Janneke Hille Ris Lambers (1), Leander DL Anderegg (2), Ian Breckheimer (3), Ailene Ettinger(4), Kevin R. Ford (5), Jerry Franklin (6), James Freund (7), Steve Kroiss (8)
1 Biology Department, University of Washington, Seattle, WA 98195‐1800, USA, jhrl@uw.edu
2 Biology Department, University of Washington, Seattle, WA 98195‐1800, USA, ldla@uw.edu
3 Biology Department, University of Washington, Seattle, WA 98195‐1800, USA, ibreckhe@uw.edu
4 Arnold Arboretum, Harvard University, Boston, MA 02131, USA, aettinger@fas.harvard.edu
5 Pacific Northwest Research Station, 3625 93rd Ave SW, Olympia, WA 98512, USA, kevinrford@fs.fed.us
6 School of Environmental and Forest Sciences, University of Washington, Seattle, WA 98195‐2100, USA, jff@uw.edu
7 School of Environmental and Forest Sciences, University of Washington, Seattle, WA 98195‐2100, USA, jafchen@uw.edu
8 Biology Department, University of Washington, Seattle Washington, 98195‐1800, USA, skroiss@gmail.com
How will climate change influence community structure? Communities are generally expected to lose cold‐ adapted species, while warm‐adapted trees increase in abundance (i.e. the ‘thermophilization’ of communities). However, compositional shifts may be significantly more complex due to variation among species and locations in the rate and magnitude of climate change responses. To address these possibilities, we use long‐term data collected from Mt. Rainier National Park (WA, USA) to: 1) examine the extent to which forest communities have already changed in response to recent warming and 2) explore which processes can explain compositional shifts that differ from simple ‘thermophilization’ predictions. We found that compositional shifts over the last 35 years were small, despite significant warming in the region, and not consistent with thermophilization predictions. Ongoing research suggests several factors contribute to the complexity of observed community shifts, and therefore, are likely to influence future community reassembly with continued climate change. Demographic inertia (slow growth and mortality) and competitive interactions constrain population growth rates of component tree species, and likely slow compositional turnover in response to warming. Additionally, because climate sensitivity varies by tree species and location and competition constrains species performance, community reassembly in these forests seems likely, particularly in low elevation forests. In all, results imply that the rate and direction of compositional change with climate change is likely to be complex, but may still be generalizable from species traits or habitat characteristics.
