Soil Response to Machine Traffic As Indicated By Soil Stress Residuals.

Ground based timber extractions are the most common harvest system in the United States as well as other timber producing countries.  Machine movements in the course of harvesting have resulted in areas in which soils have been negatively impacted leading to increased erosion and soil compaction.  This is especially true of skid trails that have been established within the stand to facilitate tree removals.  Several techniques have the potential to reduce soil compaction including corduroying skid trails with slash or using equipment that exerts lower ground pressures.  Conventional measures of compaction have included bulk density and mechanical resistance.  However, bulk density measurements require destructive sampling and are time consuming while mechanical resistance measurements are highly variable due to soil moisture content, bulk density level and operator manipulation. Therefore, we established a research project designed to accomplish two objectives: 1) compare and contrast conventional measures of soil compaction with a newer technique using soil stress residuals and 2) compare the effects of slash versus bare soil on skid trails trafficked by a grappled wheeled skidder and a cable tracked skidder.  The project will be located within a hardwood/pine stand in the Ridge and Valley physiographic region of Virginia.  The initial pilot study indicated that soil stress residuals showed an increase in compaction levels by approximately 25% after 1 pass, 12% after 2 passes and less with subsequent passes (6 total).  Comparison of the newer technique of soil compaction measurement with existing techniques, as well as the effect of cover and equipment type on compaction, will be discussed.