Scale-dependent interactions between vegetation, landscape, and climate: How critical zone structure influences ecohydrological reslience in a rapidly changing world

Abstract:

Concurrent changes in climate, land cover, and population are pushing coupled human and natural systems outside of the historical range of natural variability, presenting major challenges to the management of natural and built environments worldwide. A comprehensive understanding of how precipitation is partitioned to ecosystem and societal water resources is central to many of these challenges. Although considerable progress has been made advancing process understanding and developing ecohydrological models, a key challenge remains applying this knowledge to landscape and regional scales of resource management. Approaches to address this challenge, ranging from deterministic to probabilistic models, all face the challenge of identifying scale breaks in the coupling between biotic and abiotic processes.

We employ an alternative, complementary approach, combining newer observations (e.g. high resolution aerial LiDAR; isotopes) and established techniques to identify scale breaks and transitions in how ecological processes, occurring on relatively short timescales, are coupled to longer-term development of critical zone, that typically develops over longer time scales. At stand scales, vegetation structure strongly controls the fraction of precipitation partitioned to evaporation by influencing both solar radiation and turbulence with a net change in effective precipitation (water available for transpiration, recharge, or streamflow) of as much as 25%. At hillslope scales, topographic shading or exposure has similar magnitude effects on total evapotranspiration, while topographically driven water subsidy can double carbon storage through increases in both tree size and number. At catchment-scales, the coupling between vegetation, climate, and the physical landscape results in a predictable signature in hydrologic partitioning that reflects regional susceptibility to drought. Importantly, these transitions in biophysical interactions, occurring at scales from 0.01 to 10⁶ ha, can be used both to constrain predictive models while directly informing management decisions by identifying areas where vegetation or streamflow is more or less at risk to climate change.