Dr. Mike Battaglia, USFS Rocky Mountain Research Station, Fort Collins, CO, Dr. Charles Rhoades, USFS Rocky Mountain Research Station, Fort Collins, CO, Dr. Monique E. Rocca, Colorado State University, Fort Collins, CO, Dr. Michael G. Ryan, USFS Rocky Mountain Research Station, Fort Collins, CO
Over the past several years, fire managers have increased their use of mastication treatments, the on-site disposal of shrubs and small-diameter trees through chipping and shredding. Mastication is a relatively untested management practice that alters the chemical and physical conditions of the forest floor and may influence vegetation regrowth and fuel development for years or decades. Eighteen sites were established across four ecosystems of the southern Rocky Mountains and the Colorado Plateau: lodgepole pine (Pinus contorta), mixed conifer (Pinus ponderosa, Pseudotsuga menziesii, Pinus flexilis, and Pinus contorta), ponderosa pine (Pinus ponderosa), and pinyon pine/juniper (Pinus edulis/Juniperus sp.).
We found that mastication had few short-term negative effects on plant communities and soil processes, but that responses to the treatment cannot be generalized across western conifer ecosystems. In some ecosystems, mulch additions had no significant impact on stand-level soil N availability, herbaceous cover, or tree seedling regeneration; in others, mastication decreased soil N availability and tree seedling regeneration and increased herbaceous cover. The depth of the added mulch also had consequences on plant cover and soil N availability. Specifically, above a thickness of 7.5 cm, mulching depressed herbaceous plant cover and soil N nutrition in lodgepole pine and pinyon-juniper ecosystems. Though the initial impacts of mastication were subtle, our findings indicate that responses will vary among ecosystems and justify further research to elucidate ecosystem-specific processes and long-term consequences of these treatments.