Relationship between Site Disturbance and Forest Harvestin.g Equipment Traffic

A study was done to evaluate the use of global positioning systems (GPS) to track the position of forest harvesting equipment and use the information to assess site impacts. GPS units were attached to tree-length harvesting machinery in two clearcuts (1 feller-buncher, 2 skidders). Position of the equipment was recorded at 2-second intervals throughout the harvest of both stands. The positional data were differentially corrected, then filtered using a custom software package to calculate the area of impact based on the path taken by the machinery. Result of the. calculations were raster maps with cell values equal to the number of tire passes over that location. For the current study, grid resolution was 0.5x0.$ m. Following harvest, visual assessments of site disturbance on a chain-by-chain grid were made and the results compared to estimates from the traffic maps. Soil physical properties were measured in a 1 ha area of one stand and the values correlated with local traffic levels. Results indicated that the GPS-based approach to assessing site impacts gave results equivalent to what would be expected from an intensive visual inspection. For the conditions tested, 25 percent of the stand remained untrafficked, 25 percent received more than 5 passes, and 50 percent of the stand received 1 to 5 passes. There was no clear correlation, however, between observed number of passes and changes in measured soil properties. INTRODUCTION There is a great deal of research interest in the sustainability of forest management practices. Forest operations to implement many management objectives require the application of heavy equipment on tracts, resulting in impacts to the soil. These impacts may persist over time and result in decreased stand productivity. It is important to understand how machinery impacts a stand and what factors influence the degree of impact. A number of studies have quantified how machinery affects soils on a microenvironment scale, generally measuring changes in soil properties at a fixed point for a given traffic intensity level. Machinery impacts on soils have been shown to vary with soil type and moisture, machine type, size, and weight, number of passes, tire.and drive train characteristics, and other factors