Do mosses serve as sink for rain in the Negev Desert? A theoretical and experimental approach

Regarded as highly developed crusts, thick moss-dominated crust (MDC) provides a relatively thick protective layer over sand dunes which, together with cyanobacteria-dominated crust (CDC) play an important role in their stabilization. It was previously claimed that due to their thickness and high organic matter, MDC may serve as sink for rain in the Negev and consequently reduce water infiltration and cause shrub mortality. Due to the relatively short rainy period, we hypothesized that MDC may not serve as a potent sink for rainwater and may therefore not be responsible for plant mortality. Toward this end, the infiltration depth of sand underlying MDC and CDC was measured following sprinkling experiments and natural rain events. Whereas MDC was relatively effective in intercepting low-depth rain events (intercepting additional 0.8 mm in comparison to CDC), no significant differences in the infiltration depth were found between MDC and CDC following high-depth or consecutive rain events. Based on these measurements and long-term calculations it is concluded that MDCs does not have a significant effect on rain infiltration in the Negev and therefore cannot be held responsible for shrub mortality. Management practices that call for the reduction in MDC cover should therefore be reconsidered.