New open-access paper in Forest Ecology and Management. A meta-analysis of 220 previous papers. Thanks again to Nick Smith!
Tamm review: A meta-analysis of thinning, prescribed fire, and wildfire effects on subsequent wildfire severity in conifer dominated forests of the Western US
Abstract
Increased understanding of how mechanical thinning, prescribed burning, and wildfire affect subsequent wildfire severity is urgently needed as people and forests face a growing wildfire crisis. In response, we reviewed scientific literature for the US West and completed a meta-analysis that answered three questions: (1) How much do treatments reduce wildfire severity within treated areas? (2) How do the effects vary with treatment type, treatment age, and forest type? (3) How does fire weather moderate the effects of treatments? We found overwhelming evidence that mechanical thinning with prescribed burning, mechanical thinning with pile burning, and prescribed burning only are effective at reducing subsequent wildfire severity, resulting in reductions in severity between 62% and 72% relative to untreated areas. In comparison, thinning only was less effective – underscoring the importance of treating surface fuels when mitigating wildfire severity is the management goal. The efficacy of these treatments did not vary among forest types assessed in this study and was high across a range of fire weather conditions. Prior wildfire had more complex impacts on subsequent wildfire severity, which varied with forest type and initial wildfire severity. Across treatment types, we found that effectiveness of treatments declined over time, with the mean reduction in wildfire severity decreasing more than twofold when wildfire occurred greater than 10 years after initial treatment. Our meta-analysis provides up-to-date information on the extent to which active forest management reduces wildfire severity and facilitates better outcomes for people and forests during future wildfire events.
I think we knew most of this..but a few quibbles:
First changing wildfire behavior by means of fuel treatments can have two mechanisms.. one direct influence of the wildfire on those changed conditions, and the other an indirect influence via changing suppression tactics and strategies. From the summary, it sounds like only the direct part was considered, which limits the utility of the study. Many PODs and other projects are designed specifically to aid suppression efforts.
As to this..” Across treatment types, we found that effectiveness of treatments declined over time, with the mean reduction in wildfire severity decreasing more than twofold when wildfire occurred greater than 10 years after initial treatments.”
But we are not managing sites that are a mean of an unknown bunch of studies, we are managing specific sites, and it depends on what grows back and how quickly. So this meta-analysis may be up-to-date, but I think local fuels folks are better able to know (and have reason to know) how treatment effectiveness would decline over time.
Yes, treatment effectiveness declines over time. Back in the 1980s, I worked on thinning shaded fuel breaks ~15 – 20 years after they were first created. Lots of brush, but they would still have worked to slow a crown fire.
“reductions in severity between 62% and 72% relative to untreated areas.” John Bailey of Oregon State University said, It’s just physics. The more wood you put of a camp fire, the hotter (more intense) it burns. Put on a small amount of wood and you have a smaller fire.
It’s good to keep seeking clarity on the effectiveness of fuel treatments, but that is not the only goal we are seeking on our public lands. Relevant questions for future science might be:
— What are the ecological and other trade-offs for each fuel treatment method? (e.g., soil, water, wildlife, carbon, snags)
— Are there methods of fuel treatment that remain effective but have fewer trade-offs, such as prescribed fire and non-commercial thinning?
excellent points!
Of course, project analysis should always include site-specific conditions. I also think that the “No Treatment” option should be better analyzed, using site-specific conditions.
I have worked on projects that include multiple fuels treatments. Such non-commercial tasks are paid for with logs from commercial thinning units.
Research opportunity: how are projects evaluating the effects of no action? They should be using the best available science for the site to project the future (both desired outcomes and tradeoffs) with and without the proposed action. Which should be providing site-specific answers to the questions we talk about here in generalities.
I think such ideas are important for full transparency and thorough analysis. In some projects, forest stands on different aspects are substantially different, and we should not be using the more general ideas of Forest Service critics. Personally, I think it is important to ‘cultivate’ and enhance the idea of judicial deference to Forest Service analysis. It is important that the USFS can justify its scientific decisions, as well as tossing out ‘agenda-based science’ ideas.