Ecohydrology in the critical zone: Vegetation response to spatial and temporal variability in available water
Ongoing changes in climate threaten terrestrial ecosystems increasing drought water stress, reducing carbon uptake, predisposing vegetation to disturbance from fires, insects, and other pests, and influencing what vegetation communities will re-establish following disturbance. Because vegetation provides a critical link between terrestrial and atmospheric cycles of carbon and water, these changes in vegetation structure potentially have implications ranging from local resource management to feedbacks on regional and global climate. Predicting when and where vegetation is at risk to drought related impacts, and importantly how ecosystem structure will recover following disturbance, represents a grand challenge in ecology and ecosystem science. Addressing this challenge requires coordinated research addressing interactions between plant physiology, local climate, ecosystem structure, and landscape characteristics that influence the environment experienced by organisms and communities. Research both within the growing network of Critical Zone Observatories and elsewhere is generating new insights into the spatial and temporal variability of the abiotic environment as well as the feedbacks between biological and physical processes that determine the development of ecosystem or critical zone structure. This work harkens back to the fundamental question linking hydrology and ecology: “What happens to the rain?”
Here we review three areas of recent research where different spatial and temporal scales of research that characterize individual disciplines can be used to draw inferences into coupled ecohydrological processes across scales. Specifically, we focus on: 1) small-scale landsurface complexity and energy balance, 2) medium-scale subsurface complexity and topographically driven water subsidy or deficit, and, 3) regional-scale climate-landscape interactions that control the fraction of rain and snow that potentially is available to vegetation. These inferences allow us to build upon one-dimensional models of soil moisture-plant-atmosphere continuum by placing them in complex landscapes. Subsequently, we use this work to identify the biophysical characteristics that result in relative resistance and resilience in the face of ongoing change in climate and land cover.