PS 51-66
Effect of water addition on community response to dominant species removal in a tallgrass prairie
The “mass-ratio” hypothesis (Grime 1998) predicts that the loss or removal of dominant species is expected to have large impacts on ecosystem function. However, this impact may be moderated by the presence of other species in the community that can compensate by performing similar functions and/or by environmental conditions that favor a compensatory response. We addressed these predictions by conducting a removal experiment in a tallgrass prairie ecosystem, where the C4 grass, Andropogon geradii, dominates and can contribute >80% to aboveground productivity. We asked the following questions: 1) Will there be a compensatory response to the removal of the dominant species A. gerardii? and 2) Will a compensatory response be limited by resources (in this case water availability)? We performed our experiment in an upland site burned every four years at the Konza Prairie Biological Station, which experiences some degree of water limitation during the growing season. We applied three water addition treatments: Control, Long term Average (LTAv), and 30% above the LTAv (Plus30). Nested within these treatments, we applied two removal treatments to 0.5 x 0.5 m plots: 0% and 100% removal of A. gerardii. To assess the effects of removal of the dominant, we measured stem densities of all plant species and end-of-season aboveground productivity.
Results/Conclusions
The removal treatment resulted in on average a 79.83% (50-99%) reduction in density of A. gerardii, and thus we were not able to completely eliminate the dominant species from the study plots. The LTAv water addition treatment increased the overall stem density (minus A. gerardii) of the community (11.4%) compared with the Control (2.5%) and PLUS 30 (1.2%). There was not a significant effect of the removal treatment on total stem density, indicating that there was not a compensatory response of the remaining species in the community to the removal of A. gerardii in the short-term, but there could be water limitation for plant growth and community recovery. However, the removal of the dominant species did allow for the increase in abundance (stem density) of a few subdominant species in the community (C4 grasses Bouteloua curtipendula and B.gracilis, and C3 grasses Poa pratensis and Dichanthelium oligosanthes) for all the water treatments. This indicates that some species in the community might exhibit a compensatory response to the removal of A. gerardii over the long-term and that compensatory responses may be enhanced over time with increased resource availability.