DeMalach, N., Department of Biology, Stanford University, Stanford, CA, United States;  Shachak, M., Blaustein Institutes of Desert Research, Ben-Gurion University of the Negev, Sede-Boker Campus, Israel

We aimed to study the effect of resource redistribution on annual plant species diversity in Runoff-Harvesting Systems, termed limans, along the runoff pathway in a watershed. We tested the effect of resource redistribution (water and nutrients) relative role of biomass, grass and forb abundance as mediators of species diversity. Our research was conducted in five small watersheds located in the central Negev Highlands, Israel. We quantified nutrient addition including soil nitrogen, phosphorus, potassium, total water content, and soil organic matter, in the liman, compared with two microsites (upstream, and downstream) along watersheds. We quantified biomass, grass and forb abundance and species richness in two successive years. We used structural equation modeling to study the effect of grass and forb abundance and biomass on the species richness of herbaceous plant communities. All tested soil properties significantly improved in the liman compared with the two microsites. Annual biomass increased significantly in the liman in compared with the downstream microsite. Our results also indicate a reduction in forb abundance in the liman and the downstream, and increment in the grass abundance in the liman microsite, leading to a decline in plant species richness. We conclude that diversity responses to biomass production are both resource-specific and functional group-specific. © 2019