Elevational gradient and vegetation-environmental relationships in the central Caspian forests of northern Iran
8 September 2015
Moradi, Halime; Naqinezhad, Alireza; Siadati, Soudeh; Yousefi, Yadollah; Attar, Farideh; Etemad, Vahid; Reif, AlbertTertiary-relict Hyrcanian (Caspian) forests along the shores of the southern Caspian Sea isare centers of high biodiversity; however, there is little information on plant diversity patterns in this area. This study evaluated the plant diversity, variation in life forms, and geographical distribution of the zonal vegetation types and their relationships with environmental variables in the educational and experimental forest of Kheyrudkenar, an important protected area in the central Hyrcanian forest of northern Iran. For this purpose, 226 vegetation plots of 400 m2 were laid out along two altitudinal transects from the lowlands (100 m a.s.l.) to the timberline (2000 m a.s.l.). Four vegetation types were identified using modified TWINSPAN, and indirect (DCA) and direct (CCA) gradient analyses. Species-related (species diversity indices, life form and phytogeographical elements) and environmental variables (climate, topographic and soil variables) were calculated and subjected to one-way ANOVA and Pearson analyses amongbetween the vegetation types. Both constrained (CCA) and unconstrained (DCA) ordination analyses showed an almost identical variation of the floristic composition along their axes. Two main gradients occur in the Hyracanian forest. Elevation together with annual precipitation and mean annual temperature are were the most important factors controlling the floristic composition in the area. Topographic features such as slope inclination and heat index was shown to be effective within an elevation zone/vegetation type. Soil physical and chemical properties have had the secondarysecond level of importance on the separation of vegetation types. Subsequent research can split these environmental factor complexes, allowing a finer distinction of vegetation patterns and identification of ecological species groups. This knowledge will be useful for forest management and conservation practices in the Hyrcanian area with its distinct and, unique flora and vegetation.