Effect of Biotic and Abiotic Stress on the Development and Production of Calligonum Polygonoides Subsp.Comosum Grown in Tunisian Arid Conditions

In recent decades, pre-Saharian Tunisian consequences of desertification have gradually become a major environmental problem. We are witnessing the continuous degradation of natural vegetation, due to various human activities. These activities often lead to overgrazing, due to the decline in the size of the course (after cultivation) and increased grazing pressure, manifested by the degradation of the vegetation cover. Such quantitative and / or qualitative degradation is accompanied by irreversible changes in the flora and, therefore, plants are threatened by the dominance of numerous species of animals. To study the effects of seasonal drought and grazing on the parameters of vegetative growth and floristic diversity in canopy, several cuts were made and transects were installed in an experimental plot located in the region of El Ouara (southern Tunisia). Recovery and floristic density were measured during two seasons (fall and spring) with the use of the point quadrat method. The main results of this study show that For physically undisturbed plants, high productions were recorded in spring and summer. However for physically disturbed plants, that is to say, cut twice, the species showed in irrigated and dry higher capacity spring regrowth (cut in February-March). In general, a significant difference of biomass (B) between the two regimes was observed in spring. Grain production was limited to spring in both water regimes. The annual / perennial ratio is more influenced by seasonal drought and the effect of grazing in the sense of a reduction of vegetation cover is more remarkable in the fall. The overall recovery of the vegetation may be considered a good indicator of the structural state of the ecosystem. Alpha and beta diversity is in turn good indicators of ecosystem structure that should be followed in similar studies.