Potential Evaluation of Forest Road Trench Failure in a Mountainous Forest, Northern Iran

After road construction in steep and mountainous areas, there is always a risk for trench failure. Estimation of this probability before forest road design and construction is urgent. Besides, to decrease failures costs and risks, it is necessary to classify their occurrence probabilities and identify the factors affecting them. The present study compares three statistical models of logistic regression, frequency ratio, and maximum entropy. The robust one was applied to generate trench failures susceptibility map of forest roads of two watersheds in Northern Iran. Also, all failures repairing costs were estimated, and subsequently, all existing roads were surveyed in the study area, detecting 844 failures. Among the recorded failures, 591 random cases (70%) were used in modeling, and others (30%) were used as validation data. The digital layers, including failure locations, were prepared. Three failure susceptibility maps were simulated using the outputs of the mentioned methods in the GIS environment. The resulted maps combined with repair cost prices were analyzed to statistically evaluate the repair cost unit per meter of forest road and per square meter of failure. The results showed that the logistic regression model had an Area Under Curve (AUC) of 74.6% in identifying failure-sensitive areas. The probabilistic frequency ratio and Entropy models showed 68.2 and 65.5% accuracy, respectively. Based on the logistic regression model, the distance to faults and terrain slope factors had the highest effects on forest road trenches failures. According to the result, about 43.25% of the existing road network is located in »high« and »very high« risky areas. The estimated cost of regulating and profiling trenches and ditches along the existing roads was approximately 108,772 $/km

Damages of Skidder and Animal Logging to Forest Soils and Natural Regeneration

Extracting logs from stump to landings causes extensive damages to forest stand and soil. In this research two parcels adjacent to each other were selected in order to assess the effect of traditional and mechanized methods of logging on regeneration and soil compaction. Askid trail and a mule trail with similar longitudinal slope, skidding direction and total volume of extracted wood were chosen in the parcels. The cylindrical sampling method was used to determine wet and dry soil bulk density and the samples were taken at 0–10 cm and 10–20 cm depth from skid and mule trails. The results showed that soil dry bulk density increase in skid and mule trails compared to control at 0–10 and 10–20 cm depth, was significant (p<0.01). This increase in mule trail at 0–10 cm depth was significantly higher than at 10–20 cm depth (p<0.01), but percentage of soil dry bulk density increase compared to control in skid trail at 0–10 cm and 10–20 cm depths was not significantly different. Soil dry bulk density increase compared to control at 0–10 cm depth of mule trail is higher than skid trail, but at 10–20 cm depth the skid trail is higher than mule trail. Systematic random sampling method was used to determine damages to different regeneration groups due to logging operations. The results showed that damages to each regeneration group seedling and small sapling in mule logging method were significantly lower than mechanized logging method