One hundred years of community resistance, resilience and variance in Sierran conifer forests: A test of the insurance hypothesis.
De Clerck, Fabrice*,1, Barbour, Micheal2, Sawyer, John3, 1 The Earth Institute at Columbia University, New York, NY, United States2 University of Calfornia Davis, Davis, CA, United States3 Humboldt State University, Arcata, CA, United States
ABSTRACT- Evidence suggests reductions in species richness adversely affect ecosystem processes such as stability, however few studies have been conducted in natural systems. We use a long-lived forest system to explore the effect of species richness on three stability measures: variance, resistance and resilience. We used one hundred years of annual growth increments of 800 individual trees of four conifer species growing in mixed and pure forest stands to test three ecosystem stability/species richness hypotheses: (1) increased species richness will decrease stand variance, (2) increased species richness will increase stand resistance in response to drought years, (3) increased species richness will increase stand resilience following drought years. Although we found that each species was either more resistant, or resilient to drought, we found no evidence that compensatory growth increased the stability of mixed communities when any measure of stability was analyzed in isolation. However when multiple measures of stability were considered a net diversity effect became evident where species rich stands had increased stability. When trees were classified into two functional groups based on shade tolerance, the shade-intolerant functional group was more resistant and less variant, whereas the shade-tolerant functional group was more resilient. Stands comprised of both functional groups typically had values of variance, resistance, and resilience that were between those of the two functional groups. Although mixed stands never outperformed those with a single functional group or species, we found evidence suggesting that mixed stands are more stable when net biodiversity effects, rather than single measures of stability, are considered.
Key words: biodiversity, stability, functional compensation
All materials copyright The Ecological Society of America (ESA), and may not be used without written permission.