Impact of some physiographic and edaphic factors on quantitative and qualitative characteristics of Juniper forest (Case study: Layen region –Khorasan)

In order to investigate the effect of environmental factors including slope, aspect and elevation on quantitative and qualitative characteristics of Juniperus excelsa subsp. polycarpus, Juniper stands were selected in Hezar Masjed mountains in northern Khorasan Razavi province, north-east of Iran. Maps of slope, aspect, elevation and landform were used and combined together to prepare homogenous polygons of land units. The stratified sampling was performed and three sample plots, each 1000 m², were laid out in the land units. One sample from surface soil was taken in each plot in order to study the physico-chemical properties. Soil data were analyzed with Principle Component Analysis (PCA). Some parameters including number of trees, diameter at breast height, total height, crown diameter, crown cover, tress health and vigority and proportion of trees damaged by pest were measured. The results showed that elevation has significant effect on number of trees per plot, basal area per plot, and slenderness ratio, and mean crown diameter, number of regeneration per plot and tree's health. Slope gradient showed significant effect on some parameters including mean diameter at breast height, basal area in per plot mean crown diameter, total height and tree's health. The geographic aspect showed significant relationship with some parameters such as mean diameter at breast height, total height, slenderness ratio, mean crown diameter, crown cover, tree's health and proportion of trees damaged by pest. Landform had significant effect on total height, slenderness ratio, mean crown diameter and tree's health. Principle Component Analysis (PCA) showed that Phosphorus, clay, silts and pH are the most important factors on distribution of Juniperus excelsa subsp.  polycarpus trees and moisture saturation had the least effect on this species.