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Acacia tortilis subsp. raddiana is one of the most uncommon species and is still present in North African regions. Indeed, the region of Bled Talah, in the south of Tunisia, constitutes today an ecosystem where the species continues to grow on a large surface of 16,488 ha. There is little information on the long-term dynamics of Acacia trees. The overall objectives of this study are to know the total individuals of Acacia trees which help to assess the density, to study the structure of Acacia population, to estimate the age of Acacia population and to determine the effects of A. tortilis canopy on soil properties. In this context, all individuals of A. tortilis covering 5,114 ha in the National Park Bov Hedma, were systematically counted. Many dendrometric parameters were measured. In our study, age determination of A. tortilis is based on the counting of rings. Our results show that the population of A. tortilis subsp. raddiana in the region of Bou Hedma is characterised by an irregular structure, involved in a regressive dynamic. They show also that A. tortilis trees improve soil water availability and the nutrient status of soil.