In the western United States, forest ecosystems have been altered by natural and anthropogenic disturbance regimes. Historically, clear-cutting and timber sales removed large tracts of old-growth forests and homogenized much of the landscape. Contemporary forest management targets selective harvest and thinning treatments, but still alters the distribution and quality of forests especially relevant for forest obligate species. In addition, climate change has led to increasing temperatures and inconsistent precipitation which elevates the risk of wildfires and drought, and decreases the depth and duration of snowpack in high elevation areas. These trends directly impact forests by contributing to extensive tree mortality, altering the structure and extent of forested systems and negatively impacting many wildlife species, including sensitive forest carnivores such as the Pacific marten (Martes caurina). In the western United States, Pacific martens are generally associated with high elevation, old-growth coniferous forests. Features associated with these sites (e.g. deep, consistent snow-pack and complex woody structures) allow martens to forage efficiently, and avoid predation. As a result of continued disturbance and habitat loss, Pacific martens have declined over the last century and have been designated as a sensitive species by the U.S. Forest Service. In California, drought, wildfire, and urbanization have contributed heavily to the fragmentation of marten populations in the Sierra Nevada and Cascade mountain ranges. While previous research has highlighted the impacts of habitat loss on the range and distribution of marten populations, questions remain about the mechanisms that drive these trends. To address these questions, we are studying Pacific martens at relatively broad (Sierra Nevada Mountain Range, CA) and fine (Lassen National Forest, CA) scales. Through this research, we will quantify the impacts of forest management and natural and anthropogenic disturbance on marten foraging, space use, movement, and energetics, and ultimately how these factors influence marten populations.
To understand how extensive, drought-driven tree mortality is influencing marten dietary niche and their competitive overlap with the larger-bodied Pacific fisher (Pekania pennanti), we are partnering with the U.S. Forest Service’s Sierra Nevada Carnivore Monitoring Program. Through this partnership we will analyze hair samples collected from sites in the southern Sierra Nevada mountain range from 2005-2018, to quantify dietary shifts and niche overlap of these species in various conditions of forest structure using stable isotope analysis. We are also exploring the effects of fine-scale landscape heterogeneity on marten space use, movement patterns, and daily energetic expenditures. In collaboration with the Pacific Northwest Research Station and the U.S. Forest Service, we are using GPS collars, accelerometry, and doubly-labeled water to quantify these aspects of marten ecology in Lassen National Forest, CA. Ultimately these efforts will enrich our understanding of sensitive forest carnivores and their responses to ongoing landscape and climate changes at multiple scales.
This work is funded by the US Forest Service Sierra Nevada Carnivore Monitoring Program, US Forest Service, Pacific Northwest Research Station.