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Research Project Summary: Understory recovery after burning and reburning quaking aspen stands in central Alberta

• RESEARCH PROJECT SUMMARY CITATION
• RESEARCH PROJECT SUMMARY REFERENCES
• STUDY LOCATION
• SITE DESCRIPTION
• PREFIRE PLANT COMMUNITY
• FIRE SEASON/SEVERITY CLASSIFICATION
• PLANT PHENOLOGY
• FIRE DESCRIPTION
• FIRE EFFECTS ON PLANT COMMUNITY
• FIRE MANAGEMENT IMPLICATIONS
• REFERENCES

Source: Unless otherwise indicated, the information in this Research Project Summary comes from the following paper:

SAF 16 Aspen [1]
SRM 411 Aspen woodland [3]

Study sites were within the boreal mixed wood forest in almost pure quaking aspen (Populus tremuloides) stands that averaged 43 years old. Stands were surrounded by muskeg grasslands with scattered black spruce (Picea mariana). Quaking aspens made up 99% of the basal area and 98% of the stand density in the study area. Average quaking aspen height was 13 m, dbh was 11 cm, and basal area averaged 29 m²/ha. Within burned sites, a few white spruce (P. glauca), jack pine (Pinus banksiana), and infrequent white birch (Betula papyrifera) clumps occurred. Several tall shrubs including mountain alder (Alnus viridis ssp. crispa), pin cherry (Prunus pensylvanica), and beaked hazelnut (Corylus cornuta) populated the quaking aspen stands. Common understory small shrubs, herbs and grasses included bunchberry dogwood (Cornus canadensis), American twinflower (Linnaea borealis ssp. americana), cream pea (Lathyrus ochroleucus), wild sarsaparilla (Aralia nudicaulis), dwarf red blackberry (Rubus pubescens), bluejoint (Calamagrostis canadensis), and rough bentgrass (Agrostis scabra).

The 1972 fire effects on the understory plant community were studied jointly, and in this summary fire characteristics are averaged for the 2 fires. The 1978 spring fire reburned areas that experienced moderate intensity fires in 1972.

Temperature, relative humidity, and wind speed were lower during the spring reburn than the initial fall fire. Wind speeds were measured at a height of 1 m. The time since rainfall accumulation of 0.6 mm or more was greater on the reburned area than the fall burned sites. Presented below are the weather conditions when the 1972 and 1978 fires burned:

The Canadian forest fire indices indicate greater duff moisture and higher buildup index at the time of the 1978 reburn when compared to the 1972 fires.

Litter mass in the study area averaged 0.3 kg/m², and the average mass of downed wood was 0.37 kg/m². Researchers considered forest floor weights low compared to other forest types in Canada.

Moisture content was lower for the fermentation and humus layers on the reburned sites, and the depth of burn and forest floor reduction were greater on reburned sites. Fuel moisture conditions and forest floor reductions are summarized below:

The 1972 and 1978 fires behaved quite differently. Researchers suggest that the 1972 fires would have been rated "fairly easy to control." Fuel consumption was low as was fireline intensity during the fall fires of 1972. The increased fireline intensity during the spring reburn was due to increased fuel loads. The 1972 fires caused mortality in the quaking aspen stands that contributed to the increased fuel load on reburned sites. The researchers indicated that the 1978 fire resulted in greater "bole heating" and "downward heat transfer to the root zone." Researchers allowed the flame front to move 10 m before measuring. The amount of fuel consumed, rate of fire spread, and intensity of the fires are summarized below.

Fire effects on the understory vegetation were highly variable. Some species were sensitive to any fire, while others were sensitive to only repeated fire. Other species appeared only on burned sites, increased on burned sites, and/or increased on repeatedly burned sites.

Fire-adapted species: The following species increased on, remained the same, or were restricted to burned sites. Many species showed the greatest increases in both frequency and cover on the reburned sites. The following species had greater coverage and/or frequency on burned sites than unburned sites: prickly rose (Rosa acicularis), American red raspberry (Rubus idaeus), lingonberry (Vaccinium vitis-idaea ssp. minus), wild sarsaparilla, bluebell bellflower (Campanula rotundifolia), fireweed (Chamerion angustifolium), Virginia strawberry (Fragaria virginiana), western showy aster (Aster conspicuus), northern bedstraw (Galium boreale), tall bluebells (Mertensia paniculata), arctic sweet coltsfoot (Petasites frigidus var. palmatus), dwarf red blackberry, Lindley's aster (Symphyotrichum ciliolatum), cream pea, limber honeysuckle (Lonicera dioica var. glaucescens), American vetch (Vicia americana), bluejoint, and rough bentgrass (Agrostis scabra).

Fire-sensitive species: The number of species that decreased following fire were fewer than those that increased. A higher proportion of fire-sensitive species were shrubs. The following species had lower coverage and/or frequency or were removed from the community on burned sites: mountain alder, Saskatoon serviceberry (Amelanchier alnifolia), beaked hazelnut, pin cherry, chokecherry (Prunus virginiana), common snowberry (Symphoricarpos albus), velvetleaf blueberry (Vaccinium myrtilloides), twinflower, Canada mayflower (Maianthemum canadense), sidebells wintergreen (Orthilia secunda), and Canadian white violet (Viola canadensis).

The combined effect of season and repeated fire makes it difficult to determine whether a species was sensitive to repeated fire, a particular fire season, or a combination of these.

Below are the percent frequencies and coverages for the understory species on unburned, fall burned, and spring reburned sites. Postfire measurements were made in August of 1972 and 1978 [2].

REFERENCES:

1. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905]

2. Quintilio, D.; Alexander, M. E.; Ponto, R. L. 1991. Spring fires in a semimature trembling aspen stand in central Alberta. Information Report NOR-X-323. Edmonton, AB: Forestry Canada, Northwest Region, Northern Forestry Centre. 30 p. [19243]

3. Shiflet, Thomas N., ed. 1994. Rangeland cover types of the United States. Denver, CO: Society for Range Management. 152 p. [23362]