Abstract
There is currently considerable evidence support that plant community structures are driven by plant-plant interactions (e.g., competition and facilitation). In contrast, there is also evidence demonstrating that plant community structure is affected by the impact of consumer pressure (e.g., grazing). In this study, 15 and 10 Acacia gerrardii nurse plants were selected inside and outside Sudyrah natural reserve (protected) area in western Saudi Arabia, respectively. The understory vegetation abundance (e.g. cover and density) was measured among quadrats around the nurse trees in both protected and unprotected areas to examine the impact of grazing and the positive interaction on the understory species. I found that understory vegetation associated with nurse trees (A. gerrardii) has been driven by both the positive impact of nurse plant and the grazing. Although the understory vegetation was positively affected by the impact of facilitation, the composition of such vegetation has been changed due to the impact of herbivory. (C) 2019 Production and hosting by Elsevier B.V.