A meta-analysis of thinning, prescribed fire, and wildfire effects on subsequent wildfire severity in conifer-dominated forests of the Western US shows that mechanical thinning combined with prescribed burning, mechanical thinning with pile burning, and prescribed burning alone significantly reduce wildfire severity by 62-72% compared to untreated areas. Thinning alone was less effective, highlighting the importance of treating surface fuels. The efficacy of these treatments did not vary across forest types or fire weather conditions. Prior wildfire had complex impacts, varying with forest type and initial wildfire severity. Treatment effectiveness declined over time, with a mean reduction in severity decreasing more than twofold when wildfire occurred more than 10 years after treatment. The study emphasizes the importance of active forest management to reduce wildfire severity and improve outcomes for people and forests. Treatments like "thin and prescribed burn" were most effective, reducing severity by 72%, while "thin and pile burn" and "prescribed burn" reduced severity by 62%. "Thin only" treatments had minimal effect, and "prior wildfire" treatments showed variable results. The study underscores the need for recurring prescribed burning or follow-up treatments to maintain effectiveness. The results highlight the importance of considering site-specific conditions and the role of fire weather in treatment efficacy. The findings support the use of active forest management to mitigate wildfire severity and promote fire-resistant forests.A meta-analysis of thinning, prescribed fire, and wildfire effects on subsequent wildfire severity in conifer-dominated forests of the Western US shows that mechanical thinning combined with prescribed burning, mechanical thinning with pile burning, and prescribed burning alone significantly reduce wildfire severity by 62-72% compared to untreated areas. Thinning alone was less effective, highlighting the importance of treating surface fuels. The efficacy of these treatments did not vary across forest types or fire weather conditions. Prior wildfire had complex impacts, varying with forest type and initial wildfire severity. Treatment effectiveness declined over time, with a mean reduction in severity decreasing more than twofold when wildfire occurred more than 10 years after treatment. The study emphasizes the importance of active forest management to reduce wildfire severity and improve outcomes for people and forests. Treatments like "thin and prescribed burn" were most effective, reducing severity by 72%, while "thin and pile burn" and "prescribed burn" reduced severity by 62%. "Thin only" treatments had minimal effect, and "prior wildfire" treatments showed variable results. The study underscores the need for recurring prescribed burning or follow-up treatments to maintain effectiveness. The results highlight the importance of considering site-specific conditions and the role of fire weather in treatment efficacy. The findings support the use of active forest management to mitigate wildfire severity and promote fire-resistant forests.