Climate Change Effects on Treeline Communty Dynamics in Basin and Range Mountains

Tuesday, 16 December 2014
Brian Smithers, University of California Davis, Davis, CA, United States, Connie Millar, USDA Forest Service, PSW Research Station, Vallejo, CA, United States and Malcolm North, USDA Forest Service, Davis, CA, United States
Treeline advance is an expected sensitive indicator of climate change effects on species distributions. However, little evidence of treeline advance has been shown due to past disturbance or geomorphological limitations. The Basin and Range Mountains of Nevada and eastern California have seen minimal human impact and have been free of major glaciation, making these mountains an ideal location to test for climate change impacts on treeline. Great Basin treelines are dominated by bristlecone pine but recent observations show that usually downslope-growing limber pine appears to be pushing treeline upslope. In this study, we used modified belt transects at above and below adult treeline and at stand mid-elevation to compare species regeneration with adult, cone-bearing tree basal area. Our results show that limber pine regeneration surpasses bristlecone pine regeneration at treeline in terms of raw numbers of individuals. When adult basal area is taken into consideration, it appears that the very few adult limber pines have far more regeneration success at treeline than the bristlecone pine adults. This may have long-term ramifications on community composition of bristlecone pine forests, as these long-lived individuals largely exclude one another once established. Limber pine appears to be far better adapted to take advantage of rapid climate change. Even if bristlecone pine is ultimately better adapted to treeline in the long-term and this “changing of the guard” at treeline is temporary, due to their long lifespan, this effect could last thousands of years.