The objective of this study was to quantify the effects of protection on herbaceous species composition, total plant cover, dry matter, plant density, floristic richness and diversity. Characteristics of vegetation under continued grazing and protected area for 10 and 65 years were examined in a degraded arid environment in South Tunisia. Our results show that protection enhances significantly (two times) different vegetation parameters. However, long-term protection was found to reduce biomass production, plant density and floristic diversity. Some palatable species such as Stipagrostis ciliata, Helianthemum sessiliflorum, Eragrostis papposa, Echiochilon fruticosum and Cenchrus ciliaris were frequently found in the protected sites. In the grazed site, these species were being replaced by less desirable species: Astragalus armarus, Peganum harmala and Artemisia compestris. This emphasized the importance of conservation stocking rates and proper pasture management.