Multiscale partitioning effects of livestock grazing management on plant community composition and diversity in arid rangelands.

Arid steppe rangelands in North Africa are highly significant ecosystems that are exceedingly sensitive to global warming and are also influenced by severe grazing and heavy utilization practices. Consequently, it is imperative to conduct extensive investigations regarding the impact of overgrazing due to increased sheep populations on plant diversity in these regions. The objective of this study is to examine the effect of two grazing managements (grazing-excluded vs. free-grazing) on floristic diversity in the arid steppe rangelands of North Africa. Sampling encompassed 10 sites, with 5 freely accessible to livestock and 5 protected from grazing. Within each site, three 200-m transects were established to survey and quantify plant species abundance. Alpha (species richness and diversity) and beta (qualitative and quantitative similarity analysis) biodiversity parameters were evaluated at both small and large spatial scales. The findings demonstrated a substantial disparity in plant diversity between grazing-excluded rangelands and free-grazed rangelands. Plant community diversity and stability parameters were notably higher in grazing-excluded areas. The taxonomic structure of plant communities also exhibited greater stability in grazing-excluded steppe areas. Specifically, the grazing-excluded sites displayed superior diversity metrics, including species richness (93), Shannon index (3.2), and Simpson reciprocal index (5.5), in comparison to severely grazed sites (61, 2.6, and 4.4), respectively). The influence of severe grazing had a more pronounced effect on ephemeral species rather than perennials, emphasizing the heightened vulnerability of these plants to overgrazing effect or inadequate grassland management practices. This effect coincided with heterogeneity in floristic composition between sites with free continuous livestock access and those protected from grazing. Furthermore, analysis of similarity at different spatial scales revealed an increase in diversity at small scales contrasted with a decrease at larger scales. Grazing exerted discernible effects on floristic composition, particularly affecting ephemeral species, albeit primarily at small scales. At larger scales, the impact of grazing was not detected. These findings underscore the complex relationship between grazing practices and plant diversity dynamics in arid steppe ecosystems, emphasizing the importance of sustainable management strategies to preserve biodiversity in these vulnerable habitats.