PS 10-122 - Impacts of skidder traffic on soils and seedling growth in a longleaf pine forest

Monday, August 8, 2011
Exhibit Hall 3, Austin Convention Center
Noah A Jansen, Jason D. McGee, Steve B. Jack, Robert J. Mitchell Jansen, J.W. Jones Ecological Research Center, Newton, GA

Increasing concerns about conservation of biodiversity in working forests have created a need for silvicultural prescriptions which better maintain ecological values. In addition to removing trees, timber harvesting operations also by disturb soils, ground cover, and advanced regeneration, particularly where skid trails are located.  Working in a longleaf pine forest in southwest Georgia, we are attempting to address 1) how different silvicultural prescriptions affect skid trail spatial distribution and 2) how skidder traffic impact soils and seedling growth.  Four silvicultural treatments (single-tree selection, group selection, group selection with reserves, and uncut control) were implemented in late 2009 on eighteen 4-ha plots. Skidder traffic was manipulated to create three replicate sets of skid trails having 1, 2, 4, and 8 passes. Trail width, soil bulk density, and soil resistance to penetration were measured at 4 points along each skid trail. Longleaf pine seedlings were planted in four 1x1-m subplots on each trail to evaluate the impact of skidder traffic on seedling growth and nutrition.  Results from these experimental skid trails are compared to those from operational skid trails (0, 4, 8, 14-15, and 22-49 passes) where traffic levels were estimated based on data from GPS units placed inside the skidders. The amount of area disturbed by the different traffic levels was estimated for each silvicultural treatment using ArcGIS.


 The area disturbed by skid trails was similar among treatments (5.4 – 6.7% of plot area). However, single-tree selection plots had more trails with low traffic and fewer trails with high traffic relative to group selection and groups with reserves plots, which had an even distribution of skid trail area across traffic levels. Impacts on soils and seedling growth one year post-harvest varied with traffic intensity. Soil compaction increased with traffic level s, with the largest change in bulk density occurring between 0 (1.3 g cm-3) and 8 (1.5 g cm-3) passes. No differences in the biomass of planted pine seedlings were observed among traffic levels. Because initial impacts to soils and seedling growth did not vary substantially among skidder traffic levels and the area disturbed was similar among harvest treatments, the impact of skidder traffic may not be an important consideration when choosing a silvicultural prescription for landowners interested in conservation. However, the biologically diverse groundcover community may be affected more severely by higher traffic levels, and recovery time for soils and groundcover may be longer for skid trails with higher traffic.

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