Production and aerial application of wood shreds as a post-fire hillslope erosion mitigation treatment

Guidelines for the production and aerial application of wood shred mulch as a post-fire hillslope treatment were developed from laboratory and field studies, several field operations, and the evaluations of professionals involved in those operations. At two early trial sites, the wood shred mulch was produced off-site and transported to the area of use. At the 2010 Schultz Fire in Arizona, the wood mulches were produced on-site from burned hazard trees that were felled and skidded to a processing area where the logs were shredded by a horizontal grinder and piled. The subsequent aerial applications of the wood shreds were staged from the same landings where they were produced. At the 2010 Fourmile Canyon, 2012 High Park, and 2012 Waldo Canyon Fires in Colorado, wood shreds were produced from various combinations of on- and off-site burned and green trees that were generally shredded near the harvest or storage site. The wood shreds were transported by chip trucks to aerial application staging areas. The most challenging aspect of wood shred production was adjusting the grinder screens and through-put speed to maximize the proportion of shreds that were 2 to 8 inches (50 to 200 mm) in length. The same equipment and techniques used for aerial mulching with agricultural straw worked, with some adjustments in flight altitude and speed, for wood shreds. The Heli-Claw, an experimental device designed to replace the cargo net in aerial mulching, was tested and used to apply 80 percent of the wood shred mulch at the Beal Mountain mine reclamation site. Because wood shreds are four to six times heavier than agricultural straw, wood shred mulch took longer to apply than agricultural straw for the same area (25 to 35 ac [10 to 14 ha] per day for wood shreds; approximately 200 ac [81 ha] per day for straw). The additional flight time makes mulching with wood shreds cost three to four times more than with agricultural straw ($1700 to $2200 per ac [$4200 to $5500 per ha] for wood shreds; $500 to $700 per acre [$1200 to 1700 per ha] for straw). However, the advantages of wood shreds - on - or near-site availability, greater stability in high winds and on steep slopes, and lack of unwanted plant seeds from off-site - make wood shred mulch useful in areas where agricultural straw mulch may not be desirable.