Background/Question/Methods Water loss by soil evaporation is a critical ecohydrological process in drylands. Soil evaporation rates vary spatially with vegetation cover, as well as temporally with season and phenology, but the effects of vegetation cover are not necessarily straightforward. The effects of vegetation cover may depend on differences in overstory and litter cover in patches of woody plants, intercanopy patches that separate them, and the overall vegetation mosaic as a function of amount of woody plant cover, and/or seasonality associated with leaf phenology and climate. We assessed these interactive effects for mesquite-dominated (Prosopis velutina) ecosystems within the region of the North American monsoon, where soil evaporation rates and their seasonal variability can be particularly high. We experimentally quantified soil evaporation rates with microlysimeters at six densities of overstory canopy cover for canopy and intercanopy locations, both with and without litter.

Results/Conclusions Our results reveal seasonally-associated limitations on soil evaporation among incoming energy, patch-and/or vegetation-mosaic scale effects on energy and/or turbulence, or none of the above. These interactive and seasonally-dependent effects of vegetation cover on soil evaporation are not currently accounted for in most modeling approaches and may have widespread ecohydrological significance for drylands.