Role of Hydraulic Redistribution in Enhancing Multi-Species Vegetation Interaction and Ecosystem Productivity

The objective of our study is to understand the role of hydraulic redistribution (HR) in the interaction of above- and below-ground ecohydrologic dynamics using a modeling approach. Specifically we explore the role of HR in regulating the partitioning and tradeoffs of hydrologic fluxes between tall (Ponderosa Pine) and understory (Manzanita shrubs) vegetation and soil-evaporation. This is accomplished using a "shared resource model" where the soil serves as a common reservoir whose state is altered by the addition and withdrawal of moisture by vegetation roots in conjunction with its own moisture transport dynamics, and the non-linear dependence of vegetation uptake and release on the existing soil-moisture state. We explore how the presence of multiple species induces competitive tradeoffs in water utilization but mutualistic benefits in ecosystem productivity. Our study establishes that the tradeoff in water use occurs in a way that benefits both the tall and understory vegetation and facilitates increase in total ecosystem productivity. Further, the presence of the litter layer enhances ecosystem productivity. The study is performed for the Ameriflux study site at the Blodgett Forest in the Sierra Nevada Mountains in California. The Mediterranean climate of the region provides an ideal condition where the deep layer moisture, through hydraulic lift, supports the ecosystem productivity during the long dry summers and the wet winters replenish the soil-moisture through hydraulic descent.