Competitive and mutualistic dependencies in multispecies vegetation dynamics enabled by hydraulic redistribution

[1] The goal of this study is to understand the interaction between belowground and aboveground ecohydrologic dynamics as facilitated by hydraulic redistribution. We analyze the partitioning of moisture and energy between tall and understory vegetation, and soil evaporation. Both the competitive and facilitative dependencies are examined using a shared resource model where the soil serves as a common reservoir for the interaction between the different vegetation species. The moisture state of the reservoir is altered by the addition and withdrawal by vegetation roots in conjunction with soil-moisture transport. Vertical patterns of soil moisture state and uptake reflect the nonlinear interactions between vegetation species. The study is performed using data from the Blodgett Forest Ameriflux site in the Sierra Nevada Mountains of California. The Mediterranean climate of the region, with wet winters and long dry summers, offers an ideal environment for the study. The results indicate that deep layer uptake of water by the tall vegetation and its release in the shallow layers enhances the productivity of the understory vegetation during the summer. The presence of understory vegetation reduces direct soil-evaporative loss making more moisture available for vegetation which enhances the total ecosystem productivity. The litter layer is also found to play an important role in the partitioning of the water and energy fluxes by damping the radiation reaching the soil and thereby reducing water loss due to soil evaporation.