The influence of forest site on rate and extent of soil compaction and profile disturbance of skid trails during ground-based harvesting

Soil compaction has been considered a principal form of damage associated w ith logging, restricting root growth and reducing productivity. The rate an d extent of soil compaction on skid trails was measured at six field locati ons covering a range of dry and wet forests. Data was collected for up to 2 1 passes of a laden logging machine. A similar extent of compaction, averag ing 0.17 g.cm(-3) increase in total soil bulk density (BD), was recorded fo r all field sites despite substantial site and soil differences. On average , 62% of the compaction in the top 10 cm of the soil occurred after only on e pass of a laden logging machine. The environment under which soils had fo rmed played a major role in determining the BD of the undisturbed soil. Com paction was strongly related to the original BD, forest type, and soil pare nt material. Soil strengths obtained in the field fell below levels found t o restrict root growth. However, reduction in macropores, and the effect of that on aeration and drainage could reduce tree growth. On the wettest soi ls logged, machine forces displaced topsoils rather than causing compaction in situ. Recommended logging methods and implications for the development of sustainability indices are discussed.