Soil compaction on a mechanized timber harvest operation in eastern Oregon

Graduation date: 1989The use of mechanized harvest equipment has been\ud increasing as an economical method to harvest small diameter\ud timber. While the use of this equipment is increasing,\ud little is known about associated soil compaction. In\ud particular, little information exists on soil compaction\ud caused by feller--bunchers.\ud This study measured soil compaction caused by a\ud mechanized harvest operation using 2 swing-boom, tracked\ud feller-bunchers and 2 rubber-tired grapple skidders. The\ud study took place on the LaGrande Ranger District of the\ud Wallowa-Whitman National Forest, located in eastern Oregon\ud on volcanic ash soils. USDA Forest Service definitions of\ud detrimental compaction (20% or greater increase in soil\ud density over pre-activity levels) were used as a guideline\ud to determine if detrimental compaction had occurred.\ud Results show that 54% of the total area was impacted by\ud either the feller-bunchers, skidders or both. Fellerbunchers\ud impacted 19% of the total area and caused a\ud statistically significant increase in soil bulk density of\ud 8.8% when compared to before logging densities. Main skid\ud trails covered 12% of the total area and had a statistically\ud significant increase in soil density of 36.3%, when compared\ud to before logging densities and was considered detrimentally\ud compacted. These main skid trails were also feller-buncher\ud trails. Thus, 12% of the total area was impacted by both\ud feller-bunchers and skidders while 7% of the total area was\ud impacted only by feller-bunchers. Twenty three percent of\ud the total area received 1 to 4 skidder passes and was not in\ud identifiable skid trails. Even these non-skid trail areas\ud showed a statistically significant increase in soil density\ud of 9.6% when compared to before logging densities. An\ud additional 12% of the total area received 5 to 8 skidder\ud passes and was also not in identifiable skid trails. This\ud area showed a statistically significant increase in soil\ud density of 19.8% and was considered detrimentally compacted.\ud Regression analysis showed that slash significantly reduced\ud compaction caused by feller-bunchers and skidders