Current views of plant communities emphasize the importance of competition for resources and colonization ability in determining seedling establishment and plant distributions. Many desert shrubs are surrounded by bare zones that lack other plants or have different suites of species beneath them compared with the open desert surrounding them. Releases of biochemicals as volatiles from leaves, leachates from litter, or exudates from roots have been proposed as mechanisms for this pattern, but such phytotoxicity has been controversial. I tested the hypothesis that experimental clipping of sagebrush foliage enhances its effect as a germination inhibitor. Germination of native forbs and grasses was reduced in association with clipped, compared with unclipped, sagebrush foliage in lath house and field experiments. Sagebrush seeds were not significantly affected. Air contact was required for this inhibition of germination. Soil contact and leaf litter were not required and added little inhibition of germination. These results suggest a potentially large, indirect, and previously overlooked role for interactions between herbivory and germination that could affect plant community structure.
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