife Monographs. 48: 3–65. https://www.jstor.org/stable/3830485 (accessed 28 May 2026).
Perry, D.J.; Knowles, P. 1990. Evidence of high self-fertilization in natural populations of eastern white cedar (Thuja occidentalis). Canadian Journal of Botany. 68(3): 663–668. https://doi.org/10.1139/b90-086.
Perry, D.J.; Knowles, P.; Yeh, F.C. 1990. AIIozyme variation of Thuja occidentalis L. in northwestern Ontario. Biochemical Systematics and Ecology. 18(2–3): 111–115. https://doi.org/10.1016/0305-1978(90)90045-H.
Petraborg, W.H. 1969. Regeneration of white cedar in northern swamps. Journal of the Minnesota Academy of Science. 36(1): 20–22. https://digitalcommons.morris.umn.edu/jmas/vol36/iss1/7 (accessed 28 May 2026).
Pike, C.C.; Haase, D.L. 2024. Seed-transfer guidelines for important tree species in the eastern United States. Agric. Handb. 801. Washington, DC: U.S. Department of Agriculture, Forest Service. 135 p.
Pothier, D.; Savard, F. 1998. Actualisation des tables de production pour les principales espèces forestières du Québec. Publ. RN983054. Sainte-Foy, QC: Ministère des Ressources naturelles, Forêt Québec. 183 p.
Prasad, A.; Pedlar, J; Peters, M.; Matthews, S.; Iverson, L.; McKenney, D.; [et al.]. 2024. Understanding climate change dynamics of tree species: implications for future forests. In: McNulty, S.G., ed. Future forests: mitigation and adaptation to climate change. New York, NY: Elsevier: 151–175.
Prasad, A.; Pedlar, J.; Peters, M.; McKenney, D.; Iverson, L.; Matthews, S.; [et al.]. 2020a. Combining US and Canadian forest inventories to assess habitat suitability and migration potential of 25 tree species under climate change. Diversity and Distributions. 26: 1142–1159. https://doi.org/10.1111/ddi.13078.
Prasad, A.; Pedlar, J.; Peters, M.; McKenney, D.; Iverson, L.; Matthews, S.; [et al.]. 2020b. Data from: combining US and Canadian forest inventories to assess habitat suitability and migration potential of 25 tree species under climate change. Dryad. https://doi.org/10.5061/dryad.qz612jmbn.
Pregitzer, K.S. 1991. The ecology of northern white-cedar. In: Lantagne, D.O., ed. Proceedings of the northern white-cedar in Michigan workshop. Sault Ste. Marie, MI: Michigan State University: 7–12.
Radeloff, V.C.; Hammer, R.B.; Stewart, S.I. 2005. Rural and suburban sprawl in the U.S. midwest from 1940 to 2000 and its relation to forest fragmentation. Conservation Biology. 19(3): 793–805. https://doi.org/10.1111/j.1523-1739.2005.00387.x.
Rayfield, B.; Paul, V.; Tremblay, F.; Fortin, M.J.; Hély, C.; Bergeron, Y. 2020. Influence of habitat availability and fire disturbance on a northern range boundary. Journal of Biogeography. 48(2): 394–404. https://doi.org/10.1111/jbi.14004.
Raymond, P.; Bédard, S.; Roy, V.; Larouche, C.; Tremblay, S. 2009. The irregular shelterwood system: review, classification, and potential application to forests affected by partial disturbances. Journal of Forestry. 107(8): 405–413. https://doi.org/10.1093/jof/107.8.405.
Reiners, W.A. 1972. Foliage production by Thuja occidentalis L. from biomass and litter fall estimates. The American Midland Naturalist. 92(2): 340–345. https://doi.org/10.2307/2424299.
Reuling, L.F.; Kern, C.C.; Kenefic, L.S.; Bronson, D.R. 2019. The northern white-cedar recruitment bottleneck: understanding the effects of substrate, competition, and deer browsing. Forests. 10(6): 501. https://doi.org/10.3390/f10060501.
Rhemtulla, J.M.; Mladenoff, D.J.; Clayton, M.K. 2009. Legacies of historical land use on regional forest composition and structure in Wisconsin, USA (Mid-1800s–1930s-2000s). Ecological Applications. 19(4): 1061–78. https://doi.org/10.1111/jbi.14004.
Rich, R.L.; Frelich, L.E.; Reich, P.B. 2007. Wind-throw mortality in the southern boreal forest: effects of species, diameter and stand age. Journal of Ecology. 95(6): 1261–1273. https://doi.org/10.1111/j.1365-2745.2007.01301.x.
Riege, D.A. 1991. Habitat specialization and social factors in distribution of red and gray squirrels. Journal of Mammalogy. 72(1): 152–162. https://doi.org/10.2307/1381990.
Roe, E.I. 1947. Thinning in cedar swamps. Tech. Note 279. St. Paul, MN: U.S. Department of Agriculture, Forest Service, Lake States Forest Experiment Station. 1 p.
Rose, A.H.; Lindquist, O.H.; Nystrom, K.L. 2000. Insects of eastern larch, cedar and juniper. Natural Resources Canada Forestry Tech. Rep. No. 28. Ottawa, ON: Canadian Forest Service. 104 p.
Royo, A.A.; Raymond, P.; Kern, C.C.; Adams, B.T.; Bronson, D.; Champagne, E.; [et al.]. 2023. Desired regeneration through assisted migration (DREAM): implementing a research framework for climate-adaptive silviculture. Forest Ecology and Management. 546: 121298. https://doi.org/10.1016/j.foreco.2023.121298.
Rudolf, P.O. 1949. Handling northern white-cedar stands for wood and wildlife in the Lake States. Misc. Rep. 3. St. Paul, MN: U.S. Department of Agriculture, Forest Service, Lake States Forest Experiment Station. 6 p.
Ruel, J.C. 2000. Factors influencing windthrow in balsam fir forests: from landscape studies to individual tree studies. Forest Ecology and Management. 135(1–3): 169–178. https://doi.org/10.1016/S0378-1127(00)00308-X.
Ruel, J.C. 2020. Ecosystem management of eastern Canadian boreal forests: potential impacts on wind damage. Forests. 11(5): 578. https://doi.org/10.3390/f11050578.
Ruel, J.C.; Lussier, J.M.; Morissette, S.; Ricodeau, N. 2014. Growth response of northern white-cedar (Thuja occidentalis) to natural disturbances and partial cuts in mixed wood stands of Quebec, Canada. Forests. 5(6): 1194–1211. https://doi.org/10.3390/f5061194.
Russell, M.B.; Weiskittel, A.R. 2012. Assessing and modeling snag survival and decay dynamics for the primary species in the Acadian forest of Maine, USA. Forest Ecology and Management. 284: 230–240. https://doi.org/10.1016/j.foreco.2012.08.004.
Saucier, L.; Ruel, J.C.; Larouche, C. 2018. Variations in northern white-cedar (Thuja occidentalis) regeneration following operational selection cutting in mixed wood stands of western Quebec. Canadian Journal of Forest Research. 48: 1311–1319. https://doi.org/10.1139/cjfr-2018-0180.
Schaffer, W.W. 1996. Silvicultural guidelines for the eastern white cedar. Tech. Rep. TR-006. London, ON: Ontario Ministry of Natural Resources, Southern Region Science & Technology Transfer Unit. 62 p.
Schopmeyer, C.S. 1974. Thuja L. arborvitae. In: Schopmeyer, C.S., tech. coord. Seeds of woody plants in the United States. Agric. Handb. 450. Washington, DC: U.S. Department of Agriculture, Forest Service: 805–809.
Schulz, K.; Barry, A.; Kenefic, L.S.; Wason, J.W. 2024. Contrasting survival strategies for two northern conifer trees to extreme drought and flood events. Tree Physiology. 44(10): tpae117. https://doi.org/10.1093/treephys/tpae117.
Scott, M.L.; Murphy, P.G. 1987. Regeneration patterns of northern white cedar, an old-growth forest dominant. The American Midland Naturalist. 117(1): 10–16. https://doi.org/10.2307/2425702.
Silver, G.T. 1957. Studies on the arborvitae leaf miners in New Brunswick (Lepidoptera: Yponomeutidae and Gelechiidae). The Canadian Entomologist. 89(4): 171–182. https://doi.org/10.4039/Ent89171-4.
Smith, R. 2017. Plant species richness and diversity of northern white-cedar (Thuja occidentalis) swamps in northern New York: effects and interactions of multiple variables. Syracuse, NY: State University of New York College of Environmental Science and Forestry. 87 p. M.S. thesis.
Sousa-Silva, R.; Lambry, T.; Cameron, E.; Belluau, M.; Paquette, A. 2023. Urban forests – different ownership translates to greater diversity of trees. Urban Forestry & Urban Greening. 88: 128084. https://doi.org/10.1016/j.ufug.2023.128084.
Storm, G.L.; Kenefic, L.S. 2022. Northern white-cedar: the tree of life. East Lansing, MI: Michigan State University Press. 200 p.
Sucoff, E. 1975. Effect of deicing salts on woody vegetation along Minnesota roads. Tech. Bull. 303. St. Paul, MN: University of Minnesota, Minnesota Agricultural Experiment Station. 49 p.
Szasz Len, A.M.; Holonec, L.; Truța, A.; Rebrean, F.A. 2015. Effect of cutting size on the rooting of Thuja occidentalis 'Columna.' Bulletin of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca. Horticulture. 72(1): 233–234. https://doi.org/10.15835/buasvmcn-hort:10999.
Tardif, J.; Bergeron, Y. 1997. Comparative dendroclimatological analysis of two black ash and two white cedar populations from contrasting sites in the Lake Duparquet region, northwestern Québec. Canadian Journal of Forest Research. 27(1): 108–116. https://doi.org/10.1139/x96-150.
Toumey, J.; Stevens, C. 1928. The testing of coniferous tree seeds. Bull. No. 21. New Haven, CT: Yale University, School of Forestry. 23 p.
University of Minnesota Urban Forestry Outreach and Research Nursery and Lab. 2024. Northern white cedar – Thuja occidentalis. St. Paul, MN. https://trees.umn.edu/northern-white-cedar-thuja-occidentalis (accessed 26 February 2024).
U.S. Department of Agriculture, Forest Service [USDA Forest Service]. 1948. Thuja L. In: Woody-plant seed manual. Misc. Pub. 651. Washington, DC: U.S. Department of Agriculture, Forest Service: 354–356.
U.S. Department of Agriculture, Natural Resources Conservation Service [USDA Natural Resources Conservation Service]. [N.d.]. The PLANTS Database. Greensboro, NC. https://plants.sc.egov.usda.gov/plant-profile/TH0C2 (accessed 22 April 2026).
U.S. Environmental Protection Agency. 2024. Ecoregions of North America. https://www.epa.gov/eco-research/ecoregions-north-america (accessed 18 February 2025).
van Kampen, R.; Fisichelli, N.A.; Zhang, Y.; Wason, J. 2022. Drought timing and species growth phenology determine intra-annual recovery of tree height and diameter growth. AoB Plants. 14(3): 1–10. https://doi.org/10.1093/aobpla/plac012.
Vanderschoot, M. 2024. Higher fall precipitation rather than high summer temperature negatively impacts Thuja occidentalis growth at the boreal-temperate ecotone. Ann Arbor, MI: University of Michigan. 39 p. M.S. thesis.
Vasiliauskas, R. 2001. Damage to trees due to forestry operations and its pathological significance in temperate forests: a literature review. Journal of Forestry. 74(4): 319–336. https://doi.org/10.1093/forestry/74.4.319.
Verme, L.J. 1973. Movements of white-tailed deer in Upper Michigan. The Journal of Wildlife Management. 37(4): 545–552. https://doi.org/10.2307/3800320.
Verme, L.J.; Johnston, W.F. 1986. Regeneration of northern white cedar deeryards in Upper Michigan. The Journal of Wildlife Management. 50(2): 307–313. https://doi.org/10.2307/3801918.
Villemaire-Côté, O.; Hester, A.J.; Tremblay, J.P.; Ruel, J.C. 2023. Testing the response of northern white-cedar to simulated browsing: evidence of apparent compensatory growth. Forest Ecology and Management. 546: 121334. https://doi.org/10.1016/j.foreco.2023.121334.
Villemaire-Côté, O.; Ruel, J.C.; Sirois, L. 2017. Development of northern white-cedar (Thuja occidentalis L.) plantations within and outside deer yards. Forests. 8(9): 326. https://doi.org/10.3390/f8090326.
Villemaire-Côté, O.; Ruel, J.C.; Tremblay, J.P. 2022. Reduction in local white-tailed deer abundance allows the positive response of northern white cedar regeneration to gap dynamics. Canadian Journal of Forest Research. 52(10): 1383–1397. https://doi.org/10.1139/cjfr-2022-0063.
Villemaire-Côté, O.; Tremblay, J.P.; Kenefic, L.S.; Ruel, J.C. 2024. Partial cutting favours northern white-cedar regeneration but does not ensure recruitment to canopy: Does browsing matter? Forestry: An International Journal of Forest Research. 97(1): 162–172. https://doi.org/10.1093/forestry/cpad030.
Walter, D.W.; Beringer, J.; Hansen, L.P.; Fischer, J.W.; Millspaugh, J.J.; Vercauteren, K.C. 2011. Factors affecting space use overlap by white-tailed deer in an urban landscape. International Journal of Geographical Information Science. 25(3): 379–392. https://doi.org/10.1080/13658816.2010.524163.
Wason, J. 2022. Reproduction by layering. In: Storm, G.L.; Kenefic, L.S., eds. Northern white-cedar: the tree of life. East Lansing, MI: Michigan State University Press: Urban Forestry Outreach and Research Nursery and Lab: 48–50.
Watson, R. 1936. Northern white-cedar. Misc. Rep. U.S. Department of Agriculture, Forest Service, Region 9. 44 p.
Weiskittel, A.R.; Seymour, R.S.; Hofmeyer, P.; Kershaw, J.A. 2010. Modelling primary branch frequency and size for five conifer species in Maine, USA. Forest Ecology and Management. 259(10): 1912–1921. https://doi.org/10.1016/j.foreco.2010.01.052.
Weiskopf, S.R.; Ledee, O.E.; Thompson, L.M. 2019. Climate change effects on deer and moose in the Midwest. The Journal of Wildlife Management. 83(4): 769–781. https://doi.org/10.1002/jwmg.21649.
Wesely, N.; Fraver, S.; Kenefic, L.S.; Weiskittel, A.R.; Ruel, J.C.; Thompson, M.E.; [et al.]. 2018. Structural attributes of old-growth and partially harvested northern white-cedar stands in northeastern North America. Forests. 9(7): 376. https://doi.org/10.3390/f9070376.
Xu, H.; Tremblay, F.; Bergeron, Y. 2013. Development and multiplexed amplification of SSR markers for Thuja occidentalis (Cupressaceae) using shotgun pyrosequencing. Applications in Plant Sciences. 1(5): 1200427. https://doi.org/10.3732/apps.1200427.
Xu, H.; Tremblay, F.; Bergeron, Y. 2018. Importance of landscape features and fire refuges on genetic diversity of Thuya occidentalis L., in boreal fire dominated landscapes. Conservation Genetics. 19(5): 1231–1241. https://doi.org/10.1007/s10592-018-1091-6.
Xu, H.; Tremblay, F.; Bergeron, Y.; Paul, V.; Chen, C. 2012. Genetic consequences of fragmentation in "arbor vitae," eastern white cedar (Thuja occidentalis L.), toward the northern limit of its distribution range. Ecology and Evolution. 2(10): 2506–2520. https://doi.org/10.1002/ece3.371.
Zasada, Z.A. 1952. Reproduction on cut-over swamplands in the Upper Peninsula of Michigan. Stn. Pap. 27. St. Paul, MN: U.S. Department of Agriculture, Forest Service, Lake States Forest Experiment Station. 15 p.
Zenner, E.K.; Almendinger, J.C. 2012. Identifying restoration opportunities for northern white cedar by contrasting historical and modern inventories in an ecological classification system context. Ecological Restoration. 30(3): 169–179. https://doi.org/10.3368/er.30.3.169.
Zhao, J.; Hartmann, H.; Trumbore, S.; Ziegler, W.; Zhang, Y. 2013. High temperature causes negative whole-plant carbon balance under mild drought. New Phytologist. 200(2): 330–339. https://doi.org/10.1111/nph.12400.
Zieliński, J.; Kosiński, P.; Danielewicz, W. 2019. Hybrids of Thuja occidentalis and T. plicata (Cupressaceae) – Is this a fact or misunderstanding? Rocznik Polskiego Towarzystwa Dendrologicznego. 67: 9–24.
Zontikov, D.N.; Zontikova, S.; Sergeev, R.; Shurgin, A. 2016. The influence of nutrient medium and growth regulators on in vitro morphogenesis of Thuja occidentalis L. In: Kim, D.K.; Jung, J.; Seo, J., eds. Proceedings, international conference on civil, architectural, structural and constructional engineering. Leiden, the Netherlands: CRC Press: 153–156.
We thank Anna Buchanan for her help with citations and references, and Victoria Hunter and Neil Thompson for providing photographs.