Impacts of Forest Roads on Soil in a Timber Harvesting Area in Northwestern Mexico (a Case Study)

Abstract

The impacts of forest roads on soil were studied in a timber harvesting area of 92 ha in the municipality of San Dimas, state of Durango, Mexico. The area included 3127 m of main roads, 2907 m of secondary roads and 2979 m of tertiary roads. The timber was harvested at the beginning of 2012. After logging, soil loss by run-off during the rainy season was assessed along the truck ruts. This variable was correlated with the width and the longitudinal and transverse slopes of the road. The overall average road density (98 m/ha) indicated an average external yarding distance of 102 m. This is a short distance considering that timber was drawn with a jammer, which can pull logs over a distance of 300 m or more. Run-off in the rainy season decreased the ground level by between 38 and 58 mm along the truck ruts, and the soil loss was different in each type of road. The findings have led us to propose the elimination of some tertiary roads, to reduce the total road density to 78 m/ha. This is more than sufficient for logging, especially if the jammer capacity is improved, e.g., by applying the highlead system or the aerial yarding system with jammer. We estimate that soil loss would be reduced by 20% with the proposed changes to the road network. Additionally, the new road network would enable almost 20% of the area now occupied by roads to be reforested.