Proximity to other plants determines the effect of livestock exclusion on eight species in the semiarid scrublands of Mexico

Abstract

Exclusions are one of the most used methodologies to study the effects of herbivores on ecosystems. Although long periods are needed to detect changes in species composition, the responses of perennial plants may be visible in the short term. The ability of plants to tolerate herbivory may be influenced by the availability of resources and nearby vegetation. The aim of this study is to assess the effect of proximity to other plants on the response of adult plants to livestock exclusion. After 3 years of exclusion, we quantify the differences in size (height and canopy size) and reproductive organ production in eight predominant shrubs species. We consider three neighborhood conditions: Alone, Partially or Completely covered. Our results showed that palatable species present larger sizes inside the exclusion areas. Neighborhood influence depended on the studied species. The density of reproductive organs decreased with exclusion for four species, and proximity to neighboring plants had different effects depending on the species. The species that showed greater size inside the exclusion areas when they were Partially and/or Completely covered by other plants and did not show the same pattern for reproductive organ production, which indicated a possible process of light competition. Four of the eight species presented greater size and/or density of reproductive organs on Alone plants, especially inside the exclusion areas, which suggested that herbivore exclusion can intensify competition among plants. The present study showed that the effect of the exclusion of livestock grazing was affected by plant–plant interactions, which may affect the changes in the composition of the plant community found after permanent removal of livestock.