Analyzing the effect of abiotic and biotic factors on diameter increment of Fagus orientalisl ipsky by artificial neural network in the forests of Mazandaran province

The diameter and volume growth of forest stands are the basis for determining the annual rate or cut in the planning and management of wood utilization so, forest increment and factors affecting it are one of the most important challenges in the forest. In this study, the impact of biotic and abiotic factors on diameter increment of oriental beech (Fagus orientalis lipsky) in fixed plot-level over a period of 9 years (2003-2012) was modeled by artificial neural network techniques in north forest of Iran. 258 permanent samples were taken by a 150 × 200 inventory grid. Mean of variables such as diameter increment, basal area of stand, basal area of larger trees and number of tree per hectare were measured inside each sample segment which are equal to respectively: 30.9, 36.8, 29.4 and 421. Abiotic factors such as growing-season-cumulated potential solar radiation, seasonal air temperature, topographic wetness index and wind velocity and biotic factors such as diameter at breast height, basal area of larger trees were used as input variables and diameter increment of beech as output variable were used. Multi layer Perceptron network with back propagation algorithm and sigmoid functions were used. The results showed that the changes index of diameter at breast height (32%), Wind and solar energy in the growing season (a total of 20%) the combination of topography and soil wetness index (19.5%) and basal area (16.9 %) explain diameter increment changes in sample plot level. Also, neural networks provided acceptable accuracy for diameter increment modeling using the biotic and abiotic variable affecting on it. Also, the percentage of biotic and abiotic factors was approximately the same, which it can be concluded biotic and abiotic factors control increment of beech the same.