Date of Award

2017

Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Forestry (MS)

Administrative Home Department

School of Forest Resources and Environmental Science

Advisor 1

Joseph W. Wagenbrenner

Committee Member 1

Peter R. Robichaud

Committee Member 2

Evan S. Kane

Abstract

Post-fire salvage logging operations can induce environmental problems. This study assessed the effects of different disturbances from post-fire salvage logging on soil bulk density, water repellency, field saturated hydraulic conductivity (Kfs), ground cover, and sediment yields after the 2013 Rim Fire in California. Hillslope plots were installed in three locations (Sawmill, lower Femmons, and upper Femmons). The plot-scale disturbances were burned and untrafficked (low and high slope controls and logged only with no traffic), or burned and trafficked (few and many pass skid trails). Additional measurements were made in nearby areas that included the plot-scale disturbances as well as feller buncher tracks and mixed disturbed areas. We measured soil bulk density at two depths. Kfs was measured using a dual head ring infiltrometer. Water repellency was measured at the mineral soil surface and at 1 cm and 3 cm soil depths. Ground cover was measured in each hillslope plot. Sediment yields from the hillslope plots were measured using sediment fences. Measurements in burned areas were made in water years 2015 and 2016. Bulk density, water repellency, and Kfs measurements were also made in one unburned logged site. We assessed the effectiveness of subsoiling of skid trails in nearby burned areas, sometimes across the contour, as a mitigation practice by recording the presence or absence of rills or gullies.

The mean bulk densities in the trafficked plots were significantly higher than in untrafficked plots. Kfs was 10 times higher in untrafficked areas than in the many pass skid trails in the burned sites and significantly higher in the unburned site. There was no significant difference in KFS for any of the disturbance classes between the burned and unburned sites. In the burned areas, WDPT was highest at the 3 cm depth and was lower in trafficked areas than untrafficked areas. WDPT was also significantly lower in burned areas than in unburned areas, where strong water repellency occurred across all depths and disturbance conditions. Untrafficked areas had relatively low bare soil in 2015 and the amount of bare soil decreased significantly in 2016. The trafficked plots had more bare soil than the untrafficked plots, and sometimes the differences were significant.

The annual sediment yield in the untrafficked plots in the Sawmill site was 1.9 Mg ha-1 in the 2015 water year and this value significantly decreased to 0.14 Mg ha-1 in the 2016. The sediment yields in the trafficked skid trail plots were 6.2 and 1.2 Mg ha-1 in 2015 and 2016, respectively, and the 2016 yield was significantly greater than the untrafficked value. The annual sediment yields were also very low in untrafficked plots in the Femmons sites in 2016, and the trafficked plots produced significantly higher sediment yields. Some of the many pass skid trails were subsoiled (ripped) by logging contractors as part of the logging operation using a winged subsoiler with the wings set 45-60 cm below the soil surface. 53% of the 53 subsoiled skid trails had no rills or gullies present, and the rate of rilling or gullying increased with increasing skid trail slope. Subsoiling of skid trails with slopes more than 6% was not effective at reducing erosion because of the high incidence of rills or gullies.

These results indicate that salvage logging equipment compacted the soil in the burned forest. Soil compaction reduced water repellency and Kfs and increased bulk density, bare soil, and sediment yields. The sediment yields were most closely related to the change in bare soil. To reduce sediment yields from salvage logging, forest managers should consider increasing the ground cover on skid trails and other trafficked areas.

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