Caspian J. Environ. Sci. Vol. 19 No. 2 pp. 317~323 Received: Oct. 08. 2020 Accepted: Feb. 17. 2021 DOI: Article type: Research ©Copyright by University of Guilan, Printed in I.R. Iran Ecotones and forest communities along an elevation gradient in Hyrcanian forests, north of Iran Ashagh Ataei, Farid Kazemnezhad * , Majid Eshagh Nimvari, Ali Sheykholeslami Department of Forestry, Chalus Branch, Islamic Azad University, Chalus, Iran * Corresponding author’s E-mail: farid@iauc.ir ABSTRACT A comprehensive understanding of plant associations, especially in transition areas can be achieved by identification of vegetation and study of relationships between plant species and environment. Borders of ecotones and forest communities (Tiremrud basin in the southern part of Tonekabon, Iran) were found based on environmental factors such as elevation, slope and changes in floristic patterns. Totally, 44 plots (20 × 20 m) were collected by the transect method with at least one sample plot per contour line and 50 m interval. A total number of tree species was recorded separately in each sample plot. Herbaceous species were sampled based on the Brown-Blanket cover percentage and frequency of vegetative elements by 5 × 2 m 2 micro plots in four corners and centre of each main plot. Four ecological groups were identified on altitudes 2070, 1236, 924, and 375 m above sea level with mean slopes of 43, 50, 40, and 59%, respectively. The first and fourth ecological groups were at the highest and the lowest elevations, respectively, while the second and third ones in the middle of the two groups. A comparison of ecological groups in terms of plant biodiversity indicated significant differences altogether. In terms of species diversity indices, Shannon-Wiener and Simpson-Pilo revealed that the first, fourth, and second ecological groups had maximum, minimum, and average values, respectively. According to findings of this study, ecological groups had significant differences in terms of altitude factor. Keywords: Shannon-Wiener and Simpson species diversity, biodiversity. INTRODUCTION Conservation, maintenance, and management of natural resources require a comprehensive understanding of these issues. It is therefore, essential to utilize plant ecology and sociology to determine and identify endogenous environments, environmental uniformity, sequences and stages, as well as plant communities. Noteworthy, understanding the plant communities encompasses identification of habitats and prediction of floristic evolution in a given environment, since the emergence of vegetation is a result of the interaction between vegetative elements and physical environmental factors. Given the number of effective factors, if these factors are all equivalent and independent of each other, the variety of possible combinations would be very significant . Climate and topography are among the most fundamental drivers of plant diversity (Zhang et al. 2017). It is essential to identify and study vegetation in applied studies for solving ecological issues related to the management and conservation of natural ecosystems (De Bello et al. 2005, Díaz et al. 2007). Plants reflect a set of environmental conditions including climate, humidity, and soil variables (Muller- Dombois & Ellenberg 1974, Guilemette & Desrochers 2008, Kaufmann et al. 2017) and changes in vegetation results from the dominance of environmental factors (Awasthi et al. 2015). Species and species diversity are distributed along differing environmental gradients (Hortal et al. 2013, Slaton 2015). Development and distribution of plant species in nature are not by accident, but those with similar nature and ecological needs in nature are brought together to form plant communities. The correlation of these factors with plant communities could be determined by the study of plant communities and the analysis of different environmental gradients. The identification of plant