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Kangaroo rats are thought to play a role in promoting the establishment of woody shrubs in arid grasslands by caching mesquite seeds. We examined this hypothesis experimentally by comparing mesquite establishment on plots from which kangaroo rats have been continuously removed for either 10 or 21 years to control plots with kangaroo rats present. Contrary to the above hypothesis, mesquite establishment was lowest on plots that contained kangaroo rats and highest on plots from which kangaroo rats have been absent for 21 years. We suggest that herbivory, either by kangaroo rats or lagomorphs, who were found to be more active on plots with kangaroo rats, more negatively affects mesquite seedling establishment than the potential positive effects of kangaroo rat seed-caching behavior in arid grasslands. (C) 2001 Academic Press.