Environmental Gradients as Context Modifying Grazing Effects on Plant Communities in Arid Rangelands of Southern Tunisia

Arid rangelands face increasing threats from grazing pressure and climate variability, yet the combined effects of grazing intensity and environmental gradients on plant community structure remain poorly understood. This study investigates grazing impacts on plant communities in southern Tunisia using floristic composition, ecological indicators, and indicator species across 500 plots representing low, moderate, and high grazing intensities. Vegetation surveys during peak growth recorded 386 vascular plant species. Species diversity peaked under moderate grazing (H’ = 5.46), consistent with the Intermediate Disturbance Hypothesis, but was strongly influenced by soil nitrogen (r2 = 0.692). Heavy grazing reduced diversity (H’ = 4.82), especially in nitrogen-poor sites, indicating that environmental stress amplifies grazing effects. Indicator species analysis identified 113 significant taxa, including 42 associated with moderate grazing, reflecting compositional rather than functional responses. Redundancy analysis showed that environmental variables explained 67% of community variance, with soil nitrogen as the dominant gradient, followed by sand content, minimum temperature, and longitude. Ordination analyses revealed distinct assemblages under high grazing intensity associated with sandy, nutrient-poor soils. These findings demonstrate that grazing impacts are highly context-dependent and support the need for site-specific, soil-informed grazing management under increasing climate stress.