Effects of elevation and selective disturbance on soil climate and vegetation in big sagebrush communities

Abstract

Changing climatic conditions prompt concerns about vegetation response to disturbance under future compared to past conditions. In this long-term study, we examined soil climate and vegetation differences at lower, mid, and upper elevations in two separate locations in the Great Basin, USA. We hypothesized that soil climate and vegetation associations across the elevational gradient could help predict responses under future warming and drying. We measured soil water availability, soil temperatures, and vegetation cover in relation to fire and perennial herb removal at each elevation for 13-17 yr after treatment. Seasonal soil water availability increased, while soil temperature-related variables decreased with increasing elevation. Soil water availability in spring was positively correlated with October through June precipitation (r 2 = 0.53), while water availability in spring through fall was positively correlated with perennial plant cover (r 2 = 0.65). Partition models separated low, mid, and high elevations by spring soil water availability and growing degree days when soil water was available (R 2 = 0.93). Current soil climate and vegetation conditions at lower elevations could indicate future conditions at higher elevations under a warmer and drier climate. During the first years after removal of perennial grasses and forbs, there was an increase in soil water availability in spring at 13-30 cm soil depth that was associated with sagebrush establishment, particularly at upper elevations. In subsequent years, sagebrush continued to dominate even though little difference in soil water availability existed between disturbed and undisturbed plots. This indicates that quickly establishing sagebrush preempted resources and reduced perennial herb recovery. Resource preemption after disturbance will likely be a major driver of plant succession in the future as in the past. Species that establish best under future warmer and drier conditions are most likely to dominate after disturbance. A negative correlation (r 2 = 0.34) between the standard deviation of annual spring soil water availability and perennial vegetation cover, which helps resist annual grass invasion, supports the hypothesis that greater resource fluctuation is associated with greater plant community invasibility. Current responses to fire and loss of native plant cover across elevational gradients can indicate future responses under a warmer and drier climate.

New indicators of ecological resilience and invasion resistance to support prioritization and management in the sagebrush biome, United States

“…In the western ecoregions higher RST, like higher RSL, can be attributed largely to lower temperatures, higher precipitation, and lower climatic water deficit at higher elevations (Chambers et al, 2014a). Progressive decreases in mean soil temperature and increases in late spring, fall, and October-June soil wet-days occur over the elevational gradients characterizing this area (Roundy and Chambers, 2021). Cooler temperatures and greater resource availability at higher elevations are associated with higher productivity, more competition from perennial native grasses, and greater biodiversity resulting in more resilient and resistant ecosystems (Bansal and Sheley, 2016;Wainwright et al, 2020).…”

Combining resilience and resistance with threat‐based approaches for prioritizing management actions in sagebrush ecosystems

“…Higher proportions of perennial grasses in areas with more summer precipitation and relatively low climatic water deficits typically result in greater competition with cheatgrass and other annual invaders as well as more rapid recovery from disturbances (Bradford & Lauenroth, 2006; Larson et al, 2017; Prevéy & Seastedt, 2014). Topographic gradients are primary determinants of SEI areas and resilience and resistance indicators in more mountainous ecoregions, and both CoreSage areas and M and H + MH increase with elevation due to decreases in temperature and climatic water deficits and increases in precipitation (Roundy & Chambers, 2021). This is particularly evident in the western ecoregions, where CoreSage areas with M and H + MH resilience and resistance are often associated with mountain ranges and occur at higher elevations.…”

Ten‐year ecological responses to fuel treatments within semiarid Wyoming big sagebrush ecosystems

“…In this region's big sagebrush ecosystems, dominance of non‐native annual grasses, such as cheatgrass ( Bromus tectorum ), has dramatically changed fire regimes (Balch et al, 2013; Bradley et al, 2018; Brooks et al, 2004; D'Antonio & Vitousek, 1992; Rahlao et al, 2009) and has influenced fuel reduction or fire suppression treatments (Crist et al, 2019). Warm and dry portions of big sagebrush ecosystems are more prone (less resistant) to cheatgrass dominance than cooler and moister portions of these ecosystems (Chambers, Bradley, et al, 2014; Chambers, Miller, et al, 2014; Roundy & Chambers, 2021). Fire managers must also consider preserving and maintaining wildlife habitat, especially for species of concern, such as Greater Sage‐grouse ( Centrocercus urophasianus , hereafter called sage grouse).…”