The national Fire and Fire Surrogates study at twenty years

The “Long-term ecological effects of forest fuel and restoration treatments” Special Feature focuses on the status of the national Fire and Fire Surrogates study (FFS) after twenty years of research. The FFS study was initially proposed in response to an important finding of the Sierra Nevada Ecosystem Project (SNEP, 1996) which stated, “Although silvicultural treatments can mimic the effects of fire on structural patterns of woody vegetation, virtually no data exist on the ability to mimic ecological functions of natural fire.” Thus, the FFS was designed as a multisite, multidisciplinary study to evaluate the long-term ecological consequences of prescribed fire and its mechanical surrogates. All treatments were intended to reduce the risk of high-intensity, severe fires while restoring resiliency in widespread seasonally dry forests originally characterized by frequent, low-moderate-intensity fire regimes. It is recognized that the structure and composition of such forests have been altered by fire suppression and exclusion, livestock grazing, invasive species, and preferential harvest of large-diameter trees (Arthur et al., 2021; Hagmann et al., 2021). These changes have created conditions of increased tree density and altered species composition with generally smaller tree sizes, and increased fuel loads in the western United States (US) that help to support increasingly larger and more severe fires as seen over the last few decades (Hagmann et al., 2021). It also appears that where such forests burn severely, they are tending to burn severely in subsequent fires inhibiting recovery to forest and potentially contributing to conversion to non-forest vegetation types (Coop et al., 2020). It is widely thought that forests with these elevated hazard conditions would benefit from some form of active management such as prescribed fire, mechanical treatments, or both. In contrast, fire exclusion in many eastern US oak ecosystems reduces flammability by facilitating the increased abundance of mesophytic species, thus limiting the capacity for restoration with prescribed fire (Alexander et al., 2021). The primary goal of the FFS study was to measure and compare the long-term effectiveness and ecological consequences of using common, locally derived, fuel reduction and forest restoration treatments. The intent of the FFS fuel reduction treatments was to reduce the potential risk of high-severity fire while creating forest structures more resilient to disturbance. Each study site was to use the following three treatments—prescribed fire alone (FIRE), mechanical treatment alone (MECH), mechanical treatment followed by prescribed fire (MECH+FIRE), and untreated controls (Cont). Each treatment would be designed to achieve stand conditions where 80% of the dominant and co-dominant trees would survive a wildfire under 80th percentile fire weather conditions (McIver et al., 2009). Of the original 12 sites (see fig. 1 in Bernal et al., 2025 for site locations), four are still actively engaged in maintaining treatments and data collection on a regular basis—two in the western US and two in the eastern US (wildfires burned two other western FFS sites—Goosenest and Mission Creek—they are discussed below). The FFS network was not maintained largely due to a lack of consistent long-term financial support that has led to many of the original sites becoming paused or intermittently active. Interestingly, all four active sites are university-managed sites, whereas, many of the other sites were managed by federal agencies; however, federal researchers have been key components of all four active FFS sites. The papers presented here are intended to capture the results to date of the FFS study from the remaining four active sites. Working at the University of California Blodgett Forest Research Station, Stephens et al. (2024) found that all three active treatments (FIRE, MECH, MECH+FIRE) produced forest conditions that were much more resistant to wildfire than the untreated control. MECH produced low fire hazards beginning 7 years after the initial treatment because of the decomposition of the masticated fuel bed and MECH+FIRE had lower tree growth than controls. While FIRE reduced modeled wildfire hazard and reintroduced a fundamental ecosystem process, it was done at a net cost to the landowner. Using MECH that included mastication and restoration thinning resulted in positive revenues (see also Hartsough, 2003) and was also relatively strong as an investment in reducing modeled wildfire hazard. The MECH+FIRE treatment represented a compromise between the desire to sustain financial feasibility and the desire to reintroduce fire. The authors further found that the treatments also made forests more resilient to the effects of climate change and drought, although varying in efficacy among treatment types with MECH+FIRE having the largest impact on increasing resilience. At the Northern Rockies study site, on the University of Montana Lubrecht Experimental Forest, Hood et al. (2024) found broad support that MECH and MECH+FIRE can be used to reduce fire hazard, but that MECH+FIRE remains effective for longer. The 20+ year effectiveness of the MECH+FIRE treatment had the added benefit of increasing stable aboveground carbon stocks in the event of a wildfire. The FIRE treatment had limited effect in reducing hazard, likely because many of the Douglas-fir (Pseudotsuga menziesii) had established and grown to fire-tolerant sizes in the absence of frequent, low-intensity fire that would typically kill many smaller trees. The Lubrecht FFS study is unique among other long-term studies in that it demonstrates ecosystem effects not only of forest fuel and restoration treatments, but also of a mountain pine beetle (Dendroctonus ponderosae) outbreak, to which the MECH and MECH+FIRE treatments again promoted high resilience. However, the efficacy of these one-time treatments is waning and follow-up treatments are needed to maintain resilience to multiple disturbance agents. At the Ohio Hills mixed-oak site, Hutchinson et al. (2024) show that repeated fires of moderate and occasionally high intensity led to responses that were similar between the FIRE and MECH+FIRE treatments: reduced dominance of midstory mesophytes, improved regeneration of oaks and hickories, and greater ground-layer plant species richness. The authors also show that fire intensity and ecological responses varied significantly across topographic gradients of energy and moisture. The MECH-only treatment was not a viable fire surrogate as the process of mesophication (oak to maple transition) was actually accelerated in the absence of fire. The paper presented summarizing work from the Green River Game Lands in western North Carolina (Taylor et al., 2025) focuses on FFS treatment effectiveness for promoting oak recruitment into sapling-age classes, with an eye toward arresting (or even reversing) the process of mesophication that is ongoing in Southern Appalachian forests (Nowacki & Abrams, 2008). Repeated FIRE treatments were effective at reducing organic horizon (duff) thickness. Duff consumption in wildfires has been linked to overstory mortality in the region (Carpenter et al., 2021), but the reductions observed in FIRE plots were not associated with such mortality at Green River. As such, FIRE alone may be adequate for mitigating risk to existing overstory trees through duff reduction, but apparently does not position the oaks in the seedling/sapling layer to be competitive with mesophytic species. The only FFS treatment that resulted in increased abundance of oak saplings in the understory was the MECH+FIRE treatment, and this was related to a decrease in basal area (BA) resulting from mortality of overstory trees in those plots. This BA reduction in MECH+FIRE plots was accompanied by significant reductions in duff depth, with the greatest mortality rates associated with the greatest reduction in duff depth. In a paper that simultaneously examined the outcomes of the four active FFS sites, Bernal et al. (2025) found that 20 years after the FFS was initiated, an emerging general theme across all study sites is that fuel treatments work. However, achieving the desired outcome in the long term depends on the types of treatments used and the region where treatments were implemented. In the western, dry mixed-conifer forests of California and Montana, a combination of MECH+FIRE promoted the greatest resiliency by creating stands with larger trees, lower surface fuels, and higher composition of fire-adapted species. In the eastern hardwood forests of Ohio and North Carolina, FIRE was most effective for promoting the resilience of existing overstory trees especially when fire was repeatedly used at frequent intervals. The different interactions across regions, sites, and treatments are a testament to the diversity of fuels and vegetation that exist within frequent-fire ecosystems. Recognizing that frequent-fire ecosystems are not a monolith is a key finding of Bernal et al. (2025). The need to contextualize how we use—or mimic the use of fire to effectively meet objectives is changing over time. Although each site differed in its objectives and approach to management, we consistently found that the original prescriptions were limited by our capacity to anticipate emerging disturbances. Whether it is drought, insects, or non-native species, all sites found that adaptive management is necessary to sustain the long-term success of fuels treatments. The two western FFS sites that were partially burned by wildfires that were not part of this Special Feature also published some interesting results. At the Goosenest FFS site in the southern Cascades of California, Brodie et al. (2024) found strong mitigating effects of treatments on fire behavior and tree mortality, despite 20 years having elapsed since MECH and 10 years since the second entry of FIRE. The MECH+FIRE treatment resulted in the lowest fire severity across all four of their severity metrics and the untreated control the highest. The authors concluded that reducing canopy bulk density via mechanical thinning treatments can help to limit crown fire behavior for 20 years or more. However, reducing surface fuels is necessary to limit scorching and the total crown impacts associated with tree mortality. At the Mission Creek site in the Northeastern Cascades of Washington, Radcliffe et al. (2024) found that by approximately 15 years post-treatment and under 80th percentile fire weather conditions, most plots in all treatments and untreated controls failed to meet target thresholds for surface flame length, basal area mortality, and torching index, while most plots met thresholds for crowning index. The authors found that the MECH+FIRE treatment and intensely applied FIRE and MECH treatments can reduce tree basal area and potential for crown fire for more than a decade. However, additional maintenance treatments may be needed by 15 years after initial treatment to further reduce potential for severe surface fire and high tree mortality in subsequent wildfire. The authors suggest that understanding fuel treatment efficacy and longevity may be improved in future studies by incorporating fine-scale (i.e., plot-level) drivers of variability in stand structure, fuel profiles, and modeled fire behavior, and by using multiple methods of evaluating treatment effectiveness. Going forward, it would appear that the framework created by the FFS study is well-suited to contribute to the recently announced emphasis by US federal, state, and local land management agencies to increase the pace and scale of fuel and restoration treatments in frequent fire-adapted forests. We hope that the Joint Fire Science Program (JFSP) will continue to invest in studies focused on the longevity of fuel treatment effectiveness. Importantly, as several of the sites have experienced wildfires at different times since the FFS study was initially created, they demonstrated the effects of the treatments rather than simply modeling potential impacts. The authors declare no conflicts of interest.