Cedar Creek scientists discovered that the number of plant species in an ecosystem – its biodiversity – has a profound effect on ecosystem function. Long-term experiments show ecosystems with greater plant biodiversity are more productive and stable, and better able to soak up more of our carbon dioxide emissions as well. Moreover, the value of diversity grew over time in two long-term experiments. Consequently, local loss of even a few species will likely have greater negative impacts on ecosystem functioning than has been suggested by short-term experiments.
Importantly, plant biomass production increases with diversity (Fig 1) because of complementary interactions among species and not because of selection (sampling) effects (Figs 2 Tilman et al. 2001b, Pacala and Tilman 2002, Hille Ris Lambers et al. 2004.).
Cedar Creek’s “Big Biodiversity” experiment determines effects of plant species numbers and functional traits on community and ecosystem dynamics and functioning. It manipulates the number of plant species in 168 plots, each 9 m x 9 m, by imposing plant species numbers of 1, 2, 4, 8, or 16 perennial grassland species. The species planted in a plot were randomly chosen from a pool of 18 species (4 species, each, of C4 grasses, C3 grasses, legumes, non-legume forbs; 2 species of woody plants). Its high replication (about 35 plots at each level of diversity) and large plots allow observation of responses of herbivorous, parasitoid and predator insects and allow additional treatments to be nested within plots. Planted in 1994, it has been annually sampled since 1996 for plant aboveground biomass and plant species abundances and for insect diversity and species abundances. Root mass, soil nitrate, light interception, biomass of invading plant species, and C and N levels in soils, roots, and aboveground biomass have been determined periodically. In addition, soil microbial processes and abundances of mycorrhizal fungi, soil bacteria and other fungi, N mineralization rates, patterns of N uptake by various species, and invading plant species, have been periodically measured in subprojects in the Biodiversity Experiment.