Interactions of Acacia tortilis (Forsk.) subpsp. raddiana (Savi) with herbaceous vegetation in relation with tree size under North African Presaharan Region

Twelve individuals were selected to determine the effects of tree size (crown area) on herbaceous species composition,total cover,perennial and annual species density,species number and floristic diversity in an acacia tortilis subsp. raddiana (savi) pseudo-savanna in southeastern tunisia. except for annual species density,all vegetation parameters were increased under tree canopy compared to the open area. tree size appeared to affect tree herbaceous interaction. the positive effect of acacia tree in herbaceous vegetation increases with tree size.