Epiphytic bryophyte communities of southwestern Arabia - phytosociology, ecology and life strategies
Based on a phytosociological analysis, the epiphytic Leptodonto-Leucodontetum schweinfurthii and Orthotricho-Fabronietum socotranae were described from southwestern Arabia (Asir Mts. of Saudi Arabia, Yemen escarpment mountains). Both are typical of the monsoon-affected Juniperus procera, respectively Acacia origena woodland and form one of the most striking vegetation units on the Arabian Peninsula. Character species mainly are drought-tolerant Afromontane mosses. Higher-ranked character species, such as Orthotrichum diaphanum and Syntrichia laevipila allow to classify the new communities within the Syntrichion laevipilae alliance that reach a southern outpost in the southwestern Arabian border mountains. In addition to the syntaxonomic and ecological descriptions of the communities, a life form and life strategy analysis has been carried out. The analysis indicates that life forms and life strategies clearly correlate with the ecological site conditions. The drought-tolerant, photo- and xerophytic Orthotricho-Fabronietum socotranae is dominated by cushion, short-turf and mat forming perennial stayers with regular sporophyte formation. By contrast, tail or fan forming pleurocarpous perennial shuttle species with large spores indicating short-range dispersal and a 'passive' (e. g., moderatey low reproduction) or 'generative' reproduction, as well as liverworts, concentrate in the sciophytic, subhumid Leptodonto-Leucodontetum schweinfurthii. In additon, the latter association shows a much higer diversity in life forms and life strategies.