Investigating the Effect of Topographic factors on the distribution of oriental beech in Hyrcanian forest, Iran

Present and future distribution status of important forest species needs to be studied as a prerequisite for the need of conservation programs. This thus can play an undeniable role in tackling global climate change, land use change and air pollution. The main purpose of this study was to determine the distribution of oriental beech (Fagus orientalis Lipsky) under the influence of topographic factors in forests of northern Iran. In so doing, the present distribution status of this species in the 51 watershed of Mazandaran province was determined. Also, the relationship between the main topographic factors (slope, direction, elevation) and sub-components factors (topographic moisture, surface curvature and cross-section curvature) was analyzed and modeled using boosted regression tree (BRT) model and R software package. Under the curve area statistics (AUC) and actual threshold-related skill statistics (TSS) were used to evaluate the model. Findings showed that the AUC and TSS were 0.82 and 0.63, respectively. This indicates that the model was able to predict the distribution of this species. The results also showed that altitude and slope percentages had the most influence on the distribution of this species and the distribution was less affected by secondary topographic variables such as topographic moisture, cross-section curvature and surface curvature. This species is more likely to occur in slopes of 20 to 60 percent, in the northern and eastern directions, and at altitudes of 500 to 1500 meters above sea level. The habitats located at this topographic location are more likely to be affected by future climate change scenarios. Therefore planning and implementing conservation plans for this species in northern forests of Iran seems necessary.