Prescribed Burning and Mastication Effects on Surface Fuels in Southern Pine Beetle-killed Loblolly Pine Plantations

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Ecological Engineering

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Surface fuels were characterized in loblolly pine (Pinus taeda L.) plantations severely impacted by southern pine beetle (Dendroctonus frontalis Ehrh.) (SPB) outbreaks in the upper South Carolina Piedmont. Prescribed burning and mastication were then tested as fuel reduction treatments in these areas. Prescribed burning reduced fuelbed continuity by consuming litter (Oi layer), duff (Oe + Oa), and woody surface fuels (1-, 10-, and 100-h timelag size classes) immediately after the treatment. Total loading of 1- and 10-h fuels in burned stands (3.1 Mg ha−1) remained significantly lower than that in the control (no treatment) (5.6 Mg ha−1) in the 2nd year post-treatment. However, 100- and 1000-h fuels increased post-burn due to accelerated failure of remaining pine snags and totaled 14.5 Mg ha−1 in the 2nd year post-treatment which was not significantly different than the control (17.3 Mg ha−1). Mineral soil exposure averaged 73% of burned stands after consumption of the duff layer in many areas. Custom low, moderate, and high load fuel models were developed for SPB-killed stands and produced simulated fire behavior (flame length and rate of spread) similar to two standard slash-blowdown fuel models (SB2 and SB3) when input to the BehavePlus fire modeling system. Mastication resulted in a compacted (bulk density = 131.3 kg m−3) and continuous layer of woody debris that averaged 15.1 cm in depth. Equations were developed for estimating masticated debris load and utilize fuelbed depth as input. The masticated debris load averaged 192.4 Mg ha−1 in the 1st year post-treatment and was significantly higher than total fuel loading in burned (16.3 Mg ha−1) and control (24.3 Mg ha−1) stands. The treatments tested in this study provide different options for preparing SPB-killed areas for reforestation activities and may produce short-term reductions in fire hazard.