A regional assessment of the ecological effects of chipping and mastication fuels reduction and forest restoration treatments

A regional assessment of the ecological effects of chipping and mastication fuels reduction and forest restoration treatments. Project Title: A regional assessment of the ecological effects of chipping and mastication fuels reduction and forest restoration treatments. ABSTRACT: 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.). These sites were distributed across a wide geographic range throughout Colorado and represent treatments across several federal, state, and other land agencies. The mechanical treatment added a substantial amount of 1-hr and 10-hr woody fuel (<2.54 cm in diameter) to the forest floor which resulted in a range of depths within each. The treatments provided a relatively large input of nitrogen (N) to the forest floor, but because of the high carbon (C) to N ratio of the added material (e.g. C:N of 125-175), the woody mulch is resistant to microbial decay and the added N is largely unavailable to plants. Slow mulch decomposition in arid and cold western forests may extend the consequences of this management treatment on plant germination, soil nutrient availability, and plant productivity for many years. 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. BACKGROUND AND PURPOSE Many …