Increased biodiversity is expected to confer higher stability to ecosystem functioning. One of the mechanisms by which this stabilizing effect occur are compensatory dynamics ), where different species have asynchronous responses to environmental fluctuations. This produces a collective response at the community level know as compensation, a measure of the degree of recovery in ecosystem function following a change in the environment, in this case after species loss. The loss or reduction in abundance of dominant species has large impact on ecosystem function, but due to competitive release, also creates the opportunity for other species to become more abundant and compensate in function. However, compensation does not always occur, and three main constraints have been hypothesized: lack of functional redundancy in the community, absence of functional traits that promote compensation, and resources availability. Using field removal experiments combined with a functional trait-based approach, we addressed these constraints. Here we present the results of three years of water addition on the compensation response in a tallgrass prairie plant community after the loss of the dominant species Andropogon gerardii.
During three years, there has been no evidence of biomass compensation with increased water availability (long-term average precipitation and 30% above the long-term average, Plus30%) after the loss of A. gerardii. Although the average effect size of the response to the dominant removal in the water addition treatments was larger in all three years (Cohen’s d= 0.479 for long-term average precipitation, and d=0.313 for Plus30%), compared with ambient precipitation (d= 0.082), there is no significant effect of removal on community compensation. For the community with A. gerardii removal, the most responsive functional type to water addition was C4 grasses in 2013 (p>0.001) and 2014 (p<0.05). Within the C4 grasses, Bouteloua curtipendula and Panicum virgatum show the strongest response, and preliminary results indicate a response of Sorghastrum nutans during 2015. These last two grass species may be functionally equivalent to A. gerardii. Although increased water availability promoted a response in the community, it was not enough to fully compensate for the loss of the dominant species. We believe initial abundance of functionally equivalent species and availability of other resources, such as nitrogen, may be imposing additional constraints on compensation to the loss of the dominant species in this grassland.