Fuel Reduction Treatments Research Articles

Fuel treatment effectiveness in the context of landform, vegetation, and large, wind-driven wildfires.

Large wildfires (>50,000ha) are becoming increasingly common in semiarid landscapes of the western United States. Although fuel reduction treatments are used to mitigate potential wildfire effects, they can be overwhelmed in wind-driven wildfire events with extreme fire behavior. We evaluated drivers of fire severity and fuel treatment effectiveness in the 2014 Carlton Complex, a record-setting complex of wildfires in north-central Washington State. Across varied topography, vegetation, and distinct fire progressions, we used a combination of simultaneous autoregression (SAR) and random forest (RF) approaches to model drivers of fire severity and evaluated how fuel treatments mitigated fire severity. Predictor variables included fuel treatment type, time since treatment, topographic indices, vegetation and fuels, and weather summarized by progression interval. We found that the two spatial regression methods are generally complementary and are instructive as a combined approach for landscape analyses of fire severity. Simultaneous autoregression improves upon traditional linear models by incorporating information about neighboring pixel burn severity, which avoids type I errors in coefficient estimates and incorrect inferences. Random forest modeling provides a flexible modeling environment capable of capturing complex interactions and nonlinearities while still accounting for spatial autocorrelation through the use of spatially explicit predictor variables. All treatment areas burned with higher proportions of moderate and high-severity fire during early fire progressions, but thin and underburn, underburn only, and past wildfires were more effective than thin-only and thin and pile burn treatments. Treatment units had much greater percentages of unburned and low severity area in later progressions that burned under milder fire weather conditions, and differences between treatments were less pronounced. Our results provide evidence that strategic placement of fuels reduction treatments can effectively reduce localized fire spread and severity even under severe fire weather. During wind-driven fire spread progressions, fuel treatments that were located on leeward slopes tended to have lower fire severity than treatments located on windward slopes. As fire and fuels managers evaluate options for increasing landscape resilience to future climate change and wildfires, strategic placement of fuel treatments may be guided by retrospective studies of past large wildfire events.

Interactive effects of fuels reduction and large herbivores on shrub assemblages in dry conifer forests of the interior west, USA

Deciduous shrubs are widely distributed throughout temperate and boreal conifer forests and influence a wide range of ecological processes and forest resources. In the interior western U.S., many deciduous shrubs are highly preferred forage by wild (elk, Cervus canadensis; deer, Odocoileus spp.) and domestic (cattle) ungulates which can influence shrub abundance, composition, structural characteristics, and related ecological processes and interactions. Stand disturbances and silvicultural practices can also affect shrub assemblages and managers in the interior western U.S. are increasingly implementing fuels reduction treatments such as stand thinning and prescribed fire to reduce fuel loads caused by more than a century of fire suppression. We evaluated the effects of ungulate herbivory and fuels reduction, alone and in concert, on deciduous shrub assemblages in coniferous dry forests of the interior west. We measured shrub richness, diversity, height, abundance and community composition in forest stands that underwent fuels reduction 15–17 years earlier, compared to untreated stands where no silvicultural treatments have occurred in over 50 years. Within each stand type, we also measured shrub assemblages in stands with and without ungulate herbivory. Shrub richness, diversity, frequency and height all declined in stands subjected to either fuels reduction treatments or herbivory; effects were most pronounced under the combined effect of fuels reduction and herbivory. Fuels reduction and herbivory also resulted in significant differences in shrub abundance and assemblage composition. Fuels reduction in dry forests with abundant ungulates may contribute to suppressed, more homogenous shrub communities. These effects may result in unintended impacts or alterations to important ecosystem processes and forest resources. Our results highlight the importance of considering responses of forest resources with low economic value, such as shrubs, in forest management activities.

Fire Behavior, Fuel Consumption, and Turbulence and Energy Exchange during Prescribed Fires in Pitch Pine Forests

Prescribed fires are conducted extensively in pine-dominated forests throughout the Eastern USA to reduce the risk of wildfires and maintain fire-adapted ecosystems. We asked how fire behavior and fuel consumption during prescribed fires are associated with turbulence and energy fluxes, which affect the dispersion of smoke and transport of firebrands, potentially impacting local communities and transportation corridors. We estimated fuel consumption and measured above-canopy turbulence and energy fluxes using eddy covariance during eight prescribed fires ranging in behavior from low-intensity backing fires to high-intensity head fires in pine-dominated forests of the New Jersey Pinelands, USA. Consumption was greatest for fine litter, intermediate for understory vegetation, and least for 1 + 10 hour wood, and was significantly correlated with pre-burn loading for all fuel types. Crown torching and canopy fuel consumption occurred only during high-intensity fires. Above-canopy air temperature, vertical wind velocity, and turbulent kinetic energy (TKE) in buoyant plumes above fires were enhanced up to 20.0, 3.9 and 4.1 times, respectively, compared to values measured simultaneously on control towers in unburned areas. When all prescribed fires were considered together, differences between above-canopy measurements in burn and control areas (Δ values) for maximum Δ air temperatures were significantly correlated with maximum Δ vertical wind velocities at all (10 Hz to 1 minute) integration times, and with Δ TKE. Maximum 10 minute averaged sensible heat fluxes measured above canopy were lower during low-intensity backing fires than for high-intensity head fires, averaging 1.8 MJ m−2 vs. 10.6 MJ m−2, respectively. Summed Δ sensible heat values averaged 70 ± 17%, and 112 ± 42% of convective heat flux estimated from fuel consumption for low-intensity and high-intensity fires, respectively. Surprisingly, there were only weak relationships between the consumption of surface and understory fuels and Δ air temperature, Δ wind velocities, or Δ TKE values in buoyant plumes. Overall, low-intensity fires were effective at reducing fuels on the forest floor, but less effective at consuming understory vegetation and ladder fuels, while high-intensity head fires resulted in greater consumption of ladder and canopy fuels but were also associated with large increases in turbulence and heat flux above the canopy. Our research quantifies some of the tradeoffs involved between fire behavior and turbulent transfer of smoke and firebrands during effective fuel reduction treatments and can assist wildland fire managers when planning and conducting prescribed fires.

Wildfire Risk and Hazardous Fuel Reduction Treatments Along the US-Mexico Border: A Review of the Science (1986-2019)

The ecosystems along the border between the United States and Mexico are at increasing risk to wildfire due to interactions among climate, land-use, and fuel loads. A wide range of fuel treatments have been implemented to mitigate wildfire and its threats to valued resources, yet we have little information about treatment effectiveness. To fill critical knowledge gaps, we reviewed wildfire risk and fuel treatment studies that were conducted near the US-Mexico border and published in the peer-reviewed literature between 1986 and 2019. The number of studies has grown during this time in warm desert to forest ecosystems on primarily federal lands. The most common study topics included fire effects on native species, the role of invasive species and woody encroachment on wildfire risk, historical fire regimes, and remote sensing and modeling to study wildfire risk across the landscape. A majority of fuel treatment studies focused on prescribed burns, and fuel treatments collectively had mixed effects on mitigating future wildfire risk and threats to ecosystems depending on vegetation and fire characteristics. The diversity of ecosystems and land ownership along the US-Mexico border present unique challenges for understanding and managing wildfire risk, and also create opportunities for collaboration and cross-site studies to promote knowledge across broad environmental gradients.

Effects of fuel reduction timber harvests on forage resources for deer in northeastern Washington

Fire suppression has increased the canopy cover, stocking density, and fuel loads of dry forests in the inland northwestern United States. These changes not only lead to high-severity, stand-replacing wildfires that may threaten human safety and further alter natural forest communities, but also reduce light transmission to the forest floor, which can limit production of herbaceous and woody understory vegetation that serves as forage for wild ungulates. Therefore, forest managers have implemented fuels reduction treatments that reduce the density of standing trees in mature stands to restore historic conditions, promote healthy forests, and reduce wildfire risk. To test the hypothesis that these treatments also improve the quality and quantity of forage resources for wild ungulates, we measured biomass, plant species composition, and nutritional quality of understory vegetation in 106 untreated and treated 0.5-ha plots that ranged from 1 to 22 years since treatment and 2–100% canopy cover in Douglas-fir (Pseudotsuga menziesii)/ponderosa pine (Pinus ponderosa) forests in the Colville National Forest of northeastern Washington. On average, fuels reduction treatments halved basal area and overstory canopy cover, doubling understory vegetation biomass. The most nutritious plants (i.e., composing suitable biomass) and plants most likely to be consumed by deer (i.e., acceptable biomass) increased with decreasing forest canopy cover, and increased with time since treatment for approximately 14 years post-harvest, but suitable biomass began declining thereafter. Understory plant biomass also responded to a range of site, weather, and environmental variables, especially those influencing moisture gradients. Our results indicate that active management prescriptions intended to reduce fuel loads posed by overstocked conifers can also increase the amount of high quality forage for deer and other wild ungulates, especially when carefully planning the timing, intensity, and rotation schedules of fuels reduction treatments.

Fuel treatments change forest structure and spatial patterns of fire severity, Arizona, U.S.A.

Fuel reduction treatments are often designed to achieve multiple resource management objectives in addition to reducing potential fire hazard. In the White Mountains of Arizona State (U.S.A.), the 2014 San Juan Fire burned through several thinning prescriptions designed to achieve wildlife habitat objectives. Many studies have documented reduced fire severity for a standard set of fuel treatments, but the range of variability in fuel treatment effectiveness for alternative treatment designs is poorly understood. We used nonlinear mixed-effects modeling to estimate the distance into the treated area at which fire severity decreases and randomization tests to compare forest structure. High-severity fire effects were estimated to be reduced between 114 m and 345 m into the treated area. The range of variability in observed-distance high-severity fire effects persist into the treated area and, in conjunction with estimated relationships between posttreatment forest structure and severity, can inform the design of alternative fuel treatment prescriptions with various target prescriptions. We found that as cover was maintained in a treatment unit for wildlife habitat, the size of the fuel treatment necessary to observe a reduction in severity needs to be larger. Our study will inform decision makers on the size of treatments required to accomplish management objectives.

Evaluating Model Predictions of Fire Induced Tree Mortality Using Wildfire-Affected Forest Inventory Measurements

Forest land managers rely on predictions of tree mortality generated from fire behavior models to identify stands for post-fire salvage and to design fuel reduction treatments that reduce mortality. A key challenge in improving the accuracy of these predictions is selecting appropriate wind and fuel moisture inputs. Our objective was to evaluate postfire mortality predictions using the Forest Vegetation Simulator Fire and Fuels Extension (FVS-FFE) to determine if using representative fire-weather data would improve prediction accuracy over two default weather scenarios. We used pre- and post-fire measurements from 342 stands on forest inventory plots, representing a wide range of vegetation types affected by wildfire in California, Oregon, and Washington. Our representative weather scenarios were created by using data from local weather stations for the time each stand was believed to have burned. The accuracy of predicted mortality (percent basal area) with different weather scenarios was evaluated for all stands, by forest type group, and by major tree species using mean error, mean absolute error (MAE), and root mean square error (RMSE). One of the representative weather scenarios, Mean Wind, had the lowest mean error (4%) in predicted mortality, but performed poorly in some forest types, which contributed to a relatively high RMSE of 48% across all stands. Driven in large part by over-prediction of modelled flame length on steeper slopes, the greatest over-prediction mortality errors arose in the scenarios with higher winds and lower fuel moisture. Our results also indicated that fuel moisture was a stronger influence on post-fire mortality than wind speed. Our results suggest that using representative weather can improve accuracy of mortality predictions when attempting to model over a wide range of forest types. Focusing simulations exclusively on extreme conditions, especially with regard to wind speed, may lead to over-prediction of tree mortality from fire.

Effects of understory fire management treatments on California Hazelnut, an ecocultural resource of the Karuk and Yurok Indians in the Pacific Northwest

Before widespread fire exclusion policies, American Indians used broadcast understory fires or cultural burns to enhance resources integral for their livelihood and cultural practices. To restore ecocultural resources depleted from decades of fire exclusion and to reduce wildfire risks, the Karuk and the Yurok Tribes of Northwest California are leading regional collaborative efforts to expand broadcast fires and fuel reduction treatments on public, private, and Tribal lands in their ancestral territories. Through collaboration with Karuk and Yurok Tribal members and basketweavers, we evaluated the effects of broadcast fires and three fire proxy treatments on California hazelnut shrubs (Corylus cornuta var. californica) that produce highly valued ecocultural resources for basketry materials. Across a 10 ha Douglas-fir and mixed hardwood forest (500 m a.s.l.) in the Klamath mountains, we established 27 stratified blocks (16 m2) and within each block applied three fire proxy treatments designed and used by Tribal members with an untreated control. These treatments involved manual hazelnut stem cutting, directly blistering hazelnut stems via propane torch, and igniting surface fuels piled within hazelnut shrubs to top-kill stems. Broadcast fire was applied to 12 separate blocks. After a full growing season (12–18 months post-treatment/burn), shrubs were re-measured. We then harvested these stems (n = 604; 50 shrubs) across treatments and compared results with stems gathered independently by two experienced Karuk/Yurok basketweavers (n = 396 and n = 73) from an adjacent broadcast burned site. Compared to the untreated shrubs, pile burning, propane torching, and broadcast burning increased basketry stem production by 7–10 fold (p < 0.001), while the cutting treatment increased production by 4-fold (p = 0.006). Shrubs with relatively greater access to sunlight (southern aspect, ≥51% and <70% canopy cover) produced fewer quality stems when compared to shrubs with an eastern aspect (p < 0.01) and ≥70% canopy cover (p < 0.05). Harvested stems across all treatments displayed similar stem length distributions to those gathered by one of the two basketweavers (p > 0.05). Our results demonstrate that these fire-proxy methods are an effective means to increase the production and quality of basketry materials. Expanding the area and frequency of targeted understory fire-based forest treatments on private, public and Tribal lands in California and the Pacific Northwest would substantially increase the availability of these fire-enhanced ecocultural resources that are currently limited in supply and in high demand.

Effect of thinning and burning fuel reduction treatments on forest carbon and bushfire fuel hazard in Eucalyptus sieberi forests of South-Eastern Australia

More frequent hot and windy weather in fire prone forested landscapes requires that a full suite of fuel reduction measures be investigated for effectiveness in fuel hazard reduction, environmental impact and carbon (C) outcomes. Although prescribed fire and thinning are routinely applied in forests of North America to reduce fuel loads, there are few detailed studies from Australia. We report the impacts of fuel reduction treatments including burning, mechanical thinning and the combination of both on forest C and fuel hazard in open forests dominated by Eucalyptus sieberi in south-eastern Australia. Carbon losses to the atmosphere and redistribution within the forest were calculated from stocks within each fuel category before and after treatment. Mechanical thinning + burning was the most effective treatment for reducing aboveground C and fuel hazard, with major reductions in dead trees, stumps and understorey, as well as stems removed for sale as pulpwood. However forest floor fuel loads increased in thinned treatments relative to control forests. The overall fuel hazard rating in the burn only treatment was significantly reduced from extreme to low immediately following burning. In thinned only stands, the overall fuel hazard rating did not change from the pre-treatment rating of extreme, due to high surface and forest floor fuel loads and loose and flammable bark on the retained overstorey trees. This result suggests the current fuel hazard guide in use in Australia should be revised to enable it to better describe the benefits of thinning for fuel reduction - in this case the removal of about 50% of aboveground C mostly as overstorey trees, and a significant reduction in understorey, dead trees and stumps.

Stand Dynamics of Pinyon-Juniper Woodlands After Hazardous Fuels Reduction Treatments in Arizona

Pinyon-juniper ecosystems occur extensively across western North America, and at the landscape scale, variation in structure and composition is influenced by topographic position, soils, disturbance history, and local climate. The persistent pinyon-juniper woodland is a common structural form, and though they are known to be infrequent-fire systems, there is increasing interest in implementation of hazardous fuels reduction treatments in woodlands, especially in the wildland-urban interface. Few studies have quantified stand dynamics following fuels reduction treatments in persistent woodlands or compared treatment outcomes to conditions that develop under natural disturbance and successional processes. In 2004, we established a randomized, replicated study in woodlands of northern Arizona, and monitored stand dynamics and understory responses to determine how stand-level changes differed between common fuels reduction approaches. We compared the resulting structure with a conceptual state-and-transition model. Results showed that, over the 11 yr after treatment, juniper tree densities decreased by 8.4% and 0.9% but increased by 14.0% and 27.3% in Control, Burn, Thin, and Thin + Burn treatments, respectively. Pinyon tree densities decreased by 1.1% and 3.3%, increased by 12.2%, and decreased 7.9% in Control, Burn, Thin, and Thin + Burn treatments, respectively. All treatments showed fuel load reductions throughout the 11-yr study period and minimal rebound of tree recruitment toward pretreatment conditions. Prescribed fire alone (Burn) maintained persistent woodland conditions. Thinning treatments substantially reduced small tree densities and, with the addition of prescribed fire, produced losses of large trees. Thinning with prescribed fire (Thin + Burn) tended to produce conditions qualitatively unlike those described by our state-and-transition model. Evaluation of these commonly used fuels treatments against our state-and-transition model suggested that concerns regarding loss of ecological integrity may be warranted.

Effects of mastication of burned non-commercial Pinus pinaster Ait. trees on soil compaction and vegetation response

Mastication is commonly used as a fuel reduction treatment to minimize severe wildfires in fire-prone areas worldwide. Although mastication of non-commercial burned trees has become common practice in NW Spain in recent years, little is known about the possible effects on fuels, soil physical properties and vegetation recovery. In this study, sites in NW Spain (Arbo and Soutomaior) where non-commercial Pinus pinaster Ait. stands burned in August 2016 in NW Spain were selected for study. In both sites the fires scorched tree crowns and caused moderate soil burn severity. In January 2017, burned trees in 15 plots (10 in Arbo and 5 in Soutomaior) were masticated using a steel track tractor with a front mounted rotating toothed drum. In addition, five plots in Arbo were masticated using a walking excavator with a mulching head. In the 10 remaining plots (5 in each site) the trees were cut with a chainsaw and manually moved offsite. The fuel distribution categories were determined immediately after mastication. Soil penetration resistance and soil shear strength were measured immediately after wildfire, and also immediately, six months and one year after mastication. Species cover and pine seedling density were measured six months and one year after mastication. Percentage masticated material cover ranged from a mean of 60% (s.e. = 1.5) after mastication by tractor in Soutomaior to a mean of 81% (s.e. = 6.0) after mastication by walking excavator in Arbo. 64–75% of material was shredded after mastication. Mastication had no effect on soil shear strength or soil penetration resistance, and it also did not affect total vegetation cover. Species cover was not significantly affected by any of the environmental variables or masticated material cover. Mean pine seedling density was 0.2 seedlings m−2 in masticated and non-masticated plots, irrespective of the equipment used. Mastication did not favour the establishment of non-native species. Mastication after wildfire does not appear to be detrimental to soil conservation and vegetation recovery although further research is needed to confirm this.

Do Fuel Treatments in U.S. National Forests Reduce Wildfire Suppression Costs and Property Damage?

ABSTRACT This article tests two hypotheses on whether forest fuel reduction treatments (prescribed burning and mechanical methods) reduce wildfire suppression costs and property damages. Data were collected on fuel treatments, fire suppression costs, and property damage associated with wildfires in United States National Forests over a five-year period throughout the continental United States. The continental U.S. pooled data model results show that overall, prescribed burning reduces suppression cost and both fuel treatment types reduce property damages. Further analysis was done to separate the data into seven geographic regions of the United States. Results of the multiple regressions show that in California and the northern Rockies, mechanical fuel treatments reduce wildfire suppression costs, while only in California did prescribed burning reduce the cost. The second hypothesis tested is that fuel treatments, by making wildfires less damaging and easier to control, may reduce property damage. This hypothesis is generally confirmed for hectares treated with prescribed burning in four out of five geographic regions that had a significant coefficient on prescribed fire. Mechanical fuel reduction had a significant effect in reducing property damage in two of the three regions.

Effect of fire and thinning on fine-scale genetic structure and gene flow in fire-suppressed populations of sugar pine (Pinus lambertiana Dougl.)

Historically, frequent, low-severity fires in dry western North American forests were a major driver of ecological patterns and processes, creating resilient ecosystems dominated by widely-spaced pine species. However, a century of fire-suppression has caused overcrowding, altering forest composition to shade-tolerant species, while increasing competition and leaving trees stressed and susceptible to pathogens, insects, and high-severity fire. Exacerbating the issue, fire incidence is expected to increase with changing climate, while fire season has been observed to begin earlier and last longer than historic trends. Forest thinning and prescribed fire have been identified as important management tools to mitigate these risks. Yet little is known of how thinning, fire, or their interaction affect contemporary evolutionary processes of constituent pine species that influence fitness and play an important role in the opportunity for selection and population persistence. We assessed the impact of widely used fuel reduction treatments on fine-scale gene flow on an ecologically important and historically dominant shade-intolerant pine species of the Sierra Nevada, Pinus lambertiana Dougl. Treatment prescription (no-thin-no-fire, thin-no-fire, and fire-and-thin) was found to differentially affect both fine-scale spatial and genetic structure as well as effective gene flow in this species. Specifically, the thin-no-fire prescription increases genetic structure (spatial autocorrelation of relatives) between adults and seedlings, while seed and pollen dispersal increase and decrease, respectively, as a function of increasing disturbance intensity. While these results may be specific to the stands at our study site, they indicate how assumptions relating to genetic effects based on spatial structure can be misleading (for instance, in many stands the presence or absence of spatial structure was not indicative the presence or absence of genetic structure). It is likely that these disequilibrated systems will continue to evolve on unknown evolutionary trajectories. The long-term impacts of management practices on reduced fitness from inbreeding depression should be continually monitored to ensure resilience to increasingly frequent and severe fire, drought, and pest stresses.

Understory Vegetation Responses to 15 Years of Repeated Fuel Reduction Treatments in the Southern Appalachian Mountains, USA

Decades of fire exclusion in the Southern Appalachian Mountains led to fuel accumulation and conversion from open oak-pine woodlands to closed-canopy mesic forests dominated by shade-tolerant hardwoods and shrubs that often do not support a diverse understory. Southern Appalachian forest managers and scientists recognize this and are implementing silvicultural treatments such as prescribed burning, mechanical treatments or a combination of these to restore forest structure. In this study, conducted at the Southern Appalachian Fire and Fire Surrogate Study site in Green River Game Land, North Carolina, we assessed the effects of four fuel reduction methods: burned 4x (B), mechanical treatment 2x (M), mechanical treatment 2x + burned 4x (MB), and control (C) on the changes in understory vegetation guilds from pretreatment to post-treatment years (2001–2016). The MB treatment was most effective at meeting the restoration objectives, as it resulted in increases in oak (ΔMB = 23,400 stems/ha) and pine (ΔMB = 900 stems/ha) stem density, importance value - calculated as the sum of relative cover and frequency - for graminoids (ΔMB = 26.0), and density of oak stems &gt;50 cm in height (ΔMB = 7133 stems/ha). The B and M treatments were generally less effective, but nonetheless met a subset of the restoration objectives. The B treatment reduced ericaceous shrub cover (ΔB = −1.2%) and increased oak stems 10–50 cm in height (ΔB = 10,017 stems/ha), while the M treatment resulted in only modest increases of mesic hardwoods, specifically for yellow-poplar (ΔM = 200 stems/ha) and blackgum (ΔM = 200 stems/ha) as compared with other treatments, but significantly increased mountain laurel and rhododendron cover (ΔM = 10.0%). Overall, these fire and fire surrogate treatments had some success in restoring understory structure, but our findings suggest a slow response in understory herbaceous vegetation.

Mastication of burned non-commercial P. sylvestris L. stands: Effects on soil erosion and vegetation recovery

Forest mastication is frequently used as a fuel reduction treatment aimed at minimising severe wildfires in fire prone areas worldwide. In recent years, mastication of non-commercial burned trees has become common practice in NW Spain, as a way of providing cover on the burned soil and preventing erosion. However, little is known about the possible effects on soil conservation and vegetation recovery. In this study, 20 experimental plots were established in a Pinus sylvestris L. plantation affected by a crown fire that caused moderate-high soil burn severity in the summer of 2016. Immediately after the fire, burned trees were masticated in half of the plots, while burned trees were left standing in the other half of the plots during the first two years after the fire. The objectives of the study were to determine how mastication affected soil erosion, soil physical properties (soil penetration resistance, soil shear strength, soil bulk density) and vegetation recovery. The masticated material covered 43% of the burned soil. During the first year after wildfire + mastication, precipitation was lower than the annual mean level in the area, and the mean soil loss in the untreated burned soils (5.7 Mg ha−1) was not significantly different from that in the masticated plots (5.0 Mg ha−1). Mastication did not have any detrimental effects on either the soil physical properties analysed or on the regeneration of natural vegetation. The results indicated that in addition to mastication of severely burned non-commercial trees, extra mulch should be applied to reduce the risk of soil erosion. Mastication after wildfire is not detrimental to soil conservation. No advantage was obtained by leaving the standing burned trees on site, in relation to reducing soil erosion or enhancing vegetation recovery.

Cost and Productivity of Tethered Cut-to-Length Systems in a Dry-Forest Fuel-Reduction Treatment: A Case Study

AbstractFuel-reduction treatments on steep slopes across federal forests of the western United States have been limited by the high costs associated with cable logging on steeper slopes combined with poor market prospects for small-diameter material (Bolding 2003, Rummer 2008, Han et al. 2016). The emergence of tethered cut-to-length harvesting systems and small wood markets (e.g., biochar) could decrease costs and increase revenue generated from treatments. Over the course of 3 weeks, we observed both tethered (steeper slopes) and untethered cut-to-length fuel-reduction treatment on the Fremont-Winema National Forest in south-central Oregon and interviewed operators. We used those data to derive and contrast hourly costs and productivity for the harvester and forwarder. This was the first time a tethered harvester and forwarder were used in a fuel-reduction treatment on federal forests in this region. We developed and tested a variety of work time model forms for each machine. The mean utilization rate for the harvester was 64 percent on 17 tethered consolidated corridors but 87 percent on 28 untethered consolidated corridors. Similarly, the forwarder had a mean utilization rate of 76 percent on 30 tethered trips and 89 percent on 114 untethered trips. This reduced utilization rate could be because of the direct effects of tethering, the increased complexities of operations associated with steeper slopes, and the stand characteristics (e.g., lower stand density and tree sweep) associated with steeper slopes. Costs during tethered operations were higher than during nontethered operations, but lower than previous reports using cable logging.

Linking fuel, habitat and ground-dwelling mammals in flammable landscapes

Prescribed fire is often applied with the goal of reducing fuel loads and lessening the impact of future wildfires on humans. As fuel represents habitat for some animal species, fuel reduction treatments are likely to affect species’ access to resources. Understanding the interrelationships between fuel, habitat and animal occurrence will help managers of flammable landscapes meet the dual objective of reducing fuel loads and conserving biodiversity. In addition, should fuel hazard assessments reflect habitat structure, fuel hazard scores could be used to predict the response of animals to prescribed fire. This would be useful in many regions where fuel hazard assessments are routinely conducted, but data about habitat change or the direct response of animals are lacking. In this study, we tested the capacity of fuel hazard scores to predict both habitat structure and ground-dwelling mammal occurrence at 187 sites in the Otway Ranges, south-eastern Australia. First, we explored relationships between habitat structure and fuel hazard. Second, we investigated how animals responded to both habitat and fuel. Habitat complexity was positively related to overall fuel hazard, although this varied with net primary productivity. Habitat attributes were best at predicting the occurrence of eight out of nine ground-dwelling mammal species, although seven species were also correlated with components of fuel hazard. Some species were not strongly associated with either habitat or fuel. These species-specific relationships between habitat, fuel and fauna highlight the continuing importance of measuring habitat or animals directly when investigating faunal responses to disturbance. However, in the absence of these data, fire managers can use a common fuel assessment method to predict the effect of fuel reduction on habitat structure and the occurrence of some ground-dwelling mammals.

A stochastic programming model with endogenous uncertainty for incentivizing fuel reduction treatment under uncertain landowner behavior

Reducing the potential damage caused by a wildfire is a problem of significant importance to land and fire managers. Fuel reduction treatment is a well-known method of reducing the risk of fire occurrence and spread on landscapes. However, officials seeking fuel reduction treatments on privately owned lands can only encourage it through incentive programs such as cost-share programs. This research developed a methodology that provides the basis for a decision-making tool to help managers allocate limited cost-share resources among a set of landowners to maximize wildfire risk reduction by implementing a hazardous fuel reduction treatment. A key feature of the methodology is that it incorporates uncertainty in the landowners’ decision of whether or not to implement treatment on their lands. The methodology is based on a stochastic programming model with endogenous uncertainty where the probability that a landowner accepts a cost-share offer to implement a fuel reduction treatment on their land depends on the offer amount. To estimate the probability that a landowner accepts a given cost-share offer amount, we used a predictive modeling technique to analyze landowner survey data. The results provide insight about the effects of different cost-share allocation strategies on the expected damage. Numerical experiments show that the risk-based allocation provides up to 37.3% more reduction in damage compared to other strategies that allocate equal cost-share amounts among landowners. Additionally, the results show that the solution quality is substantially sensitive to changes in the number of resource allocation levels.

Strategically placed landscape fuel treatments decrease fire severity and promote recovery in the northern Sierra Nevada

Strategically placed landscape area treatments (SPLATs) are landscape fuel reduction treatments designed to reduce fire severity across an entire landscape with only a fraction of the landscape treated. Though SPLATs have gained attention in scientific and policy arenas, they have rarely been empirically tested. This study takes advantage of a strategically placed landscape fuel treatment network that was implemented and monitored before being burned by a wildfire. We evaluated treatment efficacy in terms of resistance, defined here as the capacity to withstand disturbance, and recovery, defined here as regeneration following disturbance. We found that the treated landscape experienced lower fire severity than an adjacent control landscape: in the untreated control landscape, 26% of land area was burned with >90% basal area mortality, according to the remote-sensing-derived relative differenced Normalized Burn Ratio (RdNBR), while in the treated landscape only 11% burned at the same severity. This difference was despite greater pre-treatment fire risk in the treatment landscape, as indicated by FARSITE fire behavior modeling. At a more local scale, monitoring plots within the treatments themselves saw greater regeneration of conifer seedlings two years following the fire than plots outside the treatments. Mean seedling densities for all conifer species were 7.8 seedlings m−2 in treated plots and only 1.4 seedlings m−2 in control plots. These results indicate that SPLATs achieved their objective of increasing forest resistance and recovery.

Asian needle ant (Brachyponera chinensis) and woodland ant responses to repeated applications of fuel reduction methods

AbstractAnts (Formicidae: Hymenoptera) are important components of forest ecosystems and can be affected by fuel reduction forest management practices. We assessed the impact of repeated applications of fuel reduction treatments on abundance and diversity of ants within upland mixed‐hardwood forests in the Southern Appalachian Mountains in North Carolina, USA. We established three replicate blocks (~56 ha each) and split each block into four fuel reduction treatments, which included prescribed burning (B), mechanical felling (M), a combination of prescribed burning and mechanical felling (MB), and a control (C; i.e., no treatment). We implemented treatments multiple times (two mechanical thinnings and four prescribed burns) over the course of a 15‐yr period. Due to tree mortality and resultant canopy gaps from high‐severity burns, forest structure was dramatically altered in MB. Over a 3‐yr period (2014–2016), we captured 54,219 ants comprised of 23 genera using pitfall and colored pan traps. Prenolepis imparis was the most common ant species collected, and it was significantly lower in abundance in MB than all other treatments. However, the non‐native species Brachyponera chinensis was more abundant in MB than all other treatments. Thus, some fuel reduction treatments may have consequences for invasive ant colonization in forests. Most ant taxa did not differ in abundance among treatments, suggesting that some fuel reduction practices may affect some, but not all ant species. Our results indicate that some fuel reduction treatments can alter forest ant communities, thus contributing to changing forest ecosystem dynamics. Monitoring of ants and other bioindicators after repeated rounds of fuel reduction treatments could provide useful knowledge that can be used to help balance forest management and biological diversity.