Does earlier work change a later wildfire?
Researchers can compare treated and untreated areas reached by wildfire. A 2024 review combined evidence from 40 studies in western US conifer forests. Several treatments involving burning were associated with substantially lower subsequent severity in the analyzed seasonally dry forests.
Lower fire severity is a measured effect. Its value depends on the trees, habitat and people we are trying to protect.
How much lower was severity in the analyzed treated areas reached by wildfire?
How to read these averages
The review combines several severity measures. Individual results vary; the full paper provides uncertainty intervals and methods. It did not establish statistically different overall effects among these three treatment categories. The bars show reported means, not a forecast for an individual project.
| Treatment | Mean reduction |
|---|---|
| Prescribed burning | 62% |
| Thinning + pile burning | 62% |
| Thinning + prescribed burning | 72% |
What the synthesis compared
Davis and colleagues reviewed 40 studies with treated and untreated observations after wildfire, comprising 172 sites and 256 observations. The analysis combines several severity measures using relative effect sizes.
The main-page bars show reported mean reductions for three treatment categories. They are not individual site forecasts. The paper’s Figure 3 and methods supply uncertainty and the treatment-age comparisons needed for a fuller interpretation.
Interpret the averages without turning them into a ranking
The review reports average reductions of 72% for thinning plus prescribed burning, and 62% for thinning plus pile burning or prescribed burning alone. It did not establish statistically different overall effects among these three categories.
These relative effects on severity measures apply to the analyzed settings where wildfire followed treatment. They are not percentages of acreage restored, fires prevented or money saved. Selection of a method also involves ecological objectives and feasibility.
The work changes over time
Across the review’s treatment and forest categories, average reduction was 66% when wildfire occurred within ten years and 28% when it occurred more than ten years later. Those groups summarize observations; they do not define a universal ten-year reburn deadline.
Maintenance and repeated activities belong in both the ecological explanation and the cost account. A treatment’s date helps interpret what it could influence when a later fire arrived.
An Oregon study, with several treatment histories
The Egley study examined the 2007 fire complex in Oregon and returned to field sites one and nine years afterward. Its treatments included harvest, thinning, piling/burning and prescribed fire; they cannot all be relabeled prescribed burns.
The study found lower initial severity in treated areas and differences in later fuels and vegetation. Its reported percentage/hectare totals contain a denominator discrepancy that needs clarification, so this guide does not derive a new acreage estimate from those figures.
Read the evidence
- Davis and colleagues · Review of 40 treatment studies ↗2024; sections 2.1–2.2 and 3.2.1; Figure 3. Relative effects on severity in treated areas subsequently reached by wildfire
- Dodge and colleagues · Egley Fire Complex study ↗2019; abstract, methods and one-/nine-year field observations. Reported percentage/hectare denominators require clarification