Reduce Crown Fire Potential Research Articles

TREE-LEVEL FUEL CONNECTIVITY TO ASSESS CROWN WILDFIRE POTENTIAL BY UAS-BASED PHOTOGRAMMETRY

Abstract. Evaluating the potential for crown fires remains a pivotal concern in wildfire management because it affects fire behavior, causing them to spread further. In this work, we propose a methodology to assess crown fire potential based on the tree connectivity at crown level from UAS (Unmanned Aircraft Systems)-based Structure-from-Motion Photogrammetry. The approach is usable in a large landscape with the aim of reducing crown fire potential by considering the spatial variability of fuels within a stand. The utilization of UAS for photogrammetry holds immense promise in transforming the approach to assessing and managing forest fires. This cutting-edge technology offers the potential to deliver highly precise and comprehensive data concerning forest structure and connectivity, thereby presenting a groundbreaking opportunity for enhanced forest fire analysis and control.

Ecological restoration guided by historical reference conditions can increase resilience to climate change of southwestern U.S. Ponderosa pine forests

Broad-scale forest restoration projects are implemented across the western United States to restore seasonally dry, frequent-fire-adapted ecosystems to improve ecological function and enhance resilience by increasing resistance to crown fire and climatic stressors. Despite the widespread use of restoration treatments that center on tree thinning and application of prescribed fire, the longevity of beneficial effects and the robustness of outcomes under future climate change predictions remains unclear. In this study, we remeasured a set of experimental areas established a minimum of 20 years ago that comprise a network of ponderosa pine (Pinus ponderosa) forest restoration study sites in northern Arizona. We analyzed ecological resiliency by evaluating forest conditions in terms of resistance to climatic stressors and potential crown fire in units that were thinned following evidence-based restoration guidelines (ERG), then burned with prescribed fire at multiple intervals, compared against paired untreated controls. Resilience indicators included forest structure, tree mortality, tree growth, regeneration, canopy fuels, and crowning index. We also simulated future forest conditions under a warming climate scenario (RCP 4.5) with a range of prescribed fire return intervals. Results indicated that experimental areas where restoration treatments were implemented remained more resilient to climate stressors compared to controls after 20 years. Treated areas had significantly lower tree mortality and greater average diameter growth compared to controls. Furthermore, forest structure generally remained similar to historical reference conditions in treated units with the exception of increases in ingrowth of sprouting species at the drier sites. Canopy fuel load and crown fire hazard in treated units remained significantly lower than controls, indicating that treatments remained effective in reducing crown fire potential over the 20-year study period without the need for additional tree thinning. Modeling basal area, crowning index, and the proportion of basal area in large trees under a future warming scenario suggested that the treated units underwent less changed than untreated areas. Under climate change, management of fire regimes even at longer-than-historical intervals (historical ≈ 5 yr, tested 5, 10, and 20 yr) would maintain basal area within our historical range of variability and maintain fire resistant forest over the next several decades. However, decline by the end of the century is concerning. Our results suggest that forest restoration treatments, guided by historical reference conditions, promote ecological resilience in the long-term and continued maintenance burning into the future is likely warranted even with continued drought and warming.

An Effects Assessment Framework for Dry Forest Conservation

On the Ground • Large patches of dry conifer forests have burned as high intensity crown fire, threatening life, property, and natural resources. • Conservation practices such as mechanical thinning can reduce crown fire potential while promoting other benefits such as restoring forest heterogeneity, reducing post-fire erosion risk, and improving wildlife habitat. • We report on a pilot study to apply landscape-scale effects modeling in the Colorado Front Range as a potential framework for forestlands CEAP. • Spatially explicit estimates of conservation benefits to multiple resources provide a quantitative means to evaluate competing projects and to prioritize conservation outreach.

Divergent trends in ecosystem services under different climate-management futures in a fire-prone forest landscape

While ecosystem services and climate change are often examined independently, quantitative assessments integrating these fields are needed to inform future land management decisions. Using climate-informed state-and-transition simulations, we examined projected trends and tradeoffs for a suite of ecosystem services under four climate change scenarios and two management scenarios (active management emphasizing fuel treatments and no management other than fire suppression) in a fire-prone landscape of dry and moist mixed-conifer forests in central Oregon, USA. Focal ecosystem services included fire potential (regulating service), timber volume (provisioning service), and potential wildlife habitat (supporting service). Projections without climate change suggested active management in dry mixed-conifer forests would create more open forest structures, reduce crown fire potential, and maintain timber stocks, while in moist mixed-conifer forests, active management would reduce crown fire potential but at the expense of timber stocks. When climate change was considered, however, trends in most ecosystem services changed substantially, with large increases in wildfire area predominating broad-scale trends in outputs, regardless of management approach (e.g., strong declines in timber stocks and habitat for closed-forest wildlife species). Active management still had an influence under a changing climate, but as a moderator of the strong climate-driven trends rather than being a principal driver of ecosystem service outputs. These results suggest projections of future ecosystem services that do not consider climate change may result in unrealistic expectations of benefits.

Exploring tree crown spacing and slope interaction effects on fire behavior with a physics-based fire model

ABSTRACTA substantial proportion of forests in the Republic of Korea are characterized by dense, young-growth pine stands which are prone to burn, particularly in the dry spring and fall seasons. Forest fuel reduction by thinning is needed to reduce the risk of catastrophic forest fire in Korea, but thinning guidelines to effectively reduce crown fire potential are not well established, particularly in areas with steep slopes. We describe an exploration of the interaction of different tree spacings, forest age classes, and slopes using the Wildland–urban interface Fire Dynamics Simulator (WFDS), a physics-based fire behavior model. A total of 36 simulations were performed using two terrain slopes, three stand ages and six tree spacings. Our results suggest that tree spacing significantly affects how fires propagate through forest canopies. We observed large reductions in fire size and intensity when tree spacing approached crown width. Also, most crown fires in our simulation stopped spreading through the canopy in less than 100 m when tree spacing was at least 6 m. We found that a different range of tree spacings was required to limit fire size, intensity, and fire spread distance according to its age class and the terrain slope. Although this exploratory study is only a first step in assessing the potential effectiveness of thinning treatments on fire behavior in steep terrain, this study demonstrates a potential use of WFDS for testing fuel reduction thinning guidelines. Future studies should assess sensitivity to different wind speeds and a broader range of fuel characteristics.

Developing a computerized approach for optimizing individual tree removal to efficiently reduce crown fire potential

Thinning is a common silvicultural treatment being widely used to restore different types of overstocked forest stands in western U.S. because of its effect on changing fire behavior. Typically, thinning is applied at the stand level using prescriptions derived from sample plots that ignore variability in tree sizes and location within stands. Thinning prescriptions usually specify tree removal in terms of number of trees or basal area, resulting in a large number of cut-tree spatial patterns that meet the same prescription. However, the effect of each pattern on reducing crown fire potential can vary widely depending on the spatial distribution of leave-trees after treatment. Additionally, stand-level thinning prescriptions ignore cut-tree locations, which influence the economic efficiency of the thinning operations. Lastly, decisions on tree selection affect future competition levels of remaining trees, but the associated spatial and temporal effects on tree growth and crown fire potential over time are not considered in the development of thinning prescriptions. To address the limitations of current stand-level thinning practices, we designed a computerized approach to optimize individual tree removal and produce site specific thinning prescriptions that efficiently reduce crown fire potential. Based on stem map and tree attributes derived from light detection and ranging (LiDAR) technology and a distance-dependent individual tree growth model, current and future tree-level fuel connections between adjacent trees were predicted and used as measures of crown fire potential. The approach makes the spatial selection of cut- and leave-trees that most efficiently reduces crown fire initiation and propagation over time while ensuring cost efficiency of the thinning treatment. Application results on a forest stand in western Montana show that the optimal tree selection provided by the computerized approach can reduce crown fire potential more efficiently than current thinning practices represented by a manual selection of tree removal.

Modeling tree-level fuel connectivity to evaluate the effectiveness of thinning treatments for reducing crown fire potential

Land managers have been using fire behavior and simulation models to assist in several fire management tasks. These widely-used models use average attributes to make stand-level predictions without considering spatial variability of fuels within a stand. Consequently, as the existing models have limitations in adequately modeling crown fire initiation and propagation, the effects of fuel treatments can only be evaluated based on average conditions, where the effects of thinning design (e.g., cut-tree locations) on changing fire behavior are largely ignored. To overcome these limitations, we coupled an advanced physics-based fire behavior model with light detection and ranging (LiDAR) technology to capture the spatial distribution of trees within stands and model crown fire initiation and propagation in more detail. Advanced physics-based fire behavior models are computationally demanding, and it is not currently feasible to run such models for large landscapes (thousands of hectares) at which fuel treatments are often considered. Thus, to extend the capabilities of these fine scale models to larger landscapes, we developed logistic regression models based on tree data and fire behavior model output to predict crown fire initiation and propagation for given tree locations and attributes for two weather scenarios, representing average and severe conditions, for our study area. We applied these regression models and used tree-level fuel connectivity prediction as measures to evaluate the effectiveness of thinning treatments for reducing crown fire potential. We demonstrate this method using LiDAR-derived stem map and tree attributes developed for a 4.6-ha forest stand in western Montana, USA.

Patterns of fuel types and crown fire potential in Pinus halepensis forests in the Western Mediterranean Basin

Using the databases from the Spanish Forest Inventories, we have classified the forest structures of Pinus halepensis plots across the Iberian Peninsula into different fuel types as a function of the most common fire types that can be supported. The purposes of this study are to determine (i) the proportion of the different fuel types and fire type associated with different disturbance scenarios (undisturbed, after a recent wildfire, after an old wildfire and after thinning), (ii) the effect of climate and soil type on the distribution of fuel types and (iii) the effect of the different disturbance scenarios on the transitions between these fuel types. After a recent wildfire the risk of spreading active crown fires was reduced but the risk increased with time since last fire and in undisturbed areas. Climate and stoniness influenced the spatial distribution of fuel types and the potential crown fire risk. There was a lower risk of active crown fires when there was higher aridity and higher stoniness. Disturbances modify the transitions between fuel types; after a wildfire there was the highest change in fuel types with an increase of fuel type one with open forest structures and the presence of plots without trees that are linked to lower risk of active crown fires. There was also a reduction of fuel types 3 and 4, which burn with high intensity during a wildfire. In the absence of disturbances or after an old wildfire, changes between fuel types were slow, usually leading to increasing canopy closure and higher risk of active crown fires. After thinning there were also important changes in fuel types, with a reduction of active crown fire risk after thinning from below and heavy thinning. Fire plays an important role in maintaining landscape heterogeneity. As a consequence of climate warming, new areas with high structural continuity will increase the risk of extreme fire behavior, and for this reason, small wildfires and specific thinning treatments are the key to reduce crown fire potential.

Restoration Treatment Effects on Stand Structure, Tree Growth, and Fire Hazard in a Ponderosa Pine/Douglas-Fir Forest in Montana

Abstract Crown fires that burned thousands of ha of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests in recent years attest to the hazardous conditions extant on the western landscape. Managers have responded with broad-scale implementation of fuel reduction treatments; however. because threats to pine forests extend beyond fire, so too must the approaches to address them. This western Montana study evaluated four treatments in a randomized complete block experiment for their effects on stand structural characteristics, growth increment, and crown fire potential. Evaluation of control, burn-only, thin-only, and thin-burn treatments showed that the combined thin-burn treatment had the greatest number of desired effects, the burn-only had the fewest, and the thin-only was intermediate. The thin-burn significantly reduced stand density, canopy cover, torching hazard, and crowning hazard and increased average diameter, height-to live-crown, and basal area increment; the thin-only reduced stand density, canopy cover, and crowning hazard and increased average diameter and basal area increment; and the burn-only reduced torching hazard and increased height-to-live crown. These structural and growth effects are related to or influence numerous stand/ecosystem properties at our site, including diameter distributions, species composition, large-tree development potential, overall tree vigor, potential for shade-intolerant tree regeneration, and resiliency to fire. Results demonstrate that well-designed restoration treatments can promote key short-term stand and ecosystem responses while significantly reducing crown fire potential.

Fire treatment effects on vegetation structure, fuels, and potential fire severity in western U.S. forests

Forest structure and species composition in many western U.S. coniferous forests have been altered through fire exclusion, past and ongoing harvesting practices, and livestock grazing over the 20th century. The effects of these activities have been most pronounced in seasonally dry, low and mid-elevation coniferous forests that once experienced frequent, low to moderate intensity, fire regimes. In this paper, we report the effects of Fire and Fire Surrogate (FFS) forest stand treatments on fuel load profiles, potential fire behavior, and fire severity under three weather scenarios from six western U.S. FFS sites. This replicated, multisite experiment provides a framework for drawing broad generalizations about the effectiveness of prescribed fire and mechanical treatments on surface fuel loads, forest structure, and potential fire severity. Mechanical treatments without fire resulted in combined 1-, 10-, and 100-hour surface fuel loads that were significantly greater than controls at three of five FFS sites. Canopy cover was significantly lower than controls at three of five FFS sites with mechanical-only treatments and at all five FFS sites with the mechanical plus burning treatment; fire-only treatments reduced canopy cover at only one site. For the combined treatment of mechanical plus fire, all five FFS sites with this treatment had a substantially lower likelihood of passive crown fire as indicated by the very high torching indices. FFS sites that experienced significant increases in 1-, 10-, and 100-hour combined surface fuel loads utilized harvest systems that left all activity fuels within experimental units. When mechanical treatments were followed by prescribed burning or pile burning, they were the most effective treatment for reducing crown fire potential and predicted tree mortality because of low surface fuel loads and increased vertical and horizontal canopy separation. Results indicate that mechanical plus fire, fire-only, and mechanical-only treatments using whole-tree harvest systems were all effective at reducing potential fire severity under severe fire weather conditions. Retaining the largest trees within stands also increased fire resistance.

Characterizing Canopy Fuels to Predict Fire Behavior in Pitch Pine Stands

Abstract Destructive sampling of 31 pitch pine (Pinus rigida P. Mill) trees ranging in dbh from 2.7 to 42.5 cm and in height from 4.1 to 23.8 m provided a complete inventory of needles and small-diameter branch weights used to characterize canopy fuels to predict fire behavior in pitch pine stands. Regression equations using dbh as an independent variable predict canopy bulk density with an r2 > 0.93. The results provide managers with a method of evaluating the effectiveness of thinning operations in reducing crown fire potential in well-stocked stands. To demonstrate the application of the method, we calculated the wind speed (Crowning Index [CI]) needed to sustain an active crown fire in thinned and unthinned pitch pine stands in Montague, Massachusetts. Thinning to 2.8 m2/ha basal area increased the CI from 34 to 98 km/hour.

Using stand-level optimization to reduce crown fire hazard

This study evaluated the ability to generate prescriptions for a wide variety of stands when the goal is to reduce crown fire potential. Forest managers charged with reducing crown fire potential while providing for commodity and ecological production have been hampered by the complexity of possible management options. A program called Stand-Level Optimization with Multiple Objectives (SLOMO) was developed that uses a dynamic programming based algorithm to find near-optimal solutions for a number of problem formulations. Sixty-four stand types from eastern Oregon were evaluated with SLOMO with the goal of reducing crown fire potential. Two attributes of stand canopies were manipulated, canopy base height (CBH) and canopy bulk density (CBD). Additionally, a baseline case of “grow only” was evaluated for each stand to help understand the potential effects of active management. Results illustrate the potential for optimization methods to provide useful management strategies to reduce crown fires. Relative to the grow only goal, treatments are derived that achieve and maintain target levels for CBH and CBD over a 100-year projection. Simulations show a substantive decrease in crown fires, especially active crown fires, with treatments derived from optimization procedures.

Forest fuel treatments in western North America: Merging silviculture and fire management

For many years silviculture and fire management have mostly been separate forestry disciplines with disparate objectives and activities. However, in order to accomplish complex and multiple management objectives related to forest structure, fuels, and fire disturbance, these two disciplines must be effectively integrated in science and practice. We have linked scientific and management tools to develop an analytical approach that allows resource managers to quantify and evaluate the effectiveness of alternative fuel treatments in dry interior forests of western North America. The principal tool is the Fire and Fuels Extension of the Forest Vegetation Simulator (FFE-FVS) for characterizing fuel succession and fire behaviour, and for quantifying and visualizing stand structure. FFE-FVS provides a user-friendly framework that facilitates rapid evaluation of thinning and surface fuel treatments intended to reduce crown fire potential and fireline intensity. This approach quantifies fire hazard at small and large spatial scales, assists with treatment priorities and schedules, and generates stand and landscape visualizations that facilitate decisions about appropriate fuel treatments. Key words: fire behaviour, fire hazard, fuel treatments, silviculture