Title: Post-fire recovery of Wyoming big sagebrush shrub-steppe in centeral and southeast Montana
Description: Sagebrush is a widespread habitat throughout our study area and a number of species including Greater Sage-grouse, pronghorn, Brewers Sparrow, Sage Sparrow, Sage Thrasher and sagebrush vole are sagebrush dependent, at least at some stage of their life cycles. Fire constitutes an important driver in structuring sagebrush ecosystems; past investigations have established that the response of the big sagebrush component (Artemisia tridentata Nutt.) varies according to subspecies. In an earlier study in southwestern Montana we statistically determined that recovery of mountain big sagebrush (A. t. ssp. vaseyana [Rydb.] Beetle) cover occurred in slightly more than 30 years, however the minimal data for Wyoming big sagebrush (A. t. ssp. wyomingensis Beetle & Young), indicated a much longer recovery period (Lesica et al. 2005).  In this study we used the same sampling protocol at 24 burned-unburned paired sites in central and southeastern Montana where Wyoming Big Sagebrush is the dominant big sagebrush taxon and the accompanying flora is more closely allied with the Great Plains than the Intermountain West. Prescribed burns and wildfires typically result in the complete mortality of Wyoming big sagebrush.  We found that Wyoming big sagebrush recovers very slowly from both types of burns at all sites, even those with relatively moist conditions. Full recovery to pre-burn sagebrush canopy cover conditions will take well over 100 years. The median time since fire was 22 years and ranged from 4 to 67 years. We found no Wyoming big sagebrush canopy cover recovery for 17 of the 24 sites after burning had occurred and the oldest burn was only 8% recovered. Livestock grazing does not seem to be casual as the only site without livestock grazing for the entire period after burning had no canopy recovery in 25 years. Burned plots were located near unburned areas to ensure that a seed source was relatively available since Wyoming big sage is known to lack a soil seed bank.  Perennial and annual grass cover increased after burning, however virtually all of the 11% increase in annual grass is from field brome (Bromus arvensis, formerly Japanese brome, Bromus japonicus), regarded as a weed with negative habitat and livestock value. Perennial grass cover increased 27% and 20% followed prescribed fi re and wildfire, respectively. Western wheatgrass (Pascopyrum smithii) increased by 17% and accounted for most of the perennial grass increase. These increases did not decline with time since burning, which may be explained by the lack of the competitive influence of sagebrush recovery. There was no change after burning in overall forb cover or the numbers of forbs of the Cichorieae Tribe of the Asteraceae family. The Cichorieae tribe forbs are important for successful Greater Sage-grouse brood rearing.  Plant species richness significantly declined in burned plots compared to their unburned control plots.  Our findings of extremely slow Wyoming big sagebrush recovery after fire are similar to the other research in the area (Eichhorn and Watts 1984) and also supports findings by Baker (2007) that fire rotations for this subspecies are about 100 to 240 years.  The slow Wyoming big sagebrush recovery and the increase in the weedy annual grass field brome suggests that managers concerned about Greater Sage-grouse and other sage-dependent species should be extremely cautious with prescribed burns and wildfires in this region. Burns may essentially eliminate sagebrush habitat, increase weedy annual grass cover, reduce species richness, and could take a century or more for recovery to pre-burn sagebrush cover conditions.
Subjects: Plant succession, Effect of fires on, Steppe plants, Prescribed burning, Fire ecology, Plant ecology, Steppe ecology, Wyoming big sagebrush