Long-Term Effects of Fuels Treatments, Overstory Structure, and Wildfire on Tree Regeneration in Dry Forests of Central Washington

The long-term effectiveness of dry-forest fuels treatments (restoration thinning and prescribed burning) depends, in part, on the pace at which trees regenerate and recruit into the overstory. Knowledge of the factors that shape post-treatment regeneration and growth is limited by the short timeframes and simple disturbance histories of past research. Here, we present results of a 15-year fuels-reduction experiment in central Washington, including responses to planned and unplanned disturbances. We explore the changing patterns of Douglas-fir regeneration in 72 permanent plots (0.1 ha) varying in overstory abundance (a function of density and basal area) and disturbance history—the latter including thinning, prescribed burning, and/or wildfire. Plots were measured before treatment (2000/2001), soon afterwards (2004/2005), and more than a decade later (2015). Thinning combined with burning enhanced sapling recruitment (ingrowth) into the overstory, although rates of ingrowth were consistently low and greatly exceeded by mortality. Relationships between seedling frequency (proportion of quadrats within a plot) and overstory abundance shifted from weakly negative before treatment to positive after thinning, to neutral in the longer term. However, these relationships were overshadowed by more recent, higher-severity prescribed fire and wildfire that stimulated seedling establishment while killing advanced regeneration and overstory trees. Our results highlight the dependence of regeneration responses on the history of, and time since, fuels treatment and subsequent disturbance. Managers must be aware of this spatial and temporal complexity and plan for future disturbances that are inevitable but unpredictable in timing and severity.

Getting back to fire suméŝ: exploring a multi-disciplinary approach to incorporating traditional knowledge into fuels treatments

Background Evaluating fuel treatment effectiveness is challenging when managing a landscape for diverse ecological, social, and economic values. We used a Participatory Geographic Information System (PGIS) to understand Confederated Colville Tribal (CCT) member views regarding the location and effectiveness of fuel treatments within their ancestral territory within the Colville National Forest (CNF) boundary. The 2015 North Star Fire burned 88 221 ha (218 000 acres) of the CCT ancestral territory. Results We sampled thirty plot pairs that were treated or untreated prior to being burned by the North Star Fire and again one growing season post fire. Species diversity was significantly increased by wildfire in both treated and untreated plots. Species richness was significantly increased in the plots that were treated, and there was no significant change in species richness from wildfire within the untreated plots. The percent canopy cover of two of the six culturally important plants (Fragaria spp. L. and Arnica cordifolia Hook.) significantly increased one growing season post wildfire within treated plots and one (Arctostaphylos uva-ursi [L.] Spreng.) significantly decreased in the treated plots post wildfire. These post-fire monitoring results were consistent with CCT member management recommendations and desired outcomes of understory thinning, prescribed fire, and natural ignition found using PGIS. Conclusions Together, the results suggest that prior thinning and prescribed burning can foster vegetation response to subsequent wildfires, including culturally important plants. Further, integrating Traditional Knowledge (TK) into fuels treatments can improve ongoing adaptive management of national forests that include tribal ancestral lands.