Plant Diversity along an Elevation Gradient in Hyrcanian Forest of Northern Iran

Abstract

Species diversity is one of the most important and fundamental issues in ecology. The present study was conducted to evaluate effects of elevation gradient on biodiversity in a temperate mountainous forest. For collection of trees' diversity data, 44 sample plots 20 × 20 m2 were set up every 50 m of the elevation interval at the altitude ranging from 100 m to 2250 m a.s.l. Also for collection of data on herbaceous vegetation, five microplots (1 × 2 m) were established (one microplot in the center and four microplots in the four corners of the plot). Species diversity values were analyzed using Simpson and modified Shannon Wiener indices. Also, species richness was calculated using Margalef and Smith-Wilson indices for each plot. The results from Simpson and modified Shannon Wiener biodiversity indices imply approximately bell-shaped diversity curves with the greatest species richness at medium elevations (800–1300 m a.s.l). However, if ecotones (gradual changes between two communities) are excluded, one can conclude that species biodiversity decreases with increasing elevation. The lowland community has the least richness that can be the result of the anthropogenic pressure. The evenness indices for the forest sites along the elevation gradient detected no trend with increasing elevation.