Relationships between tree species composition, soil properties and topographic factors in a temperate deciduous forest in northern Iran

A study to establish relationships between tree species, soil properties and topographic factors was carried out in one section of the Caspian (Hyrcanian) forest in the north of Iran. Two-Way Indicator Species Analysis (TWINSPAN) classified basal areas of tree species from 325 tree plots and were ordinate using Detrended Correspondence Analysis (DCA). Several physical and chemical properties of soil, altitude, aspect and slope were determined for a sub-sample of 83 plots amongst 325 tree plots. Oriental beech (Fagus orientalis Lipsky.) and hornbeam (Carpinus betulus Linn.) were the two most important tree species in this forest, although 11 other tree species were also present. A majority of the plots at lower altitudes were dominated by hornbeam, while beech dominated in plots at higher altitude. C% and C/N in the soil surface were significantly associated with tree species composition and altitude. C/N and carbon storage increased at higher altitude, where beech tree is dominant, while those at low altitude or with low C/N ratio were dominated by hornbeam. Although the main gradient of tree species composition, Fagus-Carpinus gradient, described by C%, C/N and altitude, distribution of Quercus castaneifolia, Acer spp. Tilia platyphyllos, as the main other tree species in the study site, explained by the other soil properties, such as bulk density and soil texture.