Partitioning floristic variance in a part of mountain rangeland of central Alborz due to soil and topographic factors

Knowledge of environmental factors and their effects on vegetation is necessary for sound rangeland management. In this study we applied multivariate analyses to determine the effects of soil and topography on upland rangeland vegetation and also the amount of variance explained by them. 30 homogenous units according to slope, aspect and elevation were determined and then vegetation was sampled in 320 plots (1x1 m). This was done along transects and cover percentage of each species present in each plot was recorded. Also, up to 3 soil samples were taken in each homogenous unit. Result of cluster analysis showed a total of 12 sub-association of vegetation and then we described them according their species composition. Thereafter, results of ordination methods showed that two measured environmental factors significantly influenced vegetation. Here we first found five groups of species in DCA analysis. Then using CCA we found how these groups were related to specific environmental factor. Also 12 sub-association of vegetation showed some correlation with environmental factors. Variance partitioning showed that 57.4% of vegetation changes in this mountain rangeland was explained by soil properties and this was only 39.4% for topographic factors. The combined effect of two factors was responsible only for 3.2% of vegetation changes.