Evaluation the skid trail effect on annual ring width fluctuations in Beech (Fagus orientalis Lipsky) and Alder (Alnus subcordata C. A. Mey.) trees (District Nav No. 1, Asalem forests, Guilan)

Each skid trail construction affects the trees located on the road margins in various extents. The present study was conducted with the aim to assess the changes in annual ring widths of Beech and Alder trees compared to the control trees inside the Nav District in Asalem forests. To this aim, 40 samples from previously felled Alder and Beech even-age trees were randomly drawn alongside and inside the forest stands. Disks were acquired from the trees and were perfectly polished with sanding machine. They were finally used to measure annual ring widths with an accuracy of 0.01 mm. Effect of species (Alder and Beech) and location (along the skid trail and inside of stand) on the average width of annual ring were analysed using a two-way ANOVA test in a complete randomized design. Results indicated larger average annual ring width of marginal trees (0.20mm and 0.38mm for Beech and Alder trees, respectively) compared to those located inside the stand. Moreover, ANOVA results indicated highly significant main effect of species and location on the average of annual ring width, while their interaction was shown to be insignificant. It can be concluded that this increase of trees growth in marginal trees may compensate the loss of volume caused by skid trails construction.