Evaluating the Effectiveness of Wood Shreds on Post-fire Erosion

Agricultural straw mulching is a commonly used post-fire hillslope erosion control treatment that is aerially applied by helicopter. While widely used and reasonably effective at reducing erosion, agricultural straw is not native to the forest environment. There is a growing consensus among Burned Area Emergency Response (BAER) teams that mulch made from native forest material would be preferable to agricultural straw. Wood shred mulch made from post-fire road hazard trees is an alternative to agricultural straw. An optimized blend of sizes of wood shreds was effective in reducing sediment yields in both indoor rainfall simulation and outdoor field experiments. Several post-wildfire field experiments showed that wood shreds and agricultural straw were effective in reducing sediment yields as compared to the controls but neither treatment had an effect on runoff. Erosion reductions from wood shred treatments ranged from 50-96% in these experiments, and the presence and effectiveness of wood shreds appears to outlast both agricultural straw and hydromulch. Wood shreds are denser than agricultural straw and, as a consequence, about 4 times more wood shreds (by weight) than straw are needed to provide the same ground cover in a designated area. As a result, a helicopter with cargo nets required about four to five times as many round trips to treat an acre with wood shreds as with agricultural straw. This made wood shred application take longer and cost more than agricultural straw ($1,500 to$2,000 per acre [$3,750 to$5,000 per ha] and $500 per acre [$1,250 per ha], respectively). Field tests using a Heli-Claw, an alternative to a cargo net for heli-mulching, suggest that the Heli-Claw is a viable option for the aerial application of wood shreds. Results from these studies were disseminated through publications and a wide range of presentations, such as webinars, national meetings, and regional specialists meetings; thus, research findings have been directly conveyed to BAER teams and land managers. [Note: Throughout this report customary (English) units are stated first and metric equivalents are parenthetical where appropriate. The use of the symbol “t” is for ton (2000 lbs) in the customary system and the symbol “t” is for tonne (1000 kg [~2200 lbs]) in the metric system.