Patch dynamics in grazed arid ecosystems
Spatially heterogeneous, or patchy, vegetation patterns are widely distributed in arid and semiarid ecosystems and their water-redistributing role is of great ecological interests. Studies have shown effects of rain and wind, vegetation interactions, and disturbances on patch pattern formation and dynamics. In the absence of a synthesis, I have undertaken a review to systematically understand effects of these interacting factors in patch pattern formation and dynamics for two types of spotted and banded patterns. These two patterns are widely distributed and have distinctive, yet complementary features that encompass most of the patch pattern characteristics. I found that: 1) wind is as important as rain in patch pattern formation; 2) shrubs have a facilitation effect on the surrounding vegetation via several mechanisms, and 3) grazing disturbances that include foraging, excretion, and trampling have different effects on vegetation dynamics depending on the patch type and amount of annual precipitation (e.g. wet or dry years).