Fuel treatments can be effective for reducing both local severity and fire extent. However, the effectiveness varies by ecoprovince, treatment type, and treatment age.
NORTHERN ROCKIES - prescribed fires as a stand-alone treatment do not mimic wildfire and is ineffective for dependable fire severity reduction and may offset the effects of thinning for the 6-10 year interval if the treatments are combined. Stand-alone thinning treatments were the most reliably effective and effectiveness lasted longer (>10 years) than wildfire (> 5 years).
SOUTHERN ROCKIES- prescribed burning with or without thinning reduces fire severity for > 10 years after treatment. Prescribed burns were more reliable and longer lasting in their effectiveness when applied as stand-alone treatments without previous thinning. Thinning alone is ineffective for reducing fire severity and should be discouraged as a fuel treatment.
PACIFIC NORTHWEST – wildfires only reduce subsequent fire severity for <10 years after the initial fire. Prescribed fire was ineffective unless combined with thinning treatments. Thinning as a stand-alone treatment was the most consistent treatment for reducing fire severity with treatment effectiveness lasting longer than 10 years after implementation.
NORTHERN CALIFORNIA - prescribed burning provides similar reductions in fire severity as wildfire; neither shows significant value beyond 10 years. Thinning reduces fire severity for more than 10 years but only after >5 years since implementation. The combination of thinning and burning may capture the short- and long-term effects, but this requires further study. Mastication/site prep is ineffective and possibly detrimental for reducing fire severity in the short term (2-5 years).
SOUTHERN CALIFORNIA - previous wildfires reduce subsequent fire severity for < 10 years while prescribed burning is most reliably effective at > 10 years after implementation and highly variable in effectiveness for the first 10 years. Both thinning and mastication are apparently effective for at least 5 years, with thinning having somewhat greater effects, but more study is needed to verify this finding.
SOUTHEAST - previous wildfires have little impact on fire severity of subsequent wildfires. In contrast, prescribed burning, although somewhat variable in its impacts, is the most effective treatment for reducing subsequent fire severity, with greater and more reliable effectiveness >5 years after implementation.Mastication/site prep is ineffective for fire severity reduction after the first 5 years, with enhanced fire severity apparent 10 years after treatment.
INTERIOR BROADLEAF ecoprovince – prescribed burning is uniquely reliable and effective at reducing fire severity for at least 10 years after implementation. All other fuels treatments appear to be ineffective or detrimental to reducing wildfire severity. The combination of thinning and burning has particularly lethal results. However, more study of fuel treatment effectiveness in needed in these systems.
SEMI-DESERT ecoprovince – prescribed burning appears ineffective until >10 years, but may have greater effectiveness than wildfire after that point. However, few fuel treatments were available for study in this province.
GREAT LAKES ecoprovinces – prescribed fire may be effective, but more study is needed to confirm this finding.