عنوان مقاله [English]
Background and objectives: Few studies have shown the effect of topographic gradient on the distribution of trees and coarse woody debris (CWD), particularly old growth beech stands. Several studies emphasized relationship between physiographical characteristics of sites and live trees distribution. Valipour et al (2013) studied the effect of physiographic characteristics of sites on dimensional properties of tress. They found that physiographic factors significantly effect on the dimension of trees, the most important factors influencing are the slope. Also Alavi et al (2008) revealed that physiographic factors impact on spatial distribution of elder. Research in the low land forests of Noushar region showed slope and altitude positively effect on diversity indices. The main goals of this research is (1) Evaluation the effect of geomorphic characteristics of sites on living tree distribution and (2) extent and distribution of dead trees
Materials and methods: The study was conducted within the Gorazbon section of the Kheyrud Experimental Forest in northern Iran which is owned and managed by the University of Tehran for education, research, and conservation. The site selection was done according to the management history. Selected sites was undisturbed and logging operation don’t was done by now. To characterize coarse woody debris within stands, 50×50 meter gird grid of sampling points established to randomized plot selection and thirty-five 0.1 ha circular plots were established within a natural beech stand using a systematic random sampling technique in order to equally sample across a wide variety of topographical factors. In each plot, we measured percent slope, aspect and land form. Meanwhile the number of dead trees and species and quality was recorded. Therefore, we investigated the influence of topographical factors including slope aspect, slope degree, and landform index (LI) on the distribution of dominant tree species and CWD in undisturbed mixed forests in northern Iran.
Results: F.orientalis had the highest mean density, volume, relative density, relative volume, and RIV of all live and dead trees. Results showed that tree density and basal area were not significantly correlated with any of the measured parameters, except basal area was negatively correlated with LI. Redundancy analysis (RDA) of the tree layer revealed a significant relationship between the measured environmental variables and species distributions on the first canonical axis and all four canonical axes. CWD volume showed significant negative correlation with percent canopy cover and was highly correlated with terrain shape index. Density of CWD in decay class IV was significantly correlated with aspect slope and percent of canopy cover.
Conclusion: Analyses of CWD distributions in relation to both living vegetation and topographic gradients showed a highly complex interplay of factors dictating the distribution of CWD across the forest stands.