COS 135-4
The long-term effects of fuel treatments on ecosystem processes: Revisiting the Lubrecht Forest Fire and Fire Surrogates Study
As a result of decades of fire suppression, many western forests previously accustomed to frequent low-intensity fire have become exceedingly dense and accumulated excessive amounts of fuels. Fuels reduction treatments such as mechanical thinning and/or prescribed burning are used by forest managers to restore fire-suppressed western forests to pre-settlement density, reduce wildfire risk and enhance biodiversity and pathogen resistance. The Fire and Fire Surrogates (FFS) Study, established in 2000, is somewhat unique in that it was among the first to comprehensively manipulate and assess the effects of alternative forest restoration treatments on a host of forest and ecological parameters. Long-term ecological datasets are rare. Our study at Lubrecht Forest is unique in that it includes data from a single controlled site and utilizes pretreatment, immediate post-treatment, mid-term and now long-term measurements. Our objective was to assess the long-term effects of commonly used forest restoration treatments on carbon (C) and nitrogen (N) pools and nutrient cycling. In summer 2013, we measured C, N and Phosphorus (P) pools and rates of nitrogen cycling as well as microclimatic conditions eleven years post-treatment in a ponderosa pine/Douglas fir forest at the Lubrecht FFS site in western Montana.
Results/Conclusions
Our data show available N pools 2-5 times smaller than those seen in prescribed burn treatments immediately post-treatment. Forest floor C pools remain significantly lower in the thin+burn treatment due to shallower forest floor, though we observed no difference in N pools in forest floor. No significant differences were seen in total C, N, or available P pools mineral soil, pine foliage or litter. Current rates of N mineralization are 3-4 times lower than those seen one and three years post-treatment in burn treatments, yet current rates show no significant differences between treatments. Soil temperatures in thinned treatments were generally higher than other treatments. These data suggest a relatively rapid attenuation of restoration effects on C and N cycling and seem to indicate resilience of these temperate forests, while effects on some abiotic processes remain. While there is evidence that forest restoration can improve tree growth and vigor, long-term sustainability of this effect will likely be influenced by nutrient availability. Considering high costs of forest restoration, treatment longevity and ecological effects are important considerations for forest managers. Understanding soil C and N dynamics will help address these concerns in terms of forest productivity, nutrient availability and post-treatment fuel accumulation.