Short and long-term effects of ponderosa pine fuel treatments intersected by the Egley Fire Complex (OR, USA)

Authors: DODGE, JESSIE - Idaho State University; STRAND, EVA - Idaho State University; HUDAK, ANDREW - Us Forest Service (FS); BRIGHT, BENJAMIN - Us Forest Service (FS); HAMMOND, DARCY - Idaho State University; Newingham, Beth

Submitted to: Fire Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: Historically, ponderosa pine forests experienced frequent low severity fires reducing tree recruitment and fuel build up. However, fire suppression has resulted in increased tree recruitment and fuel accumulation often causing large-scale higher severity fires. Land managers have implemented fuel treatments (mechanical thinning and prescribed fire) in order to reduce fuel loads and thus burn severity. We examined whether fuel treatments reduced burn severity and the effects of fuel treatments on soil and plant communities nine years after the Egley Complex fire in Oregon, USA. We found that fuel treatments reduced burn severity across the Egley Complex. Treated sites recovered to pre-fire levels in approximately three years compared to untreated sites that recovered much slower. Fuel treatments reduced tree and sapling density and decreased fuel loads in high severity. Our results suggest that fuel treatments are effective at reducing fire severity.

Technical Abstract: Fuel treatments are widely used to reduce fuel loads and alter fuel continuity in forested ecosystems for restoration and to mitigate wildfire behavior and effects. However, few studies have examined long-term ecological effects of interacting fuel treatments and wildfire. Using annually-fitted Landsat satellite-derived Normalized Burn Ratio (NBR) curves and paired pre-fire treated and untreated field sites, we tested changes in NBR (dNBR) and years since treatment as predictors of biophysical attributes one and nine years after the Egley Fire Complex in Oregon. We also assessed short- and long-term fuel treatment impacts on field-measured attributes one and nine years post-fire. Results: Burn severity (dNBR) was lower in treated than untreated sites across the Egley Complex. Annual NBR trends showed that treated sites nearly recovered to pre-fire values by approximately three years post-fire, while untreated sites had a much slower recovery rate. Time since treatment and dNBR significantly affected tree canopy cover in 2008 and surface fuel loads in 2016. This suggests an increase in live tree canopy cover in areas that were treated recently pre-fire, likely due to reduced burn severity effects with decreased time since treatment, and an increase in fuels as burn severity and time since treatment increased. Live tree density was more affected by severity than by pre-fire treatment in either year, as was dead tree density one year post-fire. None of the functional groups were affected by treatment or severity in 2008; in 2016 shrub, graminoid, forb, and invasive cover were higher in high severity sites than low severity sites. Total fuel loads nine years post-fire were highest in untreated, high severity sites. Tree canopy cover and density of mature trees, saplings, and seedlings were reduced nine years post-fire compared to one-year post-fire across treatments and severity, whereas live and dead tree basal area, understory surface cover, and fuel loads increased over time.