USING EXOTIC SHRUBS AS A RESTORATION TOOL IN TUNISIAN ARID AREAS: EFFECTS ON UNDERSTOREY VEGETATION AND SOIL NUTRIENTS

In this study, the effects of exotic and native shrubs Acacia salicinaand Retama raetamon understory vegetation and soil properties were assessed. Two sub-habitats, acanopied and anun-canopied sub-habitat (open grassland), were distinguished for each shrub species. Soil moisture was measured in both sub-habitats at 10 cm depth, and soil samples collected from theupper 10 cm soil, excluding litter and stones. Aboveground biomass, species density and species richness were also estimated. The soil organic matter, total N and extractable P were significantly higher under shrubs than open areas at all soil water contents. Soil water content did not differ significantly between studied shrubs. Aboveground biomass, species richness and the density of perennial species were significantly higher under shrub canopiesthan open areas. Among the two studied shrubs species, Retama raetamdisplayed the strongest positive effect, but without significant differences, on the understory vegetation. From this perspective, exotic shrubs can be regarded as a powerful and promising candidate that can be invested in not only theelaboration of multiple restoration programs but also in the generation of islands of resources.