Seed germination of two woody species (Periploca angustifolia and Rhus tripartita), indigenous plants from arid and semi—arid regions of Tunisia, were assessed under controlled conditions by determining the optimum temperature of germination and simulating drought stress using PEG 6000 and salt stress using different concentrations of NaCl. The germination response of the seeds in darkness were determined over a wide range of temperatures (10 °C to 30 °C), salinity (0 mM to 400 mM) and water stress (0 MPa to—3 MPa). Our results suggest that germination percentage is influenced by salt and osmotic stress at 25 °C and 15 °C respectively for P. angustifolia and R. tripartita which represent their optimum temperature of germination. However, studied species responded differently to stress induced by NaCl and PEG 6000. P. angustifolia manifested better adaptation to drought conditions compared to R. tripartita. These findings form the basis for future trials involving the use of indigenous shrubs in the restoration of rangelands.

The main objective of this study is to determine the possible reasons for regeneration failure of Acacia tortilis subsp. raddiana (Fabaceae). We conducted some laboratory experiments, simulating natural conditions. We estimated rate of infestation of seeds by Bruchidius raddianae and B. aurivillil and tested the autotoxicity effect of leaf extracts (different concentrations) of A. tortilis in the laboratory at 30 °C (optimum germination temperature). Results show that the inhibitory effect on germination increase with the increased leaf extract concentration. At 100% concentration, a significant reduction of germination rate was found compared to other concentrations. On the other hand, the study also revealed a high infestation rate of seeds by B. raddianae and B. aurivillil which reduces the possibility in inhibits natural regeneration in A. tortilis.

Interactions between plants (competition and facilitation) in terrestrial ecosystems include: (1) short-term effects primarily quantified with experimental removals; and (2) long-term effects primarily quantified with observational methods. This study, conducted in the National Park of Bou Hedma, examined (1) the relative contributions of short-term canopy and long-term soil effects of a shrub species in explaining differences in biomass, species diversity (richness) and species density of understory plants (i) between shrubs and open areas, (ii) between shrubs and removed shrubs; and (2) the role of grazing in driving changes in direction of short-term and long-term effects in shrub/understory species interactions.Differences in species richness, density and biomass of understorey communities between shrub removed and open areas were mostly due to long-term soil effects, whereas differences beneath shrubs and shrub removed were due to short-term canopy effects, in particular on soil water content.Our study provides the positive effect of savannas shrubs on the understorey vegetation biomass, species density and diversity in arid ecosystems. Additionally, grazing by large herbivores negatively influenced the dynamics of vegetation under an arid bioclimate.