Community ecology theory asserts strong links between community structure and community function, including proven correlations between community structure metrics (e.g. species richness, functional diversity) and community function metrics (e.g. productivity and stability). Compared to grasslands globally, plant communities of the northern Chihuahuan Desert exhibit low levels of community function and high levels of dominance by perennial, C4 grasses including black grama (Bouteloua eriopoda) and blue grama (Bouteloua gracilis).
In this study, we ask two basic questions: 1) what is the relationship between community structure and function in desert grasslands and 2) how important are the dominant grasses in governing the structure and function of their communities?
Data were collected by the Sevilleta Long Term Ecological Research (LTER) program in central New Mexico. Observational data of 1x1 meter plots has been collected since 2002 in a Chihuahuan Desert grassland ecosystem dominated by black grama, and a Great Plains grassland dominated by blue grama. In addition, an experimental manipulation of these grasslands included the removal of the dominant grass species within their communities. Black and blue grama have been annually removed from 3x4 meter plots and species composition and abundance data collected since 1998.
Results/Conclusions
We found strong correlations consistent with grassland community theory in the Great Plains grassland system including positive relations between species richness and productivity (p<0.001) and stability (p=0.07). However, the opposite relationship was observed in the Chihuahuan Desert grassland, that is, there was no correlation or negative correlation between species richness and productivity (p=0.79) and stability (p=0.38). The Great Plains grassland has greater species richness than the Desert grassland (p< 0.001) which exhibits more dominance within its community than the Great Plains (p< 0.001).
When the dominant grass species were removed from their communities, community function (productivity, stability) sharply fell in the Chihuahuan Desert grassland (p< 0.001, p<0.001) while function remained unchanged or increased in the Great Plains grassland post blue grama removal (p<0.21, p<0.05). These findings imply that black grama inhibits other species’ establishment, resulting in less diverse communities, and black grama is also the primary driver of community function within the Desert Grassland. At the same time, blue grama may be inhibiting community function given the marginal increase in community function after blue grama removal.