Acute and lagged fitness consequences for a sagebrush obligate in a post mega-wildfire landscape.

Species responses to disturbance influence their extinction risks. Greater sage-grouse (Centrocercus urophasianus) are bioindicators of sagebrush ecosystem health and the loss of sagebrush (Artemisia spp.) due to wildfire, can cause long-term declines in sage-grouse populations and other sagebrush obligate species. We examined the demographic response of a greater sage-grouse population following a mega-wildfire using stochastic age-structured female-based matrix models over 6 years (2013-2018). Notably, chick survival (range = 0.18-0.38) and female survival (yearling range: 0.20-0.68; adult range: 0.27-0.75) were low compared to values reported for greater sage-grouse in other parts of their distribution. Greater sage-grouse displayed variation in demographic tactics after the fire; however, adult female survival explained most of the variation in λ during each year, which reflected a declining population in 3 of 6 years with more uncertainty observed in 2015 when populations may have been increasing, and 2017 and 2018, when populations may have been declining. The continued annual population decline observed since 2016 suggested there were additional strong environmental impacts that may have been compounded by the fire effects, prolonging recovery of greater sage-grouse. Our results support others that reported negative effects to greater sage-grouse demographics from broad-scale fire and provide a baseline for understanding how this species responds to loss of sagebrush cover based on their life history strategy.

The effects of fire on the thermal environment of sagebrush communities.

Thermal heterogeneity provides options for organisms during extreme temperatures that can contribute to their fitness. Sagebrush (Artemisia spp.) communities exhibit vegetation heterogeneity that creates thermal variation at fine spatial scales. However, fire can change vegetation and thereby variation within the thermal environment of sagebrush communities. To describe spatial and temporal thermal variation of sagebrush communities following wildfire, we measured black bulb temperature (Tbb) at 144 random points dispersed within unburned and burned communities, for 24-h at each random point. We observed a wide thermal gradient in unburned (-7.3° to 63.3 °C) and burned (-4.6° to 64.8 °C) sagebrush communities. Moreover, unburned and burned sagebrush communities displayed high thermal heterogeneity relative to ambient temperature (Tair). Notably, Tbb varied by 47 °C in both unburned and burned communities when Tair was 20 °C. However, fire greatly reduced the buffering capacity and thermal refuge of Wyoming big sagebrush (A. tridentata wyomingensis) communities during low and high Tair. Furthermore, fire increased Tbb in Wyoming big sagebrush and mountain big sagebrush (A. t. vaseyana) during the mid-day hours. These results demonstrate how fire changes the thermal environment of big sagebrush communities and the importance of shrub structure which can provide thermal refuge for organisms in burned communities during extreme low and high Tair.