Print PageCertain easily measurable traits are useful indicators of plant stress tolerance and resource acquisition strategies; these include specific leaf area, leaf dry mass content, leaf C:N ratio, height, and wood density. Community-weighted mean (CWM) values of such traits can help indicate and predict community responses to human impacts, as well as responses to natural gradients of resources and stress. We resampled a 60-year-old data set in a mediterranean-climate region (Siskiyou Mts, Oregon) where the climate has since warmed by 2˚C. We asked whether the CWM of specific leaf area had declined, as would be expected if drought-tolerant species have become more prevalent; we compared the results to other indices of community change. In two other studies, we asked whether CWM trait values could predict differential community responses to natural rainfall variability (in grasslands), or to fertilization and herbivory (in tundra).
Results/Conclusions
In the Siskiyou study, we found that three low-elevation communities (primary forest, secondary forest, and serpentine woodland, <1200 m) have changed since 1949 in a direction consistent with a warmer climate, while a high-elevation community (forest >1500 m) has not. Results were fairly consistent between the trait-based test (lower CWM of specific leaf area) and two other metrics (decreased prevalence of biogeographically “northerly” species; increased resemblance to communities on more southerly slopes). In the two other studies, we found that CWM values of specific leaf area and foliar C:N were good predictors of the variability of grasslands in response to yearly rainfall, and the responses of tundra to fertilization and herbivory. We conclude that (1) communities on low-nutrient soils, where plants have “stress-tolerant” functional traits, may be resistant to change; (2) functional traits are valuable metrics for predicting and comparing change across communities that have few species in common.
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