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Research Project Summary: Vegetation recovery following a mixed-severity fire in quaking aspen groves of western Wyoming

Gucker, Corey L. 2005, compiler. Research Project Summary: Vegetation recovery following a mixed-severity fire in quaking aspen groves of western Wyoming. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [ ].

Bartos, Dale L.; Brown, James K.; Booth, Gordon D. 1994. Twelve years biomass response in aspen communities following fire. Journal of Range Management. 47:79-83.

Bartos, D. L.; Mueggler, W. F. 1981. Early succession in aspen communities following fire in western Wyoming. Journal of Range Management. 34(4):315-318.

The prescription fire burned the Breakneck Ridge site that is part of the upper Gros Ventre drainage located approximately 48 km northeast of Jackson, Wyoming. The study area is part of the Bridger-Teton National Forest [1,3].

Burned sites occurred on northeast to northwest facing slopes of 14% to 42%. Elevation ranged from 2,393 to 2,504 m [4].

This study occurs in the following vegetation classifications:

FRES29 Sagebrush [7]
K038 Great Basin sagebrush [8]
SAF 217 Aspen [6]
SRM 401 Basin big sagebrush [9]
SRM 403 Wyoming big sagebrush
SRM 411 Aspen woodland

The study area consists of quaking aspen (Populus tremuloides) groves, big sagebrush (Artemisia tridentata)-dominated grasslands, and scattered subalpine fir (Abies lasiocarpa) trees. Understory vegetation in and around the quaking aspen woodlands was targeted for the fire study. The prefire understory was dominated by forbs; sticky purple geranium (Geranium viscosissimum), lupine (Lupinus spp.), and woodland strawberry (Fragaria vesca) were most common. Mountain snowberry (Symphoricarpos oreophilus) dominated the shrub layer, and bluegrass (Poa spp.), fringed brome (Bromus ciliatus), and slender wheatgrass (Elymus trachycaulum) were the typical grasses. The composition in terms of production was 68% forbs, 15% grasses,  and 17% shrubs before the fire. Annual production of the understory was 1,800 kg/ha.

Quaking aspen groves occupied nearly 1/4 of the hillside study area. Some groves appeared "healthy" and "stable," others appeared to be seral communities being replaced by subalpine fir, while still others were decaying and becoming dominated by big sagebrush grasslands [1]. Mature aspen trees ranged from 85 to 127 years old and basal area was 33 to 45 m²/ha [4]. The average number of quaking aspen sprouts was 14,000 per hectare before burning. All sprouts were less than 1 m tall because of intense elk and moose browsing in the area. The study area is heavily utilized by elk in the winter [1].

Summer (1974 August 29)/Low, moderate, and high severity

Differences in fuel availability, fuel moistures, and wind speeds during the fire created a mosaic of fire severities within the burned area [1,2].

The phenology of the vegetation prior to burning was not described.

Researchers burned a prescription fire in degraded quaking aspen communities in an attempt to stimulate sprout growth that could withstand heavy elk browsing. The early postfire recovery of understory vegetation was monitored as well. Sites were revisited again 12 years following the fire to address longer term postfire effects on quaking aspen sprouts and the understory community [1,2].

The fire burned when air temperatures were 25 ° to 27 °C, wind speeds ranged from 13 to 32 km/hr, relative humidity was 15% to 20%, and fuel moistures were between 10% and 45% [1,3].

The variability in fuels, fuel moistures, and environmental conditions created patchy burn severities in the quaking aspen stands. Each macroplot was assigned a low, moderate, or severe severity rating. Low-severity sites had  0% to 20% of litter and duff consumed, moderate-severity sites had 21% to 80% of litter and duff consumed and most of the understory vegetation was scorched or consumed, and high-severity sites had 81% to 100% of litter and duff consumed, all of the understory vegetation consumed, and 90% of the quaking aspens killed. A total of 11 macroplots burned at low severity, 13 at moderate severity, and 12 burned at high severity [1,2].

Fire effects on the vegetation were assessed through four 10×10 m macroplots in each of 10 aspen groves. Nine of the aspen stands burned, and 1 was unburned. Production of the understory vegetation was assessed in late July or early August before the fire (1974), and 3 consecutive years following the fire (1975, 1976, and 1977). Vegetation production was reevaluated for postfire years 6 and 12. Measurements made in the 6th postfire year focused on life form groups; measurements in the 12th postfire year were made on individual species [1,2].

General community changes: Understory annual production decreased the 1st postfire year, but by the 2nd postfire year, understory production surpassed preburn levels. Production was approximately 33% lower than preburn levels in the 1st postfire year; decreases in production were greatest on severely burned sites and least on sites burned with low severity. In the 2nd postfire year, understory production was almost 66% greater than preburn levels. By the 3rd postfire year, understory production exceeded preburn levels by 12% on low-severity sites, 42% on moderate-severity sites, and 52% on severely burned sites [1]. Twelve years following the fire, understory production still exceeded prefire production by 23%, 42%, and 46% on sites burned with low, moderate, and high severities, respectively. More severely burned areas areas will likely experience longer-lived increases in production [2].

Composition of the understory was altered by the fire. The preburn understory consisted of 68% forbs, 15% grasses, and 17% shrubs. Composition the 1st postfire year composition was 83% forbs, 11% grasses, and 6% shrubs. Composition the 3rd postfire year was 80% forbs, 16% grasses, and 4% shrubs. Twelve years following the fire forbs comprised 73% to 79%, grasses were 20% or less, and shrubs made up approximately 5% of the understory.

The production of forbs decreased from prefire levels in the 1st postfire year; decreases were greatest on severely burned sites and least on sites burned at low severity. Forb production for the 2nd and 3rd postfire years was greater than preburn levels by 66% and 33%, respectively. By the 12th postfire year, annual forb production was 5% to 14% greater than preburn production.

Grass production was almost 50% less than preburn production in the 1st postfire year. In the 2nd postfire year, grass production was nearly 66% greater than preburn production on low- and moderate-severity sites. Grass production on severely burned sites was much slower to recover to preburn production. By the 12th postfire year, grass production on all burned sites exceeded that of preburn levels and control sites. On low- and high-severity sites, production was significantly (p<0.01) greater than on unburned sites 12 years following the fire. The study area was grazed following the fire, but the researchers reported no visible evidence of livestock grazing before the 1986 sampling season. Grazing may, however, have been a factor in grass production in sampling seasons prior to 1986.

Decreases in shrub (includes quaking aspen sprouts) density were greater than 50% in the 1st postfire year. While the production of quaking aspen sprouts exceeded preburn production by over 50% on moderately burned sites, these increases were short lived. By the 3rd postfire year, overall shrub production on burned sites was only 33% of preburn levels. Shrub production had still not recovered to preburn levels 12 years after the fire. Mountain snowberry, a dominant prefire shrub, drastically decreased on burned sites [1,2].

Below is the average production (dry kg/ha) of the understory before the fire (1974), 3 consecutive postfire years (1975, 1976, and 1977), and 6 (1980) and 12 (1986) years after fire on unburned and burned sites [2].

Life form Fire severity 1974 1975 1976 1977 1980 1986
Forbs control 1146 1604 1435 1220 1846 1430
low 1088 1255 2435* 1528 2354 1546
moderate 977 972* 2389* 1668 2454 1699*
high 1061 610* 2793* 2101* 3014* 1593*
Grasses control 451 376 468 189 270 291
low 447 198* 526 273 399 486*
moderate 313 132* 394 227 310 332
high 226 46* 148* 82 151 482*
Shrubs control 199 266 256 360 388 215
low 197 71* 165 108* 130* 99*
moderate 180 81* 310 158* 143* 111*
high 249 41* 197 110* 115* 111*
*Mean values with an asterisk within the same life form and year are significantly (p<0.01) different than the control.

The recovery of individual understory species's production was studied in the 3rd and 12th postfire years. A more complete review of quaking aspen's recovery following these fires is provided in quaking aspen's Fire Case Study Aspen sprouting density and elk use after prescribed fire in Wyoming. Further detail of quaking aspen recovery is provided in the original research done by Basile [5] and Bartos and others [4].

Fire-tolerant species: Many understory species could be described as fire tolerant in the quaking aspen community. Common yarrow (Achillea millefolium), northern bedstraw (Galium boreale), western valerian (Valeriana occidentalis), fireweed (Chamerion angustifolium), quaking aspen, slender wheatgrass, and bluegrass increased or remained relatively unchanged on low-, moderate-, and high-severity sites in the 3rd postfire year. Fringed brome increased from preburn levels on all burned sites by the 12th postfire year. The increases in fireweed production were dramatic and lasted into the 12th postfire year. Fremont's goosefoot (Chenopodium fremontii) was present on only burned sites in the 3rd postfire year and had highest production on severely burned sites.

Fire-sensitive species: Several species showed decreases in production following fire. Mountain snowberry, timber milkvetch (Astragalus miser), woodland strawberry, lupine, and Fendler's meadow-rue (Thalictrum fendleri) had decreased production on all burned sites regardless of burn severity and had not recovered to preburn levels by the 12th postfire year.

Species with production changes related to fire severity: The following discussion highlights species that showed interesting production trends in relation to fire severity. Woods' rose, elkweed (Frasera speciosa), Colorado blue columbine (Aquilegia caerulea), and sticky purple geranium were least sensitive to moderate-severity fire. On moderate-severity sites, the production of Woods' rose was equal to preburn levels by the 3rd postfire year and exceeded preburn levels in the 12th postfire year. Elkweed production increased by more than 50% the 3rd postfire year. Sticky purple geranium and Colorado blue columbine production increased on both low- and moderate-severity sites. However, increases were longer lived on moderate-severity sites for sticky purple geranium, and production levels for Colorado blue columbine were greatest on moderate-severity sites in the 12th postfire year.

Slender cinquefoil (Potentilla gracilis) production increased on moderate-severity sites in the 3rd postfire year, but in the 12th postfire year, production occurred only on low-severity sites. Slender wheatgrass increased on all burned sites by the 3rd postfire year; however, increases were much greater on the moderate-severity site. In the 12th postfire year, slender wheatgrass production was near preburn levels on low- and moderate-severity sites, but exceeded preburn production by 5 times on high-severity sites [1,2].

Below is the production (dry weight, kg/ha) of understory species before the fire and in the 3rd [1] and 12th [2] postfire years on sites burned at
low-, moderate-, and high-severities.

Common name Scientific name Postfire year Prefire Low Moderate Severe
quaking aspen Populus tremuloides 3 27 25 39 49
12 26 28 15
Woods' rose Rosa woodsii 3 53 30 53 16
12 34 85 51
mountain snowberry Symphoricarpos oreophilus 3 88 9 36 7
12 48 25 18
common yarrow Achillea millefolium 3 14 40 16 14
12 12 17 12
Colorado blue columbine Aquilegia caerulea 3 56 80 66 12
12 8 33 4
timber milkvetch Astragalus miser 3 46 14 7 11
12 6 10 11
fireweed Chamerion angustifolium 3 68 475 921 1,657
12 970 1067 1,114
Fremont's goosefoot Chenopodium fremontii 3 0 13 16 57
12 0 0 0
woods strawberry Fragaria vesca 3 108 94 78 51
12 75 14 45
elkweed Frasera speciosa 3 40 2 103 20
12 ---- ---- ----
northern bedstraw Galium boreale 3 33 42 31 50
12 13 14 15
sticky purple geranium Geranium viscosissimum 3 297 477 402 255
12 125 359 223
lupine Lupinus spp. 3 221 31 23 22
12 160 124 94
slender cinquefoil Potentilla gracilis 3 43 41 80 24
12 60 0 0
Fendler's meadow-rue Thalictrum fendleri 3 62 44 13 9
12 48 40 34
western valerian Valeriana occidentalis 3 3 8 5 13
12 13 21 0
fringed brome Bromus ciliatus 3 217 267 181 87
12 290 291 256
slender wheatgrass Elymus trachycaulus 3 49 57 136 60
12 53 51 259
bluegrass Poa spp. 3 41 68 107 86
12 66 47 61

The early and later postfire sampling in this area provided valuable information regarding the recovery and changes in aspen understory growth following fires of different severities. However, the management goal of producing quaking aspen growth greater than elk and moose consumption fell short. While increased quaking aspen sprout production occurred in the early postfire years, it was not maintained into the 12th postfire year. On high-severity sites quaking aspen sprout production was much lower than preburn production, and production on moderate- and low-severity sites was significantly (p<0.1) lower than production on control sites. Researchers attributed these declines to continual heavy browsing in the area [2]. Elk browsing was only low in the 1st postfire year [5].

Overall, forb production was enhanced through burning. Grass production was more variable, and fire severity, time since fire, and species were all important factors in grass recovery. Shrub production had not recovered to preburn levels by the 12th postfire year. However, the overall shrub production was driven by poor recovery of mountain snowberry, the dominant shrub in the prefire community. Woods' rose and quaking aspen were near preburn levels in 2 of 3 fire severity classes. While species composition was altered by the fire, total production of the understory increased following fire in the area [2].


1. Bartos, D. L.; Mueggler, W. F. 1981. Early succession in aspen communities following fire in western Wyoming. Journal of Range Management. 34(4): 315-318. [5100]
2. Bartos, Dale L.; Brown, James K.; Booth, Gordon D. 1994. Twelve years biomass response in aspen communities following fire. Journal of Range Management. 47: 79-83. [22891]
3. Bartos, Dale L.; Mueggler, Walter F. 1979. Influence of fire on vegetation production in the aspen ecosystem in western Wyoming. In: Boyce, Mark S.; Hayden-Wing, Larry D., eds. North American elk, ecology, behavior and management. Laramie, WY: University of Wyoming: 75-78. [5101]
4. Bartos, Dale L.; Mueggler, Walter F.; Campbell, Robert B., Jr. 1991. Regeneration of aspen by suckering on burned sites in western Wyoming. Res. Pap. INT-448. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 10 p. [16468]
5. Basile, Joseph V. 1979. Elk-aspen relationships on a prescribed burn. Res. Note INT-271. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 7 p. [4347]
6. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905]
7. 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]
8. 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]
9. Shiflet, Thomas N., ed. 1994. Rangeland cover types of the United States. Denver, CO: Society for Range Management. 152 p. [23362]

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