Lythrum salicaria, purple loosestrife
Munger, Gregory T. 2002. Lythrum salicaria, purple loosestrife. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://research.fs.usda.gov/feis/species-reviews/lytsal
| Abbreviation | Common Name | Scientific Name | Classification | Status |
|---|---|---|---|---|
| Plants | ||||
| LYTSAL | purple loosestrife | Lythrum salicaria | Life Form: Plants/Forb Kingdom: Plantae Class: Dicot Order: Myrtales Family: Lythraceae Genus: Lythrum | Fed. Protected: No Nativity: Nonnative Invasiveness: Invasive |
Taxonomy
The currently accepted scientific name of purple loosestrife is Lythrum salicaria L. (Lythraceae) [57,60,71].
Purple loosestrife will hybridize with European wand loosestrife (Lythrum virgatum) and winged loosestrife (Lythrum alatum) [3,92]. A number of different horticultural cultivars have been developed from purple loosestrife and wand loosestrife. Although some are purported to be sterile, crosses within and between cultivars and wild Lythrum spp. are often compatible, and identification of cultivars and crosses is problematic [92,118].
Synonyms
None
Other Common Names
None
General Distribution
Purple loosestrife occurs in all but 6 states of the continental United States [132]. It is found along the Atlantic coast from North Carolina to Maine [129] and is scattered but spreading in the western United States [81]. Purple loosestrife occurs most commonly in the United States in the Midwest and Northeast, corresponding closely with the geographic extent of the Wisconsin glaciation [81,125]. It is distributed across the southernmost tier of Canadian provinces from Newfoundland to British Columbia, with northern limits generally around 51° N [79]. The greatest concentrations in Canada are in southwestern Quebec, southern Ontario, southern Manitoba, and in British Columbia's lower Fraser Valley [46]. The Plants Database provides a map to purple loosestrife's distribution in the United States.
Considered native to Eurasia [125], purple loosestrife has a widespread circumpolar distribution throughout the northern hemisphere, except in extremely cold and arctic regions [111,129]. Although the precise origin of purple loosestrife colonization in North America is unknown, it was well established by the 1830s within coastal wetlands along the New England seaboard, having likely been introduced via ship ballast soil. Further introductions are thought to have occurred intentionally by early American horticulturalists. Initial spread of purple loosestrife into the interior of eastern North America occurred primarily via routes of maritime commerce, such as canals, rivers and the Great Lakes. Spread into the arid West appears to be closely related to development of irrigation systems within that region [129].
The biogeographic classification systems listed in table A1 are presented as a guide to demonstrate where purple loosestrife could potentially be found based on reported occurrence and on biological tolerance to factors likely to limit its distribution. For instance, because purple loosestrife does not tolerate salt water, classifications describing a variety of salt marsh habitats are excluded from these lists. Additionally, many of these classifications are named for predominantly upland habitats that nevertheless contain sometimes-substantial wetland areas where purple loosestrife could potentially occur. Precise distribution information is lacking because of gaps in the understanding of biological and ecological characteristics of non-native species and because introduced species may still be expanding their habitable range. Therefore these lists are speculative and may not be complete.
States and Provinces
- United States: AL AR CA CO CT DE ID IL IN IA KS KY ME MD MA MI MN MS MO MT NE NV NH NJ NY NC ND OH OK OR PA RI SD TN TX UT VT VA WA WV WI WY DC
- Canada: AB BC MB NB NF NS ON PE PQ SK
Site Characteristics
Throughout its global distribution purple loosestrife is strongly linked with temperate climate and moist or saturated soils [129]. Unshaded, newly-exposed, moist soil appears most favorable for seedling establishment. Riverine habitats subjected to periodic but infrequent scouring, or lacustrine habitats subject to periodic water level reduction such as drought-exposed lakeshore or seasonal impoundment drawdown are good examples of habitats at risk of invasion. Once purple loosestrife seedlings become established, adults are quite flood tolerant [118]. Moisture is the most critical factor for growth and reproduction, but well-established plants can persist at dry sites for many years [21]. Keddy and Ellis [64] examined purple loosestrife seedling recruitment along a water level gradient, simulating conditions ranging from water levels 2 inches (5 cm) below the soil surface to standing water up to 4 inches (10 cm) above the soil surface. They found there was no significant (p = 0.44) effect of water depth on germination and early establishment of seedlings, indicating a broad tolerance for water level in the recruitment phase of purple loosestrife life history. Stream corridors with steep elevational gradients may be less susceptible to colonization by purple loosestrife due to gravitational constraints on seed dispersal [128].
Northern limits of purple loosestrife distribution may be strongly influenced by low growing season temperature. Under controlled conditions, growth was severely restricted at 46.4 degrees Fahrenheit (8 °C) compared with more "characteristic" growth at 64.4 degrees Fahrenheit (18°C) [113].
Purple loosestrife is found on both calcareous and acidic soils [111,113,129] and tolerates low-nutrient soils [111,117,141]. Typically found in open areas, purple loosestrife will tolerate some shade, but growth, reproduction and survival may be substantially reduced under shaded conditions [110,118].
Several characteristics of wetland or riparian habitats have been identified that may be predictive of invasibility by purple loosestrife. Assuming dispersal is largely via floating propagules, isolated wetland basins may be less susceptible to purple loosestrife colonization than areas with interconnected waterways. Additionally, narrow streams with steep gradients are probably less susceptible, because they are frequently scoured and contain fewer areas of slack water, while slower, broader flows are more likely to contain habitat suitable for colonization. Riparian areas that are mostly shaded are also less susceptible because purple loosestrife seedlings require relatively high light levels. Finally, the presence of one or more commonly associated taxa, such as cattails (Typha spp.), reed canarygrass (Phalaris arundinacea), sedges (Carex spp.), and rushes (Juncus spp.) may indicate a habitat that is highly susceptible to invasion by purple loosestrife [129].
Plant Communities
Purple loosestrife is found across a variety of freshwater wetland habitats in North America, and consequently is associated with a variety of plant taxa, functional guilds and communities. Habitats where it is likely to be found include: freshwater marshes [27,93,102,105,127,129], streambanks or lakeshores [130], floodplains [80,102,129], seasonally-wet meadows/wet prairies [8,10,129], bogs [127], vernal ponds [58], openings in forested swamps [63], intermittent streams [105], shallow impoundments, and ditches and canals [102,105]. Purple loosestrife is listed by the U.S. Fish and Wildlife Service Office of Biological Services as a typical broadleaf plant of Palustrine Persistent Emergent Wetlands [94].
In a host-specificity test of potential biological control agents for purple loosestrife, Blossey and Schroeder [21] included 13 plant species said to "occur in the same habitat" as purple loosestrife and were "of wildlife importance." Although these species are not necessarily distributed homogeneously or systematically across the North American landscape, they likely represent a reasonable sample of typical plant associates. These species were common cattail (Typha latifolia), broadfruit bur-reed (Sparganium eurycarpum), broadleaf arrowhead (Sagittaria latifolia), annual wildrice (Zizania aquatica), Olney threesquare (Scirpus americanus), hardstem bulrush (Scirpus acutus), longhair sedge (Carex comosa), sandbar willow (Salix exigua), curly dock (Rumex crispus), longroot smartweed (Polygonum amphibium), lambsquarters (Chenopodium album), cursed buttercup (Ranunculus sceleratus) and St. Anthony's turnip (Ranunculus bulbosus).
Classifications describing plant communities in which purple loosestrife is a dominant species are:
- New York [105]
- Washington [58]
Botanical Description
Purple loosestrife.
Purple loosestrife is a non-native, perennial wetland herb [14,129]. Stems are erect, 1 to 8 feet (0.3-2.4 m) tall, becoming woody with age and persisting through winter and up to 2 years [9,14,73,118]. Mature, long-established plants are often 10 feet (3 m) tall and 5 feet (1.5 m) wide [129]. Plants may become increasingly bush-like by producing greater numbers of basal stems from the same rootstock each year [14,79,118,129]. Plants begin producing multiple stems from a single rootstock as early as the 2nd growing season [102]. Anderson [1] recorded single genets with over 130 stems produced from a single rootstock during a single season. He also estimated ages for individual plants up to 22 years. Observations have been recorded of particular rootstocks failing to generate shoots during a given year, but producing aboveground growth during each prior and subsequent season [129].
Leaves are 2 to 6 inches (5-14 cm) long and attached close to the stem [14]. Flower spikes vary in length from > 40 inches (1 m) to only a few inches, and only 2 to 3 inches (5.1-7.6 cm) of the spike typically display open flowers at any given time [9,73]. Fruits are capsules 2-3 mm in length [56]. Seeds measure approximately 400 x 200 microns, and weigh approximately 1.8 x 10-6 ounces (50 µg) per seed, which is comparatively quite small among North American temperate wetland plants [116,129].
Seedlings quickly develop a thick, hardened taproot [111]. Mature plants subjected to persistent flooding respond by forming aerenchymous (containing large intercellular air spaces) tissue, permitting oxygen flow to submerged roots [118].
The preceding description provides characteristics of purple loosestrife that may be relevant to fire ecology and is not meant to be used for identification. Keys for identifying purple loosestrife are available in various floras (e.g. [57,71]). Photos and descriptions of purple loosestrife are also available online from Minnesota Sea Grant. Check with the native plant society or cooperative extension service in your area for more information.
Raunkiaer Life Form
- Hemicryptophyte
- Helophyte [100]
Seasonal Development
Flowering typically occurs 8 to10 weeks following germination [111]. Onset of rapid growth and eventual flowering is strongly influenced by photoperiod length. Purple loosestrife plants grown under controlled conditions were examined for effects of day length on growth and development. It was determined a critical photoperiod of 13 hours is required to enable formation of "highly competitive morphogenetic entities". When subjected to shorter daylength, plants had substantially reduced vegetative growth and little to no flowering. [112]. Most reports indicate flowering commences sometime in June and ceases in September [20,48,102,129]. Both mature plants and seedlings whose growth rates were tracked throughout the growing season in central New York reached at least 90% of their final height by August 3 [102]. Senescence proceeds with the onset of fall frost, marked by the turning red, fading and abscission of leaves. Dead but rigid stems remain standing through winter and spring. Seed capsules also remain attached to flower stalks through winter [128].
Regeneration Processes
Pollination and Breeding System
Purple loosestrife is insect pollinated. Most reports indicate honeybees are the main pollinators [43,73]. Others include bumblebees [72,73], leaf-cutter bees and carpenter bees [72], as well as a variety of butterflies [72,73]. Hummingbirds have been observed taking nectar from purple loosestrife in British Columbia [98], although pollination by hummingbirds is undocumented.
Purple loosestrife is a tristylous species (3 different style lengths), usually in a 1:1:1 ratio, indicating sexual reproduction is probably its most important means of regeneration [9]. It is primarily an outcrosser, as self-pollination in purple loosestrife is rare, and has been shown to reduce seed production [111].
Seed Production
Purple loosestrife produces an immense number of seeds. Estimates of seed production rates range from just over 100,000 seeds per plant for young plants with single stems [111], to over 2.5 million seeds per plant for established plants with an average of 30 stems per plant [129]. Although perennial, purple loosestrife is capable of producing viable seed during its 1st growing season [116]. Seed output is largely a function of plant age, size, and vigor [129]. Shoots growing in relatively dense stands tend to produce fewer and smaller inflorescences than those growing in more open areas [102].
Seed Dispersal
Because seeds are small and light they are thought to be dispersed, at least in part, by wind [53,111]. However, Thompson and others [129] report observations that seedling densities decline sharply within a 33 foot (10 m) perimeter of the parent plant and seedlings are often distributed downslope from the parent plant rather than downwind, suggesting a limited role for wind dispersal. Dispersal via moving water is also likely [53,118,119]. Seeds and cotyledon stage seedlings are reportedly buoyant [9], although there are reports that purple loosestrife seeds don't float [119]. Floating seeds may disperse to suitable sites for establishment. Seeds that sink may germinate while submerged, then rise to the surface and drift to suitable sites for establishment [129]. Seeds may be transported in fur of mammals, plumage of waterfowl, mud attached to footgear, vehicle treads or cooling systems of outboard motors [53,128,129]. Thompson and others [129] also suggest birds may deposit ingested seeds in areas where wind or gravity-mediated dispersal seems unlikely.
Seed Banking
Given its high seed output and ability to produce seed in its 1st growing season, purple loosestrife can establish substantial soil seed banks. Seeds may remain viable for at least 2 to 3 years [102,111], although the long-term viability of seeds stored in the soil seed bank remains under investigation [139]. Seeds may remain viable even when subjected to saturating conditions. Viability of seeds that were stored underwater was tested at 4-month intervals under ideal germination conditions. Germination declined from an initial rate of 99% to 93% after 1 year and 80% after 2 years [102].
Purple loosestrife has the potential to dominate the soil seed bank where it becomes well established. Soil samples taken from within purple loosestrife stands in emergent wetlands in southeastern Minnesota contained an average of 37,963 purple loosestrife seeds per ft2 (410,000 /m2) in the top 2 in (5 cm) of soil. Seeds were distributed within this entire profile and seed density increased with proximity to the soil surface. Under greenhouse conditions chosen to promote germination, and using soil samples from the above source spread 0.4 in (1 cm) deep, recruitment failed to exhaust the seed bank [138,140]. From the same experiment, purple loosestrife seedlings were found in 91% of untreated (no herbicide) 6.6 x 6.6 feet (2 x 2 m) quadrats, the most frequently encountered species in the soil seed bank [140].
Germination
Germination is greatest in unshaded, wet soils, with temperatures >68 degrees Fahrenheit (20º C) [20]. Shamsi and Whitehead [111] demonstrated germination is constrained at low temperatures between about 50 to 59 degrees Fahrenheit (10°-15° C), and no germination occurred below 57 degrees Fahrenheit (14° C). Experimental evidence indicates seed dormancy may be enforced by burial, with germination response decreasing linearly (p = 0.001, r2 = 0.89) from 90% at the soil surface to 0% at 0.8 in (2 cm), even under conditions known to promote germination in wetland plants [138]. Any disturbance that redistributes seeds to within the upper 0.8 inch (2 cm) of soil is likely to promote germination. Although light exposure is a prerequisite for germination, length of exposure does not appear important [112]. Purple loosestrife seeds are capable of germinating underwater [64].
Seedling Establishment and Growth
Favorable recruitment conditions are largely a function of disturbance that creates areas where little to no vegetation is present [99]. Estimates of maximum initial seedling density vary greatly, from 926 to 1,852 foot-2 (10,000-20,000 m-2) on bare open mudflats [102] to 2.8 to 4.6 foot-2 (30-50 m-2) in vegetated semiflooded wetlands. In areas where large numbers of seeds are present in the seed bank, small changes in area favorable for establishment can yield large fluctuations in recruitment [1].
In order to begin successful establishment, floating seeds or propagules must settle on moist soil [129]. Purple loosestrife can establish in soil beneath standing water [64].
Growth is limited by cold temperature and is considerably slowed at around 46 to 50 degrees Fahrenheit (8-10º C) [141]. Light availability can also limit growth and development. Under diminishing light intensities, vegetative growth is slowed, the numbers of flowers, fruits, and seeds per fruit are fewer, and the average dry weight of fruits declines, but there is no change in average dry weight of individual seeds [112]. Growth is also affected by day length. Shamsi and Whitehead [112] found leaf area and plant dry weight were significantly (P<0.05) reduced when plants were subjected to a 9-hour photoperiod compared with a 16-hour photoperiod. Plants in the 9-hour treatment grew in a comparatively flattened, semi-prostrate condition.
Vegetative Reproduction and Regeneration
The rootstock is the main organ of perennation, and unaided wide vegetative spread is unlikely. New shoots arise from buds at the top of the rootstock [111]. Root crowns expand annually to accommodate increasing numbers of shoots, but may reach maximum growth at around 20 inches (0.5 m) in diameter [129].
Purple loosestrife can consistently resprout in response to aboveground damage, often fairly rapidly. A greenhouse experiment showed 91% of clipped seedlings resprouted within 42 days [39]. Live stems that are dislodged and buried can give rise to new shoots via adventitious buds [23,129].
Successional Status
The ways and extent to which purple loosestrife affects succession in wetland plant communities are not altogether clear. It is evident that purple loosestrife requires open, moist, bare substrate for establishment (see Site Characteristics and Regeneration Processes). It is generally agreed that purple loosestrife is a pioneer or gap-colonizing species that quickly responds to site disturbance by recruiting often-substantial numbers of new genets from a pre-existing seed bank [1,30,110].
Purple loosestrife displays many characteristics typical of pioneer species, such as rapid maturity, high seed production, tolerance of nutrient-poor environments, and high germination success. Yet North American populations, once established, also are potentially long-lived (22+ years), capable of growing to a relatively large size, and have shown the propensity for near-continuous, low-level recruitment in the absence of large-scale disturbance [1,129]. While evidence is somewhat limited, it is speculated natural mortality rates in adult plants are quite low [1].
Purple loosestrife, once established, can persist within a site for relatively long periods, even in the absence of frequent disturbance. After examining purple loosestrife population structure within several different communities in eastern Massachusetts, Anderson [1] concluded low levels of nearly-continuous recruitment are likely to occur in areas where mature plants (and the inevitable prodigious purple loosestrife seed bank) are present. Additionally, this trend is punctuated by occasional disturbances that provide conditions suitable for short-lived recruitment episodes in which relatively large cohorts of new plants are established.
But there is some question regarding the view that purple loosestrife inevitably dominates invaded sites in virtual monotypic stands. Anderson [2] points out that in a widely cited review by Thompson and others [129], estimates of the proportion of stand biomass attributed to purple loosestrife, which ostensibly increased over time following establishment, may instead have been attributable to increases in the number of stems per genet rather than greater numbers of individual plants. The number of annually produced stems per single genetically distinct plant has been shown to be a good predictor of the age of that individual [1]. Anderson [2] also notes observations described in Thompson and others [129] were strictly visual assessments, and since no hard data was collected, there is no way to definitively ascertain what, if any, changes in biomass distribution among species may have occurred.
In its native range, European populations of purple loosestrife may also form large monospecific stands following pregrowing season disturbance, but are prone to invasion by other species soon after stand establishment [110,111]. Whitehead [141] described the gradual yielding of monospecific stands of purple loosestrife to mixed species communities in England as being due to slow growth of purple loosestrife during periods of cool spring temperatures compared with competitors possessing low-temperature growth capabilities such as cattails or reeds (Phragmites spp.) It is likely that an aggregate of factors act to limit purple loosestrife site dominance in its native habitats [118].
Thompson and others [129] have reviewed several historical accounts of purple loosestrife stands, both in its native Europe and elsewhere. They determined that while purple loosestrife seldom maintains strong community dominance in native (European) habitats, it commonly forms dense, long-lasting, virtually monospecific stands in areas where it is not native, especially temperate North America. They considered 3 factors that could possibly account for this phenomenon: 1) the absence of many key insect predators that effectively reduce competitiveness of European purple loosestrife plants, 2) predominance of the muskrat in its native North American habitat and the impact of its selective foraging behavior on cattails (see Importance to Livestock and Wildlife or Impacts and Control), and 3) the possibility that North American purple loosestrife may have evolved adaptive traits which make it more vigorous and competitive than its European relatives.
Many factors are likely to affect the ability of purple loosestrife to form and maintain extensive monodominant stands in North American wetlands. Characteristics particular to certain classes of habitat may lead to monodominance. Auclair and others [8] have noted some trends in 2 distinct plant communities of Huntington Marsh, located along the St. Lawrence River near the junction of the Quebec, Ontario and New York borders. In the emergent aquatic community, the dominant emergent taxa tended to exclude each other, resulting in a mosaic of nearly monospecific communities. In particular, river bulrush (Schoenoplectus fluviatilis), common reed (Phragmites australis) and narrow-leaved cattail (Typha angustifolia) displayed this phenomenon. In contrast, sedge meadow communities were much more diverse and lacked the dominance and segregation of species. Instead they demonstrated subtle gradients in composition that were generally difficult to discern.
The nature of particular disturbance events may also impact initial floristics and subsequent successional trajectories. For instance, the relative competitiveness of purple loosestrife seedlings following disturbance may depend upon when initiation of the new seedling community occurs within the growing season. Because purple loosestrife growth rates are closely linked to day length [112], early summer establishment of a seedling cohort or community, compared with late summer establishment, is more likely to result in a monospecific stand of purple loosestrife because purple loosestrife seedlings will be more competitive [102].
More research is needed to help elucidate the means and extent to which purple loosestrife alters successional trajectories and community dynamics. Long-term studies that examine preinvasion vs. postinvasion data would be particularly helpful.
Immediate Fire Effects
Information describing the effect of fire on purple loosestrife is sparse, but several authors suggest that it does not burn well [83,129]. In a review, Haber [46] suggest that "fires generally do not burn at high enough temperatures to kill the root crown, especially in damp soils." Rawinski [102] indicated that individual plants will burn, but conditions that permit a fire to carry through purple loosestrife stands are probably not common.
Reports of interactions between purple loosestrife and fire usually attest to the difficulty associated with trying to burn plants as a control method. Such attempts are commonly described as being confounded by moist soil conditions and patchy fuel distribution [80,83,102,129]. Because postsenescent purple loosestrife retains persistent standing dead stem material [14], it is possible that dry winter or early spring conditions may permit dense stands to carry fire, but this is speculative.
Postfire Regeneration Strategy
- Caudex/herbaceous root crown, growing points in soil
- Ground residual colonizer (on-site, initial community) [123]
Fire Adaptations
Purple loosestrife is an herbaceous perennial, with growing points that overwinter on the root crown about 0.8 inches (2 cm) below the soil surface (see Botanical and Ecological Characteristics) [129]. Fire regimes: Because purple loosestrife is distributed across many habitats in North America (see Distribution and Occurrence), fire regimes associated with the species vary. Recurrence and behavior of fire in areas where purple loosestrife occurs is likely to be closely tied to particular local fire regimes, and cannot be easily summarized over broad spatial scales. Given purple loosestrife's moisture requirements, it is unlikely to occur in areas experiencing frequently recurring fire. Similar to many areas that experience fire infrequently, occurrence of fire in areas where purple loosestrife is found is likely to driven by drought. However, information describing interactions between purple loosestrife and fire are lacking, and information linking purple loosestrife to specific North American fire regimes is nonexistent.
Given the dearth of information on fire and purple loosestrife and our relatively poor understanding of how purple loosestrife generally affects plant community dynamics where it occurs, any description of interactions between particular fire regimes and purple loosestrife is speculative. Where purple loosestrife displaces native vegetation dependent upon recurring fire for maintenance of a seral stage, persistent stands of invasive purple loosestrife may alter fire regimes if purple loosestrife burns less frequently or less readily than the native vegetation it displaces. For example, sedge meadow communities along the St. Lawrence River in southern Quebec where purple loosestrife is sometimes found, are historically maintained by dormant season fire recurring every 1 to 3 years. If invading purple loosestrife reduces fire frequency or severity at these sites, these communities are likely to succeed to woody species such as willow (Salix spp.) or maple (Acer spp.) [8].
Plant Response to Fire
Although no direct evidence exists, it is likely that purple loosestrife will survive fire by sprouting from buds located below the soil surface on the root crown [46,111].
Fire Regimes
The table below lists fire return intervals for communities or ecosystems throughout North America where purple loosestrife may occur. This list is not intended as a description of purple loosestrife distribution, but rather as a guide to fire regimes in areas where purple loosestrife could potentially be found. (For more specific distributional information see Distribution and Occurrence). While this list mainly describes upland habitats, purple loosestrife is generally associated with wetland or riparian habitats within these communities or ecosystems. As such, this list is meant as a guideline to illustrate historic fire regimes and is not to be interpreted as a strict description of fire regimes for purple loosestrife.
For additional fire regime information, search FEIS for this species by entering the species name on the Advanced Search page and selecting “Fire Regime” as the publication type.
| Community or Ecosystem | Dominant Species | Fire Return Interval Range (years) |
|---|---|---|
| Silver fir-Douglas-fir | Abies amabilis-Pseudotsuga menziesii var. menziesii | > 200 |
| Grand fir | Abies grandis | 35-200 [5] |
| Maple-beech-birch | Acer-Fagus-Betula | > 1000 |
| Silver maple-American elm | Acer saccharinum-Ulmus americana | < 35 to 200 |
| Sugar maple | Acer saccharum | > 1000 |
| Sugar maple-basswood | Acer saccharum-Tilia americana | > 1000 [135] |
| California chaparral | Adenostoma and/or Arctostaphylos spp. | < 35 to < 100 [95] |
| Bluestem prairie | Andropogon gerardii var. gerardii-Schizachyrium scoparium | < 10 [69,95] |
| Nebraska sandhills prairie | Andropogon gerardii var. paucipilus-Schizachyrium scoparium | < 10 |
| Bluestem-Sacahuista prairie | Andropogon littoralis-Spartina spartinae | < 10 |
| Sagebrush steppe | Artemisia tridentata/Pseudoroegneria spicata | 20-70 |
| Basin big sagebrush | Artemisia tridentata var. tridentata | 12-43 [108] |
| Mountain big sagebrush | Artemisia tridentata var. vaseyana | 15-40 [6,25,85] |
| Wyoming big sagebrush | Artemisia tridentata var. wyomingensis | 10-70 (40**) [133,143] |
| Coastal sagebrush | Artemisia californica | < 35 to < 100 |
| Saltbush-greasewood | Atriplex confertifolia-Sarcobatus vermiculatus | < 35 to < 100 |
| Desert grasslands | Bouteloua eriopoda and/or Pleuraphis mutica | 5-100 |
| Plains grasslands | Bouteloua spp. | < 35 |
| Blue grama-needle-and-thread grass-western wheatgrass | Bouteloua gracilis-Hesperostipa comata-Pascopyrum smithii | < 35 |
| Blue grama-buffalo grass | Bouteloua gracilis-Buchloe dactyloides | < 35 |
| Cheatgrass | Bromus tectorum | < 10 |
| California montane chaparral | Ceanothus and/or Arctostaphylos spp. | 50-100 [95] |
| Sugarberry-America elm-green ash | Celtis laevigata-Ulmus americana-Fraxinus pennsylvanica | < 35 to 200 [135] |
| Paloverde-cactus shrub | Cercidium microphyllum/Opuntia spp. | < 35 to < 100 [95] |
| Curlleaf mountain-mahogany* | Cercocarpus ledifolius | 13-1000 [7,109] |
| Mountain-mahogany-Gambel oak scrub | Cercocarpus ledifolius-Quercus gambelii | < 35 to < 100 [95] |
| Atlantic white-cedar | Chamaecyparis thyoides | 35 to > 200 [135] |
| Blackbrush | Coleogyne ramosissima | < 35 to < 100 |
| Northern cordgrass prairie | Distichlis spicata-Spartina spp. | 1-3 [95] |
| Beech-sugar maple | Fagus spp.-Acer saccharum | > 1000 [135] |
| California steppe | Festuca-Danthonia spp. | < 35 [95] |
| Black ash | Fraxinus nigra | < 35 to 200 [135] |
| Juniper-oak savanna | Juniperus ashei-Quercus virginiana | < 35 |
| Ashe juniper | Juniperus ashei | < 35 |
| Western juniper | Juniperus occidentalis | 20-70 |
| Rocky Mountain juniper | Juniperus scopulorum | < 35 |
| Cedar glades | Juniperus virginiana | 3-7 |
| Tamarack | Larix laricina | 35-200 [95] |
| Western larch | Larix occidentalis | 25-100 [5] |
| Creosotebush | Larrea tridentata | < 35 to < 100 |
| Ceniza shrub | Larrea tridentata-Leucophyllum frutescens-Prosopis glandulosa | < 35 [95] |
| Yellow-poplar | Liriodendron tulipifera | < 35 [135] |
| Melaleuca | Melaleuca quinquenervia | < 35 to 200 [88] |
| Wheatgrass plains grasslands | Pascopyrum smithii | < 35 [95] |
| Great Lakes spruce-fir | Picea-Abies spp. | 35 to > 200 |
| Northeastern spruce-fir | Picea-Abies spp. | 35-200 [33] |
| Southeastern spruce-fir | Picea-Abies spp. | 35 to > 200 [135] |
| Engelmann spruce-subalpine fir | Picea engelmannii-Abies lasiocarpa | 35 to > 200 [5] |
| Black spruce | Picea mariana | 35-200 |
| Conifer bog* | Picea mariana-Larix laricina | 35-200 [33] |
| Blue spruce* | Picea pungens | 35-200 [5] |
| Red spruce* | P. rubens | 35-200 [33] |
| Pine-cypress forest | Pinus-Cupressus spp. | < 35 to 200 [5] |
| Pinyon-juniper | Pinus-Juniperus spp. | < 35 [95] |
| Whitebark pine* | Pinus albicaulis | 50-200 [5] |
| Jack pine | Pinus banksiana | <35 to 200 [33] |
| Mexican pinyon | Pinus cembroides | 20-70 [86,126] |
| Rocky Mountain lodgepole pine* | Pinus contorta var. latifolia | 25-300+ [4,5,107] |
| Sierra lodgepole pine* | Pinus contorta var. murrayana | 35-200 [5] |
| Shortleaf pine | Pinus echinata | 2-15 |
| Shortleaf pine-oak | Pinus echinata-Quercus spp. | < 10 [135] |
| Colorado pinyon | Pinus edulis | 10-49 [95] |
| Slash pine | Pinus elliottii | 3-8 |
| Sash pine-hardwood | Pinus elliottii-variable | < 35 |
| Sand pine | Pinus elliottii var. elliottii | 25-45 [135] |
| South Florida slash pine | Pinus elliottii var. densa | 1-5 [88,135] |
| Jeffrey pine | Pinus jeffreyi | 5-30 |
| Western white pine* | Pinus monticola | 50-200 |
| Pacific ponderosa pine* | Pinus ponderosa var. ponderosa | 1-47 |
| Interior ponderosa pine* | Pinus ponderosa var. scopulorum | 2-10 [5] |
| Table Mountain pine | Pinus pungens | < 35 to 200 [135] |
| Red pine (Great Lakes region) | Pinus resinosa | 10-200 (10**) [33,37] |
| Red-white-jack pine* | Pinus resinosa-P. strobus-P. banksiana | 10-300 [33,54] |
| Pitch pine | Pinus rigida | 6-25 [24,55] |
| Pocosin | Pinus serotina | 3-8 |
| Pond pine | Pinus serotina | 3-8 |
| Eastern white pine | Pinus strobus | 35-200 |
| Eastern white pine-eastern hemlock | Pinus strobus-Tsuga canadensis | 35-200 |
| Eastern white pine-northern red oak-red maple | Pinus strobus-Quercus rubra-Acer rubrum | 35-200 |
| Loblolly pine | Pinus taeda | 3-8 |
| Loblolly-shortleaf pine | Pinus taeda-P. echinata | 10 to < 35 |
| Virginia pine | Pinus virginiana | 10 to < 35 |
| Virginia pine-oak | Pinus virginiana-Quercus spp. | 10 to < 35 |
| Sycamore-sweetgum-American elm | Platanus occidentalis-Liquidambar styraciflua-Ulmus americana | < 35 to 200 [135] |
| Galleta-threeawn shrubsteppe | Pleuraphis jamesii-Aristida purpurea | < 35 to < 100 |
| Eastern cottonwood | Populus deltoides | < 35 to 200 [95] |
| Aspen-birch | Populus tremuloides-Betula papyrifera | 35-200 [33,135] |
| Quaking aspen (west of the Great Plains) | Populus tremuloides | 7-120 [5,45,84] |
| Mesquite | Prosopis glandulosa | < 35 to < 100 |
| Mesquite-buffalo grass | Prosopis glandulosa-Buchloe dactyloides | < 35 |
| Texas savanna | Prosopis glandulosa var. glandulosa | < 10 [95] |
| Black cherry-sugar maple | Prunus serotina-Acer saccharum | > 1000 [135] |
| Mountain grasslands | Pseudoroegneria spicata | 3-40 (10**) [4,5] |
| Rocky Mountain Douglas-fir* | Pseudotsuga menziesii var. glauca | 25-100 [5] |
| Coastal Douglas-fir* | Pseudotsuga menziesii var. menziesii | 40-240 [5,87,106] |
| California mixed evergreen | Pseudotsuga menziesii var. m.-Lithocarpus densiflorus-Arbutus menziesii | < 35 |
| California oakwoods | Quercus spp. | < 35 [5] |
| Oak-hickory | Quercus-Carya spp. | < 35 [135] |
| Oak-juniper woodland (Southwest) | Quercus-Juniperus spp. | < 35 to < 200 [95] |
| Northeastern oak-pine | Quercus-Pinus spp. | 10 to < 35 [135] |
| Oak-gum-cypress | Quercus-Nyssa-spp.-Taxodium distichum | 35 to > 200 [88] |
| Southeastern oak-pine | Quercus-Pinus spp. | < 10 [135] |
| Coast live oak | Quercus agrifolia | <35 to 200 [5] |
| White oak-black oak-northern red oak | Quercus alba-Q. velutina-Q. rubra | < 35 [135] |
| Canyon live oak | Quercus chrysolepis | <35 to 200 |
| Blue oak-foothills pine | Quercus douglasii-Pinus sabiana | <35 [5] |
| Northern pin oak | Quercus ellipsoidalis | < 35 [135] |
| Oregon white oak | Quercus garryana | < 35 [5] |
| Bear oak | Quercus ilicifolia | < 35 >[135] |
| California black oak | Quercus kelloggii | 5-30 [95] |
| Bur oak | Quercus macrocarpa | < 10 [135] |
| Oak savanna | Quercus macrocarpa/Andropogon gerardii-Schizachyrium scoparium | 2-14 [95,135] |
| Shinnery | Quercus mohriana | < 35 [95] |
| Chestnut oak | Q. prinus | 3-8 |
| Northern red oak | Quercus rubra | 10 to < 35 |
| Post oak-blackjack oak | Quercus stellata-Q. marilandica | < 10 |
| Black oak | Quercus velutina | < 35 |
| Live oak | Quercus virginiana | 10 to< 100 [135] |
| Interior live oak | Quercus wislizenii | < 35 [5] |
| Cabbage palmetto-slash pine | Sabal palmetto-Pinus elliottii | < 10 [88,135] |
| Blackland prairie | Schizachyrium scoparium-Nassella leucotricha | < 10 |
| Fayette prairie | Schizachyrium scoparium-Buchloe dactyloides | < 10 |
| Little bluestem-grama prairie | Schizachyrium scoparium-Bouteloua spp. | < 35 |
| Tule marshes | Scirpus and/or Typha spp. | < 35 [95] |
| Redwood | Sequoia sempervirens | 5-200 [5,36,124] |
| Southern cordgrass prairie | Spartina alterniflora | 1-3 [95] |
| Baldcypress | Taxodium distichum var. distichum | 100 to > 300 |
| Pondcypress | Taxodium distichum var. nutans | < 35 [88] |
| Western redcedar-western hemlock | Thuja plicata-Tsuga heterophylla | > 200 [5] |
| Eastern hemlock-yellow birch | Tsuga canadensis-Betula alleghaniensis | > 200 [135] |
| Western hemlock-Sitka spruce | Tsuga heterophylla-Picea sitchensis | > 200 |
| Mountain hemlock* | Tsuga mertensiana | 35 to > 200 [5] |
| Elm-ash-cottonwood | Ulmus-Fraxinus-Populus spp. | < 35 to 200 [33,135] |
| *fire return interval varies widely; trends in variation are noted in the species summary **mean | ||
Fire Management Considerations
The use of fire as a control measure for purple loosestrife largely has been dismissed as ineffective [80,83,129]. In large part, this has been due to typically wet soil condition where it occurs, combined with a well-protected rootstock from which it produces annual stem growth. Attempts to burn residual biomass following cutting or herbicide treatments, to the extent that material will actually combust, may merely result in recruitment of purple loosestrife seedlings due to exposure of bare substrate containing a substantial seed bank [118]. Rawinksi [102] compared the effects of burning following cutting with cutting alone on mean shoot density in a central New York wetland. Attempts to burn cut purple loosestrife stems were generally ineffective, although some dense clumps of cut material "burned rather completely." Reasons given for ineffectiveness of burn treatments were diffuse fuel arrangements, presence of substantial soil moisture, and the retention of moisture within cut materials.
Federal Status
None
Other Status
As of this writing (2002), purple loosestrife is listed as a noxious weed in 29 states in the U.S. and 2 Canadian provinces. See the Invaders or Plants databases for current information. The state of Minnesota has prohibited the sale of European wand loosestrife and any cultivars from crosses between purple and European wand loosestrife [139].
Importance to Wildlife and Livestock
Purple loosestrife shoots may be grazed by white-tailed deer [2,102], muskrat [2,129], and rabbits [2,113], but extent of mammal herbivory is sometimes difficult to determine due to rapid regrowth of multiple new stems from browse points. In a mixed stand of purple loosestrife and cattail, foraging muskrats were observed to occasionally cut stems of purple loosestrife but preferentially fed on roots and overwintering shoots of cattail [102].
While purple loosestrife invasion is often reported as detrimental to wetland-bird habitat, some evidence indicates little to no harmful effect. American coot, pied-billed grebe, black-crowned night heron, American goldfinch and gray catbird have all been observed nesting in purple loosestrife stands [2,102]. Red-winged blackbirds preferentially nest in purple loosestrife over cattails [101,142]. American goldfinch construct nests in purple loosestrife, utilizing the relatively stable stalks to attach nests above the ground or water surface [68]. Pied-billed grebes use dead purple loosestrife stems as nest substrate in habitat with standing and emergent vegetation [77]. In a 2-year survey of birds in wetlands surrounding Lake Huron's Saginaw Bay in eastern Lower Michigan, swamp sparrow nests were most abundant in areas of purple loosestrife dominance [142].
Although purple loosestrife, with its tiny seeds, has been assumed to provide little to no food for birds [129], there are several reports of ducks and red-winged blackbirds consuming purple loosestrife seeds [2], and a report of damage to experimental seedling plots in England caused by ring-necked pheasants and pigeons [113].
Palatability and Nutritional Value
No information.
Cover Value
Purple loosestrife stands may provide cover habitat for wood ducks [121], ring-necked pheasants and cottontail rabbits [120].
Other Uses
Purple loosestrife was previously used by European immigrants in herbal remedies for a variety of maladies [129]. Purple loosestrife, as well as other loosestrifes, have long been popular with gardeners for their abundant and attractive floral displays and are still sold legally in some places. However, many North American horticulturalists have now abandoned its promotion because of its potential for escape [15,34,48,59,82,129]. It has also been utilized as a honey plant by beekeepers [96,129]. Purple loosestrife seed has occasionally been included in commercial "wildflower" seed mixes [129].
Impacts
Infestation of purple loosestrife (CC BY-NC).
Purple loosestrife can be highly competitive, often reported as occurring in dense, monospecific stands, with the potential to dominate wetland plant communities where it occurs (see Successional Status) [1,41,65,66,78,129,136,137]. While it is evident that invading purple loosestrife may have harmful impacts on native flora and fauna, more research is needed to clarify the extent of these impacts. Hager and McCoy [47] and Anderson [2] provide critical reviews of literature describing purported negative impacts caused by purple loosestrife in North America. Both papers express concern that widespread claims of ecological harm caused by purple loosestrife are largely unproven. In a widely cited review of purple loosestrife literature in North America, Thompson and others [129] describe encroachment of purple loosestrife around the margins of a waterfowl impoundment in central New York. Their estimates of percent of total plant biomass contributed by purple loosestrife along dike areas of the impoundments describe "dramatic" increases over about a 15-year period. Based on visual estimates of plant biomass, the authors contend that native plant species were displaced, vegetation structure was altered, and habitat quality for nesting waterfowl was seriously degraded. The paper by Thompson and others [129] demonstrates how untested hypotheses can be perpetuated in the literature until they become widely accepted, without the benefit of experimental analysis [47]. As emphasized by Anderson [2], "detailed, quantitative data are needed to understand loosestrife's natural history, population dynamics, and impacts on native ecosystems if we are to effectively manage this plant."
Because purple loosestrife has demonstrated strong competitive abilities where it has invaded North American wetland communities, there is concern that it may diminish native plant diversity. For instance, competition with purple loosestrife has been suggested as a contributing factor in the decline of the rare Long's bulrush (Scirpus longii) in Massachusetts [28]. However, studies published to date have failed to demonstrate a deleterious effect of purple loosestrife on native plant diversity. Treberg and Husband [130] examined the association between purple loosestrife abundance and vascular plant richness along the Bar River in Ontario. Purple loosestrife had been present in this area for at least 12 years and there was a wide range in established plant densities. They found no significant (P<0.05) difference in mean species richness associated with the presence or percent cover of purple loosestrife, and no plant species was significantly (P<0.05) more likely to be found in the absence of purple loosestrife than in its presence. Anderson [1] showed no significant (P<0.05) correlation between total species richness and either percent cover, genet density or median age of purple loosestrife, even in plots containing 18-20 year old purple loosestrife plants. He suggested areas with apparent purple loosestrife monocultures perhaps had low species richness to begin with, and species richness more likely resulted from habitat heterogeneity rather than the presence of innately competitive species. More research is needed in this area.
Purple loosestrife colonization has been purported to have detrimental effects on birds, based on: a) creation of unsuitable nesting habitat and b) low food potential of purple loosestrife relative to vegetation it displaces. However, published studies and observations indicate impacts on birds are not yet clear. Marsh wrens prefer cattails to purple loosestrife for nesting [101,142]. There is speculation that invasion of riparian areas in Nebraska may have adverse effects on important night-roosting habitat for migratory sandhill cranes. Purple loosestrife invasion is predicted to have detrimental effects on nesting habitat of black terns and canvasbacks in the north-central United States, but this has not been tested [129]. Whitt et al. [142] found purple loosestrife-dominated habitats had significantly (P=0.003) higher bird densities but significantly (P=0.03) fewer bird species than other habitats. These higher densities were mainly due to increases in populations of a single species, the swamp sparrow.
Purple loosestrife colonization can substantially reduce or eliminate open water in small marsh areas, potentially reducing its usefulness for waterfowl. In areas with substantial seed banks, mudflats that are commonly used as feeding areas by shorebirds are impacted by rapid, dense colonization by purple loosestrife seedlings. Decline in the extent of open water habitats from increased emergent purple loosestrife can retard access to aquatic prey items such as fish and aquatic invertebrates. Important aquatic food plants for wildlife such as pondweeds (Potamogeton spp.) are inhibited under the shade of emergent purple loosestrife [102]. Invading purple loosestrife in coastal British Columbia's Fraser River estuary may have negative effects on detrital food chains [44].
Thompson and others [129] have illustrated how muskrats might interact with purple loosestrife in a manner detrimental to muskrats. Muskrats apparently find stems of purple loosestrife much less palatable then those of cattail, but they do cut purple loosestrife stems. As they forage they favor cattail stems, potentially shifting the competitive balance toward the less palatable purple loosestrife. The ability of muskrats to shift the competitive balance between cattails and purple loosestrife was corroborated by Rawinski [102] from observations of mixed stands where muskrats were present. At a particular site, muskrats removed entire patches of cattail, leaving purple loosestrife the only remaining emergent. Muskrats may further favor purple loosestrife seedling establishment following den construction. This activity can cause substantial soil disturbance that is rapidly colonized by purple loosestrife seedlings during lower summer water levels. Because of their ability to generate new vegetative growth, partially eaten purple loosestrife stems also represent potential new propagules, adding to its competitive advantage [23]. As community composition shifts from cattails to purple loosestrife dominance, habitat quality and subsequent muskrat carrying capacity apparently decline [129].
Conversion of wetland pasture to predominantly purple loosestrife is believed to reduce forage value for livestock and deer [128]. As purple loosestrife density increases and mature plants produce greater numbers of shoots, the woody nature of purple loosestrife stems diminishes forage value [118].
Purple loosestrife may have adverse effects on habitat of the threatened bog turtle, although details are scant [26,67].
Purple loosestrife invasion may be detrimental to production of natural and domestic wild rice in areas of the upper Midwest, particularly in commercial wild rice paddy operations where water level manipulation presents ideal germination conditions. Dense purple loosestrife infestations can also undermine the functionality of drainage waterways, such as irrigation ditches [118].
Water level manipulations in impoundments have been hindered by threat of purple loosestrife invasion. A 1000-fold increase in acreage containing purple loosestrife was noted over a 23-year period in a central New York wetland and the cause was speculated to be recurrent drawdown of impoundments [102]. In areas managed for waterfowl production, such as many federal and state wildlife refuges, water level drawdowns in impoundments may provide establishment opportunities for purple loosestrife. Drawdowns are often executed to encourage recruitment of plants valuable to waterfowl such as cattails, smartweed (Polygonum spp.) and wild millet (Echinochloa spp.) on exposed soils [90].
Invading purple loosestrife is being monitored in the middle Snake River corridor in Idaho for effects on stream channel dynamics. Purple loosestrife is colonizing gravel bars under low flow conditions. Once established, it appears able to withstand inundation and flowing water conditions better than native annuals. It is feared that persistent purple loosestrife plants may contribute substantially to sediment trapping, leading to gravel bar aggradation, closure of small channels, and despoiling of secure, predator-free island nesting habitat for local waterfowl [32].
Prevention
It is important to avoid management activities that may enhance the risk of purple loosestrife invasion and expansion. Examples of mitigative efforts are a) encourage establishment, growth, or perpetuation of native woody cover that might provide enough shade to depress or discourage purple loosestrife, b) minimize water level fluctuations in manipulated wetlands or waterways that might encourage establishment of purple loosestrife seedlings, especially early-season drawdowns that expose bare substrate, and c) avoid any form of stress or disturbance to extant native plant communities in susceptible areas, such as disturbing soil with heavy machinery, and where such activities are unavoidable, monitoring impacted areas to detect invaders [129].
Periodic, systematic monitoring of susceptible habitats is strongly encouraged [144]. Development of local populations, as expressed by percent biomass constituted by purple loosestrife, is roughly a logistic function through time. Initial rate of spread of local infestations is slowed when extant competition is strong. As a result, early detection and eradication of colonizing plants is highly preferred. Fortunately, early detection is aided by the tall, showy flower stalks and lengthy period of bloom. Once purple loosestrife becomes strongly established, with many (>10) flowering stems per rootstock, multiple clumps forming monospecific patches or stands, and establishment of a seed bank, eradication becomes more expensive, intrusive, and difficult [129].
Spread of purple loosestrife in natural areas likely has been accelerated by the development, sale and use of various loosestrife cultivars for horticultural purposes. Sale and utilization of ornamental loosestrife cultivars should be curtailed to prevent the risk of further dissemination into previously uncolonized areas. Cultivars are capable of contributing viable seed and pollen to wild populations, and claims of sterile hybrids have been shown to be mainly false [3,74,92].
As with most invasive species, public education plays an important role in preventing establishment and spread of purple loosestrife. Planting of loosestrife cultivars for horticultural purposes should be strongly discouraged. Individuals who frequent areas susceptible to invasion can aid in prevention by washing boots, clothing, equipment, etc. before exiting such areas, and should be encouraged to identify and report potential new infestations to authorities.
Control
Land managers concerned about invasive purple loosestrife should focus on eliminating small, recently-established populations before tackling large, well-established populations. Buildup and persistence of purple loosestrife seed in the soil seed bank appears to be the most problematic, long-term obstacle in eradicating, or at least controlling purple loosestrife. Preventing seed production and seed bank accumulation within recently-established stands is a pragmatic goal, especially in the face of limited resources and knowledge [138,139]. Welling and Becker [138] demonstrated the potential difficulty managers face with attempts to exhaust seed banks in areas where purple loosestrife is well established, although not necessarily monodominant. Because seed dormancy is enforced by burial at relatively shallow (>0.8 inch (2 cm)) depth, and because purple loosestrife seed banks may contain thousands of seeds per square foot at these depths, even successful eradication of extant adult plants and new recruits from near-surface germinants may not suffice for successful long-term control. Even the ability to exhaust near-surface (<0.4 inch (1 cm)) seed banks by promoting germination and removing emergent seedlings is in question.
Any disturbance or management activity that fragments live stem or root tissue is likely to result in the spread, rather than containment of purple loosestrife [23,118]. Live stems that are dislodged and buried can give rise to new shoots via adventitious buds [23,129]. Carp may play an important role where they co-occur with purple loosestrife. Carp eat the roots of purple loosestrife, sometimes until the plants are dislodged and float away. These plants then become potential propagules if they lodge on suitable substrate [102].
Detection and control efforts may be hindered by purple loosestrife's propensity to occasionally remain dormant for an entire growing season. Some plants fail to generate aboveground shoots during a particular year, but exhibit normal growth from the same rootstock in preceding and following years [42,129].
Fire
See Fire Management Considerations
Physical and Mechanical Control
Cutting stems or removing flower heads prior to seed dissemination can prevent local seed bank accumulation. Late-summer cutting appears to reduce vegetative growth more effectively than mid-summer treatments. However, cutting stems is unlikely to prevent perennial stem growth [46,102]. Cutting flower heads may be useful in preventing further seed production when primary control activities, such as herbicide application, require more than 1 season to completely eradicate purple loosestrife [13]. Cutting purple loosestrife stems underwater at various times in summer was ineffective [51].
Digging or hand-pulling plants is recommended for early infestations or a few scattered plants. Digging or pulling young plants in recently colonized areas can be effective in preventing establishment of dense, intractable stands and buildup of substantial seed banks. Early detection is important since established plants may rapidly become too large and deep-rooted for easy removal [102,129]. Because growing points of the plant are located on the root crown, removal of as much rootstock as possible is strongly encouraged [23,46]. Pulling entire plants is easiest when the soil is wet [102,131]. All pulled plant material should be removed from the site to prevent vegetative reproduction from discarded fragments [23]. Spot spraying individual plants with herbicide may be less time and labor intensive when infestations become too large for removal by pulling or digging [129].
Cultural Control
Seeding of competitive vegetation in areas where bare soil has been exposed may be a useful mitigative measure. This may be especially helpful where presence of seed in the soil seed bank indicates potential for robust purple loosestrife regeneration. Experiments examining the effectiveness of seeding Japanese millet (Echinochloa esculenta) to reduce the impact of purple loosestrife recruitment have shown mixed results [80,140]. In addition to providing competition against purple loosestrife seedlings, Japanese millet may be used by waterfowl and is thought to represent a minimal threat of invasiveness, although it is not native to North America [129]. Seeding native species may provide a desirable postdisturbance community, but explicit tests of the competitive abilities of various native plants when seeded with purple loosestrife are lacking. Seeding of competitors should take place immediately following exposure of soil to maximize their competitive abilities [80].
Flooding infested areas by raising water levels for extended periods may eliminate purple loosestrife from impoundment sites [46]. Flooding duration is more likely to influence mortality than depth of flooding, but specific guidelines are lacking [9]. Persistent high water conditions can slow the growth and reproductive capacity of purple loosestrife and over several years may eliminate extant stands, but results are variable and interactions with other factors poorly understood [80]. In plots subjected to consistently high water levels (16 inch (40 cm) mean depth)), competition with narrow-leaved cattail significantly (P<0.001) reduced stem densities of purple loosestrife compared with flooded stands where purple loosestrife was the predominant species [101]. More research is needed to determine optimal flooding duration and factors that influence variability in the effect of flooding duration [9].
Effectiveness of flooding as a control measure may be enhanced by cutting purple loosestrife stems prior to raising water levels [80]. Cut material should always be removed from the site to prevent spread of vegetative propagules. The efficacy of flooding may be influenced by the presence of carp within contiguous waterways, although the ultimate effects are unclear. Carp may reduce purple loosestrife by grazing its roots or enhance its spread by disseminating vegetative propagules [102]. Carp are not native to North America and should not be introduced as a means to control purple loosestrife.
Consistent spring and early-summer flooding may inhibit purple loosestrife seedling establishment [9,137]. Flooding seedlings 0.8 to 4 inches (2-10 cm) tall for 9 weeks at depths up to 12 inches (30 cm) did not significantly (P<0.05) reduce mean stem densities. Most plants continued to grow, if slowly, while submerged, and plants which emerged above the surface quickly resumed rapid growth [52]. Established purple loosestrife plants can survive in deepwater emergent habitat, in part by development of aerenchymous (containing large intercellular air spaces) stem tissue that facilitates gas exchange in aquatic environments.
Several factors may hinder the effectiveness of controlling purple loosestrife by flooding. Managers may be constrained in their ability to manipulate water levels by the geologic profile of the site or by development along its margins. Substantial warm season evaporation can contribute to this problem. Sustained high water levels may be detrimental to desirable native emergent or shoreline vegetation. Once purple loosestrife has been killed, managers should consider species composition within the remnant seed bank, and the ensuing colonizing community, when water levels have been reduced. It is likely that purple loosestrife seedlings will recolonize the newly exposed soil and further management may be inevitable.
Biological Control
The objective of biological control is to re-establish ecological relationships that have evolved between purple loosestrife and its native predators in order to suppress invasive populations and reduce harmful impacts. Potential advantages of biological control are cost effectiveness at large scales, sustainability, and benign effects in the nontarget environment [22,131]. The Nature Conservancy's Weed Control Methods Handbook provides a comprehensive discussion of considerations and safety issues in developing and implementing a biological control program.
Plant communities where purple loosestrife is found are similar in North America and Europe. Because native insect herbivory inhibits purple loosestrife performance in Europe, it is hoped introductions of European insect herbivores may work to reduce the competitiveness of purple loosestrife in North America, while releasing native plants from suppression [18,19].
The following table lists non-native insects released in North America to control purple loosestrife:
| Control Agent | Mode of Action | Release Sites |
|---|---|---|
| Galerucella calmariensis (beetle) | Larvae and adults feed on foliage and flowers | MB, ON |
| Galerucella pusilla (beetle) | Larvae and adults feed on foliage and flowers [18] | MB, ON, WA [29,31,97] |
| Hylobius transversovittatus (weevil) | Larvae and adults feed on roots [17] | WA [97] |
| Nanophyes marmoratus (weevil) | Larvae feed on flowers and adults feed on foliage and flowers [21] | MB [49] |
Galerucella beetles have been the most effective biocontrol agents used against purple loosestrife in North America thus far [29,62,97]. G. calmariensis and G. pusilla are similar in appearance and habit and are most effective when released together, and both species appear to be unaffected by exposure to the herbicides glyphosate and triclopyr [75,76]. Because of "dramatic" success at some Galerucella release sites, release of other agents should focus on sites where Galerucella have been ineffective. In Europe, H. transversovittatus herbivory on purple loosestrife is strongest in the northern range of the plant, indicating that higher latitude sites may be a good choice for its release in North America [50].
Myzus lythri, a European aphid that has probably been present in the Eastern United States since the early 1930's, might become an effective biological control agent. It has a host-alternating life cycle, utilizing loosestrife and Epilobium spp. in summer and Prunus spp. as primary hosts the rest of the year. Populations of M. lythri could be manipulated to impact local purple loosestrife populations by mass-rearing bugs for targeted early-spring release and/or by planting Prunus spp. near targeted sites [134].
Research examining the potential use of pathogenic fungi as biocontrol agents is ongoing [91].
Chemical Control
A variety of herbicides are effective at controlling purple loosestrife in infested areas. Below is a list of herbicides that have been used effectively against purple loosestrife in North America, as well as a brief discussion of important considerations regarding their use. This is not intended as an exhaustive review of chemical control methods. For more detailed information regarding appropriate use of herbicides in natural areas against this and other invasive plant species, see The Nature Conservancy's Weed Control Methods Handbook.
| Chemical | Considerations |
|---|---|
| 2,4-D [13,90,118,140] | Mixed results against purple loosestrife; harmful to dicots, but little impact on neighboring monocots |
| Triclopyr [12,38,61,89,118] | Generally effective at killing purple loosestrife; results are variable with spray volume; selective against dicots |
| Glyphosate [12,80,102,104,118,122,131] | Highly effective against purple loosestrife; specific formulations available for use in aquatic environments; also damages or kills most other plants which it contacts |
| Imazapyr [11] | Effective against purple loosestrife; negatively impacts cattail |
A serious challenge to controlling purple loosestrife infestations with herbicides is preventing its re-establishment from the seed bank. In the presence of large purple loosestrife seed banks, removal of a considerable fraction of extant vegetation (weed or otherwise) can result in a dense monoculture of purple loosestrife seedlings. The result may be a worse infestation than was originally present [90]. Broadcast application of broad-spectrum herbicides, such as glyphosate, will likely result in widespread exposure of bare substrate and a dense, monotypic stand of purple loosestrife seedlings [118]. By carefully targeting glyphosate spray application to only purple loosestrife, damage to nontarget plants can be minimized. Continued careful treatments over several years can eventually reduce dense populations of purple loosestrife to minimal levels while promoting native plants [104,122]. Native plants are not just inherently valued, but can also provide competition against inevitable purple loosestrife recruitment from existing seed banks [118].
An apparent tradeoff exists when determining the best time to treat adult stands with herbicides. Managers must attempt to balance preventing seed production in established plants with treatments early in the growing season and preventing establishment of a viable new stand of purple loosestrife seedlings by delaying treatments long enough to inhibit recruitment. By conducting herbicide treatments on adult plants late in the growing season, newly established seedlings may not develop sufficiently to survive winter [89]. Late-summer herbicide application also appears to reduce negative effects on desirable native plants [80]. Rawinski [102] found that glyphosate application during late-bloom (mid-August in central New York) period, compared with late-vegetative (mid-June) period, resulted in fewer loosestrife seedlings the following season and increased presence of naturally established, beneficial plants such as shallow sedge (Carex lurida), rice cutgrass (Leersia oryzoides), smartweed and marsh seedbox (Ludwigia palustris). Late-season application of glyphosate in Minnesota wetlands tended to reduce cattail mortality compared with mid-summer treatments, perhaps because the onset of cattail senescence reduced herbicide uptake [12].
Another tradeoff exists between spray volume and target vs. nontarget effects. Purple loosestrife in Wisconsin was examined for response to variation in spray coverage of glyphosate (Rodeo at 1.5%). Individual genets were spot treated in mid-September and received either low (10-25% leaf area coverage), medium (40-60%), or high (75-90%) dosages. Reduction in adult purple loosestrife density was greatest in the high dosage treatment (90-100% reduction) and lowest in the low dosage treatment (75-90% reduction). Surviving purple loosestrife plants in all treatments were greatly reduced in size and vigor. Because glyphosate is nonselective in its effect, survival of nontarget vegetation was also closely related to dosage. High dosage treatment resulted in dense stands of purple loosestrife seedlings with little to no interspecific competition. In contrast, low dosage treatment resulted in high survival rates of desirable perennials and greatly reduced germination of purple loosestrife seedlings. Effective long-term control of purple loosestrife with glyphosate might best be achieved using low-dosage spot applications and conducting followup treatments in subsequent years as necessary [104].
To minimize non-target effects, managers in Michigan have developed a cut-and-herbicide method for purple loosestrife control. They propose cutting plants high on the stem (just below infloresence), allowing them to continue growing and better absorb the applied herbicide throughout the entire plant. Cutting too low apparently risks forcing the plant to "give up" on the leader and instead producing new ramets from the rootstock. Sponge applicators have been developed that limit contact between chemicals and nontarget plants [131]. These methods may be particularly useful in areas where mitigation of damage to indigenous species is important. Encouraging competition from extant native plants often helps reduce the vigor of invasives. For more detailed information regarding these methods, see Tu [131] and the TNC Weed Control Methods Handbook.
Integrated Management
A single method may not be effective for long-term control or removal of purple loosestrife. Integrated management involves using several management techniques in a well-planned, coordinated and organized program. Many combinations of control methods can achieve desired objectives. Methods selected for a specific site will be determined by land-use objectives, desired plant community, extent and nature of infestation, environmental factors (nontarget vegetation, habitat types, climate, hydrology, etc.), economics, and effectiveness and limitations of available control techniques [103,114].
Table A1
Table A1— Forest and range ecosystems, Bureau of Land Management (BLM) physiographic regions, Kuchler plant associations, Society for American Foresters (SAF) forest cover types, and Society for Rangeland Management (SRM) rangeland cover types in which this species occurs.
Forest and Range Ecosystems (Garrison et al. 1977)
- FRES10 White-red-jack pine
- FRES11 Spruce-fir
- FRES12 Longleaf-slash pine
- FRES13 Loblolly-shortleaf pine
- FRES14 Oak-pine
- FRES15 Oak-hickory
- FRES16 Oak-gum-cypress
- FRES17 Elm-ash-cottonwood
- FRES18 Maple-beech-birch
- FRES19 Aspen-birch
- FRES20 Douglas-fir
- FRES21 Ponderosa pine
- FRES22 Western white pine
- FRES23 Fir-spruce
- FRES24 Hemlock-Sitka spruce
- FRES25 Larch
- FRES26 Lodgepole pine
- FRES27 Redwood
- FRES28 Western hardwoods
- FRES29 Sagebrush
- FRES30 Desert shrub
- FRES31 Shinnery
- FRES32 Texas savanna
- FRES33 Southwestern shrubsteppe
- FRES34 Chaparral-mountain shrub
- FRES35 Pinyon-juniper
- FRES36 Mountain grasslands
- FRES37 Mountain meadows
- FRES38 Plains grasslands
- FRES39 Prairie
- FRES40 Desert grasslands
- FRES41 Wet Grasslands
- FRES42 Annual grasslands
- FRES44 Alpine
BLM Physiographic Regions (Bernard and Brown 1977)
- 1 Northern Pacific Border
- 2 Cascade Mountains
- 3 Southern Pacific Border
- 4 Sierra Mountains
- 5 Columbia Plateau
- 6 Upper Basin and Range
- 7 Lower Basin and Range
- 8 Northern Rocky Mountains
- 9 Middle Rocky Mountains
- 10 Wyoming Basin
- 11 Southern Rocky Mountains
- 12 Colorado Plateau
- 13 Rocky Mountain Piedmont
- 14 Great Plains
- 15 Black Hills Uplift
- 16 Upper Missouri Basin and Broken Lands
Kuchler Plant Associations (Kuchler 1964)
- K001 Spruce-cedar-hemlock forest
- K002 Cedar-hemlock-Douglas-fir forest
- K003 Silver fir-Douglas-fir forest
- K004 Fir-hemlock forest
- K005 Mixed conifer forest
- K006 Redwood forest
- K007 Red fir forest
- K008 Lodgepole pine-subalpine forest
- K009 Pine-cypress forest
- K010 Ponderosa shrub forest
- K011 Western ponderosa forest
- K012 Douglas-fir forest
- K013 Cedar-hemlock-pine forest
- K014 Grand fir-Douglas-fir forest
- K015 Western spruce-fir forest
- K016 Eastern ponderosa forest
- K017 Black Hills pine forest
- K018 Pine-Douglas-fir forest
- K020 Spruce-fir-Douglas-fir forest
- K021 Southwestern spruce-fir forest
- K022 Great Basin pine forest
- K023 Juniper-pinyon woodland
- K024 Juniper steppe woodland
- K025 Alder-ash forest
- K026 Oregon oakwoods
- K028 Mosaic of K002 and K026
- K029 California mixed evergreen forest
- K030 California oakwoods
- K031 Oak-juniper woodland
- K032 Transition between K031 and K037
- K033 Chaparral
- K034 Montane chaparral
- K035 Coastal sagebrush
- K036 Mosaic of K030 and K035
- K037 Mountain-mahogany-oak scrub
- K038 Great Basin sagebrush
- K039 Blackbrush
- K040 Saltbush-greasewood
- K041 Creosote bush
- K042 Creosote bush-bur sage
- K043 Paloverde-cactus shrub
- K045 Ceniza shrub
- K046 Desert: vegetation largely lacking
- K047 Fescue-oatgrass
- K048 California steppe
- K049 Tule marshes
- K050 Fescue-wheatgrass
- K051 Wheatgrass-bluegrass
- K052 Alpine meadows and barren
- K054 Grama-tobosa prairie
- K055 Sagebrush steppe
- K056 Wheatgrass-needlegrass shrubsteppe
- K057 Galleta-threeawn shrubsteppe
- K059 Trans-Pecos shrub savanna
- K060 Mesquite savanna
- K061 Mesquite-acacia savanna
- K062 Mesquite-live oak savanna
- K063 Foothills prairie
- K064 Grama-needlegrass-wheatgrass
- K065 Grama-buffalo grass
- K066 Wheatgrass-needlegrass
- K067 Wheatgrass-bluestem-needlegrass
- K068 Wheatgrass-grama-buffalo grass
- K069 Bluestem-grama prairie
- K070 Sandsage-bluestem prairie
- K071 Shinnery
- K072 Sea oats prairie
- K073 Northern cordgrass prairie
- K074 Bluestem prairie
- K075 Nebraska Sandhills prairie
- K076 Blackland prairie
- K077 Bluestem-sacahuista prairie
- K078 Southern cordgrass prairie
- K081 Oak savanna
- K082 Mosaic of K074 and K100
- K083 Cedar glades
- K084 Cross Timbers
- K085 Mesquite-buffalo grass
- K086 Juniper-oak savanna
- K087 Mesquite-oak savanna
- K088 Fayette prairie
- K089 Black Belt
- K090 Live oak-sea oats
- K093 Great Lakes spruce-fir forest
- K094 Conifer bog
- K095 Great Lakes pine forest
- K096 Northeastern spruce-fir forest
- K097 Southeastern spruce-fir forest
- K098 Northern floodplain forest
- K099 Maple-basswood forest
- K100 Oak-hickory forest
- K101 Elm-ash forest
- K102 Beech-maple forest
- K103 Mixed mesophytic forest
- K104 Appalachian oak forest
- K106 Northern hardwoods
- K107 Northern hardwoods-fir forest
- K108 Northern hardwoods-spruce forest
- K109 Transition between K104 and K106
- K110 Northeastern oak-pine forest
- K111 Oak-hickory-pine
- K112 Southern mixed forest
- K113 Southern floodplain forest
- K114 Pocosin
SAF Cover Types (Eyre 1980)
- 1 Jack pine
- 5 Balsam fir
- 12 Black spruce
- 13 Black spruce-tamarack
- 14 Northern pin oak
- 15 Red pine
- 16 Aspen
- 17 Pin cherry
- 18 Paper birch
- 19 Gray birch-red maple
- 20 White pine-northern red oak-red maple
- 21 Eastern white pine
- 22 White pine-hemlock
- 23 Eastern hemlock
- 24 Hemlock-yellow birch
- 25 Sugar maple-beech-yellow birch
- 26 Sugar maple-basswood
- 27 Sugar maple
- 28 Black cherry-maple
- 30 Red spruce-yellow birch
- 31 Red spruce-sugar maple-beech
- 32 Red spruce
- 33 Red spruce-balsam fir
- 34 Red spruce-Fraser fir
- 35 Paper birch-red spruce-balsam fir
- 37 Northern white-cedar
- 38 Tamarack
- 39 Black ash-American elm-red maple
- 40 Post oak-blackjack oak
- 42 Bur oak
- 43 Bear oak
- 44 Chestnut oak
- 45 Pitch pine
- 46 Eastern redcedar
- 50 Black locust
- 51 White pine-chestnut oak
- 52 White oak-black oak-northern red oak
- 53 White oak
- 55 Northern red oak
- 57 Yellow-poplar
- 58 Yellow-poplar-eastern hemlock
- 59 Yellow-poplar-white oak-northern red oak
- 60 Beech-sugar maple
- 61 River birch-sycamore
- 62 Silver maple-American elm
- 63 Cottonwood
- 64 Sassafras-persimmon
- 65 Pin oak-sweetgum
- 66 Ashe juniper-redberry (Pinchot) juniper
- 67 Mohrs (shin) oak
- 68 Mesquite
- 69 Sand pine
- 70 Longleaf pine
- 71 Longleaf pine-scrub oak
- 72 Southern scrub oak
- 73 Southern redcedar
- 74 Cabbage palmetto
- 75 Shortleaf pine
- 76 Shortleaf pine-oak
- 78 Virginia pine-oak
- 79 Virginia pine
- 80 Loblolly pine-shortleaf pine
- 81 Loblolly pine
- 82 Loblolly pine-hardwood
- 83 Longleaf pine-slash pine
- 84 Slash pine
- 85 Slash pine-hardwood
- 87 Sweetgum-yellow-poplar
- 88 Willow oak-water oak-diamondleaf (laurel) oak
- 89 Live oak
- 91 Swamp chestnut oak-cherrybark oak
- 92 Sweetgum-willow oak
- 93 Sugarberry-American elm-green ash
- 94 Sycamore-sweetgum-American elm
- 95 Black willow
- 96 Overcup oak-water hickory
- 97 Atlantic white-cedar
- 98 Pond pine
- 100 Pondcypress
- 101 Baldcypress
- 102 Baldcypress-tupelo
- 103 Water tupelo-swamp tupelo
- 104 Sweetbay-swamp tupelo-redbay
- 107 White spruce
- 108 Red maple
- 109 Hawthorn
- 110 Black oak
- 201 White spruce
- 202 White spruce-paper birch
- 203 Balsam poplar
- 204 Black spruce
- 205 Mountain hemlock
- 206 Engelmann spruce-subalpine fir
- 207 Red fir
- 208 Whitebark pine
- 209 Bristlecone pine
- 210 Interior Douglas-fir
- 211 White fir
- 212 Western larch
- 213 Grand fir
- 215 Western white pine
- 216 Blue spruce
- 217 Aspen
- 218 Lodgepole pine
- 219 Limber pine
- 220 Rocky Mountain juniper
- 221 Red alder
- 222 Black cottonwood-willow
- 223 Sitka spruce
- 224 Western hemlock
- 225 Western hemlock-Sitka spruce
- 226 Coastal true fir-hemlock
- 227 Western redcedar-western hemlock
- 228 Western redcedar
- 229 Pacific Douglas-fir
- 230 Douglas-fir-western hemlock
- 231 Port-Orford-cedar
- 232 Redwood
- 233 Oregon white oak
- 234 Douglas-fir-tanoak-Pacific madrone
- 235 Cottonwood-willow
- 236 Bur oak
- 237 Interior ponderosa pine
- 238 Western juniper
- 239 Pinyon-juniper
- 242 Mesquite
- 243 Sierra Nevada mixed conifer
- 244 Pacific ponderosa pine-Douglas-fir
- 245 Pacific ponderosa pine
- 246 California black oak
- 247 Jeffrey pine
- 248 Knobcone pine
- 249 Canyon live oak
- 250 Blue oak-foothills pine
- 251 White spruce-aspen
- 252 Paper birch
- 253 Black spruce-white spruce
- 254 Black spruce-paper birch
- 255 California coast live oak
- 256 California mixed subalpine
SRM Rangeland Cover Types (Shiflet 1994)
- 101 Bluebunch wheatgrass
- 102 Idaho fescue
- 103 Green fescue
- 104 Antelope bitterbrush-bluebunch wheatgrass
- 105 Antelope bitterbrush-Idaho fescue
- 106 Bluegrass scabland
- 107 Western juniper/big sagebrush/bluebunch wheatgrass
- 108 Alpine Idaho fescue
- 109 Ponderosa pine shrubland
- 110 Ponderosa pine-grassland
- 201 Blue oak woodland
- 202 Coast live oak woodland
- 203 Riparian woodland
- 204 North coastal shrub
- 205 Coastal sage shrub
- 206 Chamise chaparral
- 207 Scrub oak mixed chaparral
- 208 Ceanothus mixed chaparral
- 209 Montane shrubland
- 210 Bitterbrush
- 211 Creosote bush scrub
- 212 Blackbush
- 213 Alpine grassland
- 214 Coastal prairie
- 215 Valley grassland
- 216 Montane meadows
- 217 Wetlands
- 301 Bluebunch wheatgrass-blue grama
- 302 Bluebunch wheatgrass-Sandberg bluegrass
- 303 Bluebunch wheatgrass-western wheatgrass
- 304 Idaho fescue-bluebunch wheatgrass
- 305 Idaho fescue-Richardson needlegrass
- 306 Idaho fescue-slender wheatgrass
- 307 Idaho fescue-threadleaf sedge
- 308 Idaho fescue-tufted hairgrass
- 309 Idaho fescue-western wheatgrass
- 310 Needle-and-thread-blue grama
- 311 Rough fescue-bluebunch wheatgrass
- 312 Rough fescue-Idaho fescue
- 313 Tufted hairgrass-sedge
- 314 Big sagebrush-bluebunch wheatgrass
- 315 Big sagebrush-Idaho fescue
- 316 Big sagebrush-rough fescue
- 317 Bitterbrush-bluebunch wheatgrass
- 318 Bitterbrush-Idaho fescue
- 319 Bitterbrush-rough fescue
- 320 Black sagebrush-bluebunch wheatgrass
- 321 Black sagebrush-Idaho fescue
- 322 Curlleaf mountain-mahogany-bluebunch wheatgrass
- 323 Shrubby cinquefoil-rough fescue
- 324 Threetip sagebrush-Idaho fescue
- 401 Basin big sagebrush
- 402 Mountain big sagebrush
- 403 Wyoming big sagebrush
- 404 Threetip sagebrush
- 405 Black sagebrush
- 406 Low sagebrush
- 407 Stiff sagebrush
- 408 Other sagebrush types
- 409 Tall forb
- 410 Alpine rangeland
- 411 Aspen woodland
- 412 Juniper-pinyon woodland
- 413 Gambel oak
- 414 Salt desert shrub
- 415 Curlleaf mountain-mahogany
- 416 True mountain-mahogany
- 417 Littleleaf mountain-mahogany
- 418 Bigtooth maple
- 419 Bittercherry
- 420 Snowbrush
- 421 Chokecherry-serviceberry-rose
- 422 Riparian
- 501 Saltbush-greasewood
- 505 Grama-tobosa shrub
- 506 Creosotebush-bursage
- 507 Palo verde-cactus
- 508 Creosotebush-tarbush
- 601 Bluestem prairie
- 602 Bluestem-prairie sandreed
- 603 Prairie sandreed-needlegrass
- 604 Bluestem-grama prairie
- 605 Sandsage prairie
- 606 Wheatgrass-bluestem-needlegrass
- 607 Wheatgrass-needlegrass
- 608 Wheatgrass-grama-needlegrass
- 609 Wheatgrass-grama
- 610 Wheatgrass
- 611 Blue grama-buffalo grass
- 612 Sagebrush-grass
- 613 Fescue grassland
- 614 Crested wheatgrass
- 615 Wheatgrass-saltgrass-grama
- 701 Alkali sacaton-tobosagrass
- 702 Black grama-alkali sacaton
- 703 Black grama-sideoats grama
- 704 Blue grama-western wheatgrass
- 705 Blue grama-galleta
- 706 Blue grama-sideoats grama
- 707 Blue grama-sideoats grama-black grama
- 708 Bluestem-dropseed
- 709 Bluestem-grama
- 710 Bluestem prairie
- 711 Bluestem-sacahuista prairie
- 712 Galleta-alkali sacaton
- 713 Grama-muhly-threeawn
- 714 Grama-bluestem
- 715 Grama-buffalo grass
- 716 Grama-feathergrass
- 717 Little bluestem-Indiangrass-Texas wintergrass
- 718 Mesquite-grama
- 719 Mesquite-liveoak-seacoast bluestem
- 720 Sand bluestem-little bluestem (dunes)
- 721 Sand bluestem-little bluestem (plains)
- 722 Sand sagebrush-mixed prairie
- 723 Sea oats
- 724 Sideoats grama-New Mexico feathergrass-winterfat
- 725 Vine mesquite-alkali sacaton
- 726 Cordgrass
- 727 Mesquite-buffalo grass
- 728 Mesquite-granjeno-acacia
- 729 Mesquite
- 730 Sand shinnery oak
- 731 Cross timbers-Oklahoma
- 732 Cross timbers-Texas (little bluestem-post oak)
- 733 Juniper-oak
- 734 Mesquite-oak
- 735 Sideoats grama-sumac-juniper
- 801 Savanna
- 802 Missouri prairie
- 803 Missouri glades
- 804 Tall fescue
- 805 Riparian
- 807 Gulf Coast fresh marsh
1. Anderson, Mark G. 1991. Population structure of Lythrum salicaria in relation to wetland community structure. Durham, NH: University of New Hampshire. 93 p. Thesis. [39754]
2. Anderson, Mark G. 1995. Interactions between Lythrum salicaria and native organisms: a critical review. Environmental Management. 19(2): 225-231. [37517]
3. Anderson, Neil O.; Ascher, Peter D. 1993. Male and female fertility of loosestrife (Lythrum) cultivars. Journal of the American Horticultural Society. 118(6): 851-858. [40318]
4. Arno, Stephen F. 1980. Forest fire history in the Northern Rockies. Journal of Forestry. 78(8): 460-465. [11990]
5. Arno, Stephen F. 2000. Fire in western forest ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 97-120. [36984]
6. Arno, Stephen F.; Gruell, George E. 1983. Fire history at the forest-grassland ecotone in southwestern Montana. Journal of Range Management. 36(3): 332-336. [342]
7. Arno, Stephen F.; Wilson, Andrew E. 1986. Dating past fires in curlleaf mountain-mahogany communities. Journal of Range Management. 39(3): 241-243. [350]
8. Auclair, Allan N.; Bouchard, Andre; Pajaczkowski, Josephine. 1973. Plant composition and species relations on the Huntingdon Marsh, Quebec. Canadian Journal of Botany. 51: 1231-1247. [14498]
9. Balogh, Gregory Robert. 1986. Ecology, distribution, and control of purple loosestrife (Lythrum salicaria) in northwest Ohio. Columbus, OH: Ohio State University. 122 p. Thesis. [40074]
10. Beauregard, N.; Leclair, R., Jr. 1988. Multivariate analysis of the summer habitat structure of Rana pipiens Schreber, in Lac Saint Pierre (Quebec, Canada). In: Szaro, Robert C.; Severson, Kieth E.; Patton, David R., technical coordinators. Management of amphibians, reptiles, and small mammals in North America: Proceedings of the symposium; 1988 July 19-21; Flagstaff, AZ. Gen. Tech. Rep. RM-166. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 129-143. [22679]
11. Becker, Roger L.; Warnes, Dennis D.; Kinkaid, Bradley D.; Miller, Douglas W. 1990. Purple loosestrife control with 1989 applications of triclopyr and imazapyr and commercial standards, Morris, MN. North Central Weed Science Society Research Report. 47: 75-76. [40213]
12. Becker, Roger L.; Warnes, Dennis D.; Ralston, Dennis F. 1989. Purple loosestrife control in 1989 with 1988 applications of triclopyr, White Bear Lake and Morris, MN. North Central Weed Science Society Research Report. 46: 103. [40212]
13. Benedict, Jim. 1990. Purple loosestrife control in Voyageurs National Park. Park Science: A Resource Management Bulletin. 10(3): 21-22. [12720]
14. Benefield, Carri. 2000. Lythrum salicaria L. In: Bossard, Carla C.; Randall, John M.; Hoshovsky, Marc C., eds. Invasive plants of California's wildlands. Berkeley, CA: University of California Press: 236-240. [38336]
15. Berghage, Robert; Sellmer, Jim. 1998. A note on purple loosestrife. Ornamental Horticulture Monthly Newsletter, [Online]. University Park, PA: Penn State University. 1(3), 5ff. Available: http://hortweb.cas.psu.edu/ohortex/news/1998/May_98.html [2002, March 19]. [40340]
16. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434]
17. Blossey, Bernd. 1993. Herbivory below ground and biological weed control: life history of a root-boring weevil on purple loosestrife. Oecologia. 94: 380-387. [40092]
18. Blossey, Bernd. 1995. Impact of Galerucella pusilla and G. calariensis (Coleoptera: Chrysomelidae) on field populations of purple loosestrife (Lythrum salicaria). In: Delfosse, E. S.; Scott, R. R., eds. Proceedings, 8th international symposium on biological control of weeds; 1992 February 2-7; Canterbury, New Zealand. Melbourne, Australia: DSIR/CSIRO: 27-31. [40248]
19. Blossey, Bernd; Notzold, Rolf. 1995. Evolution of increased competitive ability in invasive nonindigenous plants: a hypothesis. Journal of Ecology. 83: 887-889. [39780]
20. Blossey, Bernd; Schat, Marjolein. 1997. Performance of Galerucella calmariensis (Coleoptera: Chrysomelidae) on different North American populations of purple loosestrife. Environmental Entomology. 26(2): 439-445. [37549]
21. Blossey, Bernd; Schroeder, Dieter. 1995. Host specificity of three potential biological weed control agents attacking flowers and seeds of Lythrum salicaria (purple loosestrife). Biological Control. 5: 47-53. [37523]
22. Bourchier, R. S.; DeClerck-Floate, R. A. 2000. Weed biological control and insect ecology, [Online]. In: Agriculture and Agri-Food Canada, Research Branch, Lethbridge Research Centre, Biocontrol Projects. Available: http://res2.agr.ca/lethbridge/crops/bioproj.htm [2002, March 23]. [40342]
23. Brown, Beverly J.; Wickstrom, Conrad E. 1997. Adventitious root production and survival of purple loosestrife (Lythrum salicaria) shoot sections. Ohio Journal of Science. 97(1): 2-4. [37526]
24. Buchholz, Kenneth; Good, Ralph E. 1982. Density, age structure, biomass and net annual aboveground productivity of dwarfed Pinus rigida Moll. from the New Jersey Pine Barren Plains. Bulletin of the Torrey Botanical Club. 109(1): 24-34. [8639]
25. Burkhardt, Wayne J.; Tisdale, E. W. 1976. Causes of juniper invasion in southwestern Idaho. Ecology. 57: 472-484. [565]
26. Bury, R. Bruce. 1979. Review of the ecology and conservation of the bog turtle, Clemmys muhlenbergii. Special Scientific Report--Wildlife No. 219. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 9 p. [40263]
27. Caldwell, Fredricka Ann; Crow, Garrett E. 1992. A floristic and vegetation analysis of a freshwater tidal marsh on the Merrimack River, West Newbury, Massachusetts. Rhodora. 94(877): 63-97. [18126]
28. Coddington, Jonathan; Field, Katharine G. 1978. Rare and endangered vascular plant species in Massachusetts. Cambridge, MA: New England Botanical Club. 52 p. [40282]
29. Corrigan, J. E.; Mackenzie, D. L.; Simser, L. 1998. Field observations of non-target feeding by Galerucella calmariensis [Coleoptera: Chrysomelidae], an introduced biological control agent of purple loosestrife, Lathrum salicaria [Lythraceae]. Proceedings, Entomological Society of Ontario. 129: 99-106. [37533]
30. Day, R. T.; Keddy, P. A.; McNeill, J.; Carleton, T. 1988. Fertility and disturbance gradients: a summary model for riverine marsh vegetation. Ecology. 69(4): 1044-1054. [39768]
31. Diehl, Jason K.; Holliday, N. J.; Lindgren, C. J.; Roughley, R. E. 1997. Insects associated with purple loosestrife, Lythrum salicaria L., in southern Manitoba. Canadian Entomologist. 129: 937-948. [39781]
32. Dixon, Mark D.; Johnson, W. Carter. 1999. Riparian vegetation along the middle Snake River, Idaho: zonation, geographical trends, and historical changes. Great Basin Naturalist. 59(1): 18-34. [37548]
33. Duchesne, Luc C.; Hawkes, Brad C. 2000. Fire in northern ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 35-51. [36982]
34. Ducks Unlimited Canada. 2000. Don't give purple loosestrife a home this summer, [Online]. 2000 News Release. Available: http://www.ducks.ca/NEWS/2000/000526.html [2002, March 3]. [40341]
35. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905]
36. Finney, Mark A.; Martin, Robert E. 1989. Fire history in a Sequoia sempervirens forest at Salt Point State Park, California. Canadian Journal of Forest Research. 19: 1451-1457. [9845]
37. Frissell, Sidney S., Jr. 1968. A fire chronology for Itasca State Park, Minnesota. Minnesota Forestry Research Notes No. 196. Minneapolis, MN: University of Minnesota. 2 p. [34527]
38. Gabor, T. Shane; Haagsma, T.; Murkin, H. R.; Armson, E. 1995. Effects of triclopyr amine on purple loosestrife and non-target wetland plants in south-eastern Ontario, Canada. Journal of Aquatic Plant Management. 33: 48-51. [37505]
39. Gabor, T. Shane; Murkin, H. R. 1990. Effects of clipping purple loosestrife seedlings during a simulated wetland drawdown. Journal of Aquatic Plant Management. 28: 98-100. [40091]
40. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; Lewis, Mont E.; Smith, Dixie R. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p. [998]
41. Gaudet, Connie L.; Keddy, Paul A. 1995. Competitive performance and species distribution in shoreline plant communities: a comparative approach. Ecology. 76(1): 280-291. [37524]
42. Gilbert, N.; Lee, S. B. 1980. Two perils of plant population dynamics. Oecologia. 46: 283-284. [40247]
43. Grabas, Gregory P.; Laverty, Terence M. 1999. The effect of purple loosestrife (Lythrum salicaria L.; Lythraceae) on the pollination and reproductive success of sympatric co-flowering wetland plants. Ecoscience. 6(2): 230-242. [37534]
44. Grout, Jeff A.; Levings, Colin D.; Richardson, John S. 1997. Decomposition rates of purple loosestrife (Lythrum salicaria) and Lyngbyei's sedge (Carex lyngbyei) in the Fraser River estuary. Estuaries. 20(1): 96-102. [37537]
45. Gruell, G. E.; Loope, L. L. 1974. Relationships among aspen, fire, and ungulate browsing in Jackson Hole, Wyoming. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 33 p. In cooperation with: U.S. Department of the Interior, National Park Service, Rocky Mountain Region. [3862]
46. Haber, Erich. 2001. Invasive plant data summary and control options: Purple loosestrife. In: Invasive plants of Canada: Guide to species and methods of control, [Online]. Available: http://www.magi.com/%%7Eehaber/lyth_sal.html [2002, January 25]. [40051]
47. Hager, Heather A.; McCoy, Karen D. 1998. The implications of accepting untested hypotheses: a review of the effects of purple loosestrife (Lythrum salicaria) in North America. Biodiversity and Conservation. 7(8): 1069-1079. [37538]
48. Harper, Bonnie L. 1986. A Minnesota counterattack on purple loosestrife (Lythrum salicaria). In: Clambey, Gary K.; Pemble, Richard H., eds. The prairie: past, present and future: Proceedings of the 9th North American Prairie Conference; 1984 July 29 - August 1; Moorhead, MN. Fargo, ND: Tri-College University Center for Environmental Studies: 262-264. [3589]
49. Harris, P. 2002. Established biocontrol agent: Nanophyes marmoratus (Goeze). flower-feeding weevil, [Online] In: Biological control of weeds--Biology of target weeds. Lethbridge, AB: Agriculture and Agri-Food Canada, Research Branch, Lethbridge Research Centre (producer). Available: http://res2.agr.ca/lethbridge/weedbiol/agents/ananmar.htm [2002, March 23]. [40344]
50. Harris, P.; Corrigan, J. 2000. Purple loosestrife (Lythrum salicaria L.), [Online]. In: Biological control of weeds--Biology of target weeds. Lethbridge, AB: Agriculture and Agri-Food Canada, Research Branch, Lethbridge Research Centre (producer). Available: http://res2.agr.ca/lethbridge/weedbio/hosts/blosstrf.htm [2002, January 25]. [39822]
51. Haworth-Brockman, Margaret J.; Murkin, H. R.; Clay, R. T.; Armson, E. 1991. Effects of underwater clipping of purple loosestrife in a southern Ontario wetland. Journal of Aquatic Plant Management. 29: 117-118. [19420]
52. Haworth-Brockman, Margaret J.; Murkin, Henry R.; Clay, Robert T. 1993. Effects of shallow flooding on newly established purple loosestrife seedlings. Wetlands. 13(3): 224-227. [37516]
53. Heidorn, Randy; Anderson, Brian. 1991. Vegetation management guideline: purple loosestrife (Lythrum salicaria L.). Natural Areas Journal. 11(3): 172-173. [15019]
54. Heinselman, Miron L. 1970. The natural role of fire in northern conifer forests. In: The role of fire in the Intermountain West: Symposium proceedings; 1970 October 27-29; Missoula, MT. Missoula, MT: Intermountain Fire Research Council: 30-41. In cooperation with: University of Montana, School of Forestry. [15735]
55. Hendrickson, William H. 1972. Perspective on fire and ecosystems in the United States. In: Fire in the environment: Symposium proceedings; 1972 May 1-5; Denver, CO. FS-276. [Washington, DC]: U.S. Department of Agriculture, Forest Service: 29-33. In cooperation with: Fire Services of Canada, Mexico, and the United States; Members of the Fire Management Study Group; North American Forestry Commission; FAO. [17276]
56. Hickman, James C., ed. 1993. The Jepson manual: Higher plants of California. Berkeley, CA: University of California Press. 1400 p. [21992]
57. Hitchcock, C. Leo; Cronquist, Arthur. 1973. Flora of the Pacific Northwest. Seattle, WA: University of Washington Press. 730 p. [1168]
58. Huang, Chih-Lin; del Moral, Roger. 1988. Plant-environment relationships on the Montlake wildlife area, Seattle, Washington, USA. Vegetatio. 75: 103-113. [9742]
59. Johnson, Wayne S. 2000. I repent, repent, repent! Kill purple loosestrife--that beautiful weed. Nevada's Horticulture Connection, [Online]. Reno, NV: University of Nevada, Cooperative Extension. 1(1), 3ff. Available: http://www.extension.unr.edu/horticulture/april2000/purpleloosestrife.htmt [2002, March 19]. [40339]
60. Kartesz, John T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. 1st ed. In: Kartesz, John T.; Meacham, Christopher A. Synthesis of the North American flora (Windows Version 1.0), [CD-ROM]. Chapel Hill, NC: North Carolina Botanical Garden (Producer). In cooperation with: The Nature Conservancy; U.S. Department of Agriculture, Natural Resources Conservation Service; U.S. Department of the Interior, Fish and Wildlife Service. [36715]
61. Katovich, Elizabeth J. Stamm; Becker, Roger L.; Kinkaid, Brad D. 1996. Influence of nontarget neighbors and spray volume on retention and efficacy of triclopyr in purple loosestrife (Lythrum salicaria). Weed Science. 44(1): 143-147. [37520]
62. Katovich, Elizabeth J. Stamm; Becker, Roger L.; Ragsdale, David W. 1999. Effect of Galerucella spp. on survival of purple loosestrife (Lythrum salicaria) roots and crowns. Weed Science. 47(3): 360-365. [37512]
63. Kearsley, Jennifer. 1999. Inventory and vegetation classification of floodplain forest communities in Massachusetts. Rhodora. 101(906): 105-135. [35963]
64. Keddy, Paul A.; Ellis, Timothy H. 1985. Seedling recruitment of 11 wetland plant species along a water level gradient: shared or distinct responses? Canadian Journal of Botany. 63(10): 1876-1879. [37503]
65. Keddy, Paul A.; Twolan-Strutt, Lisa; Wisheu, Irene C. 1994. Competitive effect and response rankings in 20 wetland plants: are they consistent across three environments? Journal of Ecology. 82: 635-643. [23700]
66. Keddy, Paul; Fraser, Lauchlan H.; Wisheu, Irene C. 1998. A comparative approach to examine competitive response of 48 wetland plant species. Journal of Vegetative Science. 9(6): 777-786. [37551]
67. Kiviat, Erik. 1978. Bog turtle habitat ecology. Bulletin of the Chicago Herpetological Society. 13: 29-42. [40232]
68. Kiviat, Erik. 1996. American goldfinch nests in purple loosestrife. The Wilson Bulletin. 108(1): 182-186. [39420]
69. Kucera, Clair L. 1981. Grasslands and fire. In: Mooney, H. A.; Bonnicksen, T. M.; Christensen, N. L.; Lotan, J. E.; Reiners, W. A., tech. coords. Fire regimes and ecosystem properties: Proceedings of the conference; 1978 December 11-15; Honolulu, HI. Gen. Tech. Rep. WO-26. Washington, DC: U.S. Department of Agriculture, Forest Service: 90-111. [4389]
70. Kuchler, A. W. 1964. United States [Potential natural vegetation of the conterminous United States]. Special Publication No. 36. New York: American Geographical Society. 1:3,168,000; colored. [3455]
71. Larson, Gary E. 1993. Aquatic and wetland vascular plants of the Northern Great Plains. Gen. Tech. Rep. RM-238. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 681 p. Jamestown, ND: Northern Prairie Wildlife Research Center (Producer). Available: http://www.npwrc.usgs.gov/resource/plants/vascplnt/vascplnt.htm [2006, February 11]. [22534]
72. Levin, Donald A. 1970. Assortative pollination in Lythrum. American Journal of Botany. 57(1): 1-5. [39787]
73. Levin, Donald A.; Kerster, Harold W. 1973. Assortative pollination for stature in Lythrum salicaria. Evolution. 27: 144-152. [39778]
74. Lindgren, Cory J.; Clay, Robert T. 1993. Fertility of `Morden Pink' Lythrum virgatum L. transplanted into wild stands of L. salicaria L. in Manitoba. HortScience. 28(9): 954. [37504]
75. Lindgren, Cory John; Gabor, T. Shane; Murkin, Henry R. 1998. Impact of triclopyr amine on Galerucella calmariensis L. (Coleoptera: Chrysomelidae) and a step toward integrated management of purple loosestrife Lythrum salicaria L. Biological Control. 12(1): 14-19. [37508]
76. Lindgren, Cory John; Gabor, T. Shane; Murkin, Henry R. 1999. Compatibility of glyphosate with Galerucella calmariensis; a biological control agent for purple loosestrife (Lythrum salicaria). Journal of Aquatic Plant Management. 37: 44-48. [37540]
77. Lor, Socheata Krystyne. 2000. Population status and breeding ecology of marsh birds in western New York. Ithaca, NY: Cornell University, Department of Natural Resources. 126 p. Thesis. [40280]
78. Mal, Tarun K.; Lovett-Doust, Jon; Lovett-Doust, Lesley. 1997. Time-dependent competitive displacement of Typha angustifolia by Lythrum salicaria. Oikos. 79(1): 26-33. [37498]
79. Mal, Tarun K.; Lovett-Doust, Jon; Lovett-Doust, Lesley; Mulligan, G. A. 1992. The biology of Canadian weeds. 100. Lythrum salicaria. Canadian Journal of Plant Science. 72(4): 1305-1330. [37554]
80. Malecki, Richard A.; Rawinski, Thomas J. 1985. New methods for controlling purple loosestrife. New York Fish and Game Journal. 32(1): 9-19. [18331]
81. Malecki, Richard. 1995. Purple loosestrife. In: Non-native species. In: Laroe, Edward T.; Farris, Gaye S.; Puckett, Catherine E.; [and others], eds. Our living resources: a report to the nation on the distribution, abundance, and health of U.S. plants, animals, and ecosystems, [Online]. Washington, DC: U.S. Department of the Interior, National Biological Service (Producer). Available: http://biology.usgs.gov/s+t/noframe/x193.htm [2002, February 6]. [39788]
82. Mason, Sandra. 1999. Homeowner's column: Some plants are illegal to grow in Illinois, [Online]. Champaign, IL: University of Illinois at Urbana-Champaign, University Extension, Urban Programs Resource Network (Producer). Available: http://www.urbanext.uiuc.edu/champaign/homwowners/hc990515.html [2002, March 19]. [40336]
83. McKeon, W. H. 1959. A preliminary report on the use of chemical herbicides to control purple loosestrife (Lythrum salicaria) on a small river. Proceedings, Northeast Weed Control Conference. 13: 329-332. [40097]
84. Meinecke, E. P. 1929. Quaking aspen: A study in applied forest pathology. Tech. Bull. No. 155. Washington, DC: U.S. Department of Agriculture. 34 p. [26669]
85. Miller, Richard F.; Rose, Jeffery A. 1995. Historic expansion of Juniperus occidentalis (western juniper) in southeastern Oregon. The Great Basin Naturalist. 55(1): 37-45. [25666]
86. Moir, William H. 1982. A fire history of the High Chisos, Big Bend National Park, Texas. The Southwestern Naturalist. 27(1): 87-98. [5916]
87. Morrison, Peter H.; Swanson, Frederick J. 1990. Fire history and pattern in a Cascade Range landscape. Gen. Tech. Rep. PNW-GTR-254. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 77 p. [13074]
88. Myers, Ronald L. 2000. Fire in tropical and subtropical ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 161-173. [36985]
89. Nelson, Linda S.; Getsinger, K. D.; Freedman, J. E. 1996. Efficacy of triclopyr on purple loosestrife and associated wetland vegetation. Journal of Aquatic Plant Management. 34: 72-74. [37507]
90. Notestein, Anne. 1986. The spread and management of purple loosestrife (Lythrum salicaria L.) in Horicon National Wildlife Refuge, Wisconsin. Madison, WI: University of Wisconsin. 126 p. Thesis. [40233]
91. Nyvall, Robert F.; Hu, An. 1997. Laboratory evaluation of indigenous North American fungi for biological control of purple loosestrife. Biological Control. 8(1): 37-42. [37522]
92. Ottenbreit, Kimberly A.; Staniforth, Richard J. 1994. Crossability of naturalized and cultivated Lythrum taxa. Canadian Journal of Botany. 72: 337-341. [40288]
93. Otto, Sibylle; Groffman, Peter M.; Findlay, Stuart E. G.; Arreola, Anna E. 1999. Invasive plant species and microbial processes in a tidal freshwater marsh. Journal of Environmental Quality. 28(4): 1252-1257. [37547]
94. Patoine, A.; Pinel-Alloul, B.; Prepas, E. E. 2002. Effects of catchment perturbations by logging and wildfires on zooplankton species richness and composition in Boreal Shield lakes. Freshwater Biology. 47: 1996-2014. [3482]
95. Paysen, Timothy E.; Ansley, R. James; Brown, James K.; Gottfried, Gerald J.; Haase, Sally M.; Harrington, Michael G.; Narog, Marcia G.; Sackett, Stephen S.; Wilson, Ruth C. 2000. Fire in western shrubland, woodland, and grassland ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 121-159. [36978]
96. Pellett, Melvin. 1977. Purple loosestrife spreads down river. American Bee Journal. 117: 214-215. [40055]
97. Piper, G. L. 1996. Biological control of the wetlands weed purple loosestrife (Lythrum salicaria) in the Pacific northwestern United States. Hydrobiologia. 340: 291-294. [39782]
98. Pojar, Jim. 1975. Hummingbird flowers of British Columbia. Syesis. 8: 25-28. [6537]
99. Rachich, J.; Reader, R. J. 1999. An experimental study of wetland invasibility by purple loosestrife (Lythrum salicaria). Canadian Journal of Botany. 77(10): 1499-1503. [37552]
100. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. [2843]
101. Rawinski, Thomas J.; Malecki, Richard A. 1984. Ecological relationships among purple loosestrife, cattail and wildlife at the Montezuma National Wildlife Refuge. New York Fish and Game Journal. 31(1): 81-87. [18330]
102. Rawinski, Thomas James. 1982. The ecology and management of purple loosestrife (Lythrum salicaria L.) in central New York. Ithaca, NY: Cornell University. 88 p. Thesis. [40281]
103. Rees, N. E.; Quimby, P. C., Jr.; Mullin, B. H. 1996. Section I. Biological control of weeds. In: Rees, Norman E.; Quimby, Paul C., Jr.; Piper, Gary L.; [and others], eds. Biological control of weeds in the West. Bozeman, MT: Western Society of Weed Science. In cooperation with: U.S. Department of Agriculture, Agricultural Research Service; Montana Department of Agriculture; Montana State University: 3-24. [38273]
104. Reinartz, James A.; Popp, James W.; Kuchenreuther, Margaret A. 1986. Purple loosestrife control: minimum glyphosate dose sought (Wisconsin). Restoration & Management Notes. 4(2): 83-84. [40243]
105. Reschke, Carol. 1990. Ecological communities of New York State. Latham, NY: New York State Department of Environmental Conservation, Natural Heritage Program. 96 p. [21441]
106. Ripple, William J. 1994. Historic spatial patterns of old forests in western Oregon. Journal of Forestry. 92(11): 45-49. [33881]
107. Romme, William H. 1982. Fire and landscape diversity in subalpine forests of Yellowstone National Park. Ecological Monographs. 52(2): 199-221. [9696]
108. Sapsis, David B. 1990. Ecological effects of spring and fall prescribed burning on basin big sagebrush/Idaho fescue--bluebunch wheatgrass communities. Corvallis, OR: Oregon State University. 105 p. Thesis. [16579]
109. Schultz, Brad W. 1987. Ecology of curlleaf mountain mahogany (Cercocarpus ledifolius) in western and central Nevada: population structure and dynamics. Reno, NV: University of Nevada. 111 p. Thesis. [7064]
110. Shamsi, S. R. A. 1976. Some effects of density and fertilizer on the growth and competition of Epilobium hirsutum and Lythrum salicaria. Pakistan Journal of Botany. 8(2): 213-220. [40265]
111. Shamsi, S. R. A.; Whitehead, F. H. 1974. Comparative eco-physiology of Epilobium hirsutum L. and Lythrum salicaria L. I. General biology, distribution and germination. Journal of Ecology. 62(79): 272-290. [18329]
112. Shamsi, S. R. A.; Whitehead, F. 1974. Comparative eco-physiology of Epilobium hirsutum L. and Lythrum salicaria L. II. Growth and development in relation to light. Journal of Ecology. 62: 632-645. [39786]
113. Shamsi, S. R. A.; Whitehead, F. 1977. Comparative eco-physiology of Epilobium hirsutum L. and Lythrum salicaria L. IV. Effects of temperature and inter-specific competition and concluding discussion. Journal of Ecology. 65: 71-84. [39785]
114. Sheley, Roger L.; Kedzie-Webb, Susan; Maxwell, Bruce D. 1999. Integrated weed management on rangeland. In: Sheley, Roger L.; Petroff, Janet K., eds. Biology and management of noxious rangeland weeds. Corvallis, OR: Oregon State University Press: 57-68. [35710]
115. Shiflet, Thomas N., ed. 1994. Rangeland cover types of the United States. Denver, CO: Society for Range Management. 152 p. [23362]
116. Shipley, B.; Parent, M. 1991. Germination responses of 64 wetland species in relation to seed size, minimum time to reproduction and seedling relative growth rate. Functional Ecology. 5(1): 111-118. [14554]
117. Shipley, Bill; Peters, Robert H. 1990. A test of the Tilman model of plant strategies: relative growth rate and biomass partitioning. The American Naturalist. 136(2): 139-153. [14502]
118. Skinner, Luke C.; Rendall, William J.; Fuge, Ellen L. 1994. Minnesota's purple loosestrife program: history, findings, and management recommendations. Special Publication 145. St. Paul, MN: Minnesota Department of Natural Resources, Division of Fish and Wildlife, Ecological Services Section. 27 p. [39783]
119. Skoglund, S. Jerry. 1990. Seed dispersing agents in two regularly flooded river sites. Canadian Journal of Botany. 68: 754-760. [11486]
120. Smith, Ralph H. 1964. Experimental control of purple loosestrife (Lythrum salicaria). New York Fish and Game Journal. 11(1): 35-46. [18332]
121. Sousa, P. J.; Farmer, A. H. 1983. Habitat suitability index models: wood duck. FWS/OBS-82/10.43. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 27p. [29456]
122. Spinks, Preston; Packard, Stephen. 1988. Control of purple loosestrife (Illinois). Restoration & Management Notes. 6(1): 50. [5555]
123. Stickney, Peter F. 1989. Seral origin of species comprising secondary plant succession in Northern Rocky Mountain forests. FEIS workshop: Postfire regeneration. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT. 10 p. [20090]
124. Stuart, John D. 1987. Fire history of an old-growth forest of Sequoia sempervirens (Taxodiaceae) forest in Humboldt Redwoods State Park, California. Madrono. 34(2): 128-141. [7277]
125. Stuckey, Ronald L. 1980. Distributional history of Lythrum salicaria (purple loosestrife) in North America. Bartonia. 47: 3-20. [40053]
126. Swetnam, Thomas W.; Baisan, Christopher H.; Caprio, Anthony C.; Brown, Peter M. 1992. Fire history in a Mexican oak-pine woodland and adjacent montane conifer gallery forest in southeastern Arizona. In: Ffolliott, Peter F.; Gottfried, Gerald J.; Bennett, Duane A.; Hernandez C., Victor Manuel; Ortega-Rubio, Alfred; Hamre, R. H., tech. coords. Ecology and management of oak and associated woodlands: perspectives in the southwestern United States and northern Mexico: Proceedings; 1992 April 27-30; Sierra Vista, AZ. Gen. Tech. Rep. RM-218. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 165-173. [19759]
127. Taft, John B.; Solecki, Mary Kay. 1990. Vascular flora of the wetland and prairie communities of Gavin Bog and Prairie Nature Preserve, Lake County, Illinois. Rhodora. 92(871): 142-165. [14522]
128. Thompson, Daniel Q. 1989. Control of purple loosestrife. Fish and Wildlife Leaflet 13.4.11. Washington, DC: U.S. Department of Interior, Fish and Wildlife Service. 6 p. [18333]
129. Thompson, Daniel Q.; Stuckey, Ronald L.; Thompson, Edith B. 1987. Spread, impact, and control of purple loosestrife (Lythrum salicaria) in North American wetlands. Fish and Wildlife Research 2. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 55 p. [39777]
130. Treberg, Michael A.; Husband, Brian C. 1999. Relationship between the abundance of Lythrum salicaria (purple loosestrife) and plant species richness along the Bar River, Canada. Wetlands. 19(1): 118-125. [37542]
131. Tu, Mandy, ed. 2000. Techniques from TNC stewards for the eradication of Lythrum salicaria (purple loosestrife) and Phragmites australis (common reed/Phrag) in wetlands. In: Control comments from stewards. Weeds on the web: Wildland invasive species program, [Online]. Available: http://tncweeds.ucdavis.edu/esadocs/lythsali.html. [40056]
132. U.S. Department of Agriculture, Natural Resources Conservation Service. 2008. PLANTS Database, [Online]. Available: https://plants.usda.gov /. [34262]
133. Vincent, Dwain W. 1992. The sagebrush/grasslands of the upper Rio Puerco area, New Mexico. Rangelands. 14(5): 268-271. [19698]
134. Voegtlin, David J. 1995. Potential of Myzus lythri (Homoptera: Aphididae) to influence growth and development of Lythrum salicaria (Myrtiflorae: Lythraceae). Biological Control. 24(3): 724-729. [37513]
135. Wade, Dale D.; Brock, Brent L.; Brose, Patrick H.; Grace, James B.; Hoch, Greg A.; Patterson, William A., III. 2000. Fire in eastern ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 53-96. [36983]
136. Weiher, Evan; Keddy, Paul A. 1995. The assembly of experimental wetland plant communities. Oikos. 73(3): 323-335. [37497]
137. Weiher, Evan; Wisheu, Irene C.; Keddy, Paul A.; Moore, Dwayne R. J. 1996. Establishment, persistence, and management implications of experimental wetland plant communities. Wetlands. 16(2): 208-218. [37514]
138. Welling, Charles H.; Becker, Roger L. 1990. Seed bank dynamics of Lythrum salicaria L.: implications for control of this species in North America. Aquatic Botany. 38(2-3): 303-309. [17423]
139. Welling, Charles H.; Becker, Roger L. 1992. Life history and taxonomic status of purple loosestrife in Minnesota: implications for management and regulation of this exotic plant. Special Publication 146. St. Paul, MN: Department of Natural Resources, Division of Fish and Wildlife. 15 p. [40255]
140. Welling, Charles H.; Becker, Roger L. 1993. Reduction of purple loosestrife establishment in Minnesota wetlands. Wildlife Society Bulletin. 21(1): 56-64. [37502]
141. Whitehead, F. H. 1971. Comparative autecology as a guide to plant distribution. In: Duffey, E. O.; Watt, A. S., eds. The scientific management of animal and plant communities for conservation: Proceedings of the 11th symposium of the British Ecological Society; [Date unknown]; [Location unknown]. Oxford, England: Blackwell Scientific: 167-176. [40245]
142. Whitt, Michael B.; Prince, Harold H.; Cox, Robert R., Jr. 1999. Avian use of purple loosestrife dominated habitat relative to other vegetation types in a Lake Huron wetland complex. The Wilson Bulletin. 111(11): 105-114. [37525]
143. Young, James A.; Evans, Raymond A. 1981. Demography and fire history of a western juniper stand. Journal of Range Management. 34(6): 501-505. [2659]
144. Zamora, David L.; Thill, Donald C. 1999. Early detection and eradication of new weed infestations. In: Sheley, Roger L.; Petroff, Janet K., eds. Biology and management of noxious rangeland weeds. Corvallis, OR: Oregon State University Press: 73-84. [35712]