US Forest Research Articles

Climate change, tree demography, and thermophilization in western US forests

Climate change is driving widespread changes in ecological communities. Warming temperatures often shift community composition toward more heat-tolerant taxa. The factors influencing the rate of this "thermophilization" process remain unclear. Using 10-y census data from an extensive forest plot network, we show that mature tree communities of the western United States have undergone thermophilization. The mean magnitude of climate warming over the 10-y study interval was 0.32 °C, whereas the mean magnitude of thermophilization was 0.039 °C. Differential tree mortality was the strongest demographic driver of thermophilization, rather than growth or recruitment. Thermophilization rates are associated with recent changes in temperature and hydrologic variables, as well as topography and disturbance, with insect damage showing the strongest standardized effect on thermophilization rates. On average, thermophilization occurred more rapidly on cool, north-facing hillslopes. Our results demonstrate that warming temperatures are outpacing the composition of western US forest tree communities, and that climate change may erode biodiversity patterns structured by topographic variation.

Mycorrhiza Better Predict Soil Fungal Community Composition and Function than Aboveground Traits in Temperate Forest Ecosystems

Forests in the northeastern US are experiencing shifts in community composition due to the northward migration of warm-adapted tree species and certain species’ declines (for example, white ash and eastern hemlock) due to invasive insects. Changes in belowground fungal communities and associated functions will inevitably follow. Therefore, we sought to investigate the relative importance of two important tree characteristics—mycorrhizal type [ectomycorrhizal (EcM) or arbuscular mycorrhizal (AM)] and leaf habit (deciduous or evergreen) on soil fungal community composition and organic matter cycling. We sampled soil in the organic and mineral horizons beneath two AM-associated (Fraxinus americana and Thuja occidentalis) and two ECM-associated tree species (Betula alleghaniensis and Tsuga canadensis), with an evergreen and deciduous species in each mycorrhizal group. To characterize fungal communities and organic matter decomposition beneath each tree species, we sequenced the ITS1 region of fungal DNA and measured the potential activity of carbon- and nitrogen-targeting extracellular enzymes. Each tree species harbored distinct fungal communities, supporting the need to consider both mycorrhizal type and leaf habit. However, between tree characteristics, mycorrhizal type better predicted fungal communities. Across fungal guilds, saprotrophic fungi were the most important group in shaping fungal community differences in soils beneath all tree species. The effect of leaf habit on carbon- and nitrogen-targeting hydrolytic enzymes depended on tree mycorrhizal association in the organic horizon, while oxidative enzyme activities were higher beneath EcM-associated trees across both soil horizons and leaf habits.

The magnitude and pace of photosynthetic recovery after wildfire in California ecosystems

Wildfire modifies the short- and long-term exchange of carbon between terrestrial ecosystems and the atmosphere, with impacts on ecosystem services such as carbon uptake. Dry western US forests historically experienced low-intensity, frequent fires, with patches across the landscape occupying different points in the fire-recovery trajectory. Contemporary perturbations, such as recent severe fires in California, could shift the historic stand-age distribution and impact the legacy of carbon uptake on the landscape. Here, we combine flux measurements of gross primary production (GPP) and chronosequence analysis using satellite remote sensing to investigate how the last century of fires in California impacted the dynamics of ecosystem carbon uptake on the fire-affected landscape. A GPP recovery trajectory curve of more than five thousand fires in forest ecosystems since 1919 indicated that fire reduced GPP by [Formula: see text] g C m[Formula: see text] y[Formula: see text]([Formula: see text]) in the first year after fire, with average recovery to prefire conditions after [Formula: see text] y. The largest fires in forested ecosystems reduced GPP by [Formula: see text] g C m[Formula: see text] y[Formula: see text] (n = 401) and took more than two decades to recover. Recent increases in fire severity and recovery time have led to nearly [Formula: see text] MMT CO[Formula: see text] (3-y rolling mean) in cumulative forgone carbon uptake due to the legacy of fires on the landscape, complicating the challenge of maintaining California's natural and working lands as a net carbon sink. Understanding these changes is paramount to weighing the costs and benefits associated with fuels management and ecosystem management for climate change mitigation.

Borrowing from Our Foremothers: Reexamining the Women's Movement through Material Culture, 1848–2017

Borrowing from Our Foremothers: Reexamining the Women's Movement through Material Culture, 1848–2017

Vegetation History and Estuarine Ecology of the Texas Gulf Coastal Plain in Relation to Climate and Sea-Level Changes According to Three Pollen Cores

The vegetation history of the Texas Gulf Coastal Plain in the Holocene is considered according to pollen evidence from three coring sites where both terrestrial and marine ecology are reconstructed. These pollen sites record oscillations in the limit of the Southeastern US Forest zone in relation to climate changes, with a major, southward migration of the forest limit and expansion of the range limit of Betula nigra being recorded in the 6th millennium BP and a northward migration in the 4th millennium BP. The appearance of Rhizophora pollen also indicates increased tropical influence in the Middle Holocene. Moreover, changes in the salinity profiles of estuaries are reconstructed in relation to broader coastal environmental changes, such as sea-level oscillations and the formation of barrier islands, with a major sea-level transgression phase being recorded in the 4th millennium BP and still-stand conditions after the 3rd millennium BP. These vegetation changes are finally compared to occupational evidence of prehistoric humans in the Central Texas Gulf Coastal Plain region in relation to ecological factors. Here, human occupation of the coastal zone is correlated with afforestation, the proliferation of pecan and the emergence of low-salinity estuaries.

Regional Stem Volume Mapping: A Feasibility Assessment of Scaling Tree-Level Estimates

Spatially detailed monitoring of forest resources is important for sustainable management but limited by a lack of field measurements. The increasing availability of multisource datasets offers the potential to characterize forest attributes at finer resolutions with regional coverage. This study aimed to assess the potential of mapping stem volume at a 30 m scale in eastern Texas using multisource datasets: airborne lidar, Landsat and LANDFIRE (Landscape Fire and Resource Management Planning Tools Project) datasets. Gradient-boosted trees regression models relating total volume, estimated from airborne lidar measurements and allometric equations, and multitemporal Landsat and LANDFIRE predictors were developed and evaluated. The fitted models showed moderate to high correlation (R2 = 0.52–0.81) with reference stem volume estimates, with higher correlation in pine forests (R2 = 0.70–0.81) than mixed forests (R2 = 0.52–0.67). The models were also precise, with relative percent mean absolute errors (pMAE) of 13.8–21.2%. The estimated volumes also consistently agreed with volumes estimated in independent sites (R2 = 0.51, pMAE = 34.7%) and with US Forest Service Forest Inventory Analysis county-level volume estimates (R2 = 0.93, pBias = −10.3%, pMAE = 11.7%). This study shows the potential of developing regional stem volume products using airborne lidar and multisource datasets, supporting forest productivity and carbon modeling at spatially detailed scales.

Cross-boundary cooperation in wildfire management during the custodial management period of the US Forest Service: A case study of the eastern Cascades of Oregon, USA, 1905–1945

In the U.S., federal, tribal, state, local, and private land management entities seek to implement a wildfire management strategy that spans large spatial extents and multiple ownerships to achieve wildfire risk reduction and forest restoration. This strategy requires cross-boundary cooperation. Cooperative cross-boundary forest management is not new; yet little case study research has documented historical examples. This study provides insight into how potentially overlooked models of cross-boundary cooperation of the past may be applicable to renewed cross-boundary cooperation today. We examined cooperation during the custodial management period (1905–1945) of Forest Service history. This study identifies the governance institutions, partner roles, and practices that promoted the establishment and durability of cross-boundary cooperation under two governance models adopted by the Forest Service and partners. The models are: cooperative federalism, for partnering with state and private landowner local entities – forest protective associations (FPAs); and federal interagency cooperation, for partnering with the Bureau of Indian Affairs Forestry Division, historically responsible for managing tribal lands. Using case study methods, we examined two examples of each model from the eastern Cascades of Oregon, USA. Two governance characteristics promoted durable cooperation, regardless of model: (1) the development of a bundle of cooperation-focused institutions (cross-organizational policy alignment; headquarters-level cooperative policies, laws, and/ or interagency agreements; unit-level cooperative agreements) that linked multiple Forest Service administrative levels (agency headquarters, local unit) to those of partner entities; and (2) the performance of a diversity of partner roles— operating at both headquarters and local levels — that enabled management entities to offset capacity constraints. Several governance characteristics promoted cooperation in the model that engaged private landowners (cooperative federalism). These were: the state-granted authorities of a special purpose district, whereby self-organized FPAs garnered resources and developed and enforced cooperative practices that coordinated upward with state and federal policies; recognition by the state and Forest Service of authorized, local entities that represented private landowners (FPAs) as essential partners; an administrative structure for state transfer of federal funding to local entities, resulting in cost-sharing; and the state’s performance of the roles of cost-sharing administrator and liaison between Forest Service and local entities. We suggest that the more partners can integrate these features into cross-boundary wildfire management cooperation today, the better its chances of establishment and durability.

Economic Effects of Federal Grazing Programs

Livestock grazing supports a considerable amount of economic activity across the United States. Federal grazing permits support numerous ranching operations by providing relatively low-cost grazing on federal lands. While grazing supports employment, labor income, and economic activity within a given state, the extent to which federal grazing permits play a role remains uncertain. In this paper we develop a method for estimating state-level economic contributions of livestock grazing for cattle grazing, as well as sheep and goat grazing, that is applicable to both the US Forest Service and Bureau of Land Management. We report state-level direct response coefficients, defined as the economic effects per 1 000 animal unit months of grazing use. We apply our coefficients to grazing lands for both US Forest Service and the Bureau of Land Management to estimate state-level economic contributions of federal grazing, finding that the economic effects of federal grazing are highest in western states where there are large amounts of public land. The measures of economic impact produced in this study were developed for consistent nationwide analyses. These measures may be used by researchers and land managers for conducting policy impacts and analysis of livestock grazing (e.g., increases or decreases of permitted grazing on public land) but are not intended to replace project- or site-specific economic analyses.

Understanding Perceptions of Climate Change Scenario Planning in United States Public Land Management Agencies

As climate change increasingly challenges the capacity of traditional decision-making modalities to contend with mounting complexities and uncertainties, natural resource management agencies have increasingly turned to nontraditional modes of planning and decision-making such as ‘futuring. Futuring methods, such as scenarios, have been increasingly utilized around the world. In the US, however, there has been a limited uptake of these tools across public land management and a preference for more traditional forecasting tools. This article explores some possibilities about why this is the case and aims to identify potential pathways forward. Drawing on 28 exploratory interviews with public land managers from the US Forest Service and others, a variety of benefits to scenario use were identified including: (1) mitigation of climate skepticism; (2) more robust capture of uncertainty, complexity, and the potential for surprise posed by climate change; and (3) potential for social learning. Barriers identified included: (1) difficulty in understanding the process, (2) bureaucratic concerns about time, staffing, and funding, and (3) a lack of an agency ‘champion’. However, concerns about the epistemological and institutional fit of nontraditional planning and decision-making tools like scenario processes predominated across the interviews. Interviewees also identified what we call ‘streamlining’ and ‘mainstreaming’ as potential pathways to integrate scenario processes into planning and decision-making.

Evaluation of Model-Based PM2.5 Estimates for Exposure Assessment during Wildfire Smoke Episodes in the Western U.S.

Investigating the health impacts of wildfire smoke requires data on people's exposure to fine particulate matter (PM2.5) across space and time. In recent years, it has become common to use machine learning models to fill gaps in monitoring data. However, it remains unclear how well these models are able to capture spikes in PM2.5 during and across wildfire events. Here, we evaluate the accuracy of two sets of high-coverage and high-resolution machine learning-derived PM2.5 data sets created by Di et al. and Reid et al. In general, the Reid estimates are more accurate than the Di estimates when compared to independent validation data from mobile smoke monitors deployed by the US Forest Service. However, both models tend to severely under-predict PM2.5 on high-pollution days. Our findings complement other recent studies calling for increased air pollution monitoring in the western US and support the inclusion of wildfire-specific monitoring observations and predictor variables in model-based estimates of PM2.5. Lastly, we call for more rigorous error quantification of machine-learning derived exposure data sets, with special attention to extreme events.

Unequal Treatments: Federal Wildfire Fuels Projects and Socioeconomic Status of Nearby Communities

With wildfires becoming more severe and more damaging in the western United States, fuels management projects intended to reduce the severity of wildfire are becoming an increasingly important management tool. Yet the statutory requirements for federal agencies to incorporate public input in their siting decisions combined with the greater political efficacy of wealthier, more educated communities have the potential to lead to inequities in their distribution. In this paper, we show that the likelihood that a community receives a nearby fuels management project is greater for wealthier, whiter, and more educated communities, even after controlling for differences in risk from wildfire. We further investigate the Collaborative Forest Landscape Restoration Program (CFLRP), a cost-share program operated by the US Forest Service. Communities near CFLRP projects tend to have higher socioeconomic status. However, participation in cost-share programs does not appear to depend critically on wealth because we find no difference in the wealth of communities near CFLRP projects compared with all US Forest Service fuels projects, including those with no matching requirements. Rather, the racial makeup and educational attainment of communities are more strongly associated with nearby cost-share projects.

Use of the Wildland Fire Decision Support System (WFDSS) for full suppression and managed fires within the Southwestern Region of the US Forest Service

Background United States federal wildland fire policy requires the use of formal decision support systems (DSS) for fire incidents that last for an extended time. However, the ways that wildfire managers use DSSs in decisions regarding fire management remain understudied, including how users engage with or utilise them to make strategic decisions. Aims Researchers sought to understand how users engage with the Wildland Fire Decision Support System (WFDSS), their view of its utilities and challenges, and their perspectives about WFDSS training. Methods We present the results of thematic analysis from 46 semi-structured interviews with employees in the US Forest Service Southwestern Region with a WFDSS user account. Key results Users indicated that the program is viewed as efficient for sharing information about wildfires and documenting management decision rationale. They identified emerging gaps in technical proficiency and the need for specialised training that creates high-level users to help guide teams using the program. Conclusions We offer suggestions about continued use of WFDSS including modifications to information distribution, revision of user roles, and expanded support for skills training. Implications Our results suggest that small changes to the WFDSS program and training curriculum may improve the experience of end-users and better match how they are using the program.

Effect of Sawing Variation on Hardwood Lumber Recovery—Part I: Volume

Abstract Sawing variation (SV), the degree of deviation from a specified target lumber size, is an unavoidable component of the sawing process. SV is influenced by several factors such as machine, material, set works, feed works, and cutting parameters. To account for these factors resulting in deviations from the desired target size, the target thickness of the lumber cut must be increased such that only a minimal number of boards is less than target thickness. Thus, the greater the amount of SV, the larger the target thickness must be such that a minimal quantity of undersized lumber is produced. Hence, with larger amounts of SV come greater waste and decreased opportunities for optimizing lumber recovery. However, the decrease in material loss due to a reduction in SV may not necessarily translate into a statistically significant increase in lumber product recovery by volume. This study explored the effect of varying degrees of SV on lumber recovery by volume for a range of hardwood log diameters using the US Forest Service's LOg ReCovery Analysis Tool sawmill simulation software. A minimal average recovery improvement of 3 percent due to reduced SV was observed across all kerf thicknesses, equating to a production value improvement of $336,000 for an 8 million board feet mill. Results indicate that the recovery gains realized by volume depend upon the log diameters sawn, the lumber target thickness, and the change (reduction) in SV.

Changes in bark properties and hydrology following prescribed fire in Pinus taeda and Quercus montana

AbstractIn the eastern United States, the use of prescribed fire as a silvicultural technique to manage for desirable upland tree species is increasing in popularity. Bark physical properties such as thickness, density, and porosity have known associations with fire tolerance among species. These physical properties simultaneously influence rainfall interception and canopy storage and thus are of interest across a range of disciplines. Furthermore, while these characteristics are innate to a species, it is unknown whether repeated exposure to fire facilitates physical change in bark structure and whether these changes are consistent among species. To answer these questions, bark samples were collected from mature pine (Pinus taeda L.) and oak (Quercus montana Willd.) trees from sites across the Bankhead National Forest in Alabama, USA under three different burn regimes: 3‐year cycle, 9‐year cycle, and no fire. Samples were analysed in the laboratory for bulk density, porosity, water storage capacity, and hygroscopicity (the amount of atmospheric water vapour absorbed by bark during non‐rainfall conditions). Drying rates of saturated samples under simulated wetting conditions were also assessed. Oak bark had higher bulk density, lower porosity, and dried slower than pine bark. Interestingly, bark from both species had lower bulk density, higher porosity, greater water storage capacity, and dried faster in stands that were burned every 3 years compared to other fire regimes (p < 0.001). In summary, this study demonstrates that prescribed fire regimes in an eastern US forest alter bark structure and thus influence individual tree control on hydrological processes. The increase in bark water storage capacity, coupled with faster bark evaporation times may lead to less water inputs to the forest floor and drier overall conditions. Further investigation of this fire‐bark‐water feedback loop is necessary to understand the extent of these mechanisms controlling landscape‐scale conditions.

Unburied Lives: The Historical Archaeology of Buffalo Soldiers at Fort Davis, Texas, 1869–1875 by Laurie A. Wilkie (review)

Reviewed by: Unburied Lives: The Historical Archaeology of Buffalo Soldiers at Fort Davis, Texas, 1869–1875 by Laurie A. Wilkie Ayme J. Swartz Unburied Lives: The Historical Archaeology of Buffalo Soldiers at Fort Davis, Texas, 1869–1875. By Laurie A. Wilkie. Albuquerque: University of New Mexico Press, 2021. ix + 267 pp. Illustrations, tables, notes, bibliography, index. $65.00 cloth. Laurie Wilkie wrote Unburied Lives: The Historical Archaeology of Buffalo Soldiers at Fort Davis, Texas, 1869–1875 intending to showcase the daily life of the African American soldier on the western frontier, post emancipation, filling the gap between legal slavery and the Jim Crow South during the westward expansion era. Her research in archival documents, archaeological excavation, and a fresh look at old architecture help bring to light the footprint of the African American community at a western military base. Wilkie's archival "excavation" of both what is still there and the ever-important "what has gone missing" and why, along with recovery of the tangible artifacts from the archaeological record, provide a detailed narrative of the troubles African Americans still experienced in the post-emancipation American West. The written and archaeological records illustrate how individual Black men could still express themselves and their beliefs regardless of military conformity. Wilkie shows how history continues to create a world where structural racism toward Black soldiers was ignored, accepted, and/or dismissed. This is evident when she explains how the National Archives did not curate failed pension applications and associated documents. The disposal of those records further emphasizes the burial of African American history. The book is very well organized, each chapter going into great detail about the topic presented while building on the previous chapter. Wilkie's specificity of individuals' accounts, referenced by newspapers and oftentimes limited archival documents, continued to illustrate the hardships and racist tensions African Americans faced on a daily basis. There are a few explicit discussions of sexual activities and behaviors that did not contribute to the overall book. A sufficient amount of evidence seemed to be lacking to make such bold assumptions. Likewise, the "best guess" about certain artifacts seemed to be persuaded by a particular theory rather than objectivity. At times the projection of modern ideology and meaning of imagery onto a past context seemed to derail the hardships Black military men already undoubtedly faced. Unburied Lives is a long-overdue narrative. It is needed to help complete the history of the American West and westward expansion. Wilkie attempted and succeeded in capturing the daily life, with struggles included, of [End Page 109] the African American soldier stationed in an undesirable location. Ayme J. Swartz Heritage Department Beaverhead-Deerlodge National Forest US Forest Service Copyright © 2023 Center for Great Plains Studies, University of Nebraska–Lincoln

Effect of Sawing Variation on Hardwood Lumber Recovery—Part II: Board Count

Abstract Sawing variation (SV) describes all variations that exist in the production of lumber due to machine, material, set works, feed works, and cutting parameters. The necessary oversizing of board thickness due to SV diminishes sawmill profits and hence efforts must be made to reduce the variation. However, such efforts are costly and sawmill personnel generally do not know at which point efforts to reduce (SV) become more costly than oversizing the boards. In an accompanying paper we examined the impact of SV on lumber volume recovery and found that volume recovery increased comparatively more for thinner than for thicker kerfs and that the effect of reduced SV became more pronounced as diameter increased. In this second manuscript, the effect of SV on the quantity of boards sawn for a range of hardwood log diameters using the US Forest Service's LOg ReCovery Analysis Tool sawmill simulation software was researched and compared with the volume improvement from an earlier paper. Results showed that significant differences in the number of boards obtained was dependent on the log diameters sawn, the lumber target thickness, and the change (reduction) in SV. A minimal average recovery improvement of 3 percent due to reduced SV was observed across all kerf thicknesses, equating to a potential production value improvement of $336,000 for an 8 million board feet mill. All sawmills can benefit from reducing SV, but mills that saw large-diameter logs might consider pursuing SV reduction more aggressively than a sawmill sawing mostly small-diameter logs.

Wilderness First Responder Medical Clearance - A Scoping Review with Recommendations

Background and Purpose Due to environmental extremes, as well as the nature of the work itself, wilderness first responders are at risk of incurring medical events in the line of duty. There currently do not exist standardized and scientifically supported methods to screen for a wilderness first responder’s risk of incurring a medical event. Methods We performed multiple scoping reviews using PubMed and CINAHL. The reviews covered six medical screening criteria based on previous recommendations from the National Fire Protection Association (NFPA) and the US Forest Service, and we grouped our reviews into two categories: articles that addressed objective screening criteria, and articles that addressed subjective findings with the first responder. Results Of the objective criteria, our reviews identified 21 articles addressing the ability to screen for risk of incurring a medical event by evaluation of a first responder's heart rate, 12 by blood pressure assessment, and 56 by assessment of body temperature. Of the subjective criteria we identified 19 articles focused on self-assessment, 34 articles on the use of standardized tools to assess for fatigue and sleepiness, and two articles on assessment of a first responder's urine to determine level of dehydration. We also identified seven additional articles through a hand search. Overall, there were 151 articles identified in our scoping reviews. These articles were largely of low quality, consisting mostly of case series without comparison groups. Conclusion There is a dearth of high-quality research into the medical assessment of first responders. We recommend that this paper, and measures discussed within it, be used as a starting point in the development of an evidence-based assessment protocol for wilderness first responders. We also recommend the development of a national database of medical events incurred by wilderness first responders to facilitate higher-quality research of screening protocols in this community.

Over 25 Years of Partnering to Conserve Chiricahua Leopard Frogs (Rana chiricahuensis) in Arizona, Combining Ex Situ and In Situ Strategies

The Phoenix Zoo has partnered with US Fish and Wildlife Service, Arizona Game and Fish Department, US Forest Service, and other organizations for more than 25 years to help recover Chiricahua leopard frogs (Rana [=Lithobates] chiricahuensis) in Arizona, USA. This federally threatened species faces declines due to habitat loss and degradation, long-term drought, disease, and invasive species. Over 26,000 larvae, froglets, and adults, as well as 26 egg masses produced by adults held at the Phoenix Zoo have been released to the wild, augmenting and/or re-establishing wild populations. Chiricahua leopard frog-occupied sites in Arizona have increased from 38 in 2007, when the species’ recovery plan was published, to a high of 155 in the last five years, as a result of ex situ and in situ conservation efforts. As one of the longest-running programs of its kind in the United States, communication among partners has been key to sustaining it. Recovery strategies and complex decisions are made as a team and we have worked through numerous management challenges together. Though Chiricahua leopard frogs still face significant threats and a long road to recovery, this program serves as a strong example of the positive effects of conservation partnerships for native wildlife.

Integrating Social and Ecological Predictors to Understand Variation within Ecosystems: A Case Study of the Great Smoky Mountains National Park PACE

Land management decisions have profound impacts on biological communities. Various administrative units are likely to implement different management decisions, with the result that consistent biological patterns that track administrative boundaries may emerge. To assess these relationships, we collected data on land cover, disturbance evidence, and tree communities in randomized sampling sites located in National Park, US Forest Service Wilderness, and US Forest Service Non-wilderness distributed across the Great Smoky Mountains National Park Protected Area-Centered Ecosystem (GRSM PACE). We examined how present-day values for these ecological responses were linked to both biophysical site characteristics (as the foundation for ecological communities) and jurisdiction type (as categories that integrate the combination of dynamic social decisions and management practices since initial designation). The variable representing administrative unit, jurisdiction type, acted as an umbrella indicator of the management trajectory and social influences that have affected a site and emerged as an important predictor of groundcover types (grass and litter), tree diversity, and wildlife sign at sites across the GRSM PACE. This was an exploratory study with limited sample size, so more data are needed to explore the mechanisms driving these relationships. These initial findings, however, suggest that differences in management activities alter the ecological trajectory of sites across the PACE. Given dynamic and diverse management practices, our data suggest jurisdiction overlaid on biophysical site information may be useful to rapidly assess how socially defined landscape activities impact biological responses, particularly when both are stressed by global change.

Stand and environmental conditions drive functional shifts associated with mesophication in eastern US forests

There is a growing body of evidence that mesic tree species are increasing in importance across much of the eastern US. This increase is often observed in tandem with a decrease in the abundance and importance of species considered to be better adapted to disturbance and drier conditions (e.g.,Quercusspecies). Concern over this transition is related to several factors, including the potential that this transition is self-reinforcing (termed “mesophication”), will result in decreased resiliency of forests to a variety of disturbances, and may negatively impact ecosystem functioning, timber value, and wildlife habitat. Evidence for shifts in composition provide broad-scale support for mesophication, but we lack information on the fine-scale factors that drive the associated functional changes. Understanding this variability is particularly important as managers work to develop site-and condition-specific management practices to target stands or portions of the landscape where this transition is occurring or is likely to occur in the future. To address this knowledge gap and identify forests that are most susceptible to mesophication (which we evaluate as a functional shift to less drought or fire tolerant, or more shade tolerant, forests), we used data from the USDA Forest Service Forest Inventory and Analysis program to determine what fine-scale factors impact the rate (change through time) and degree (difference between the overstory and midstory) of change in eastern US forests. We found that mesophication varies along stand and environmental gradients, but this relationship depended on the functional trait examined. For example, shade and drought tolerance suggest mesophication is greatest at sites with more acidic soils, while fire tolerance suggests mesophication increases with soil pH. Mesophication was also generally more pronounced in older stands, stands with more variable diameters, and in wetter sites, but plots categorized as “hydric” were often highly variable. Our results provide evidence that stand-scale conditions impact current and potential future changes in trait conditions and composition across eastern US forests. We provide a starting point for managers looking to prioritize portions of the landscape most at risk and developing treatments to address the compositional and functional changes associated with mesophication.