Size Structure and Floristic Diversity of Acacia trees population in Taif Area, Saudi Arabia

摘要

Acacia trees are considered keystone species in many desert ecosystems and suffer from different anthropogenic effects. This study estimated the size structure of Acacia trees population in El-Taif area, which indicated that all the populations of Acacia present in El-Taif Area seems to be young as the proportion of small and medium individuals is greater than that of large individuals except the species Acacia albida. Absence of plant species under the canopy of Acacia trees may be due to the severe impact of grazing. In general, distribution of Acacia trees is controlled by physiographic features, and topographical irregularities. Phytosociologically, the area is inhabited by (79) species belonging to (59) genera and related to (26) families. the most characteristic family is Fabaceae (16 species) followed by Asteraceae (15 species). The life-form spectrum in the present study is characteristic of an arid desert region with the dominance of chamaephytes (43% of the recorded species) followed by phanerophytes (31%), therophytes (16%) and hemicryptophytes (10%). The preponderance of annuals and shrubs reflects a typical desert flora, where it is closely related to topography. Phytogeographically, the shrub layer is composed mainly of the Saharo-Arabian with a Sudano-Zambezian focus on distribution. Pure Mediterranean taxa are not represented in the therophyte and chamaephyte layers, whereas they are represented in the bi- and pluriregional taxa. This may be attributed to the fact that plants of the Saharo-Arabian region are good indicators for desert environmental conditions, while Mediterranean species represent more mesic environments.