Effects of fuels reductions on plant communities and soils in a Piñon-juniper woodland

Over the past decade, a variety of fuels reduction strategies have been implemented across western US forests to lower the risk of high severity fires. In two separate studies, we evaluated the short-term effects (<two growing seasons) of hand thinning (lop & scatter, pile burn) and mechanical mastication on understory plant communities and soil resources in an upland Piñon-juniper woodland. All treated sites were compared to a nearby untreated control site. After one growing season, understory plant cover was 4-5.5 times greater in hand-thinned treatments (lop & scatter pile burn), while understory cover in mastication treatments was 15 times greater following two growing seasons, compared to untreated controls. Bromus tectorum, an invasive annual grass, was present in all treated sites and absent from controls. Soil aggregate stability, an indicator of overall soil quality, was lower in the pile burn and mastication sites. Nitrogen fixation potential was low across all sites, but lowest in two treated sites (lop & scatter and mastication). This study suggests that different fuels reduction techniques generally have positive effects on total understory plant cover, but treatments that involve burning of slash materials may have more negative effects on site stability than alternative treatment options.