Abstract
Species-rich native grasslands are frequently converted to species-poor exotic grasslands or pastures; however, the consequences of these changes for ecosystem functioning remain unclear. Cattle grazing (ungrazed or intensely grazed once), plant species origin (native or exotic), and species richness (4-species mixture or monoculture) treatments were fully crossed and randomly assigned to plots of grassland plants. We tested whether (1) native and exotic plots exhibited different responses to grazing for six ecosystem functions (i.e., aboveground productivity, light interception, fine root biomass, tracer nitrogen uptake, biomass consumption, and aboveground biomass recovery), and (2) biodiversity–ecosystem functioning relationships depended on grazing or species origin. We found that native and exotic species exhibited different responses to grazing for three of the ecosystem functions we considered. Intense grazing decreased fine root biomass by 53% in exotic plots, but had no effect on fine root biomass in native plots. The proportion of standing biomass consumed by cattle was 16% less in exotic than in native grazed plots. Aboveground biomass recovery was 30% less in native than in exotic plots. Intense grazing decreased aboveground productivity by 25%, light interception by 14%, and tracer nitrogen uptake by 54%, and these effects were similar in native and exotic plots. Increasing species richness from one to four species increased aboveground productivity by 42%, and light interception by 44%, in both ungrazed and intensely grazed native plots. In contrast, increasing species richness did not influence biomass production or resource uptake in ungrazed or intensely grazed exotic plots. These results suggest that converting native grasslands to exotic grasslands or pastures changes ecosystem structure and processes, and the relationship between biodiversity and ecosystem functioning.
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Acknowledgments
We thank Dan Isbell, Steve Goepferd, Leah Isbell, Kathryn Yurkonis, Joe Reynolds, Chris Johnson, Cedar Johnson, Kim Isbell, Joni Richmond, Robert Handler, Leanne Martin, Adam Heathcote, Wayne Roush, and Don Hummel for help with field work. This project was supported by a grant from the US National Science Foundation (DEB-0639417) to B.J.W. and a grant from the Leopold Center for Sustainable Agriculture to B.J.W. and F.I.I. We thank Jason Kaye and anonymous reviewers for helpful comments on an earlier version of this manuscript.
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Communicated by Jason Kaye.
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Isbell, F.I., Wilsey, B.J. Increasing native, but not exotic, biodiversity increases aboveground productivity in ungrazed and intensely grazed grasslands. Oecologia 165, 771–781 (2011). https://doi.org/10.1007/s00442-010-1877-9
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DOI: https://doi.org/10.1007/s00442-010-1877-9