After a more than a century of fighting to keep fire out of forests, reintroducing it is now an important management goal. Yet changes over the past century have left prescribed burning with a big job to do. Development, wildfire suppression, rising global temperatures, extended droughts, exotic species invasions, and longer fire seasons add complexity to using this practice.
Managers must consider how often, how intensely, and what time of year to burn; for insights they often look to how and when fires burned historically. However, attempting to mimic historical wildfires that burned in hot, dry conditions is risky. Burning in fall or spring when temperature and humidity are low reduces the risk of prescribed fires becoming uncontrollable, but does it have the intended effects? How do forest ecosystems that historically were adapted to fire respond when fire is reintroduced after so much time without it?
Forest Service researchers Becky Kerns and Michelle Day conducted a long-term experiment in the Malheur National Forest, Oregon, to assess how season and time between prescribed burns affect understory plant communities in ponderosa pine forests. They found that some native plants persisted and recovered from fire but didn’t respond vigorously, while invasive species tended to spread. These findings may help forest managers design more effective prescribed-fire treatments and avoid unintended consequences.
In recent years, many forest managers have become interested in managing forests for a wider range of objectives than previously. As an initial or intermediate treatment, variable-density thinning (VDT) can help meet objectives such as improving wildlife and plant habitats, increasing structural and compositional diversity, and enhancing aesthetic values in stands that are currently lacking spatial variability. The “skips and gaps” method of VDT is flexible, allowing for the preservation of existing desirable features. Areas that are not thinned (“skips”) will protect existing features that are best preserved by being within an area where logging equipment is excluded. “Gaps” can be created to closely approximate natural disturbance regimes through harvest of small groups or patches of trees. Gaps can increase growth and crown lengths of neighboring trees. Furthermore, gaps can be created that favor underrepresented tree species that are either already present or are planted after treatment. Areas that are not within skips or gaps (the “matrix”), are thinned to encourage growth of the overstory trees and the development of understory plants. This publication demonstrates the steps necessary to implement this type of VDT based on lessons learned from eight sites on the Olympic Habitat Development Study and two western Washington state parks.
Large wildfires (>50,000 ha) 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 highseverity 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.
A key assumption of epidemiological models is that population-scale disease spread is driven by close contact between hosts and pathogens. At larger scales, however, mechanisms such as spatial structure in host and pathogen populations and environmental heterogeneity could alter disease spread. The assumption that small-scale transmission mechanisms are sufficient to explain large-scale infection rates, however, is rarely tested. Here, we provide a rigorous test using an insect-baculovirus system. We fit a mathematical model to data from forest-wide epizootics while constraining the model parameters with data from branch-scale experiments, a difference in spatial scale of four orders of magnitude. This experimentally constrained model fits the epizootic data well, supporting the role of small-scale transmission, but variability is high. We then compare this model’s performance to an unconstrained model that ignores the experimental data, which serves as a proxy for models with additional mechanisms. The unconstrained model has a superior fit, revealing a higher transmission rate across forests compared with branch-scale estimates. Our study suggests that small-scale transmission is insufficient to explain baculovirus epizootics. Further research is needed to identify the mechanisms that contribute to disease spread across large spatial scales, and synthesizing models and multiscale data are key to understanding these dynamics.
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.
The Rocky Mountain Research Station works with National Forest planning teams to understand and maximize an important resource: forest data collected by the Forest Service’s Forest Inventory and Analysis (FIA) program. The program’s website, found at https://www.fia.fs.fed. us, provides a variety of tools that allow users to download standard reports and create custom queries that can be used to improve the efficiency of their planning process. By integrating or putting FIA data to work, National Forest planners are able to meet the 2012 Planning Rule’s requirements for monitoring and using the best available science. For example, National Forest planning teams can use FIA data to better understand forest characteristics and conditions using readily available data and FIA analysis skills. Additional information on FIA resources for the Interior West region can be found at https://www.fs.usda.gov/rmrs/ interior-west-forest-inventory-analysis-fia. Other resources for National Forest plan revision teams include riparian and groundwater-dependent ecosystems assessments and a nationwide toolset of National Forest Climate Change Maps.
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.
Climate change poses a clear danger to salmon and steelhead in the Columbia River basin. Rising water temperatures increasingly limit their ability to migrate, spawn, and successfully produce the next generation of fish.
Steve Wondzell, a research ecologist with the USDA Forest Service’s Pacific Northwest Research Station, conducted a study on the upper Middle Fork of eastern Oregon’s John Day River. By using computer modeling, he and colleagues found that adding shade was the single most effective way to cool the water and preserve habitat for salmon into the future. With enough added shade, they found that future water temperature in the river could be cooler than today, even as air temperatures warm.
Adding sufficient shade involves strategically planting streamside vegetation that will grow tall enough to shield long sections of the river from sunlight. The Forest Service and other federal agencies, the state of Oregon, and the Confederated Tribes of Warm Springs are leading an effort to do just this. They are also working to reconfigure sections of the river that were artificially straightened in the past. Wondzell’s research confirms the importance of coupling riparian planting with those efforts and is helping the different parties involved direct their efforts in a more strategic way.
Stem-maps, maps of tree locations with optional associated measurements, are increasingly being used for ecological study in forest and plant sciences. Analyses of stem-map data have led to greater scientific understanding and improved forest management. However, availability of these data for reuse remains limited. We present a description of eight 4-ha stem-maps used in four prior research studies. These stem-maps contain locations and associated measurements of residual trees and stumps measured after forest restoration cuttings in Colorado, Arizona, and New Mexico. Data are published in two file formats to facilitate reuse.