Abstract
Abstract. Changing fire regimes in western North America may impact biological soil crust (BSC) communities that influence many ecosystem functions, such as soil stability and C and N cycling. However, longer-term effects of wildfire on BSC abundance, species richness, functional groups, and ecosystem functions after wildfire (i.e., BSC resilience) are still poorly understood. We sampled BSC lichen and bryophyte communities at four sites in Idaho, USA, within foothill steppe communities that included wildfires from 12 to 16 years old. We established six plots outside each burn perimeter and compared them with six plots of varying severity within each fire perimeter at each site. BSC cover was most strongly negatively impacted by wildfire at sites that had well-developed BSC communities in adjacent unburned plots. BSC species richness was estimated to be 65 % greater in unburned plots compared with burned plots, and fire effects did not vary among sites. In contrast, there was no evidence that vascular plant functional groups or fire severity (as measured by satellite metrics differenced normalized burn ratio (dNBR) or relativized differenced normalized burn ratio (RdNBR)) significantly affected longer-term BSC responses. Three large-statured BSC functional groups that may be important in controlling wind and water erosion (squamulose lichens, vagrant lichens, and tall turf mosses) exhibited a significant decrease in abundance in burned areas relative to adjacent unburned areas. The decreases in BSC cover and richness along with decreased abundance of several functional groups suggest that wildfire can negatively impact ecosystem function in these semiarid ecosystems for at least 1 to 2 decades. This is a concern given that increased fire frequency is predicted for the region due to exotic grass invasion and climate change.
Highlights
Fire regimes are changing throughout western North America as a result of climate change, human management, and exotic invasive species (D’Antonio et al, 1992; Westerling et al, 2006; Millar et al, 2007)
We considered these variables in the exploratory functional group analysis, but not for hypothesis testing because we designed our study to focus on fire effects rather than spanning the regional gradient of soil and climate with enough replication to ensure a robust test or ability to discriminate among those variables
We found that the impacts of wildfire on Biological soil crust (BSC) lichen and bryophyte communities last at least 1 to 2 decades and perwww.biogeosciences.net/14/3957/2017/
Summary
Fire regimes are changing throughout western North America as a result of climate change, human management, and exotic invasive species (D’Antonio et al, 1992; Westerling et al, 2006; Millar et al, 2007). Many sagebrush steppe ecosystems of the western USA have seen a fire surplus in recent decades, presumably due to increased human ignitions and introduced annual grasses (Parks et al, 2015). It is expected that wildfires will continue to increase in frequency and severity with climate change (Westerling et al, 2006; Millar et al, 2007) and exotic grass invasion (D’Antonio et al, 1992) in much of the western USA. Darker BSCs usually fix nitrogen (Belnap, 2002), and larger-statured
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