Köchy, M., and F. Jeltsch (2006)
To improve the understanding of consequences of climate change for annual plant communities, we used a detailed, spatially explicit model that simulates the effect of daily rainfall variability on individual plants in the eastern Mediterrenean. The model explicitly considers moisture storage in the soil. We manipulated daily rainfall variability by increasing the number of days with rainstorms (NDR) and decreasing intervals between rainy days while keeping the annual volume constant. In factorial combination, we also increased mean annual precipitation (MAP). Increasing NDR decreased establishment when MAP was >200 mm but increased establishment in more arid sites. The negative effect of NDR reversed in sites with <600 mm MAP as plants matured. These patterns were strongly tied to water availability in upper and lower soil layers and modified by competition among seedlings and adults. Increasing MAP generally increased water availability, establishment, and biomass. The order of magnitudes of NDR and MAP overlapped partially so that their combined effect is important for projections of climate change effects on annual vegetation. The effect size of MAP and NDR followed a sigmoid curve along the MAP gradient indicating that the semi-arid region (300 mm MAP) is the most sensitive to precipitation change.