Classification and ordination of the main plant communities of the Eastern Hajar Mountains, Oman

This article presents a quantitative description of the plant communities of the Eastern Hajar Mountains of Oman and the primary environmental variables affecting their composition and distribution. Species inventories and environmental data were collected from 110 vegetation plots covering elevation from 1000 m to the highest point in the mountains at about 2200 m. Measurements of 12 environmental variables were used in the analysis: aspect, slope, annual rainfall, soil pH, salinity, soil nutrients (N, P, K, Ca) and soil texture (clay and silt). Two Way Indicator Species Analysis (TWINSPAN) classification, Detrended Correspondence Analysis (DCA) and Canonical Correspondence Analysis (CCA) ordinations showed four well-distinguished plant communities. Although some species overlap occurred in the transition zones between the communities, these plant communities were characteristic for their zones. Annual rainfall, total nitrogen and total calcium were the most important environmental factors affecting the distribution of plant communities. The high-altitude community was always distinctly identified using all different data treatments, while the lower-altitude communities tended mostly to overlap. Any grazing effect on plant community distribution appears to be overridden by the other environmental variables.