PJB-2018-761
Do exotic trees threaten southern arid areas of Tunisia? A case study
Zouhaier Noumi
Abstract
Aims This study was conducted in an afforested Stipa tenacissima steppe in arid southern Tunisia during the years 2012 and 2013. It aims to compare the effects of exotic and native planted trees (Acacia salicina and Pinus halepensis, respectively) on the understory vegetation and soil properties. Methods For each tree species, two sub-habitats were distinguished: the canopied sub-habitat (under the tree crown) and the un-canopied sub-habitat (open grassland). Soil moisture was measured in both sub-habitats at 10 cm depth. In parallel to soil moisture, we investigated the effect of tree species on soil fertility. Soil samples were collected from the upper 10 cm soil, excluding litter and stones. For vegetation structure, we determined floristic composition, species density (mean number of individuals of each species per plot), species richness, total plant cover (%) and dry matter. Important Findings The nutrient status of soil (organic matter, total N, extractable P) was found to be significantly higher under A. salicina compared to P. halepensis and open areas. This tendency remained constant with the soil water content which was significantly higher under trees compared to open sub-habitats. For water content, there were no significant differences between studied trees. Total plant cover, species richness and the density of perennial species were significantly higher under the exotic species compared to other sub-habitats. Among the two tree species, Acacia salicina had the strongest positive effect on the understory vegetation. It seems to be more useful as a restoration tool in arid areas and more suitable to create islands of resources and foster succession than the other investigated tree species.
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