Fire effects and a refined fire prescription after low-intensity spring fires in low-elevation mixed-conifer forests of Yosemite National Park, California
Fryer, Janet L., comp. 2007. Research Project Summary: Fire effects and a refined fire prescription after low-intensity spring fires in low-elevation mixed-conifer forests of Yosemite National Park, California. 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/fire-studies/van-wagtendonk-2007
| Abbreviation | Common Name | Scientific Name | Classification | Status |
|---|---|---|---|---|
| Plants | ||||
| CALDEC | incense-cedar | Calocedrus decurrens | Life Form: Plants/Tree Kingdom: Plantae Class: Dicot Order: Salicales Family: Cupressaceae Genus: Calocedrus | Fed. Protected: No Nativity: Native Invasiveness: Noninvasive |
| CHAFOL | mountain misery | Chamaebatia foliolosa | Life Form: Plants/Shrub Kingdom: Plantae Class: Dicot Order: Rosales Family: Rosaceae Genus: Chamaebatia | Fed. Protected: No Nativity: Native Invasiveness: Noninvasive |
| PINPONP | Columbia ponderosa pine | Pinus ponderosa var. ponderosa | Life Form: Plants/Tree Kingdom: Plantae Class: Conifer Order: Pinales Family: Pinaceae Genus: Pinus | Fed. Protected: No Nativity: Native Invasiveness: Noninvasive |
Sources
Unless otherwise indicated, the information in this Research Project Summary comes from the following papers:
- van Wagtendonk, Jan W. 1972. Fire and fuel relationships in mixed conifer ecosystems of Yosemite National Park. Berkeley, CA: University of California. 163 p. Dissertation. [6].
- van Wagtendonk, Jan W. 1974. Refined burning prescriptions for Yosemite National Park. National Park Service Occasional Paper Number 2. Washington, DC: U.S. Department of the Interior, National Park Service. 21 p. [4].
- van Wagtendonk, Jan W. 1977. Fire management in the Yosemite mixed-conifer ecosystem. In: Mooney, Harold A.; Conrad, C. Eugene, technical coordinators. Proceedings of the symposium on the environmental consequences of fire and fuel management in Mediterranean ecosystems; 1977 August 1-5; Palo Alto, CA. Gen. Tech. Rep. WO-3. Washington, DC: U.S. Department of Agriculture, Forest Service: 459-463 [5].
This study compared the effects of 2 types of prescribed fire in 4 fuel types. There were 2 study sites, located in the Wawona and Yosemite Valley areas of Yosemite National Park, northern California [4,6].
Site Description
Wawona―Elevation is 1,400 m, and slopes mostly face the southwest. The Wawona study site was stratified into 3 fuel types based on the dominant understory species and/or primary forest floor cover: Sierra mountain misery (Chamaebatia foliolosa) draped with Pacific ponderosa pine (Pinus ponderosa var. ponderosa), hereafter ponderosa pine) needles; needles (mostly ponderosa pine) with sparse live vegetation; and incense-cedar (Calocedrus decurrens) seedlings [4,6].
Yosemite Valley―The 4th fuel type studied was in Yosemite Valley. The valley floor is nearly level and surrounded by steep canyon walls. The study area is on the south side of the valley near Sentinel Creek. Elevation was not reported but is approximately 1,400 m. Steep, high canyon walls result in moister sites on the south than the north end of the valley [6]. Like the needle fuel type at Wawona, forest floor cover was mostly ponderosa pine needles with sparse live vegetation, although there was more groundlayer herbaceous vegetation than on the Wawona needle type. This fuel type was called valley fuel [4,6].
Wawona―The overstory was dominated by ponderosa pine. Associated overstory species were incense-cedar and California black oak (Quercus kelloggii). Patches of Sierra mountain misery were interspersed with incense-cedar seedlings in the understory. There were some downed trees that succumbed to insect infestations. Wawona was logged in 1948 [6].
Yosemite Valley―Ponderosa pine and canyon live oak (Quercus chrysolepis) dominated the overstory. Pole-sized incense-cedar was successionally replacing canyon live oak. Incense-cedar seedlings dominated the understory. There were occasional coast Douglas-fir (Pseudotsuga menziesii var. menziesii), white fir (Abies concolor), and ponderosa pine seedlings in the understory. Fuel loads were heavy due to tree mortality from insect and fomes root rot (Fomes annusus) infestations [6].
Stand structure was similar at the 2 sites. Over half the basal area was ponderosa pine, mostly large ponderosa pines (>50 cm in diameter). Scattered large and numerous smaller incense-cedars comprised about one-third of the overstory. The rest of the basal area was mixed Douglas-fir, white fir, and California black oak. The Yosemite Valley site had more downed trees than Wawona. Basal area was not significantly different (all significance levels are 0.05 for this study) between sites. Overall basal area for the 2 sites was [6]:
| Species | Basal area | Percent of total basal area |
|---|---|---|
| Ponderosa pine | 48.90 | 61.2 |
| Incense-cedar | 27.17 | 33.9 |
| California black oak | 3.64 | 4.5 |
| Other | 0.30 | 0.40 |
| Total | 80.01 | 100.0 |
Understory basal area and density varied among fuel types, with significantly more vegetative cover on the Sierra mountain misery fuel type compared to other fuel types [6]:
| Species | Wawona fuel types | Yosemite Valley fuel type | ||||||
|---|---|---|---|---|---|---|---|---|
| Sierra mountain misery | Needle | Incense-cedar | Valley | |||||
| Basal area | Percent of total basal area | Basal area | Percent of total basal area | Basal area | Percent of total basal area | Basal area | Percent of total basal area | |
| Ponderosa pine | 0.00 | 0.00 | 0.00 | 0.00 | 1.96 | 5.5 | 0.00 | 0.00 |
| Incense-cedar | 2.34 | 100.0 | 1.48 | 100.0 | 33.34 | 94.5 | 0.13 | 100.0 |
| Total | 2.34 | 100.0 | 1.48 | 100.0 | 0.13 | 100.0 | 35.41 | 100.0 |
| Species and height class (m) | Sierra mountain misery fuel type | Needle fuel type | Incense-cedar fuel type | Valley fuel type |
|---|---|---|---|---|
| Sierra mountain misery | ||||
| 0-0.3 | 9,780 | 300 | 1,148 | 0 |
| Ponderosa pine | ||||
| 0-0.3 | 0 | 0 | 2 | 98 |
| 0.3-1.0 | 0 | 3 | 3 | 0 |
| 1.0-3.0 | 0 | 0 | 27 | 0 |
| Total | 0 | 3 | 32 | 98 |
| Incense-cedar | ||||
| 0-0.3 | 8 | 20 | 40 | 20 |
| 0.3-1.0 | 0 | 13 | 90 | 0 |
| 1.0-3.0 | 3 | 10 | 178 | 3 |
| Total | 11 | 43 | 308 | 23 |
| All species | ||||
| 0-0.3 | 9,788 | 320 | 1,190 | 118 |
| 0.3-1.0 | 0 | 16 | 93 | 0 |
| 1.0-3.0 | 3 | 10 | 205 | 3 |
| Total | 9,791 | 346 | 1,488 | 121 |
Plant Phenology
Plant phenology was not described. Plants would have been actively growing when burning was conducted.
The general study objective was to evaluate the effectiveness of spring prescribed fires for fire hazard reduction under varying fuel and weather conditions in Yosemite's mixed-conifer ecosystem. The study hypothesis was that prescribed spring fires in the 4 understory fuel types in mixed-conifer communities of Yosemite National Park would have differential effects on fire characteristics, fuel reduction, and understory plant composition [6].
On the 2 study sites, ignitions were started in spring 1970 at 4 fuel moisture contents (19%, 16%, 13%, and 10%) and with 2 methods of burning (backfires and head fires). Areas with "excessive" rock outcrops or heavy fuels were not included in analyses [6].
The general fire prescription called for windspeeds ≤10 mph, air temperatures from 20 to 84 ºF, and relative humidities from 29% to 65%. Backing fires were ignited either at the perimeter edge away from the wind or the upper end of the plots. Head fires were ignited from either the windward or bottom side of the plots [4,6]. Burn areas were 5 to 10 ha [6].
Prefire mean fuel loads were [4]:
| Layer | Sierra mountain misery fuel type | Needle fuel type | Incense-cedar fuel type | Valley fuel type |
|---|---|---|---|---|
| Surface fuels* | 166.4 | 22.6 | 18.0 | 28.2 |
| Fresh litter | 318.0 | 422.3 | 292.0 | 383.9 |
| Weathered litter | 565.7 | 604.5 | 431.5 | 532.5 |
| Duff | 4,127.4 | 3,565.7 | 2,830.9 | 2,971.0 |
| Total fine fuel | 5,177.5 | 4,615.1 | 3,572.4 | 3,915.5 |
| Heavy fuel (>2.5 cm diameter) | 508.6 | 1,726.5 | 1,261.3 | 5,062.4 |
| Total | 5,656.1 | 6,341.6 | 4,833.7 | 8,977.9 |
| *Not including litter. | ||||
Fire Behavior
Energy released by the fire for the 4 understory and forest floor fuel types was: Sierra mountain misery, 575.5 kcal/m²; needle, 98.5 kcal/m²; incense-cedar, 402.1 kcal/m²; and valley, 94.1 kcal/m². Total energy release did not differ between backfires and head fires. Windspeed, fuel type, and fuel moisture content variables significantly affected energy release, and there was a significant 2-way interaction between fuel type and fuel moisture for energy release [6].
Energy release was significantly higher in Sierra mountain misery and incense-cedar fuel types compared to needle and valley fuel types. Fireline intensity was significantly less at fuel moisture contents of 19% and 16% than at 13% and 10% [6]:
| Fuel moisture content (%) | Fire type | |
|---|---|---|
| Backfire | Head fire | |
| 19 | 0.0 | 3.5 |
| 16 | 2.2 | 14.2 |
| 13 | 5.6 | 63.1 |
| 10 | 14.1 | 60.8 |
Fuel Reduction
These low-intensity spring fires consumed most understory fine fuel and fresh needles but burned only slightly into weathered needle and organic soil layers. Since the bulk of the fine fuel load on these sites was in the organic soil layer, total fine fuel reduction from fires was not significant. Fuel type and percent fuel moisture significantly affected fuel reduction, while fire type did not. When fires carried, both backfires and head fires consumed similar amounts of fine fuel at any particular moisture content. As is typical for Yosemite Valley, heavy fuels did not dry until midsummer in the low elevations of Yosemite National Park, so none of the fires reduced heavy fuel loads. Sierra mountain misery and incense-cedar fuel types had greater fine-fuel reductions than needle and valley fuel types. Sierra mountain misery plots burned at higher fuel moisture contents than other fuel types largely because needles draped on Sierra mountain misery plants provided a well-aerated fuel bed. The fuel bed was more compact for the incense-cedar type, so the fires did not carry until fuel moistures were ≤10%. Fuel reduction was significantly greater on needle than valley fuel types, probably because added moisture content of herbaceous vegetation on valley plots caused less fresh needle reduction. Fuel reductions are shown below [6].
| Fuel moisture content (%) | Sierra mountain misery fuel type | Needle fuel type | Incense-cedar fuel type | Valley fuel type |
| 19 | 167.0 | 0.0 | 79.0 | 0.0 |
| 16 | 140.5 | 41.5 | 60.0 | 0.0 |
| 13 | 186.5 | 31.5 | 115.5 | 101.5 |
| 10 | 106.5 | 40.0 | 169.5 | 0.0 |
Fire Season/Severity Classification
Spring/low to moderate intensity
As hypothesized, fires with different fuel moisture contents had different effects on understory ponderosa pine and incense-cedar. Total understory basal area of ponderosa pine was not affected by the fires, while total understory basal area for incense-cedar was significantly affected by fuel type, fuel moisture, and the interactive effects of fuel type and fuel moisture. On incense-cedar fuel plots, only plots at the 10% fuel moisture content were sufficiently dry to kill incense-cedars 1 to 3 m in height. Ponderosa pine showed insignificant mortality in all fuel types [6]:
| Species | Sierra mountain misery fuel type | Needle fuel type | Incense-cedar fuel type | Valley fuel type | ||||
|---|---|---|---|---|---|---|---|---|
| basal area reduction | % mortality | basal area reduction | % mortality | basal area reduction | % mortality | basal area reduction | % mortality | |
| Incense-cedar | 2.34 | 100.0 | 0.00 | 0.0 | 7.17 | 21.4 | 0.00 | 0.0 |
| Ponderosa pine | 0.00 | 0.00 | 0.00 | 0.0 | 14.8 | 14.8 | 0.00 | 0.0 |
| Total | 2.34 | 100.0 | 0.00 | 0.0 | 21.0 | 21.0 | 0.00 | 0.0 |
Fuel type, fuel moisture contents, and their interactive effects significantly affected density levels for Sierra mountain misery, incense-cedar, ponderosa pine, and all understory species combined in the 0- to 0.3-m height class. Significance for all species combined was mainly due to the large number of Sierra mountain misery stems on Sierra mountain misery fuel plots. Ponderosa pine in the 0- to 0.3-m (first-year seedling) size class was well represented in the understory only on valley plots. There, the fires killed the ponderosa pine seedlings [6].
Fuel moisture content affected densities of Sierra mountain misery and ponderosa pine in the 0- to 0.3-m size class but not did affect 0- to 0.3-m incense-cedars. For Sierra mountain misery, plots burned at 19% and 16% fuel moisture contents showed significantly greater density losses than plots burned at 13% and 10% fuel moisture contents. For ponderosa pine, plots burned at 10% fuel moisture content showed significantly greater density loss compared to plots burned at 13% fuel moisture content. In the 0.3- to 1.0-m size class, density reductions were insignificant for all 3 species. Most trees in the 1- to 3-m height class were on incense-cedar fuel types. Again, density reductions were due to fuel type, fuel moisture contents, and their interactive effects. Density reductions for the 0- to 0.3-m and 1- to 3-m height classes are shown in the table below [6].
| Species | Sierra mountain misery fuel type | Needle fuel type | Incense-cedar fuel type | Valley fuel type | ||||
|---|---|---|---|---|---|---|---|---|
| density reduction | % reduction | density reduction | % reduction | density reduction | % reduction | density reduction | % reduction | |
| Sierra mountain misery | 7,900 | 80.7 | 283 | 94.0 | 42 | 3.7 | 0 | 0.0 |
| Incense-cedar | 0 | 0.0 | 0.0 | 0.0 | 0 | 0.0 | 0 | 0.0 |
| Ponderosa pine | 0 | 0.0 | 0.0 | 0.0 | 0 | 0.0 | 57 | 58.1 |
| All species | 7,900 | 80.1 | 80.1 | 87.6 | 42 | 3.5 | 57 | 348.3 |
| Species | Sierra mountain misery fuel type | Needle fuel type | Incense-cedar fuel type | Valley fuel type | ||||
|---|---|---|---|---|---|---|---|---|
| density reduction | % reduction | density reduction | % reduction | density reduction | % reduction | density reduction | % reduction | |
| Incense-cedar | 3 | 100.0 | 0 | 0.0 | 48 | 26.9 | 0 | 0.0 |
| Ponderosa pine | 0 | 0.0 | 0 | 0.0 | 3 | 11.1 | 0 | 0.0 |
| All species | 3 | 100.0 | 0 | 0.0 | 51 | 24.9 | 0 | 0.0 |
This study demonstrated that low- and moderate-intensity spring fires can reduce flashy fuels such as Sierra mountain misery and fresh needles, and cause some reduction in the understory of the incense-cedar fuel type [6].
Fuel moisture content was the single most important factor affecting fire characteristics, fuel consumption, and fire effects on vegetation. Fuel type also influenced fire behavior. Fires on the 10% fuel moisture plots caused greatest changes in postfire understory composition. Reduction of Sierra mountain misery is particularly important for fire hazard reduction. Although Sierra mountain misery sprouts after fire, new sprouts are less flammable than old stems because sprouts have higher moisture contents and less dead biomass [6]. Based on these findings and other prescribed fires on similar mixed-conifer Yosemite sites from 1972 through 1976, van Wagtendonk [4,5,6] presented the following prescription for the lower mixed-conifer zone of Yosemite National Park. This prescription may be applicable in lower mixed-conifer zones elsewhere in California.
| Prescription variable | Spring | Fall |
|---|---|---|
| Windspeed (mph) | 1-10 | 0-10 |
| Air temperature (°F) | 30-84 | 30-89 |
| Relative humidity (%) | 25-64 | 25-64 |
| 1-hr timelag fuelstick moisture (%) | 5-8 | 5-8 |
| 10-hr timelag fuelstick moisture (%) by fuel type | ||
| Sierra mountain misery | 6-16 | 6-16 |
| Needle (ponderosa pine) | 6-16 | 6-16 |
| Meadows | 6-16 | 6-16 |
| Incense-cedar | 6-11 | 6-16 |
| Chaparral (Manzanita and Ceanothus spp.) | 9-17 | 9-17 |
| 100-hr timelag fuelstick moisture (%) | 13-25 | 13-18 |
| Fine fuel moisture (%) | 6-12 | 6-10 |
| Ignition component | 16-50 | 21-53 |
| Spread component | 1-2 | 1-2 |
| Energy release component | 13-32 | 26-39 |
| Burning index | 8-15 | 10-16 |
| *Fuel model G is dense conifer stands with heavy accumulations of downed woody debris and deep litter. Adapted from [5]. Van Wagtendonk [5] also provides prescriptions for upper mixed conifer (1,700-2,400 m) and giant sequoia (Sequoiadendron giganteum) groves. | ||
| Biophysical Setting | Mean Fire Interval (years) | Fire Severity Percent (%) | ||||||
|---|---|---|---|---|---|---|---|---|
| Code | Fire Regime Group | Low | Mixed | Replacement | All | Low | Mixed | Replacement |
| Series 10310 - California Montane Jeffrey Pine(-Ponderosa Pine) Woodland | ||||||||
| 10310_2_3_4_5_6_12 | I-B | 11 | 84 | 165 | 9 | 83 | 11 | 6 |
| Summary | ||||||||
| Minimum | 11 | 84 | 165 | 9 | 83 | 11 | 6 | |
| Maximum | 11 | 84 | 165 | 9 | 83 | 11 | 6 | |
| Mean | 11 | 84 | 165 | 9 | 83 | 11 | 6 | |
| Median | 11 | 84 | 165 | 9 | 83 | 11 | 6 | |
| Percentage of fires in 3 fire severity classes, derived from LANDFIRE succession modeling. Replacement-severity fires cause >75% kill or top-kill of the upper canopy layer; mixed-severity fires cause 26%-75%; low-severity fires cause <26%. | ||||||||
| LANDFIRE. 2020. Biophysical settings models and descriptions, [Online]. Washington, DC: U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior; U.S. Geological Survey; Arlington, VA: The Nature Conservancy, (Producers). Available: https://www.landfirereview.org/search.php [96496] | ||||||||
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3. LANDFIRE Rapid Assessment. 2007. Rapid assessment reference condition models, [Online]. In: LANDFIRE. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Lab; U.S. Geological Survey; The Nature Conservancy (Producers). Available: http://www.landfire.gov/models_EW.php [2008, April 18] [66533]
4. van Wagtendonk, Jan W. 1974. Refined burning prescriptions for Yosemite National Park. National Park Service Occasional Paper Number 2. Washington, DC: U.S. Department of the Interior, National Park Service. 21 p. [50524]
5. van Wagtendonk, Jan W. 1977. Fire management in the Yosemite mixed-conifer ecosystem. In: Mooney, Harold A.; Conrad, C. Eugene, technical coordinators. Proceedings of the symposium on the environmental consequences of fire and fuel management in Mediterranean ecosystems; 1977 August 1-5; Palo Alto, CA. Gen. Tech. Rep. WO-3. Washington, DC: U.S. Department of Agriculture, Forest Service: 459-463. [4895]
6. van Wagtendonk, Jan Willem. 1972. Fire and fuel relationships in mixed conifer ecosystems of Yosemite National Park. Berkeley, CA: University of California. 163 p. Dissertation. [40173]