Investigation some of the Biotic and Abiotic Variables Effective on the Diameter Increment of the Beech Trees at Fixed Sample Plots level by Growth Models

Quantifying forest growth and determination of its affective factors are fundamental for forest management. This study examines the effects of biotic and abiotic factors on the diameter increment of oriental beech (Fagus orientalis Lipsky) in a high-elevation forest in northern Iran using permanent sample plots. The aim of this study was identification and quantifying environmental factors such as potential solar radiation in growing season, topographic wetness index in representing soil water distribution seasonal air temperature, topographic wetness index (as indicator of soil water distribution), wind velocity generated from simulation of fluid-flow dynamic models of complex terrains, temperature and humidity and their relation with diameter increment of beech. On the basis of diameter measurements in a 9 year period (2003-2012) a model was used in order to estimate diameter increment. Also, mean of DBH and basal area of beech trees were implemented in model as biotic factors. The results showed that DBH, combination of topographic and soil water index factors and basal area are the most important factors affecting diameter increment of beech trees, respectively. Eventually, the results showed that by using increment models, it is possible to determine the increment of diameter and factors affecting it with high accuracy.