Bulk density and soil resistance to penetration as affected by commercial thinning in northeastern Washington.

Abstract

Bulk density and soil resistance to penetration were measured in ten, 3- to 11-ha operational units in overstocked, mixed-conifer stands in northeast Washington. Resistance was measured with a recording penetrometer to the 33-cm depth (13 in) at 10 stations on each of 8 to 17, 30.5-m-long, randomly located transects in each unit. Subsequently, different combinations of felling and yarding equipment were used to thin eight units; no combination was replicated. Two units remained as nonharvested controls. Soil measurements were repeated after harvest. Most trails were designated, others were supplemental, especially where designated trails were spaced at 40 m (130 ft) (center to center). Trails occupied 6 to 57 percent of the area of harvested units. In the 15- to 25- cm depth, average resistance to penetration on trails increased by 500 kPa or more in six of the eight units. Drier soil in the after-harvest sampling on the flat terrain may have contributed to increased resistance. Bulk density on trails after harvest (fall 1999) averaged 3 to 14 percent greater than that in nontrail portions. Area and severity of soil compaction were less on steep terrain than on flat terrain, probably because soil textures were sandier. Whether compaction was sufficiently severe to hinder root penetration or reduce tree growth is unknown. The absence of replication precluded statistical testing for differences among the several combinations of harvesting equipment and trail spacing.

Citation

Landsberg, Johanna D.; Miller, Richard E.; Anderson, Harry W.; Tepp, Jeffrey S. 2003. Bulk density and soil resistance to penetration as affected by commercial thinning in northeastern Washington. Res. Pap. PNW-RP-551. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 35 p