COS 99-1
Pikas under fire: Responses to disturbance
Wildfires have increased in frequency and severity due to climate change, but little is known about the potential threat of altered fire regimes to species distributions, particularly for those with a limited ability to disperse between patches of habitat. Here, we leverage an unexpected opportunity to investigate the impact of a severe wildfire on a climate-sensitive mammal, the American pika (Ochotona princeps). Despite widespread recent interest in climate-mediated pika extirpations, little is known about how this species responds to disturbances like wildfire. In August 2011, we surveyed for pikas at several sites in the Mt. Hood National Forest. Each site is a distinct patch of talus separated by at least 25m from other patches. Shortly thereafter, a large forest fire burned many of these sites, including 2 sites where dataloggers were collecting temperature data in the talus interstices. In the post-fire years (2012 and 2013), we returned to measure vegetation availability and pika abundance at 24 sites on Mt. Hood. We enumerated individuals by recording locations of unequivocal evidence of pikas (e.g., sightings, vocalizations or active food caches) in the morning, when these animals are most active. We also classified the burn severity of each site according to standard metrics.
Results/Conclusions
During the fire, temperatures remained cool in the talus interstices (18-19°C), suggesting that pikas could have survived in situ. Indeed, pikas were quick to recolonize most sites, even those with very few food resources. Although most sites were occupied, pika density was 2-5 times lower at severely burned sites, compared to unburned sites. Furthermore, pika abundance did not exceed 2 individuals until a critical threshold of vegetation mass was reached. Notably, at all sites, pika densities were higher in fall than in spring, which suggests that these populations are actively reproducing and recruiting juveniles. Taken together, these results suggest that pikas may not be severely affected by altered fire regimes because they are more flexible in their habitat requirements, particularly with respect to food resources, than previously thought. This study is particularly timely because the current pika distribution overlaps extensively with areas predicted to experience more frequent and severe wildfires as a result of climate change. Defining these thresholds can improve distributional predictions under environmental change and identify practical targets for conservation. Large-scale studies of wildfires are impossible to plan and conduct; thus, capitalizing on information provided by such unpredicted events is important for understanding their impacts.