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Protected areas such as national parks are often assumed to be the best way to conserve plant diversity and maintain ecosystem composition and structure. To evaluate this assertion, we sampled two areas with two different levels of grazing: a national park where the protection level was high and an open area where human populations have unrestricted access to ecosystem resources. Species diversity (Shannon diversity index, species richness), species cover, perennial species density, plant biomass and total plant cover were determined inside and outside the park. Results show considerable and positive effects of protection on the parameters scored. Some species known by it high palatability such as Cenchrus ciliaris, Salvia aegyptiaca, Echiochilon fruticosum and Helianthemum sessiliflorum are more abundant in the protected area