The effects of browsing on the structure of Acacia tortilis (Forssk.) Hayne ssp raddiana (Savi) Brenan along a gradient of water availability in arid zones of Tunisia
Résumé
In the past, Acacia tortilis colonised thousands of hectares in central and southern Tunisia. Nowadays, A. tortilis is restricted to central Tunisia. The aim of this research was to explore the effects of browsing on the structure of a population of A. tortilis along a gradient of soil water availability. We selected three plant communities differing in soil water availability and pressure of disturbances by livestock (browsing). We explored populations of A. tortilis by measuring dendrometric parameters to check the regeneration potentialities of this tree. We hypothesised that the regeneration of A. tortilis is positively correlated with both soil water content and browsing. The dominance of young trees of A. tortilis demonstrates that this tree definitely shows a natural regeneration mainly in the browsed areas. The variation in water availability regime may have considerable effects on the structure of A. tortilis populations and the regeneration of A. tortilis is positively correlated with water availability. Finally, browsing seems to be a negative factor affecting the general structure of the A. tortilis populations (decreasing in density, canopy cover and canopy diameter) but a positive factor in terms of regeneration (higher abundance of young trees in browsed areas).