Population structure and dynamics of Seriphidium herba-alba (Asso) Soják in different habitats in Jardas Jerrari, Al-Jabal Al- Akhdar, Libya

Abstract

Seriphidium herba-alba (Asso) Sojàk is a dwarf shrub fast growing in arid and warm climates and muddy areas at southern Al-Jabal Al- Akhdar, Libya. The present work aims to study the size structure of Seriphidium herba-alba populations in relation to their physiographic and soil conditions. Cover percentage of the species was assessed in ten selected quadrates (20 x 20 m) representing three habitats. The number of individuals of species was counted while the height (H) and mean crown diameter (D) were measured. The size index of each individual was calculated and then used to classify population into 7 size classes: 1 cm size 7 cm. Generally, the height to diameter ratio was less than unity for Seriphidium herba-alba, this means that the diameter of these species tend to expand horizontally rather than vertically , The total size structure of Seriphidium herba-alba in the study area is characterized by the preponderance of the young individuals comparing with the old ones. Five forms of size distributions along the different elevations were recognized: more or less inverse J-shaped distribution, positive skewed distribution, and bell shaped distribution. Soil of the upstream has the highest values of SO4--, Cl-, Ca++, Na+, and K⁺, while, while that of mid-stream has the lowest values. The populations of Jardas Jerrari trees, one of the most important tree components of the desert wadis in the central region of Al-Jabal Al- Akhdar area subjected to tremendous pressure from human impacts. Apart from human caused changes in the unprotected habitats, other biotic and abiotic factors may also play a role in the decline of the plant population.