Dry Mixed Conifer Forests Research Articles

Creating Boundary Objects Supports Knowledge Co-development Processes: A Case Study Evaluation from the Colorado Front Range

Abstract This qualitative case study evaluates manager and researcher perceptions of the impact of a place-based, collaborative knowledge co-development process and examines the outcomes of that co-development for changes to management approaches. The USDA Forest Service (Forest Service) Rocky Mountain Research Station General Technical Report 373 (GTR-373) is a codeveloped science synthesis that functions as a boundary object providing a framework for planning, designing, and implementing management action for restoration of ponderosa and dry mixed-conifer forests. The process of creating and socializing the GTR-373 framework fostered continual knowledge exchange and engagement between researchers and managers across different organizations and levels of decision-making. This built trust in the information, improved justification for management action, developed a common foundation for cross-boundary implementation, and increased communication. The framework has been applied across jurisdictions and has been used as a foundational tool for training staff and designing projects. However, adapting the GTR-373 framework across scales remains challenging. Study Implications: This qualitative case study evaluates a co-development process in which researchers and managers from multiple organizations and agencies collaborated to produce a science-informed restoration framework to support forest management on the Colorado Front Range (GTR-373). The process built trust, improved justification for management action, developed a common foundation for implementation, and increased communication. However, cross-boundary management across spatial scales remains challenging, and managers interpret information through organizational mandates and site-specific context. Sustained collaboration between researchers and land managers can help make science actionable and relevant at the appropriate scale for planning and management across expertise and jurisdictional boundaries.

Prescribed fire lessens bark beetle impacts despite varied effects on fuels 13 years after mastication and fire in a Sierra Nevada mixed-conifer forest

Mastication, thinning, and prescribed fire can help shift fire-prone forests to a structure and composition more resilient to wildfire, but the ability to evaluate treatment effectiveness requires monitoring forest response to disturbances over time after treatment. In this study, we investigated fuel loadings, forest structure, and tree growth to assess treatment legacies thirteen years after mastication, prescribed fire, and surface fuel pull-back from tree boles in Sierra Nevada mixed-conifer forest. An outbreak of bark beetles between 2011 and 2018 impacted all plots but burned treatments had lower overstory mortality relative to unburned treatments which experienced an 80 % decline in live tree biomass. Tree diameter, canopy density, and surface fuel loadings became similar across all treatments during the 13 year time period. Height to live crown remained elevated in burned treatments relative to the control but had lowered by an average of 1.9 ± 0.3 (SE) m across all treatments. Radial tree growth did not have a sustained response to treatment and was greater in burned treatments for only a single year, 2011, several years post-treatment. Prescribed fire decreased duff mass by 56 % relative to unburned treatments but did not affect forest floor bulk density. Downed woody fuel loadings (1-h – 1000-h) were similar across treatments. The invasive Bromus tectorum (cheatgrass) had uniformly high cover across treatments. Whereas treatments were largely ineffective at producing long-term reductions in surface fuel loadings, the enduring reductions in duff loadings and reduced overstory mortality support the long-term utility of prescribed fire. Cumulatively, our results highlight the potential for prescribed fire to reduce overstory mortality and duff loadings in dry mixed-conifer forests, thereby contributing more effectively to fire-resilient characteristics relative to other fuel reduction treatments.

Modeling Juvenile Stand Development and Fire Risk of Post-Fire Planted Forests under Variations in Thinning and Fuel Treatments Using FVS–FFE

In the past, the dry mixed conifer forests of California’s Sierra Nevada mountains experienced frequent low to mixed severity fires. However, due to fire suppression and past management, forest structure has changed, and the new fire regimes are characterized by large, high severity fires which kill a majority of the overstory trees. These new disturbance patterns require novel approaches to regenerate the forest as they are not adapted to large, high severity fires. We forecasted growth and fire behavior of young plantations for 100 years into the future using the Forest Vegetation Simulator (FVS) and its Fire and Fuels Extension (FFE). In these simulations, we tested combinations of different fuel treatments (mastication only, mastication with prescribed burning, and no fuels treatments) with different overstory thinning intensities (residual densities of 370 SDI (stand density index), 495 SDI, 618 SDI (TPH), and no overstory thinning) on stand growth and potential fire behavior using analysis of variance. We compared growth and crowning index at the end of the simulation and the simulation age when the flame length, basal area mortality, and fire type reached low severity between fuel treatment, thinning intensity, and original management of stands (plantation with PCT [precommercial thinning], plantation without PCT, and natural regenerating stands). These comparisons are essential to identify which fuel treatment categories reduce fire risk. We found an overall pattern of decreasing crown fire occurrence and fire induced mortality across all simulations due to increasing canopy base height and decreasing canopy bulk density. In particular, stands with mastication and prescribed burning transitioned from crown fire types to surface fires 10 years earlier compared to mastication only or no fuel treatment. Furthermore, pre-commercially thinned stands transitioned from crown fire states to surface fires 10 years earlier in the simulations compared to un-thinned and naturally regenerating stands. Stands with mastication and burning went below 25% reference threshold of basal area mortality 11 and 17 years earlier before the mastication only and no fuel treatment, respectively. In addition, pre-commercially thinned stands went below 25% basal area mortality 9 and 5 years earlier in the simulation compared to un-thinned or naturally regenerated stands, respectively. Mastication with prescribed burning (MB) was the most effective treatment for quickly reducing fire behavior by consuming surface fuels, thus drastically lowing flame length (e.g., surface flame length of MB was 0.6 m compared to mastication only [1.3 m] and no treatment [1.4 m]). Furthermore, intensive thinning reduced risk of active crown fires spreading through the stand. Prioritizing prescribed burning, when possible, and thinning (both pre-commercially and from below) are the most effective ways to quickly improve fire resistance in mixed conifer plantations. Our results highlight the different stressors that post-fire planted forests experience and how different silvicultural treatments interact over time to reduce fire risk, which demonstrates the importance of treating stands early and the effectiveness of surface fuel treatments.

Too hot, too cold, or just right: Can wildfire restore dry forests of the interior Pacific Northwest?

As contemporary wildfire activity intensifies across the western United States, there is increasing recognition that a variety of forest management activities are necessary to restore ecosystem function and reduce wildfire hazard in dry forests. However, the pace and scale of current, active forest management is insufficient to address restoration needs. Managed wildfire and landscape-scale prescribed burns hold potential to achieve broad-scale goals but may not achieve desired outcomes where fire severity is too high or too low. To explore the potential for fire alone to restore dry forests, we developed a novel method to predict the range of fire severities most likely to restore historical forest basal area, density, and species composition in forests across eastern Oregon. First, we developed probabilistic tree mortality models for 24 species based on tree characteristics and remotely sensed fire severity from burned field plots. We applied these estimates to unburned stands in four national forests to predict post-fire conditions using multi-scale modeling in a Monte Carlo framework. We compared these results to historical reconstructions to identify fire severities with the highest restoration potential. Generally, we found basal area and density targets could be achieved by a relatively narrow range of moderate-severity fire (roughly 365-560 RdNBR). However, single fire events did not restore species composition in forests that were historically maintained by frequent, low-severity fire. Restorative fire severity ranges for stand basal area and density were strikingly similar for ponderosa pine (Pinus ponderosa) and dry mixed-conifer forests across a broad geographic range, in part due to relatively high fire tolerance of large grand (Abies grandis) and white fir (Abies concolor). Our results suggest historical forest conditions created by recurrent fire are not readily restored by single fires and landscapes have likely passed thresholds that preclude the effectiveness of managed wildfire alone as a restoration tool.

Using Airborne LiDAR to Monitor Spatial Patterns in South Central Oregon Dry Mixed-Conifer Forest

Abstract A common forest restoration goal is to achieve a spatial distribution of trees consistent with historical forest structure, which can be characterized by the distribution of individuals, clumps, and openings (ICO). With the stated goal of restoring historical spatial patterns comes a need for effectiveness monitoring at appropriate spatial scales. Airborne light detection and ranging (LiDAR) can be used to identify individual tree locations and collect data at landscape scales, offering a method of analyzing tree spatial distributions over the scales at which forest restoration is conducted. In this study, we investigated whether tree locations identified by airborne LiDAR data can be used with existing spatial analysis methods to quantify ICO distributions for use in restoration effectiveness monitoring. Results showed fewer large clumps and large openings, and more small clumps and small openings relative to historical spatial patterns, suggesting that the methods investigated in this study can be used to monitor whether restoration efforts are successful at achieving desired tree spatial patterns. Study Implications: Achieving a desired spatial pattern is often a goal of forest restoration. Monitoring for spatial pattern, however, can be complex and time-consuming in the field. LiDAR technology offers the ability to analyze spatial pattern at landscape scales. Preexisting methods for evaluation of the distribution of individuals, clumps, and openings were used in this study along with LiDAR individual tree detection methodology to assess whether a forest restoration project implemented in a Southern Oregon landscape achieved desired spatial patterns.

Designing forest restoration projects to optimize the application of broadcast burning

Active forest restoration programs on western US national forests face multiple challenges to meet their broad ecological goals while designing projects that generate sufficient revenue to build and maintain private forest management capacity needed to expand the scale and scope of treatments. We explored ways to design projects where admixing of treatments along gradients of dry and moist mixed conifer forest types could maximize financial viability while including substantial area where broadcast burning could be applied in conjunction with other treatments. In general, we found that restoration treatments in dry forests that included density reduction thinning and broadcast burning resulted in a net projected cost ranging from $110 to $8000 per ha. By contrast, density reduction thinning in moist mixed conifer forests on more productive microsites generated significant commercial timber volume and projected revenue that ranged from $4000 to $20,000 per ha. We used spatial optimization methods to identify potential project areas that maximized revenue while meeting constraints to treat a minimum proportion of each project with broadcast burning. Multiple project area sizes were also explored to understand the effect of restoration scale on financial outcomes. We found that optimal projects in terms of generating revenue to subsidize density reduction and broadcast burning were 810 ha and contained >50% dry forest area. Larger projects and those with a higher percentage of dry forest area resulted in lower revenue, eliminating revenue when projects reached 2700 ha. Forest restoration programs can use these methods to plan and design restoration projects that are financially viable while addressing the broadcast burn backlog in dry forests that require relatively expensive fuel reduction treatments prior to re-introducing fire.

Pelletized inoculation of fire mosses in severely burned conifer forests overcomes initial barriers to Bryum argenteum establishment but does not increase cover

As wildfires increase in extent and severity, we need new tools to rehabilitate burned landscapes. We tested the effectiveness of adding fire moss tissue, produced in the greenhouse, as a bio-inoculant to severely burned soils in dry mixed conifer forests. We conducted three sequential experiments using knowledge gained from previous experiments to fine-tune fire moss delivery methods. The first two experiments began in July 2017, less than ten days after a wildfire in Arizona, United States. First, we added disaggregated (passed through a 2 mm sieve) cultivated moss tissue to burned soil surfaces, which was immediately collected by ants. In a second experiment, we added two preparations designed to reduce ant collection: moss rolled into pellets using diatomaceous earth and moss ground to a powder. Pelletization increased Bryum argenteum cover (F[3,55] = 12.32, p < 0.001) and the number of distinct moss colonies (F[3,55] = 11.87, p < 0.001) when compared to untreated control plots, although cover remained low (1%). A third experiment took place four months postfire in New Mexico. Sieved moss, pelletized moss, and pelletized moss at a high (5×) application rate were added to a burned forest. The high-rate pelletized treatment increased B. argenteum colony count by 140% compared to controls (F[3,44] = 2.37, p = 0.084), but did not increase cover (F[3,44] = 1.19, p = 0.325). At both sites, an extreme drought (Palmer Drought Severity Index < −4) during the winter of 2017–18 likely reduced success. We recommend further refinement and testing of pelletization in non-drought conditions.

Long-Term Effects of Fuel Reduction Treatments on Surface Fuel Loading in the Blue Mountains of Oregon

Fire exclusion and a lengthening fire season has resulted in an era of megafires. Fuel reduction treatments in forested ecosystems are designed to guard against future extreme wildfire behavior. Treatments create a heterogenous landscape and facilitate ecosystem function and resilience in fire-adapted forests of the western United States. Despite widespread recognition that repeated fuel treatments are needed to maintain desired stand characteristics over time, few field studies have evaluated treatment longevity. The Blue Mountains Fire and Fire Surrogate site in northeastern Oregon presented an opportunity to investigate woody fuel loading 15–17 years after four treatments: mechanical thin, prescribed burn, both thin and burn, and no treatment control. The principal findings were: (1) fine fuel load 15 years post-burn remained slightly below pre-treatment values; (2) rotten coarse fuel load was reduced post-burn, but sound coarse fuel was not altered by any active treatment; and (3) total woody fuel load 15–17 years post-treatment was similar to pre-treatment values. Understanding surface fuel loading is essential for predicting fire behavior. Overall, the effects of fuel reduction treatments on woody surface fuels were transitory in dry mixed conifer forests. Frequent maintenance treatments are recommended to protect values at risk in areas with high fire hazards. Quantifying the persistence of changes in forest conditions aids in the planning and analysis of future fuel treatments, along with scheduling maintenance of existing treated areas.

Mid-Scale Drivers of Variability in Dry Mixed-Conifer Forests of the Mogollon Rim, Arizona

The structure and composition of southwestern dry mixed-conifer forests have changed significantly, decreasing forest resiliency to uncharacteristic disturbances which also threaten ecosystem services. Restoration of these forests can be informed by historical conditions; however, managers and researchers still lack a full understanding of how environmental factors influence forest conditions. We investigated historical and contemporary variability in dry mixed-conifer forests in northern Arizona and identified important environmental drivers. We utilized forest sample plots and dendrochronological reconstruction modelling to describe forest conditions in 1879 and 2014, respectively. We used correlogram analysis to compare spatial autocorrelation of average diameter, basal area and tree density, and structural equation modeling to partition the causal pathways between forest structure, forest composition, and a suite of environmental factors reflecting climate, topography, and soil. Historical (1879) reconstructed forests had significantly fewer trees, lower basal area, and higher average diameter than contemporarily (2014). Composition has shifted from ponderosa pine dominance towards a more mixed-species composition. Historically, forest structure did not exhibit strong spatial autocorrelation, but contemporary tree density and diameter were strongly autocorrelated. Environmental factors described little variation in historical forest conditions but are more important for contemporary conditions. Managers can utilize this increased understanding of variation to tailor silvicultural prescriptions to environmental templates.

Disjunct and decoupled? The persistence of a fire-sensitive conifer species in a historically frequent-fire landscape

Local and regional species extirpations may become more common as changing climate and disturbance regimes accelerate species’ in situ range contractions. Identifying locations that function as both climate and disturbance refugia is critical for biodiversity conservation. Here, we investigate the persistence of a disjunct, fire-sensitive conifer population, yellow-cedar (Callitropsis nootkatensis), in the historically frequent-fire landscape of the Blue Mountains in eastern Oregon, USA. We used tree rings to reconstruct multi-century fire histories, which were then used to compare historical mean fire return intervals (MFRIs) inside of the cedar grove to the surrounding dry forest matrix, as well as to examine relationships between historical fire occurrence and reconstructed climate. We also examined trends in post-fire yellow-cedar mortality and regeneration between 2006, when the grove burned in a wildfire, through 2017. Results indicated that fire was less frequent in the cedar grove (MFRI = 35.8 years) than in the surrounding dry mixed-conifer forest (MFRI = 14.4 years). Historical fire occurrence was associated with hotter and drier conditions. Following the 2006 fire, cedar mortality was high (>90 %), but by 2017 post-fire regeneration was abundant (median = 8125 seedlings ha−1). The eastern Oregon cedar grove appears to occupy a fire refugium historically decoupled from the frequent-fire regime of the broader landscape. The topographic position of the grove suggests it is also a climate refugium. Managing for climate and disturbance refugia has been identified as an important option for conservation in the context of rapid global change, and this study provides evidence that locations where climate and disturbance refugia overlap may be disproportionately important for the maintenance of regional biodiversity. However, active management may be required for populations to persist in some of these locations as anthropogenic change is capable of overwhelming the underlying buffering capacity of refugia.

Millennial-Scale Climate and Human Drivers of Environmental Change and Fire Activity in a Dry, Mixed-Conifer Forest of Northwestern Montana

Warmer temperatures and longer fire seasons are promoting larger, and in some cases, more severe fires in low- and mid-elevation, dry mixed-conifer forests of the Northern Rocky Mountains. Long-term historical fire conditions and human influence on past fire activity are not well understood for these topographically and biophysically heterogeneous forests. We developed reconstructions of millennial-scale fire activity, vegetation change, and human presence at Black Lake, a small closed-basin lake on the Flathead Indian Reservation in the Mission Valley, northwestern Montana, USA. Fossil pollen, charcoal, and biomarkers associated with human presence were used to evaluate the interaction between climate variability, fire activity, vegetation change and human activity for the past seven thousand years. Multi-proxy comparisons suggest climate variability acted as the primary control on fire activity and vegetation change from the early Holocene until the late Holocene when records suggest fire activity and climate variability decoupled. Specific biomarkers (5β-stanols including coprostanol and epi-coprostanol) associated with human presence indicate humans were present within the Black Lake watershed for thousands of years, although the inferred intensity of human presence was highly variable. A strong relationship between climate variability and fire activity during the early and mid-Holocene weakens during the last few thousand years, suggesting possible increased influence of humans in mediating fire activity in recent millennia. Human-set fires during the cooler and wetter late Holocene may have been aimed at maintaining important cultural resources associated with the heterogeneous mosaic of mixed conifer forests within the Black Lake watershed. The paleoenvironmental reconstruction at Black Lake provides one of the first independent records of human presence in the NRM, and suggests humans were present within the Black Lake watershed for over 7000 years. Further research is needed to evaluate the evidence for this continuous presence and the possible role that people played in shaping fire regimes and vegetation within low- to mid-elevation mixed-conifer ecosystems of the NRM.

The Environmental Justice Implications of Managing Hazardous Fuels on Federal Forest Lands

U.S. federal government agencies play an important role in mitigating some risks posed to communities by natural hazard events, especially communities with high proportions of low-income or minority residents. Ongoing efforts of the U.S. Forest Service (USFS) to reduce the buildup of forest fuels on national forests, particularly in dry mixed-conifer forests of the U.S. West, are an example. Federal land management agencies must comply with the Executive Order on Environmental Justice (EJ Order, 59 Fed. Reg 7629, 1994), but there is scant documentation of whether these agencies have substantively complied with the EJ Order in implementing land management activities. There is also little quantitative environmental justice (EJ) research on dispersed rural populations, such as those often found adjacent to national forests. Our research addresses these gaps. We apply a novel mixed-methods approach, including quantitative pattern analysis and interviews with forest managers, to examine whether the benefits of wildfire risk reduction created on twelve national forests in four western U.S. states were equitably distributed among nearby populations. We found that EJ impacts might have occurred on all twelve forests, but they tended to be localized and context specific. We also learned from interviewees that EJ was not considered in decisions about where and how to conduct wildfire hazard reduction and that EJ populations rarely engaged in collaborative project planning apart from the formal tribal consultation process. Our research expands the range of quantitative geographical analysis of EJ issues and our methods could be adopted by land management agencies to achieve more equitable distribution of costs and benefits from their management activities.

Simulating the Effectiveness of Improvement Cuts and Commercial Thinning to Enhance Fire Resistance in West Coast Dry Mixed Conifer Forests

Abstract Nine multipurpose silvicultural treatments, formulated as a synthesis of recently implemented prescriptions offered by forest managers, were simulated to evaluate their effectiveness at enhancing fire resistance. The Forest Vegetation Simulator was applied, within the BioSum Framework, on over 3,000 Forest Inventory and Analysis plots representing 5 million hectares of dry mixed conifer forests in eastern Washington and Oregon and California’s Sierra Nevada Mountains. We developed a composite fire-resistance score based on four fuel modification principals and metrics: fuel strata gap, canopy bulk density, proportion of basal area in resistant species, and predicted tree survival. The trajectories of stands with and without treatment were compared to evaluate effectiveness immediately post-treatment, and over the three decades that followed. Seventy percent of these forests could be effectively treated in the short term by at least one prescription. Pretreatment forest condition, particularly fire-resistant species abundance, strongly influenced short-term treatment success, and the post-treatment stand dynamics that limit treatment longevity. Treatment effectiveness endured only 10 or 20 years, depending on fire-resistant species abundance, owing to growing space for crown expansion generated by treatment plus regeneration and release and growth of understory tree strata.

Variability in Mixed Conifer Spatial Structure Changes Understory Light Environments

In fire-adapted conifer forests of the Western U.S., changing land use has led to increased forest densities and fuel conditions partly responsible for increasing the extent of high-severity wildfires in the region. In response, land managers often use mechanical thinning treatments to reduce fuels and increase overstory structural complexity, which can help improve stand resilience and restore complex spatial patterns that once characterized these stands. The outcomes of these treatments can vary greatly, resulting in a large gradient in aggregation of residual overstory trees. However, there is limited information on how a range of spatial outcomes from restoration treatments can influence structural complexity and tree regeneration dynamics in mixed conifer stands. In this study, we model understory light levels across a range of forest density in a stem-mapped dry mixed conifer forest and apply this model to simulated stem maps that are similar in residual basal area yet vary in degree of spatial complexity. We found that light availability was best modeled by residual stand density index and that consideration of forest structure at multiple spatial scales is important for predicting light availability. Second, we found that restoration treatments differing in spatial pattern may differ markedly in their achievement of objectives such as density reduction, maintenance of horizontal and tree size complexity, and creation of microsite conditions favorable to shade-intolerant species, with several notable tradeoffs. These conditions in turn have cascading effects on regeneration dynamics, treatment longevity, fire behavior, and resilience to disturbances. In our study, treatments with high aggregation of residual trees best balanced multiple objectives typically used in ponderosa pine and dry mixed conifer forests. Simulation studies that consider a wide range of possible spatial patterns can complement field studies and provide predictions of the impacts of mechanical treatments on a large range of potential ecological effects.

A Framework for Quantifying Resilience to Forest Disturbance

The concept of ecological resilience is an invaluable tool to assess the risk of state transitions and predict the impact of management on an ecosystem’s response to future disturbances. However, resilience is difficult to quantify and the factors contributing to resilience are often unknown in systems subject to multiple disturbances. Here, we develop and demonstrate a framework to assess the potential of ponderosa pine and dry mixed conifer forests to be resilient to future disturbance (recover as the same forest type within a managerially significant timeframe) by combining indicators of short-term resilience (ability to withstand disturbance) to fire, insect, and drought disturbances using data from the Rio Tusas-Lower San Antonio landscape in northern New Mexico. The dry mixed conifer forests displayed an average resilience score of 4.54, while ponderosa pine forests had an average score of 3.45 (total possible of nine points) Stand density index was the most important driver of the overall score in the dry mixed conifer type. In the ponderosa pine type, overall basal area was the strongest driver of the overall score. These indicators have the greatest impact on the resilience score and provide the most effective targets for management to increase the possibility of resilience in these forest types. We applied the model in both forest types by comparing individual stands to an ‘ideal’ score for a stand that is within the historic range of variation (HRV) of forest structure for each forest type and confirmed that stands outside of HRV had a low possibility of resilience and stands that had received restoration-based treatments were more likely to be resilient. Our results provide evidence that the changes to forest structure and species composition that have occurred since the onset of fire exclusion have degraded the potential of these forest types to be resilient to future fire, insect, and drought-related disturbances. By modifying disturbances and resilience indicator thresholds this model can be applied to assess resilience to other disturbances within these forest types and across various regions and ecosystem types.

How Much Forest Persists Through Fire? High-Resolution Mapping of Tree Cover to Characterize the Abundance and Spatial Pattern of Fire Refugia Across Mosaics of Burn Severity

Wildfires in forest ecosystems produce landscape mosaics that include relatively unaffected areas, termed fire refugia. These patches of persistent forest cover can support fire-sensitive species and the biotic legacies important for post-fire forest recovery, yet little is known about their abundance and distribution within fire perimeters. Readily accessible 30-m resolution satellite imagery and derived burn severity products are commonly employed to characterize post-fire landscapes; however, coarse image resolution, generalized burn severity thresholds, and other limitations can constrain accurate representation of fire refugia. This study quantifies the abundance and pattern of fire refugia within 10 fires occurring in ponderosa pine and dry mixed-conifer forests between 2000 and 2003. We developed high-resolution maps of post-fire landscapes using semi-automated, object-based classification of 1-m aerial imagery, conducted imagery- and field-based accuracy assessments, and contrasted these with Landsat-derived burn severity metrics. Fire refugia area within burn perimeters ranged from 20% to 57%. Refugia proportion generally decreased with increasing Landsat-derived burn severity, but still accounted for 3–12% of areas classified as high severity. Patch size ranged from 1-m2 isolated trees to nearly 8000 ha, and median patch size was 0.01 ha—substantially smaller than a 30-m Landsat pixel. Patch size was negatively related to burn severity; distance to fire refugia from open areas was positively related to burn severity. Finally, optimized thresholds of 30-m post-fire normalized burn ratio (NBR) and relative differenced normalized burn ratio (RdNBR) delineated fire refugia with an accuracy of 77% when validated against the 1-m resolution maps. Estimations of fire refugia abundance based on Landsat-derived burn severity metrics are unlikely to detect small, isolated fire refugia patches. Finer-resolution maps can improve understanding of the distribution of forest legacies and inform post-fire management activities including reforestation and treatments.

Woodpecker nest survival, density, and a pine beetle outbreak

ABSTRACTMountain pine beetle (Dendroctonus ponderosae) outbreaks in western North American coniferous forests are increasing in size and severity. An understanding of wildlife population responses to pine beetle outbreaks is needed to inform habitat conservation strategies. We monitored 355 nests of 5 woodpecker species during 2 sampling periods, before (2003–2006) and after (2009–2014) the peak of a pine beetle outbreak in dry mixed conifer forest of Montana, USA. Three of 5 woodpecker species represented the beetle‐foraging group: American three‐toed (Picoides dorsalis), hairy (Dryobates villosus), and downy (D. pubescens) woodpeckers. The other 2 species studied were northern flicker (Colaptes auratus), a foraging and habitat generalist, and red‐naped sapsucker (Sphyrapicus nuchalis), a sap forager and bark‐gleaning insectivore. We analyzed daily survival rate of nests in relation to pine beetle outbreak (445,000 ha) severity and timing, along with covariates unrelated to the outbreak (temp, nest height, and nest tree diameter). Our results provided stronger evidence for relationships between woodpecker nest survival and the non‐outbreak variables than those associated with outbreaks. Our results indicated limited support for nest survival relationships with beetle severity (annual and cumulative pine tree mortality at 0.81‐ha and 314‐ha scales). Nevertheless, we observed a significant increase in densities of hatched nests for beetle‐foraging woodpeckers following the outbreak. Our results suggest that woodpeckers, particularly beetle foragers, respond numerically to pine beetle outbreaks through increased nesting densities more so than functionally via nest survival. © 2019 The Authors. Journal of Wildlife Management Published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.

A multi-century history of fire regimes along a transect of mixed-conifer forests in central Oregon, U.S.A.

Dry mixed-conifer forests are widespread in the interior Pacific Northwest, but their historical fire regimes are poorly characterized, in particular the relative mix of low- and high-severity fire. We reconstructed a multi-century history of fire from tree rings in dry mixed-conifer forests in central Oregon. These forests are dominated by ponderosa pine (Pinus ponderosa Lawson &amp; C. Lawson), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), and grand fir (Abies grandis (Douglas ex D. Don) Lindl.). Across four, 30-plot grids of ∼800 ha covering a mosaic of dry mixed-conifer forest types, we sampled 4065 trees for evidence of both high- and low-severity fire. From 1650 to ∼1900, all four sites sustained frequent, often extensive, low-severity fires that sometimes included small patches of severe fire (50–150 ha during 18%–28% of fire years). Fire intervals were similar among sites and also among forest types within sites (mean intervals of 14–32 years). To characterize the continuous nature of the variation in fire severity, we computed a plot-based index that captures the relative occurrence of low- and high-severity fire. Our work contributes to the growing understanding of variation in past fire regimes in the complex and dynamic forests of North America’s Interior West.

Improving long-term fuel treatment effectiveness in the National Forest System through quantitative prioritization

Predicting the efficacy of fuel treatments aimed at reducing high severity fire in dry-mixed conifer forests in the western US is a challenging problem that has been addressed in a variety of ways using both field observations and wildfire simulation models. One way to describe the efficacy of fuel treatments is to quantify how often wildfires are expected to intersect areas prioritized for treatment. In real landscapes treatments are static, restricted to a small portion of the landscape and against a background of stochastic fire and dynamic vegetation, thus the likelihood of fire encountering a treatment during the period treatments remain effective is small. In this paper we simulate a wide range of different treatment prioritization schemes using the forest landscape simulation model Envision to examine 50 years of fire-treatment interactions and forest succession. We first reviewed 47 fuel management projects in Oregon, USA to build prioritization schemes that addressed different fuel management objectives. We then simulated different priority schemes in the 18 planning areas of the Deschutes National Forest in central Oregon and measured potential fire-treatment interactions over time. Simulated annual area burned was used to calculate the success odds for each priority scheme and planning area. Out of the ten metrics considered only three had higher success odds than a random prioritization of planning areas. Spatial allocation of projects based on burn probability and transmitted wildfire had the highest success odds among the tested metrics. However, success odds declined sharply as desired success levels increased suggesting that fuel management goals need to be tempered to consider the stochastic nature of wildfire. Meeting long-term multiple management goals over time can benefit from consideration of short- and long-term tradeoffs from different treatment prioritization schemes. Our work contributes towards a better framing of both management and public expectations regarding the performance of fuel treatments programs.

Investigating the contribution of the coarse fraction to total pyrogenic carbon stocks in forest soil

Pyrogenic carbon (PyC) quantification methods based on visual identification typically measure only the PyC particles >0.5 mm, whereas oxidative methods are usually conducted on the <2 mm soil fraction. To reconcile the discrepancy between these two methods, we used the weak nitric acid digestion method to quantify the PyC mass in the <2 mm soil, and in the charcoal particles >2 mm, in a California dry mixed conifer forest spatially heterogeneous in fire severity. We found that charcoal particles >2 mm represented 5–10% of mineral soil PyC in recently burned areas (three years post-fire in our study) and 3% in the unburnt areas (>100 years since the last fire). We, therefore, stress the importance of considering the size fraction of the charcoal quantified.