Continuous or discrete-an altitudinal transect of vegetation and soil on a de-glaciated Valley, Western Himalaya, Pakistan

The study area is a Himalayan forest-alpine ecotone extending over a 100 km north to south transect. The altitudinal change in vegetation was studied between 2000 m, a.s.l. and 4100 m, a.s.l. to test the vegetation pattern either continuum or zonation. A total of 300 species of vascular plants occurred in 280 repeated samples of 0.1ha at 14 sites. Ordination (DCA) and classificatory techniques were used to examine these data. The major axes brought out by DCA were related to altitude and its associated climatic factors, although it is possible to relate the units of classification to broad soil types. The overlay of the classification groups on the ordination axes indicated that the vegetation closely followed a topographic sequence and the vegetation composition changed continuously with altitude. No clearly disjunct vegetation patterns emerged and the distribution of samples and species along two axes of ordination resemble more closely to the continuous nature of the vegetation than to the grouping produced by classification. The distribution of plant species along the altitudinal transects support the individualistic hypothesis of community organization.