Competition mediates the effect of climate on tree growth across a longitudinal gradient in Southwest Alaska

Authors: Rosemary Sherriff*, Humboldt State University
Topics: Biogeography, Global Change, Physical Geography
Keywords: white spruce, Picea glauca, climate change, tree growth, dendroecology, biogeography, disturbance ecology, spruce beetle
Session Type: Paper
Day: 4/12/2018
Start / End Time: 5:20 PM / 7:00 PM
Room: Grand Ballroom C, Astor, 2nd Floor
Presentation File: No File Uploaded

Warming temperatures have had a disproportionate effect on boreal ecosystems, influencing the establishment and growth of tree species across their respective ranges. However, less is known about how competitive interactions influence growth-climate relationships. We used tree-ring data from 26 (0.9 ha) study plots in southwest Alaska, near the western frontier of the boreal forest, to investigate how the growth patterns of white spruce (Picea glauca) respond to variation in competition and climate across a longitudinal gradient. We used linear mixed effects models, which included covariates for competition, climate (temperature, precipitation), spruce beetle mortality, and geographic location. Our results suggest that the effects of warming vary across broad ecological gradients. We also found that the effect of temperature varies with stand-level crowding; specifically, the negative effects of temperature are stronger in more crowded (i.e. higher relative basal area) stands. Stand-level dynamics were more influential than tree-level competition. The effects of precipitation were independent of stand density. Our results suggest that as temperatures increase, historically productive stands show declines in growth and/or increased mortality. These results corroborate the findings of previous work from this area, suggesting that there has been a shift in the optimal white spruce growing locations that may help contribute to range expansion.

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