US Forest Research Articles

Field-testing whitebark pine resistance to white pine blister rust: A simple, effective approach to progeny testing for restoration

The endangered conifer whitebark pine (Pinus albicaulis), native to high elevation forests of western North America, is declining mainly due to the introduced pathogen Cronartium ribicola, causing the disease white pine blister rust. Low levels of genetic resistance to blister rust are present in whitebark pine populations. Traditional methods of inoculating seedlings to determine resistance to the rust are costly, labour intensive, and have limited capacity due to facilities. This presents a bottleneck in the development of resistant material for restoring stands that have been heavily infected by the rust. Here we test an alternative approach to controlled inoculations that could screen large numbers of families with lower costs and requiring fewer specialized resources. We screened 214 open-pollinated families from 44 provenances from British Columbia (BC), Washington (WA), Oregon (OR), Idaho (ID), Montana (MT), and Nevada (NV) to determine: (1) the effectiveness of natural rust inoculation from Ribes nigrum in a common garden; (2) family- and provenance-level resistance to blister rust; and (3) climate variables related to population-level rust resistance. Eighty-one of these families were previously screened by the US Forest Service in Cottage Grove, Oregon using standard artificial inoculation methods. The natural inoculation was effective, with 73 % of seedlings displaying stem symptoms of the disease, and 95 % showing rust infection. A clear relationship was found between distance from the nearest Ribes nigrum plant and severity of blister rust. Linear mixed models with spatial correlations were fitted to rust infection data using ASReml-R to estimate breeding values, heritability, and among-population differentiation (QST) for rust resistance. Population differentiation for rust resistance was moderate, with the highest resistance in provenances from the Cascade Mountains of Washington, and the most susceptible families from the BC Chilcotin and Okanagan regions. Heritability of rust resistance was moderate (0.23). The field testing was broadly consistent with classifications of families into resistant, moderate, and susceptible groups based on artificial inoculations. This method of screening could be used at a broader scale to determine families resistant to white pine blister rust without specialized testing facilities and increase the availability of resistant seedlings for restoration.

Forest restoration and fuels reduction work: Different pathways for achieving success in the Sierra Nevada.

Fire suppression and past selective logging of large trees have fundamentally changed frequent-fire-adapted forests in California. The culmination of these changes produced forests that are vulnerable to catastrophic change by wildfire, drought, and bark beetles, with climate change exacerbating this vulnerability. Management options available to address this problem include mechanical treatments (Mech), prescribed fire (Fire), or combinations of these treatments (Mech + Fire). We quantify changes in forest structure and composition, fuel accumulation, modeled fire behavior, intertree competition, and economics from a 20-year forest restoration study in the northern Sierra Nevada. All three active treatments (Fire, Mech, Mech + Fire) produced forest conditions that were much more resistant to wildfire than the untreated control. The treatments that included prescribed fire (Fire, Mech + Fire) produced the lowest surface and duff fuel loads and the lowest modeled wildfire hazards. Mech produced low fire hazards beginning 7 years after the initial treatment and Mech + Fire had lower tree growth than controls. The only treatment that produced intertree competition somewhat similar to historical California mixed-conifer forests was Mech + Fire, indicating that stands under this treatment would likely be more resilient to enhanced forest stressors. While Fire reduced modeled wildfire hazard and reintroduced a fundamental ecosystem process, it was done at a net cost to the landowner. Using Mech that included mastication and restoration thinning resulted in positive revenues and was also relatively strong as an investment in reducing modeled wildfire hazard. The Mech + Fire treatment represents a compromise between the desire to sustain financial feasibility and the desire to reintroduce fire. One key component to long-term forest conservation will be continued treatments to maintain or improve the conditions from forest restoration. Many Indigenous people speak of "active stewardship" as one of the key principles in land management and this aligns well with the need for increased restoration in western US forests. If we do not use the knowledge from 20+ years of forest research and the much longer tradition of Indigenous cultural practices and knowledge, frequent-fire forests will continue to be degraded and lost.

Climate Change Habitat Model Forecasts for Eight Owl Species in the Southwestern US.

The high-resolution forecasting of vegetation type shifts may prove essential in anticipating and mitigating the impacts of future climate change on bird populations. Here, we used the US Forest Service Ecological Response Unit (ERU) classification to develop and assess vegetation-based breeding habitat profiles for eight owl species occurring in the foothills and mountains of the Southwestern US. Shifts in mapped habitat were forecast using an ecosystem vulnerability model based on the pre-1990 climate envelopes of ERUs and the Intergovernmental Panel on Climate Change's (IPCC) A1B moderate-emission scenario for the future climate. For five of the eight owl species, the regional breeding habitat extent was projected to decline by at least 60% by 2090. Three species, the boreal owl (Aegolius funereus; at the trailing edge of its distribution), flammulated owl (Psiloscops flammeolus), and northern pygmy-owl (Glaucidium gnoma), were projected to experience the steepest habitat loss rates of 85%, 85%, and 76%, respectively. Projected vegetation shifts overlaid with well-documented flammulated owl breeding populations showed the complete or near complete loss of habitat by 2090 in areas of montane forest currently supporting dense aggregations of owl territories. Generalist or lower-elevation owl species were predicted to be less impacted, while, for the whiskered screech-owl (Megascops trichopsis), the contraction of the current habitat was nearly offset by a projected northward expansion. In general, the results of this study suggest high exposure to climate change impacts for the upper-elevation forest owls of semi-arid Southwestern North America. Long-distance migration and low natal philopatry may prove important to some montane owl populations in adapting to the regional loss of habitat.

Assessing Complexity and Stakeholder and Rightsholder Trust in Outdoor Recreation Management on the Pacific Northwest National Scenic Trail

The Pacific Northwest National Scenic Trail (PNT) traverses 1,200 miles from the Continental Divide to the Pacific Ocean. The portion of the trail in Northwest Montana and the Idaho Panhandle is at the nexus of a complex conflict situation involving outdoor recreation, wildlife conservation, and social-cultural values. This evolving conflict has gained national attention due to the diverse stakeholder interests and litigation against the US Forest Service, who administers the trail. The tension among the stakeholder groups and the various ecological and social-cultural dimensions at play illuminate the complexity of managing long-distance trails. Administrators of long-distance trails must evaluate and mitigate social, ecological, and cultural risks. This research note explores complexity and trust ecology among key PNT stakeholders, and discusses opportunities for incorporating trust research in transboundary recreation planning and research.

A theory of demographic optimality in forests

Carbon uptake by the land is a key determinant of future climate change. Unfortunately, Dynamic Global Vegetation Models have many unknown internal parameters which leads to significant uncertainty in projections of the future land carbon sink. By contrast, observed forest inventories in both Amazonia and the USA show strikingly common tree-size distributions, pointing to a simpler modelling paradigm. The curvature of these size-distributions is related to the ratio of mortality to growth in Demographic Equilibrium Theory (DET). We extend DET to include recruitment limited by competitive exclusion from existing trees. From this, we find simultaneous maxima of tree density and biomass in terms of respectively the ratio of mortality to growth and the proportion of primary productivity allocated to reproduction, an idea we call Demographic Optimality (DO). Combining DO with the ratio of mortality to growth common to the US and Amazon forests, results in the prediction that about an eighth of productivity should be allocated to reproduction, which is broadly consistent with observations. Another prediction of the model is that seed mortality should decrease with increasing seed size, such that the advantage of having many small seeds is nullified by the higher seed mortality. Demographic Optimality is therefore consistent with the common shape of tree-size distributions seen in very different forests, and an allocation to reproduction that is independent of seed size.

The Worth of Nature: Valuations of Glaciers in Alaskan and Norwegian Media Discourse

ABSTRACT This article presents a comparative case study of public valuation of glaciers in Alaska and Norway. The first case examines Alaska’s Mendenhall Glacier, which has been central in public debate over the US Forest Service’s proposed expansion of the Mendenhall Glacier Recreation Area. The second case centers on Norway’s Svartisen glacier, which garnered international attention when the startup company, Svaice, announced its intent to extract glacier ice cubes for cocktail coolers at high-end bars and restaurants. A rhetorical analysis of newspaper coverage relevant to each case reveals that in both debates, instrumental, relational, and intrinsic values are attributed to the respective glaciers, and that government, business, and community actors hold the most power in these conversations. However, nuances within articulations of instrumental value suggest that Norwegian actors strive to balance human and glacier needs, whereas Alaskan actors largely prioritize human needs by constituting the glacier as a utilitarian object.

Western US Residents’ Knowledge of Wild Free-Roaming Horses and Their Management on Federal Public Lands

Wild free-roaming (WFR) horses (Equus ferus caballus) occur on lands administered by the Bureau of Land Management and US Forest Service in 10 western US states. Little is known about public knowledge concerning management of WFR horse populations. In 2020, we conducted a survey to assess public knowledge with the intent of establishing baseline information that may be used to shape horse management programs and policies on the nation's public lands. We obtained responses from 1 124 residents of the western United States. Our survey asked eight knowledge-based questions of WFR horse ecology and management in the western United States. We conducted chi-square analyses to determine the influence of age, gender, region of residence, and income on respondents’ ability to answer these questions appropriately. Our results indicate that these demographic characteristics had little predictive ability to explain the level of the western US public's knowledge of WFR horse ecology and management (for all comparisons, λ < 0.10). Furthermore, our respondents had little knowledge of WFR ecology and management. Approximately 30% of respondents correctly identified WFR horse origins, 8% correctly indicated WFR horse population size, and 37.5% indicated that they were unaware of legal management options. The lack of basic understanding of WFR horse ecology and management may influence the public's ability to support management efforts or determine fact from propaganda. Approximately 60% of the respondents indicated they primarily used government, university, and organization websites when seeking information. Efforts to increase dissemination of facts on multiple venues, such as social media, websites, and newspapers that link back to government and university websites, could increase public support of future management actions. Additionally, the announcement of management actions, such as round-ups, should consistently include basic background information regarding WFR horse ecology and populations to ensure that the public can make informed conclusions.

Environmental impact assessments not the main barrier to timely forest management in the United States

Environmental impact assessment (EIA) processes are commonly used by government agencies to evaluate the merits and environmental risks of natural resource management decisions. Citing EIA as red tape, decision makers from across the political spectrum are increasingly circumventing EIA to expedite implementation of necessary actions for climate resilience and clean energy. Few studies have quantified the extent that EIA is the main barrier to efficient implementation. We combine administrative data from the US Forest Service with survival analysis to show that, for most actions, the Forest Service takes as long or longer to award first contracts and roll out initial activities than to comply with the 1970 National Environmental Policy Act (NEPA), and that NEPA compliance accounts for approximately one-fifth of planned implementation time.

Phenology of Leucotaraxis argenticollis, a specialist predator of the invasive hemlock woolly adelgid, in the eastern United States.

In hemlock stands within eastern US forests, classical biological control has been one of the main strategies used to manage the hemlock woolly adelgid, Adelges tsugae Annand. Specialist predator species may offer a management solution to help regulate A. tsugae populations. In the Pacific Northwest, a suite of specialist predators has been a focus of research and includes 2 species of silver fly, Leucotaraxis argenticollis (Zetterstedt) and Leucotaraxis piniperda (Malloch) (Diptera: Chamaemyiidae). Leucotaraxis spp. phenology has been documented in the Pacific Northwest, but the phenology of either western Leucotaraxis species is unknown in the eastern United States. This study sought to document the phenology of Le. argenticollis in NY in 2021 and in VA in 2021 and 2022. Nylon mesh cages were applied over eastern hemlock branches infested with A. tsugae to contain Le. argenticollis adults. Biweekly and monthly branch samples were taken in 2021 and 2022, documenting all life stages of A. tsugae and of Le. argenticollis that were observed. In 2021 and 2022, Le. argenticollis adults and eggs were present during the oviposition stage of the 2 generations of A. tsugae. In addition, Le. argenticollis larvae were present when A. tsugae ovisacs had eggs and while A. tsugae nymphs of both generations were present. These observations indicate that Le. argenticollis phenology is well synchronized with A. tsugae in the eastern United States.

Mapping historical forest biomass for stock-change assessments at parcel to landscape scales

Understanding historical forest dynamics, specifically changes in forest biomass and carbon stocks, has become critical for assessing current forest climate benefits and projecting future benefits under various policy, regulatory, and stewardship scenarios. Carbon accounting frameworks based exclusively on national forest inventories are limited to broad-scale estimates, but model-based approaches that combine these inventories with remotely sensed data can yield contiguous fine-resolution maps of forest biomass and carbon stocks across landscapes over time. Here we describe a fundamental step in building a map-based stock-change framework: mapping historical forest biomass at fine temporal and spatial resolution (annual, 30 m) across all of New York State (USA) from 1990 to 2019, using freely available data and open-source tools. Using Landsat imagery, US Forest Service Forest Inventory and Analysis (FIA) data, and off-the-shelf LiDAR collections we developed three modeling approaches for mapping historical forest aboveground biomass (AGB): training on FIA plot-level AGB estimates (direct), training on LiDAR-derived AGB maps (indirect), and an ensemble averaging predictions from the direct and indirect models. Model prediction surfaces (maps) were tested against FIA estimates at multiple scales. All three approaches produced viable outputs, yet tradeoffs were evident in terms of model complexity, map accuracy, saturation, and fine-scale pattern representation. The resulting map products can help identify where, when, and how forest carbon stocks are changing as a result of both anthropogenic and natural drivers alike. These products can thus serve as inputs to a wide range of applications including stock-change assessments, monitoring reporting and verification frameworks, and prioritizing parcels for protection or enrollment in improved management programs.

Sensitive tree species remain at risk despite improved air quality benefits to US forests.

Atmospheric nitrogen (N) and sulfur (S) deposition can significantly affect forest biodiversity and production by altering the growth and survival of trees. Three decades of air quality regulations in the United States (U.S.) have led to large reductions in oxides of N (44-81%) and S (50-99%) emissions and associated deposition. Here, we evaluated the magnitude and extent of effects over 20 years from atmospheric N and S deposition on the growth and survival of 94 tree species - representing 96.4 billion trees and an average of 88% of forest basal area across the contiguous U.S. (CONUS). Overall, species' growth and survival rates have responded positively to declining deposition, but we find that decreases of at least 2.5 kg N ha-1 yr-1 are needed across 19.8% (growth) and 59.5% (survival) of the CONUS to prevent detrimental effects to sensitive species. Reduced forms of N (NHx = NH3 + NH4 +) are now the dominant form of N deposition in 45.4% of the CONUS - notably in agricultural regions - and exclusively need to be reduced by ≥ 5.0 kg N ha-1 yr-1 in some areas. Further S deposition decreases of ≥ 1.0 kg S ha-1 yr-1 are needed in 50.4% (growth) and 56.2% (survival) of the CONUS to protect sensitive species and notably, evergreen trees. Total basal area is increasing in much of the country (85.2%) because of N fertilizing effects, but these growth increases could result in biodiversity loss. Our findings can be used to evaluate past successes of air quality policies and the future benefits of air pollution reductions to terrestrial ecosystems.

Wood Supply from Family Forests of the United States: Biophysical, Social, and Economic Factors

Abstract Wood products are an essential provisioning ecosystem service with US forests providing nearly one-fifth of global wood supply. As of 2018, an estimated 46% of the annual wood harvested came from corporate forests, 42% came from family forests, and the remainder came from other private, public, and Tribal forests. The supply of wood from corporate forests is well described by traditional economic models, but the supply from family forests is much less well understood. This article combines data from three components of the USDA Forest Service’s Forest Inventory and Analysis program—plots, landowner surveys, and mill surveys—with other data to model the wood supply from family forests in the United States. Results are summarized in terms of bivariate relationships and a logistic regression model. The model results show that basal area, stand origin, forest type, having timber as an ownership objective, the amount of annual income derived from their forestland, proximity to a mill, management advice, and region are significantly associated with family forest timber harvesting. The results should be useful for forest industry analysts and others interested in understanding the current and potential future supply of wood from family forests. Study Implications: Family forests provide an estimated 42% of the annual timber harvested in the United States. It is important to understand the factors affecting their harvesting behaviors to design effective policies and programs to ensure a continual supply and sustainable management of this critical resource. This article shows that timber harvesting by family forest owners is influenced by a combination of biophysical, social, and economic factors, including basal area, stand origin, forest type, having timber as an ownership objective, the amount of annual income derived from their forestland, proximity to a mill, management advice, and region. These results suggest that programs aimed at increasing the area covered by planted stands, the area covered by softwood stands, and the number of owners receiving forest management advice may be particularly influential in maintaining and increasing the amount of wood harvested from family forests.

Future climate change effects on US forest composition may offset benefits of reduced atmospheric deposition of N and S.

Climate change and atmospheric deposition of nitrogen (N) and sulfur (S) are important drivers of forest demography. Here we apply previously derived growth and survival responses for 94 tree species, representing >90% of the contiguous US forest basal area, to project how changes in mean annual temperature, precipitation, and N and S deposition from 20 different future scenarios may affect forest composition to 2100. We find that under the low climate change scenario (RCP 4.5), reductions in aboveground tree biomass from higher temperatures are roughly offset by increases in aboveground tree biomass from reductions in N and S deposition. However, under the higher climate change scenario (RCP 8.5) the decreases from climate change overwhelm increases from reductions in N and S deposition. These broad trends underlie wide variation among species. We found averaged across temperature scenarios the relative abundance of 60 species were projected to decrease more than 5% and 20 species were projected to increase more than 5%; and reductions of N and S deposition led to a decrease for 13 species and an increase for 40 species. This suggests large shifts in the composition of US forests in the future. Negative climate effects were mostly from elevated temperature and were not offset by scenarios with wetter conditions. We found that by 2100 an estimated 1 billion trees under the RCP 4.5 scenario and 20 billion trees under the RCP 8.5 scenario may be pushed outside the temperature record upon which these relationships were derived. These results may not fully capture future changes in forest composition as several other factors were not included. Overall efforts to reduce atmospheric deposition of N and S will likely be insufficient to overcome climate change impacts on forest demography across much of the United States unless we adhere to the low climate change scenario.

Precise and unbiased biomass estimation from GEDI data and the US Forest Inventory

Atmospheric CO2 concentrations are dependent on land-atmosphere carbon fluxes resultant from forest dynamics and land-use changes. These fluxes are not well-constrained, in part because reliable baseline estimates of forest carbon stocks and the associated uncertainties are lacking. NASA's Global Ecosystem Dynamics Investigation (GEDI) produces estimates of aboveground biomass density (AGBD) that are unique because GEDI's hybrid estimation framework enables formal uncertainty calculations that accompany the biomass estimates. However, GEDI's estimates are not without issue; a recent validation using design-based AGBD estimates from the US Forest Inventory and Analysis (FIA) program revealed systematic differences between GEDI and FIA estimates within a hexagon tessellation of the continental United States. Here, we explored these differences and identified two issues impacting GEDI's estimation process: incomplete filtering of low quality GEDI observations and regional biases in GEDI's footprint-level biomass models. We developed a solution to each, in the form of improved data filtering and GEDI-FIA fusion AGBD models, developed in a scale-invariant small area estimation framework, that were compatible with hybrid estimation. We calibrated 10 regional Fay-Herriot models at the hexagon scale for application at the unit scale of GEDI footprints, for which we provide a mathematical justification and empirical testing of the models' scale-invariance. These models predicted realistic distributions of unit level AGBD, with equal or improved performance relative to GEDI's L4A models for all regions. We then produced GEDI-FIA fusion estimates that were more precise than the FIA estimates and resulted in a bias reduction of 86.7% relative to the original GEDI estimates: 19.3% due to improved data filtering and 67.5% due to the new AGBD models. Our findings indicate that (1) small area estimation models trained in a scale-invariant framework can produce realistic predictions of AGBD, and (2) there is substantial spatial variability in the relationship between GEDI forest structure metrics and AGBD. This work is a step toward achieving reliable baseline forest carbon stocks, provides a viable methodology for training remote sensing biomass models, and may serve as a reference for other investigations of GEDI AGBD estimates.

Haptic Rapport: more-than-human movement, sensing, and communion in US forest service trails

ABSTRACT This research explores how belonging and communion emerge from the human body engaging directly with more-than-human (MtH) during nature-based recreation. It asks: how are nature-based recreators experiencing relationships with more-than-human via their movement and sensing in US Forest Service trails? This research presents the conceptual tool haptic rapport to better explore and represent the intimate, sensory-based, meaningful, and embodied relationships that come about through haptic contact occurring specifically between human and MtH natures. Contact-based and flow-based haptic rapport are explored here. This data serve to contradict structurally presumed separations between humans and MtHs; between recreational mobilities and belonging; and between cutaneous touch and internalisation of that touch experience. This research highlights USFS land spaces as essential sites for nature-based recreation, belonging and sensing place, mobility, and the human-MtH relationships they make possible. Haptic rapport can be applied in all contexts and fields to better understand the intimacies and meaning-making associated with MtH-human engagements.

Spatial Structure of Lightning and Precipitation Associated with Lightning-Caused Wildfires in the Central to Eastern United States

The horizontal storm structure surrounding 92,512 lightning-ignited wildfires is examined in the mid to eastern sections of the United States from 2003 to 2015 using Vaisala’s National Lightning Detection Network (NLDN), NCEP’s Stage IV gauge-corrected radar precipitation mosaic, and the US Forest Service’s Fire Occurrence Database. Though lightning flash density peaks strongly around fire ignitions on the instantaneous 1 km scale, on the hourly 10 km scale, both the lightning and precipitation peaks are typically offset from fire ignitions. Lightning density is higher, and precipitation is lower around ignition points compared to non-ignition points. The average spatial distribution of total lightning flashes around fire ignitions is symmetrical, while that of precipitation and positive flashes is not. Though regression is consistent with the claim that positive flashes have a stronger association with ignition than negative flashes, the statistical significance is ambiguous and is contradicted by an unchanging positive flash fraction in the vicinity of wildfires.

Progress of carbon sequestration in urban green space based on bibliometric analysis

To understand the development progress and relevant Frontier research of urban green space carbon sequestration, based on the core databases such as Web of Science, CiteSpace software, and bibliometric analysis methods were used to analyze the research status. The results showed that the number of papers on urban green space carbon sequestration research was on the rise. China and the United States had closer cooperation from the perspective of international cooperation institutions. Peking University, the Chinese Academy of Sciences, and the US Forest Service made the greatest contributions to this research field. Analyzing the keywords and the literature co-citation map, it was inferred that the hot keywords of future urban green space carbon sequestration research include carbon sequestration, ecosystem services, and climate change. It was found that carbon sequestration of urban green space ecosystems research primarily focuses on the correlation between urban green space and ecosystem services, and UGS carbon sequestration accounting and urban green space management. Finally, two perspectives were proposed: 1) Urban green spaces diversified ecological benefits are achieved through the function of carbon sequestration, and 2) Urban green space carbon sequestration accounting and urban green space management promote the development of urban green space. An overview of the international progress and basic state of urban green spaces and carbon sequestration theme research is presented in this paper, Additionally, it provides valuable references for future research and helps gain a comprehensive understanding of this field of research.

Functional diversity affects tree vigor, growth, and mortality in mixed-conifer/hardwood forests in California, U.S.A, in the absence of fire

Mixed tree-species forest management can increase forest resilience by reducing the impacts of disturbances that disproportionately affect a single tree species or closely related groups of tree species. Beyond disturbance-risk reduction, tree-species diversification may foster functional-diversity effects (e.g., complementarity or facilitation) that alter the performance of a given tree species in mixed versus pure stands, potentially benefitting carbon sequestration and wildlife habitat. Tree species-mixture effects have been explored to only a limited degree in western US forests and, particularly, in California. Establishing whether vigor, growth, and mortality of common tree species vary with stand composition would help inform restoration and modeling of these forests under climate change. Using data from USDA Forest Service Forest Inventory and Analysis (FIA) plots from California, we examined how individual-tree vigor, as indicated by live crown ratio (LCR), periodic basal area increment (BAI), and mortality odds varied with functional dissimilarity (FDis). We quantified FDis using an index based on 11 traits related to resource acquisition, competition, environmental tolerances, and fire ecology. We classified major tree species into ponderosa pine (Pinus ponderosa), Jeffrey pine (Pinus jeffreyi), incense-cedar (Calocedrus decurrens), true firs (Abies spp.), Douglas-fir (Pseudotsuga menziesii), live oaks (Quercus spp.), and deciduous oaks (Quercus spp.) response groups. We tested for the main effects of FDis on tree responses, as well as for interactions with tree, site, stand, and climate factors. We found that initial tree height modulated the effects of FDis on ponderosa pine, Jeffrey pine, incense-cedar, and true fir LCR, whereas FDis interacted with climate to alter live oak and deciduous oak LCR. FDis decreased BAI in ponderosa pine and increased BAI in live oaks. FDis interacted with tree size to influence BAI for Jeffrey pine, Douglas-fir, and true firs. We found no evidence that climate or site quality modulated FDis effects on BAI for any species group. Tree mortality was not responsive to FDis, except for the true firs, where both initial tree height and competition interacted with FDis to increase and decrease mortality odds, respectively. FDis effects commonly shifted from positive to negative along gradients of stand structure and site quality, indicating that these effects vary with site and stand conditions. Our results have implications for balancing the ecosystem benefits of mixed stands, such as disturbance risk, carbon sequestration, and habitat during forest restoration projects in the region, as well as for more accurate modeling of complex stands.

Advances in the study of global forest wildfires

PurposeWildfire is one of the most important natural disturbances in forest and multi-vegetation ecosystems, directly or indirectly affecting the structural processes and functions of forest ecosystems with varying degrees. Wildfire releases vast amounts of carbon dioxide and other substances by destroying vegetation, making itself an important topic for the study of global change and environmental impacts. Therefore, a deeper understanding of this topic is particularly crucial for managing forest ecosystems.MethodsThis paper was based on a literature search of the Web of Science database for international forest wildfire research, utilizing bibliometric and quantity statistical analysis methods.ResultsThe results show that forest wildfire research has been rapidly growing over the last 20 years, with the number of relevant articles generally increasing yearly at an average annual growth rate of about 22.45%. The US tops the list in terms of total and independent publications, with a total of 3111 articles (49.88%). The key journals publishing on this topic include 12 journals, Stephens S.L., Bergeron Y., and Lindenmayer D.B. are the key contributing authors to the field, and research institutions are primarily concentrated in the US Forest Service. Keyword co-occurrence analysis shows that current forest wildfire research is focused on seven main areas. This paper systematically reviewed the progress and hotspots of international forest wildfire research in recent decades, mainly focusing on occurrences, severity, management, and warning techniques for wildfires, as well as the impact of climate change and human activities on wildfires.ConclusionsThe study concludes that research trends in this field have undergone a significant evolution in recent decades. The future forest wildfire research moves towards a combination of typical mechanisms and large-scale effects across spatial and temporal scales, deep integration of aerospace and earth observations and precise simulations, discipline fusion, and couplings research. We believe that this study provides a comprehensive and systematic overview for future forest wildfire observation, prediction, management, and investigation of ecological effects.

Quantifying the contribution of major carbon producers to increases in vapor pressure deficit and burned area in western US and southwestern Canadian forests

Increases in burned forest area across the western United States and southwestern Canada over the last several decades have been partially driven by a rise in vapor pressure deficit (VPD), a measure of the atmosphere’s drying power that is significantly influenced by human-caused climate change. Previous research has quantified the contribution of carbon emissions traced back to a set of 88 major fossil fuel producers and cement manufacturers to historical global mean temperature rise. In this study, we extend that research into the domain of forest fires. We use a global energy balance carbon-cycle model, a suite of climate models, and a burned area (BA) model to determine the contribution of emissions traced to the major carbon producers to the long-term increase in VPD during 1901–2021 and to cumulative forest fire area during 1986–2021 in the western US and southwestern Canada. Based on climate model data, we find that emissions traced to these carbon producers contributed 48% (interquartile range (IQR) 38%–63%) of the long-term rise in VPD between 1901 and 2021. BA modeling indicates that these emissions also contributed 37% (IQR 26%–47%) of the cumulative area burned by forest fires between 1986 and 2021 in the western US and southwestern Canada. The increase in VPD in this region is linked to both increased fire activity and the region’s current and prolonged megadrought. As loss and damage from these hazards mounts, this research can inform public and legal dialogues regarding the responsibility carbon producers bear for addressing past, present, and future climate risks associated with fires and drought in the western US and southwestern Canada.