Intensity, extent and persistence of soil disturbance caused by timber harvesting in jarrah (Eucalyptus marginata) forest on FORESTCHECK monitoring sites

Abstract

Summary The intensity and extent of soil compaction caused by timber harvesting was examined in the jarrah (Eucalyptus marginata) forest of south-west Western Australia. The extent of soil compaction was determined by mapping soil disturbance categories. The intensity of compaction was determined from the bulk density of these disturbance categories. Bulk density of surface soil (0–100 mm) was measured across monitoring grids established for the FORESTCHECK project on eleven harvested sites and seven sites that had never been harvested. Surface soils on sites that had never been harvested had a mean fine earth bulk density of 0.71 g cm−3. Timber harvesting increased the bulk density of surface soils by a mean of 0.15 g cm−3. Compaction was greatest on log landings and primary and secondary extraction tracks where fine earth bulk density was increased by 0.27 g cm−3 compared to never-harvested forest. Compaction on the general harvested area (0.13 g cm−3), which excludes the extraction tracks, was about half that of log landings and extraction tracks. The intensity of soil compaction was consistent with increases observed as a result of timber harvesting in a range of other forests. Although the intensity of harvesting activity and the volume of logs removed is typically greater in gap release than in shelterwood treatments, there was no significant difference in soil compaction between these treatments. Soil compaction did decline as the intensity of individual disturbance activities inside harvested areas declined. Given the potential and demonstrated effects of soil compaction and disturbance on jarrah forest ecosystems, and the potentially long time periods indicated for the amelioration of soil compaction in these forests, ongoing operational management and monitoring of this disturbance is required to limit long-term effects on the productive capacity of jarrah forest.