The complex interaction between global change (i.e., climate change, land use change, and species invasions) and vegetation will have a profound influence on the water cycle at multiple scales. Plants directly modify their environment through their physiology and morphology (e.g., water extraction and canopy cover); these modifications are propagated to communities, ecosystems, and landscapes through feedback and feed-forward processes (i.e., water interception, nutrient input to soils, and biogeochemical cycling). Since global change influences hydrology and species composition, these processes will be fundamentally altered and the changes propagated through communities, ecosystems, and watersheds. Conventional research on global change is inherently compartmentalized (i.e., plant or ecosystem response to elevated CO2 or warming, or disturbance and invasion) which fails to capture the linkages among levels of ecological organization; these linkages will ultimately determine how global change is manifest. Our objective was to develop a suitable framework for investigating the role of vegetation in linking global change influences among multiple scales.
We developed a conceptual framework that captured known ecohydrological processes and created links within and among scales. Four scales were identified that encompass the breadth of ecohydrological processes: individual plant, community, landscape, and global. Lower-scale processes are linked to higher scales through emergent properties. Emergent properties are functions manifest in complex systems by the interaction of simple components (i.e., rate of decomposition emerging from tissue quality input). We argue that changes in ecohydrological processes at the plant and community scales are often more important than competition or disturbance as mechanisms involved in community stability or change. At the landscape scale, community structure and juxtaposition of community types are important, but often overlooked, components that affect landscape ecohydrological processes. The ecohydrological processes occurring in three Great Basin, USA plant communities (quaking aspen, pinyon-juniper and sagebrush steppe) are presented that illustrate many of the identified processes and how these processes link across scales. We propose this framework to promote a meaningful understanding of ecohydrological processes and resulting global change consequences that can be incorporated into management and planning.