University of Minnesota
University of Minnesota
College of Biological Sciences
http://www.cbs.umn.edu/

Experiment 123

Biodiversity I: Effects of Plant Biodiversity on Population and Ecosystem Processes

Biodiversity I (E123), also called the “small biodiversity experiment,” was designed to determine how the number of species affects the dynamics of ecological processes at the population, community, and ecosystem levels. By experimentally manipulating the number of species and the kinds of species, the amount of plant growth and the change from year to year that result can be examined. Also, the effects of number of species on carbon and nitrogen in the soil and on the ability of other species to invade can be studied. The experiment contains 147 3 x 3m plots that were randomly allocated 1, 2, 4, 6, 8, 12 or 24 plant species. The particular species in a plot were randomly selected from a set of 24 prairie-grassland species which included seven warm-season (C4) grasses, four cool-season (C3) grasses, four legumes, nine non-legume forbs. Each level of number of species has 20 to 24 replicates. In this experiment not all of the species are in monocultures. The study was established in 1994 by lead investigators David Tilman, David Wedin, Peter Reich, and Johannes Knops. Experiment 123 is similar to Experiment 120, but it uses smaller plots and did not categorize by type of plant species prior to randomizing species to plots. This size of plot in Experiment 123 means that the soils are relatively more homogeneous and the desired number of species can be more easily maintained by frequent hand weeding than with larger plots. However, the small size of plots limits sampling and the nesting of other studies within the plots.