Natural recovery assessment of some physical properties of forest soil compacted by ground base skidding

Skidding machinery traffic can have a long-term detrimental impact on soil physical properties such as bulk density and strenght. Therefore, the trial was conducted to investigate the recovery status of soil physical properties, compacted during twenty-year period at Asalem Forest, north of Iran. For this purpose, three parcels of the first and the second districts of Nave Asalam Forest, were chosen. The treatments consisted of three periods after skidding (1, 10 and 20 years), two slope classes (>20% and <20%) and two traffic levels (high and low or control). In order to assess soil bulk density and soil strenght a sample plot of 12×5 m. was located at each treatment (totally 12 plots). At each plot, soil strength was measured directly by penetrometer and iitact cores werer sampled to measure bulk density in laboratory. The results showed that longitudinal slope gradient classes and traffic intensity levels were very important factors in soil recovery process in skid trails. Overall, it might be concluded that the most soil disturbances occured on gradient more than 20% and high traffic levels. The result also showed that 20 years after skidding, soil bulk density and soil strenght were under process of recovery, but have significant difference with the control treatment.