Fire regimes of Alaskan dry grassland communities


Citation:
Innes, Robin J. 2014. Fire regimes of Alaskan dry grassland communities. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Missoula Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us/database/feis/fire_regimes/AK_dry_grassland/all.html [ ].

Fire Regime Syntheses bring together information from 2 sources: the scientific literature as of 2014, and the Biophysical Settings (BpS) models and associated Fire Regime Data Products developed by LANDFIRE, which are based on literature, local data, and/or expert estimates. Syntheses intend to:

Dry grassland (also called "grassland steppe") communities occur across boreal regions of Alaska on dry, south-facing slopes or well-drained to excessively well-drained lowland sites [2,4,7,10,17]. Soil conditions often result in the occurrence of dry grasslands in boreal forest regions [11]. For a list of plant communities in Alaskan dry grasslands, see Appendix A. For a list of common species occurring in Alaskan dry grassland communities, see Appendix B. Dry grassland communities are typically adjacent to quaking aspen (Populus tremuloides)-steppe bluff communities [4].

Dry grasslands were widespread in Alaska and northern Canada during the cold, dry climate of the late Pleistocene ([2,18,19], Hopkins and others 1982 cited in [12]), but in contemporary times these communities are uncommon ([2,3,7,17], Yurtsev 1982 cited in [12]).

LANDFIRE did not map the BpSs for this group.

As of this writing (2014), there is little published information on historical fire regimes in Alaskan dry grassland communities or in adjacent quaking aspen-steppe bluff communities (but see the Fire Regime Synthesis of Alaskan quaking aspen and balsam poplar communities), and most of the existing information is anecdotal. Grasslands generally have a higher fire frequency than forests and woodlands in the same climatic zone because they have more fine fuels and a hotter, drier microclimate [1].

Starfield and Chapin [16] estimated a fire-return interval of 40 years in dry grasslands in boreal regions of Alaska, based on the assumption that Alaskan dry grasslands have a higher fire frequency than other ecosystem types in the same region. Based on inputs derived from expert opinion, LANDFIRE models estimated a mean fire-return interval of 83 years in Alaskan dry grasslands. The experts assumed a regime comprised of replacement (58%) and mixed-severity (42%) fires, with no low severity fires (Appendix A). Researchers studying dry grasslands in northwestern British Columbia stated that fires occurred more frequently and were more variable in size, seasonality, and severity in grasslands than in surrounding forests or wetlands [3], but they did not provide supporting data.

Native Americans in boreal regions probably burned some dry grasslands in spring [3,5,6,14,15]. Researchers in northwestern British Columbia stated that Native Americans, and then European settlers, likely burned dry grasslands in spring [3]. Information from interviews with Native American elders in northern Alberta combined with anecdotal information suggests that Native American burning in spring, grazing animals, and frequent fire, may have historically maintained and/or expanded dry grasslands by reducing shrubs and trees [5,6,14,15]. A review noted that European settlers observed fires set by Native Alaskans in the 1890s and early 1900s [8]. However, the frequency and locations of fires historically set by Native Alaskans were not well documented. Historical and contemporary accounts of native Gwich’in Athabaskan groups in eastern, interior Alaska describe intentional burning of the landscape when conditions were not conducive to extensive fire spread. In central, interior Alaska, however, Koyukon Athabaskan groups did not historically use fire to modify the landscape [9].

Some authors suggest that fire may both initiate and maintain Alaskan dry grassland communities [12,17], and some suggest that these communities are likely to increase in extent due to climate change [12,13,16]. Simulations of a warming climate in northwestern Alaska that included a single, 40-year drought 100 years into the simulation led to the replacement of about half of existing forest and tundra with dry grassland. Because the fire-return interval was assumed to be short (10 years), the dry grassland persisted indefinitely, resulting in permanent increases in fire frequency in both dry grassland and adjacent communities [12]. The authors assumed a 10-year fire-return interval because this was the average frequency of severe fire years in North American boreal forest from 1953 to 1980 (Flannigan and Harrington 1988 cited in [12]). Thus, a dry, warm climate may lead to widespread dry grasslands, just as dry grasslands were widespread during the dry, cold climate of the late Pleistocene. However, the species composition would likely differ [2,12,13,16].

APPENDIX A: Summary of fire regime information for Biophysical Settings covered in this synthesis


APPENDIX B: Common and scientific names of plant species

These species are common to dominant in Alaskan dry grassland communities. Follow the links to FEIS reviews for additional information.
Common name Scientific name
Shrubs
Alaska wormwood Artemisia alaskana
prairie sagewort Artemisia frigida
Forbs
yarrow Achillea spp.
Graminoids
arctic brome Bromus pumpellianus
bluebunch wheatgrass Pseudoroegneria spicata
bluegrass Poa spp.
boreal wildrye Leymus innovatus
northern rough fescue Festuca altaica
purple reedgrass Calamagrostis purpurascens
red fescue Festuca rubra

REFERENCES:


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