Print PageSpatial variation in plant species composition within and among communities (beta diversity) may reflect either deterministic influences of the underlying environment on community assembly (species-environment sorting) or historical and stochastic processes that work independently of environmental factors (endogenously-generated spatial structure). To the extent to which individual species, functional groups, or alpha diversity may influence the productivity of localities, stochastic processes that generate spatial patterns of community structure may contribute substantially to landscape heterogeneity in ecosystem processes. Here we report early results from a long-term grassland community assembly experiment that investigated the influence of community assembly history on aboveground productivity. In 2007, 270 experimental plots were established in an abandoned hay field in Eastern Kansas with relatively homogeneous soils. Plots were randomly assigned to one of several planting treatments that resulted in a large degree of random initial spatial variability in alpha diversity, species composition and relative abundances of species among the experimental plots. In the third growing season, soil edaphic variables were measured and plant communities were surveyed for species composition and diversity in each plot. The dependence of plant productivity on these independent variables was analyzed using simple regression and a variety of multivariate models.
Results/Conclusions
When considered alone, species richness was a significant but weak predictor of plant production, consistent with the diversity-productivity hypothesis. However, when the significant influence of dominant species and overall species composition were taken into account, the apparent dependence of productivity on species richness was no longer significant. Overall, plant species composition was by far the most important factor explaining spatial variation in plant productivity at the early stages of community assembly. Additionally, the presence and abundance of certain dominant species, independent of overall species composition, showed a strong and significant association with productivity. Soil factors, plant species diversity, and functional diversity had little to no relationship with productivity. These findings provide little support for the diversity-productivity hypothesis, but indicate that community assembly history and stochastic variation in species composition and abundance can contribute significantly to spatial heterogeneity in plant productivity.
