Road geometric design and its effect on some chemical and biochemical indicators of soil of adjacent forest stands

Forest roads are the most important infrastructure to access and apply the forest management activities, which they can impose a significant impact on adjacent stands. The objective of this study was to investigate the effect of the forest road geometric plan (switchback, curve, and straight road) on some chemical and biochemical indicators of soil in adjacent stands for forest road planning. Considering three different road geometric plans, from the edge of the road up to 100 meters toward the forest interior, the rate of organic carbon, nitrogen, and dehydrogenase and urease enzymes activity in forest soil at the depth of 0-10 and 10-20 cm in two forest types was measured. Data were analyzed by using t-test, ANOVA, and broken-line regression model. The results of ANOVA showed significant effect of forest type and geometric plans of the road on measured variables. In addition, results indicated that by increasing the depth of soil, the impact of the road on some measured indicators was not significant. The results of broken line regression model showed that the lowest range of road effect was related to the straight road (13 m) and its highest range was related to switchback road (42 m). Results of this study can provide guidelines for forest road planners and evaluators to design the road effect buffer at the stage of forest roads network planning and to minimize the effect of forest road on its adjacent stands.