Utah juniper and two-needle piñon reduction alters fuel loads

Abstract

Juniper (Juniperus spp.) and piñon (Pinus spp.) trees have encroached millions of hectares of sagebrush (Artemisia spp.)-bunchgrass communities. Juniper-piñon trees are treated to reduce canopy fuel loads and crown fire potential. We measured the effects of juniper-piñon infilling and fuel-reduction treatments on fuel load characteristics at four locations in Utah. At each location, treatment areas were burned, left untreated, or trees were cut or masticated in a randomised complete-block design. We measured standing and downed fuels by size and type along 30-m transects on 15 subplots (30×33m) per location before and 1-3 years after treatment. Increased tree cover was associated with decreased shrub and herbaceous fuel loads (P<0.01). By 2 years post-treatment, herbaceous fuel loads were greater than pretreatment in all treated areas (P<0.01). Cut and mastication treatments increased surface woody 10- and 100-h fuel loads and wood/bark cover (P<0.01). Masticated-tree depth was a good estimator of fuel loads (R2=92). The conversion of canopy fuels to surface fuels reduced fuels that enable crown fire and extreme fire intensity. Cool-season prescribed fire may need to follow mechanical treatments to reduce surface fuel and the potential for wildfire damage to perennial understorey vegetation.