Biodiversity and ecosystem stability in a decade-long grassland experiment

Vol 441|1 June 2006|doi:10.1038/nature04742LETTERSBiodiversity and ecosystem stability in a decadelong grassland experimentDavid Tilman1, Peter B. Reich2 & Johannes M. H. Knops3Human-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 productivity16, its effects on stability are debated613.

Here we present a long-term experimental field test of the

diversitystability 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.The hypothesis that greater ecological diversity leads to greater

stability7 has been a point of interest and debate for a half century714.

Field observations10,11,14,15 and laboratory experiments1618 have

generally shown that greater diversity is associated with greater

ecosystem stability but lower species stability, much as predicted by

models of multispecies competition8,19. However, well-replicated

field experiments that manipulate variables of interest have become

indispensable in ecology. The only such field experiment to test for

diversitystability relations so far has been an eight-week study that

had mixed results13,20, leading a major review to conclude that the

effects of diversity on stability remained unresolved6. We propose

that diversity has consistent stabilizing effects on ecosystem processes

once timescales are sufficient to incorporate the average net effects of

diversity on both resistance to and recovery from perturbations.Here we present the dependence of the temporal stability of

ecosystems and species on plant...