The restoration technique importance resides on the assessment of its impact on biodiversity. This assessment is possible by the use of some environmental indicators extracted from a diachronic study of land cover changes in protected areas. Our study is carried out with the evaluation of some indicators inside Sidi Toui national park. These indicators are measured on the one hand from a land cover map of 1988 (3 years before the creation of the park) and the map of 2007 on the other hand (16 years after the park creation). An important landscape heterogeneity, as a result of the progressive vegetation dynamic, was observed in 2007. This heterogeneity is indicated by an increasing of the Shannon diversity index under fencing impacts. The majority of 1988 vegetation units are replaced by new ones in 2007. The cover of all vegetation units is more important in 2007. 1. Introduction It is considered that the Mediterranean region, subjected to pronounced climatic and edaphic droughts, does not contain any unaltered terrestrial ecosystems [1–3]. In Presaharian Tunisia, defined by Floret and Pontanier [4] as the zone located between the isohyets 100 and 200？mm, the consequences of desertification became progressively a major environmental problem during the last decades [5]. In this zone the natural vegetation cover, mainly composed by very sparse steppic vegetation units, is altered by various human activities [6, 7]. Usually these activities lead to overgrazing after losing rangeland area (cultivation and ploughing impact) and increasing the number of animals (mainly sheep and goats). In order to protect natural vegetation units and limit their degradation, it should be necessary to decrease the human impact and enhance the ecosystems regeneration. This last can be carried out with protection, reducing grazing pressure and soil fertility improvement [8, 9]. Otherwise, it is necessary to identify and to use a lot of ecological indicators [10] in order to facilitate the vegetation dynamic monitoring. The environmental monitoring indicators can be considered like a particular case of indicators ([11] (OSS: Observatoire du Sahara et du Sahel (Sahara and Sahel Observatory); ROSELT: Réseau d’Observatoires de Surveillance écologique à Long-Terme (Long-Term Ecological Monitoring Observatories Network))). They permit, on the basis of data collected from the observation sites, the invention of structural elements describing and valuing the environmental status. These indicators are considered like an adapted tool for the natural resource managers and policies makers.
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