Plant communities of the arid deserts are subjected to several biotic and abiotic stresses, such as high temperatures, repeated drought, and overgrazing. The impacts of protection from grazing for two years on plant diversity, richness, abundance, and community structure were assessed in three sites in each of two major habitats that differ in substrate type (sand dunes and gravel plains) in the Dubai Desert Conservation Reserve. During the two years, the study area received significantly less rainfall than the average. Consequently, it was a good chance to assess the impact of drought and protection from grazing on the community attributes of the two substrate types. In addition, in three sandy sites, enclosures were drip-irrigated with the equivalent of 200 mm rainfalls during a growing season. In all sites, soil physical and chemical properties and several plant community attributes, including density, frequency, species richness (Shannon and Brillouin and Simpson indices). Besides, plant growth and productivity were estimated for each site.
Results/Conclusions
Gravel soil was richer than sandy soils in most nutrients. Besides, the nutrients’ concentrations were greater in the non-protected plots of both sandy and gravel habitats compared to the protected plots. Plant diversity was significantly greater on dunes than gravel plains. Protection for two years significantly increased plant diversity, abundance, and sizes in sandy habitats. However, in gravel plains, protection resulted in a reduction in most community attributes. The reduction was significant in the grazed but not in the protected sites of the gravel plains, indicating that grazing exaggerated the negative effects of drought in that habitat. The positive effect of protection from grazing in sand dunes, despite the drought effect, indicates that many of the dune plants are less affected by drought; many of them were grown nicely after very little rainfalls. Irrigation of both protected and grazed sites on dunes enhanced the establishment of the perennial plants; the species richness and abundance in the irrigated enclosures were twice that in the irrigated open grazed sites. The results conclude that both rainfall and grazing are limiting factors in shaping plant community structure, and their impact is dependent on the soil type
