Alteration of riparian plant community structure UNDER climate change scenarios: The effects of temperature and hydroperiod

Background/Question/Methods

We assess how predicted climate and land use driven changes in hydrologic flux and temperature regimes of floodplain ecosystems affect plant communities in terms of their vulnerability to the establishment and spread of invasive species and, in turn, ecosystem functions and services. Future climate scenarios for the southeastern U.S. predict that surface water temperatures will warm (in concert with air temperature) and that stream flows will likely decrease, with a greater proportion of annual watershed hydrologic yield occurring during major storm events.  We focus on the relationships among native species composition, diversity, productivity, and invasibility of floodplain ecosystems affected by alterations of water temperature and annual hydrographs driven by climate change and land use change. We utilize a combination of varying scale experimental studies and one novel large-scale regional study to verify our experimental results. Temperature and hydrology effects were evaluated using three experimental treatments (warm, cold and control) using a total of 13 wetland sites.  We demonstrate temperature contrasts of at least 5^oC between sets of surface-releasing and bottom-releasing dams to develop our warm and cold treatment sites, while control (ambient) sites are located in watersheds with no upstream dams.

Results/Conclusions

We performed statistical analysis of the correspondences between plant community structure, temperature regime, hydroperiod, and local soil properties. Temperature was the most important predictor of riparian plant community structure followed by hydroperiod, flood energy, soil texture, soil organic matter, and nutrient availability.  Increased temperature was associated with increased diversity and a decreased degree of invasion, while increased flood energy was associated with decreased diversity and an increased degree invasion.  The dominance of invasive species, as measured by peak biomass, differed significantly between our treatments and along temperature gradients within individual sites.  These results will inform projections of the invasibility of floodplain communities in the face of altered temperature and flood regimes.