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Abstract Protected areas are foundational to the conservation of biological diversity, and many scientists have called for increased protections in the face of the current extinction and climate‐change crises. Currently in the United States, the most recognized way to track the amount of protected land is the Gap Analysis Project classification system, which we argue is deficient in three ways: it does not, in a systematic way, specify the typical uses and constraints associated with each conservation designation; it is not fine‐tuned or nuanced enough to distinguish the levels of protection among designations within “protected” or “unprotected” areas that allow quite different human activities; and it largely ignores the durability of the designations, failing to account for an area's vulnerability to downsizing, downgrading, or degazetting. We propose a new classification system to address these deficiencies and demonstrate this method for several of the most common federal land designations in the United States.

Because of its importance to both carbon storage and biodiversity, old forest has regained currency as a focus of forest management and policy. However, absence of a systematic approach to classifying stages of forest development across all forest types precludes our understanding of the current distribution of the mature and old-growth forest estate. Here, we propose functional definitions of mature and old-growth forests consistent with theories of forest stand development and evaluate the implications for assessing their spatial distribution nationwide. Using plot data from a national forest inventory and assuming space-for-time substitution, we modeled forest carbon accumulation over time using saturating, non-linear growth models. We define the onset of old-growth characteristics as occurring at the age when the density of total forest carbon stored in live and dead biomass reaches 95% of the empirically derived maximum, and the mature forest stage as occurring between the peak average carbon increment and the age of onset of old growth. We fit models within unique forest type-groups and, where possible, accounted for differences in site productivity. Population-level estimates of the mature and old-growth forest estate were calculated using sample design-based estimators. Across forest type-groups, the age at onset of old growth varied from 34 to 577 years, and the onset of mature forest conditions ranged between 16 and 313 years. Within forest type-groups, the effect of site quality on the age at onset of mature and old-growth forest varied but generally supported our hypothesis that high site quality accelerates forest development and increases forest carbon storage in old forests. We classified 6.3% of current forested lands in the United States as old growth and almost one-third as mature. Of the current old-growth forest estate, approximately 46% is found on federal public lands, and 11% is currently in congressional reserves. We posit that continued improvements to modeling the dynamic process of forest development and integration with structural definitions of old growth will be needed to ensure targets for old-growth retention and development are achieved.

Inventoried roadless areas (IRAs) in national forests in the contiguous United States (CONUS) are public lands that are ecologically intact and could be prime candidates for addition to the protected-area system, thereby contributing to the goal of protecting 30% of the Earth by 2030. Despite calls both to protect roadless areas and to downgrade them, we know surprisingly little about the importance of IRAs as habitat for vulnerable wildlife species. We assessed the importance of IRAs—in total and individually—as habitat for wildlife species of conservation concern (SCCs) and, for context, compared their habitat value to that of other national forest lands and CONUS lands in general. We also quantified how well the protected-area system would provide habitat for wildlife SCCs if all unprotected IRAs were added to it. Of the 537 wildlife SCCs in CONUS, 308 species (57%) have at least some suitable habitat in one or more IRAs. The median IRA contains suitable habitat for 10 wildlife SCCs, with a maximum of 62 wildlife SCCs. Despite their geographic and elevational clustering and predominance of a single biome type, IRAs provide a larger proportion of suitable habitat for multiple wildlife SCCs than non-IRA CONUS lands. The median number of wildlife SCCs’ suitable habitat per 900-m2 pixel is also slightly higher in IRAs than in most national forest wilderness areas, national monuments, and other currently protected areas. If all IRAs were added to the protected-area system in CONUS, there would be a substantial decrease (−38) in the number of wildlife SCCs that are currently considered “poorly represented” in protected areas. In this study we provide quantitative information about the importance of IRAs as habitat for vulnerable wildlife species so that stakeholders, agency staff, and lawmakers can make informed choices about where to invest limited resources for conservation.

Conservation efforts should target the few remaining areas of the world that represent outstanding examples of ecological integrity and aim to restore ecological integrity to a much broader area of the world with intact habitat and minimal species loss while this is still possible. There have been many assessments of “intactness” in recent years but most of these use measures of anthropogenic impact at a site, rather than faunal intactness or ecological integrity. This paper makes the first assessment of faunal intactness for the global terrestrial land surface and assesses how many ecoregions have sites that could qualify as Key Biodiversity Areas (KBAs – sites contributing significantly to the global persistence of biodiversity) based on their outstanding ecological integrity (under KBA Criterion C). Three datasets are combined on species loss at sites to create a new spatially explicit map of numbers of species extirpated. Based on this map it is estimated that no more than 2.9% of the land surface can be considered to be faunally intact. Additionally, using habitat/density distribution data for 15 large mammals we also make an initial assessment of areas where mammal densities are reduced, showing a further decrease in surface area to 2.8% of the land surface that could be considered functionally intact. Only 11% of the functionally intact areas that were identified are included within existing protected areas, and only 4% within existing KBAs triggered by other criteria. Our findings show that the number of ecoregions that could qualify as Criterion C KBAs could potentially increase land area up to 20% if their faunal composition was restored with the reintroduction of 1–5 species. Hence, if all necessary requirements are met in order to reintroduce species and regain faunal integrity, this will increase ecological integrity across much of the area where human impacts are low (human footprint ≤4). Focusing restoration efforts in these areas could significantly increase the area of the planet with full ecological integrity.

Abstract Conservation scientists call for establishing additional protected areas amidst ongoing threats of expanding human development. Nevertheless, some existing protected areas are being downsized and demoted of their existing conservation protections. In 2001, the Roadless Area Conservation Rule prohibited road construction and timber harvest in 240,000 km2 of inventoried roadless areas (IRAs) located on United States Department of Agriculture Forest Service lands. IRAs represent a non‐legislative protected status that is in jeopardy of conservation demotion or “degazettement,” and few national protected area assessments recognize the IRA designation. Since the rule's conception two decades ago, little research has been conducted to assess the conservation values of IRAs and the values they could add to the existing system of highly protected areas in the continental United States. To increase understanding of these conservation values, we assessed three aspects of roadless areas: (a) how wild and intact are IRA lands compared to state, national, and protected lands, (b) how do IRAs complement the size, connectedness, and representation of protected lands, and (c) how do IRAs contribute to protection of important ecosystem services (drinking water and annual carbon capture)? Through this analysis we found that many IRAs are among the most wild, undeveloped areas both in the nation and within their respective states. IRAs increase the size of—and reduce isolation between—protected areas, likely buffering them from external stressors. In some places, IRAs protect watersheds that deliver drinking water to hundreds of thousands of people. IRAs also add significantly to the total carbon captured by existing protected areas. The results of our evaluation demonstrate the potential of IRAs to contribute to the conservation value of the U.S. protected area system and to deliver important ecosystem services.

Abstract Protected areas represent a key strategy to conserve biodiversity. However, human land use and other impacts outside protected areas boundaries significantly influence species and ecosystems within protected areas. Therefore, identifying and delineating important lands surrounding protected areas may be critical to developing conservation strategies to sustain biodiversity. Here, we identify greater ecosystems of protected areas in the contiguous United States by delineating permeable wildlands located adjacent to protected area borders using the global human footprint map as the basis for estimating permeability. We evaluated how elevating the conservation status of greater ecosystems could help achieve aspirational targets for protecting additional terrestrial land area while better representing ecological diversity. We then assessed the feasibility of elevating conservation in greater ecosystems by quantifying the composition of land ownership and existing conservation status. Greater ecosystems of different protected areas often occur as large complexes that could be used to manage protected areas and monitor their status under regional conservation strategies. Elevating the conservation status of greater ecosystems could aid in achieving international targets while increasing the representation of vegetative types within conservation reserves. The most connected and permeable lands surrounding protected areas are dominated by public land (managed by the U.S. federal and state governments), though the amount of public land within greater ecosystems decreased with distance from protected areas. Public lands may provide opportunities to elevate the conservation status of greater ecosystems surrounding protected areas through policy and management changes. We focused on the contiguous United States, but our methods could be applied globally (which we demonstrate). To achieve bold international conservation goals, identifying the greater ecosystems around protected areas and developing conservation strategies of their landscape context will ultimately benefit species and ecosystems in protected areas.

Conservationists are calling for bold strategies to connect wildlands and halt extinctions. A growing number of scientists recommend that 50% of all land must be held in a protected area network to maintain biodiversity. We assessed lands adjacent to the Pacific Crest Trail (PCT) and Continental Divide Trail (CDT) as possible wildlife corridors connecting protected areas in the American West. We evaluated the connectivity, wildness, and biodiversity values of the lands of each corridor and determined the conservation and land management status. We found that our corridors connect 95 protected areas creating two linear protected area chains from Mexico to Canada. Both the PCT and CDT corridors follow many of the best corridor routes previously found in the literature and hold high wildland conservation values. The American public already owns the majority of land units around the modeled PCT (88%) and CDT (90%) corridor. Therefore, we recommend further analysis of the lands adjacent to recreational trails as wildlife corridors. Employing our methodology on multiple scales could reveal that other recreational trails should be buffered and conserved for wildlife movement.

Before the advent of intensive forest management and fire suppression, western North American forests exhibited a naturally occurring resistance and resilience to wildfires and other disturbances. Resilience, which encompasses resistance, reflects the amount of disruption an ecosystem can withstand before its structure or organization qualitatively shift to a different basin of attraction. In fire-maintained forests, resilience to disturbance events arose primarily from vegetation pattern-disturbance process interactions at several levels of organization. Using evidence from 15 ecoregions, spanning forests from Canada to Mexico, we review the properties of forests that reinforced qualities of resilience and resistance. We show examples of multi-level landscape resilience, of feedbacks within and among levels, and how conditions have changed under climatic and management influences. We highlight geographic similarities and important differences in the structure and organization of historical landscapes, their forest types, and in the conditions that have changed resilience and resistance to abrupt or large-scale disruptions. We discuss the role of the regional climate in episodically or abruptly reorganizing plant and animal biogeography and forest resilience and resistance to disturbances. We give clear examples of these changes and suggest that managing for resilient forests is a construct that strongly depends on scale and human social values. It involves human communities actively working with the ecosystems they depend on, and the processes that shape them, to adapt landscapes, species, and human communities to climate change while maintaining core ecosystem processes and services. Finally, it compels us to embrace management approaches that incorporate ongoing disturbances and anticipated effects of climatic changes, and to support dynamically shifting patchworks of forest and non-forest. Doing so could make these shifting forest conditions and wildfire regimes less disruptive to individuals and society.

Wildfire regimes are changing in the western United States, yet the ways in which wildfires influence native bees, the resources they depend on for food and nesting, or the traits that influence their interactions with plants are poorly understood. In burned and unburned areas in Montana, USA, we investigated the abundance and diversity of native bees, floral and nesting resources, nesting success, and traits of flowers and bees. In two of the three localities studied, burned areas, including areas that burned with high-severity wildfires, supported higher density and diversity of native bees and the flowers they depend on for food and larval provisioning. Burned areas also had more bare ground for ground-nesting bees and more available coarse woody debris for cavity-nesting bees than unburned areas. Moreover, cavity-nesting bees were completely unsuccessful at nesting in artificial nesting boxes in unburned areas, while nesting success was 40% in burned areas. Mean bee intertegular distance (a trait strongly correlated with tongue length, foraging distance, and body size) was similar between burned and unburned areas. However, wildfires influenced both interspecific and intraspecific trait variation of bees and plants. Intraspecific variation in bee intertegular distance was higher in unburned than burned areas. Both interspecific and intraspecific variation in floral traits important for interactions with pollinators were generally higher in burned than unburned areas. Thus, wildfires generally increased the density and species diversity of bees and flowers as well as trait variation at both trophic levels. We conclude that wildfires—even large, high-severity wildfires—create conditions that support native bees and the resources they need to flourish, but that unburned areas maintain trait variation in landscape mosaics with heterogeneous fire conditions.

Abstract The Appalachian Trail (AT) traverses the Appalachian Mountains across 11 degrees of latitude from Springer Mountain in Georgia to Maine's Mt. Katahdin. The 3,524 km (2,190‐mile) long trail is buffered within a conserved corridor that is at least ~ 305 m wide and covers approximately 101,000 hectacres (250,000 acres) overseen by the National Park Service (NPS), making it one of the largest NPS units in the East. Although a continuous marked trail has been established since 1937, protection of the corridor was not complete until the last couple of decades. Additional conservation designations exist adjacent to much of the trail corridor, but significant gaps in protection remain. A variety of land trusts and other nonprofit conservation organizations, federal and state land management agencies, and regional trail clubs overseen by the Appalachian Trail Conservancy (ATC) actively seek to add to the local, regional, and national conservation significance of this landscape or to improve the management of lands already protected. Here, we assess biodiversity and ecological integrity along the entire AT among 2,123 trail sampling segments and four planning regions. We evaluated gradients of biodiversity and ecological integrity in relation to the existing management status of trail sampling segments to identify gaps in protection of high value areas. The AT possesses high species diversity at the southern end, where much of it exists in federal multiple‐use management, and high ecological integrity in the north on private timberlands. Inadequately protected areas of such high biological diversity and ecological integrity occur throughout the trail. Our data are analyzed at the scale of the entire AT with summaries and comparisons among broad sections, regions, states, and some specific locations. We include our spatial data so that it may be used for analyses and prioritization at multiple scales from the local maintenance club to the ATC.

Wildlands are increasingly lost to human development. Conservation scientists repeatedly call for protecting the remaining wildlands and expanding the land area protected in reserves. Despite these calls, conservation reserves can be eliminated through legislation that demotes their conservation status. For example, legislation introduced to the Congress of the United States recently would demote 29 Wilderness Study Areas (WSAs) from the protections afforded by their existing status. The proposed legislation suggests that the 29 areas are not suitable for a promotion and future inclusion in the National Wilderness Preservation System based on decades-old local evaluations. Local evaluations, notwithstanding, it may be important to consider the value of lands from a national perspective. Without a national perspective, local evaluations alone may lead to overlooking the national significance of lands. With this in mind, I used five qualities of wildland value (wildness, intactness of night sky, lack of human-generated noises, intactness of mammals, and intactness of mammal carnivores of conservation concern) to compare the 29 WSAs to all national parks and wilderness areas located within the contiguous United States. The pool of 29 WSAs was similar to the pool of national parks and wilderness areas with respect to the five qualities assessed, and some of the WSAs were characterized by higher values than most of national parks and wilderness areas. This analysis demonstrates the national significance of the WSAs targeted for demotion of their existing conservation status. Such an approach could be used in future land management legislation and planning to ensure that a national perspective on conservation value is brought to bear on decisions facing federally-managed lands.

Conservation scientists recognize that additional protected areas are needed to maintain biological diversity and ecological processes. As regional conservation planners embark on recommending additional areas for protection in formal ecological reserves, it is important to evaluate candidate lands for their role in building a resilient protected areas system of the future. Here, we evaluate North Carolina’s Mountain Treasures with respect to their (1) ecological integrity, (2) role in connecting existing core protected areas, (3) potential to diversify the ecosystem representation of reserves, and (4) role in maintaining hotspots of biologically-rich areas that are not well protected. Mountain Treasures represent a citizen inventory of roadless areas and serve as candidates for elevated levels of conservation protection on U.S. federal lands. We compared Mountain Treasures to other candidate lands throughout the country to evaluate their potential national significance. While the Mountain Treasures tended to be more impacted by human modifications than other roadless areas, they are as important as other roadless areas with respect to their role in connecting existing protected areas and diversifying representation of ecosystems in conservation reserves. However, Mountain Treasures tended to have a much higher biodiversity priority index than other roadless areas leading to an overall higher composite score compared to other roadless areas. Our analysis serves as an example of how using broad-scale datasets can help conservation planners assess the national significance of local areas.

Conservation scientists emphasize the importance of maintaining a connected network of protected areas to prevent ecosystems and populations from becoming isolated, reduce the risk of extinction, and ultimately sustain biodiversity. Keeping protected areas connected in a network is increasingly recognized as a conservation priority in the current era of rapid climate change. Models that identify suitable linkages between core areas have been used to prioritize potentially important corridors for maintaining functional connectivity. Here, we identify the most "natural" (i.e., least human-modified) corridors between large protected areas in the contiguous Unites States. We aggregated results from multiple connectivity models to develop a composite map of corridors reflecting agreement of models run under different assumptions about how human modification of land may influence connectivity. To identify which land units are most important for sustaining structural connectivity, we used the composite map of corridors to evaluate connectivity priorities in two ways: (1) among land units outside of our pool of large core protected areas and (2) among units administratively protected as Inventoried Roadless (IRAs) or Wilderness Study Areas (WSAs). Corridor values varied substantially among classes of "unprotected" non-core land units, and land units of high connectivity value and priority represent diverse ownerships and existing levels of protections. We provide a ranking of IRAs and WSAs that should be prioritized for additional protection to maintain minimal human modification. Our results provide a coarse-scale assessment of connectivity priorities for maintaining a connected network of protected areas.