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Biodiversity and ecosystem stability in a decade-long grassland experiment


Human-driven ecosystem simplification has highlighted questions about how the number of species in an ecosystem influences its functioning. Although biodiversity is now known to affect ecosystem productivity1,2,3,4,5,6, its effects on stability are debated6,7,8,9,10,11,12,13. Here we present a long-term experimental field test of the diversity–stability hypothesis. During a decade of data collection in an experiment that directly controlled the number of perennial prairie species4, growing-season climate varied considerably, causing year-to-year variation in abundances of plant species and in ecosystem productivity. We found that greater numbers of plant species led to greater temporal stability of ecosystem annual aboveground plant production. In particular, the decadal temporal stability of the ecosystem, whether measured with intervals of two, five or ten years, was significantly greater at higher plant diversity and tended to increase as plots matured. Ecosystem stability was also positively dependent on root mass, which is a measure of perenniating biomass. Temporal stability of the ecosystem increased with diversity, despite a lower temporal stability of individual species, because of both portfolio (statistical averaging) and overyielding effects. However, we found no evidence of a covariance effect. Our results indicate that the reliable, efficient and sustainable supply of some foods (for example, livestock fodder), biofuels and ecosystem services can be enhanced by the use of biodiversity.

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Figure 1: Dependence of temporal stability of each plot on experimentally imposed species-number treatment.
Figure 2: Dependence of ecosystem temporal stability from 1996 to 2005 on realized species number.
Figure 3: Effects of plant diversity on the relationship between mean biomass and its temporal standard deviation.

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We thank J. Fargione for insightful comments, and T. Mielke, N. Larson, S. Bauer and our summer interns for assistance. The National Science Foundation, the Bush Foundation and the Andrew Mellon Foundation provided financial support.

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Correspondence to David Tilman.

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Tilman, D., Reich, P. & Knops, J. Biodiversity and ecosystem stability in a decade-long grassland experiment. Nature 441, 629–632 (2006).

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