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.

Connecting protected areas remains an important global conservation strategy in the face of ongoing and future threats to biodiversity. Amid our growing understanding of how species’ distributions will respond to climate change, conservation scientists need to plan for connectivity conservation across entire continents. We modeled multiscale connectivity priorities based on the least human‐modified lands between large protected areas of North America using least‐cost and circuit theory approaches. We first identified priority corridors between large protected areas, then characterized the network’s structure to unveil priority linkages most important for maintaining network‐ and regional‐level connectivity. Agreement between least‐cost corridors and current flow varied throughout North America, reflecting permeable landscape conditions and “pinch points” where potential ecological flows may concentrate between protected areas. Priority network‐level linkages derived from each approach were similar throughout the continental network (e.g., Rocky Mountains and Canadian boreal), but critical linkages that bridged regional protected‐area networks varied. We emphasize the importance of planning for connectivity at continental scales and demonstrate the utility of multiple methods when mapping connectivity priorities across large spatial extents with wide gradients in landscape conditions.

Human‐caused changes in disturbance regimes and introductions of nonnative species have the potential to result in widespread, directional changes in forest community structure. The degree that plant community composition persists or changes following disturbances depends on the balance between local extirpation and colonization by new species, including nonnatives. In this study, we examined species losses and gains, and entry of native vs. exotic species to determine how oak forests in the Appalachian Mountains might shift in species composition following a gradient of pulse disturbances (timber harvesting). We asked (1) how compositional stability of the plant community (resistance and resilience) was influenced by disturbance intensity, (2) whether community responses were driven by extirpation or colonization of species, and (3) how disturbance intensity influenced total and functional group diversity, including the nonnative proportion of the flora through time. We collected data at three spatial scales and three times, including just before, one year post‐disturbance, and 10 years post‐disturbance. Resistance was estimated using community distance measures between pre‐ and one year post‐disturbance, and resilience using community distance between pre‐ and 10‐year post‐disturbance conditions. The number of colonizing and extirpated species between sampling times was analyzed for all species combined and for six functional groups. Resistance and resilience decreased with increasing timber‐harvesting disturbance; compositional stability was lower in the most disturbed plots, which was driven by colonization, but not extirpation, of species. Colonization of species also led to increases in diversity after disturbance that was typically maintained after 10 years following disturbance. Most of the community‐level responses were driven by post‐disturbance colonization of native forbs and graminoids. The nonnative proportion of plant species tended to increase following disturbance, especially at large spatial scales in the most disturbed treatments, but tended to decrease through time following disturbance due to canopy development. The results of this study are consistent with the theory that resources released by disturbance have strong influences on species colonization and community composition. The effects of management activities tested in this study, which span a gradient of timber‐harvesting disturbance, shift species composition largely via an increase in species colonization and diversity.

Context: Conservation scientists recommend maintaining and restoring ecological connectivity to sustain biodiversity in the face of land-use and climate change. Alternative connectivity assessments conducted at multiple spatial scales are needed to understand consequences of varying assumptions and for use in multi-scale conservation planning. Objectives: We compared mapped output from different model scenarios conducted to identify areas important for ecological connectivity across North America. We asked how areas important for connectivity vary with spatial scale and assumptions regarding the way in which human modification affects landscape resistance. Methods: We conducted a factorial experiment using omnidirectional connectivity analyses across North America where we crossed “treatments” represented by four moving window sizes and three resistance surfaces. The three resistance surfaces represent a gradient in species’ sensitivity to human modification. Results: Maps of connectivity importance varied among scenarios. The effects of moving window size were more conspicuous than effects of different resistance surfaces. Outputs from small moving windows revealed mottled patterns of connectivity importance, while outputs from larger moving windows revealed broad swaths of connectivity importance across mountainous and boreal areas of North America. Patterns of connectivity importance tended to be more channelized from resistance surfaces produced to represent more human-sensitive species and more diffuse from resistance surfaces produced to represent more human-tolerant species. Conclusions: Our scenarios and output represent alternative hypotheses and predictions about how multiple species may move in response to varying degrees of human modification. Our output can be compared to species-specific models to investigate which of our scenarios best matches observed movements of organisms. Our output can also be used as coarse-filter and multi-scale connectivity assessments for conservation plans. Notably, our outputs highlight the importance of small and isolated fragments of relatively natural land while simultaneously identifying broad regions important for maintaining connectivity across natural areas of North America.

Addressing uncertainties in climate vulnerability remains a challenge for conservation planning. We evaluate how confidence in conservation recommendations may change with agreement among alternative climate projections and metrics of climate exposure. We assessed agreement among three multivariate estimates of climate exposure (forward velocity, backward velocity, and climate dissimilarity) using 18 alternative climate projections for the contiguous United States. For each metric, we classified maps into quartiles for each alternative climate projections, and calculated the frequency of quartiles assigned for each gridded location (high quartile frequency = more agreement among climate projections). We evaluated recommendations using a recent climate adaptation heuristic framework that recommends emphasizing various conservation strategies to land based on current conservation value and expected climate exposure. We found that areas where conservation strategies would be confidently assigned based on high agreement among climate projections varied substantially across regions. In general, there was more agreement in forward and backward velocity estimates among alternative projections than agreement in estimates of local dissimilarity. Consensus of climate predictions resulted in the same conservation recommendation assignments in a few areas, but patterns varied by climate exposure metric. This work demonstrates an approach for explicitly evaluating alternative predictions in geographic patterns of climate change.

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.