Altitudinal Zonation of Perennial Vegetation in Al-Jabal Al-Akhdar Forest Ecosystem, Libya

Abstract

This study aimed to investigate the impact of altitudinal gradients on diversity, species composition, and dominance structures of perennial plant cover in Al-Jabal Al-Akhdar (the Green Mountain) forest in northeastern Libya. The research was conducted along a 5 km wide elevational transect, extending from sea level near Ras Al-Helal village to 650 m near Lamlouda village, the transect was stratified into three elevation levels: Level A (High: 434–650 m), Level B (Mid: 217–434 m), and Level C (Coastal: 0–217 m). At each level, perennial plant species were systematically recorded and quantitatively assessed for frequency, Abundance, and density. The study recorded a total of 12 perennial species at the high level, and 15 species each at the mid and coastal levels. A clear hump-shaped pattern of species richness was observed, with peak diversity at mid-elevations. The dominance structure shifted markedly across the gradient: Level A was strongly co-dominated by Ononis mitissima (30.2% cover) and Pistacia lentiscus (24.5% cover). Level B exhibited a more balanced co-dominance of four species, including Rhamnus alaternus (18.8% cover) and Juniperus phoenicea (15.6% cover). Level C was overwhelmingly dominated by Juniperus phoenicea (33.3% cover). Key species showed significant shifts in cover with elevation; Juniperus phoenicea increased with altitude, while Pistacia lentiscus decreased. The vegetation structure in Al-Jabal Al-Akhdar follows a distinct elevational gradient driven by a combination of abiotic filtering (climate, soil factors) and biotic interactions. The results confirm the classic hump-shaped diversity pattern for perennial plants, aligning with global and Mediterranean mountain studies.