Ecohydrology of a seasonal cloud forest in Dhofar: 2. Role of clouds, soil type, and rooting depth in tree-grass competition

Using a dynamic ecosystem model, we investigate the role of summer cloud immersion in the ecohydrology of a seasonal deciduous forest in Oman. This is a semiarid region where vegetation is immersed in dense cloud during a 3-month-long monsoon season. The simulated vegetation at equilibrium depends strongly on cloud cover during the wet season, with trees predicted under cloudy conditions and grasses when assuming a cloud-free monsoon. By varying soil type and rooting depth, we identify a rooting depth at which tree performance is optimal. This is the depth at which transpiration is maximized and the sum of all other fluxes from the soil is minimized. Our analysis shows that cloud cover creates a favorable seasonality in this ecosystem that is crucial for maintaining trees. This is achieved by (1) prolonging the growing season from 3 months to 6 months and (2) allowing deeper infiltration, which assures competitiveness of trees in an otherwise too dry environment.