In arid and semi-arid regions of the western US, climate change is expected to affect stream flow through increases in temperature and changes in precipitation patterns. In many cases, baseflows are expected to decline, snow melt runoff will occur earlier, and rain-driven flood events may be more intense. Low flow and peak flow changes in streamflow regime will affect riparian plant communities, potentially forcing dramatic changes in riparian forest composition. To understand how riparian plant communities will shift under future hydrologic conditions, we use a functional guilds approach to distribution modeling. We identify suites of traits (guilds) that modify species’ response to flow variables related to moisture availability and fluvial disturbance. We use historic streamflow data to model riparian species distribution along rivers in the southwestern US. We then use rainfall-runoff models driven by future climate data to project future riparian plant distribution along western rivers.
Results/Conclusions
Results show that riparian guild occurrence varies considerably along hydrologic gradients both within river reaches and between river basins. We were able to project guild occurrence along rivers in different ecoregions and under different hydrologic regimes to understand how riparian plant communities vary across broad spatial scales and under both current and future hydroclimate conditions. Drought-tolerant guilds that included deep-rooted and high wood density species are present at the margins of floodplain communities where drier conditions exist and more hydric guilds composed of wetland-obligate species occurred closer to the active channel. By using plant guilds instead of individual species, we are able to understand where similar guilds, composed of different species, occur across broad, regional spatial scales. Functional guild models can be used as restoration and land management tools to guide and understand plant community composition under future climate and management scenarios.