Brett G. Dickson’s research while affiliated with Northern Arizona University and other places

In response to mounting wildfire risks, land managers across the country will need to dramatically increase proactive wildfire management (e.g. fuel and forest health treatments). While human communities vary widely in their vulnerability to the impacts of fire, these discrepancies have rarely informed prioritizations for wildfire mitigation treatments. The ecological values and ecosystem services provided by forests have also typically been secondary considerations. To identify locations across the conterminous US where proactive wildfire management is likely to be effective at reducing wildfire severity and to yield co‐benefits for vulnerable communities and ecological values, we developed a set of spatial models that estimated wildfire mitigation potential (based on wildfire hazard and biophysical forest conditions) and either included or excluded information on vulnerable human communities, ecological values and ecosystem services. We then compared areas with high wildfire mitigation potential alone to refined ‘focal areas’ that overlaid social and ecological considerations to quantify the potential benefits of targeted wildfire mitigation treatments. Inclusion of social and ecological considerations substantially increased representation of vulnerable communities and ecological values in focal areas relative to the model that considered wildfire alone. For instance, restoration in these refined focal areas would cover 28% greater imperilled species richness, 45% greater water importance and 26% more families falling below the poverty line. By examining overlap between our refined focal areas and U.S. Forest Service top ranked firesheds (a prominent existing wildfire prioritization scheme), we show that our analysis can help to target wildfire mitigation efforts within firesheds to areas with particularly high social vulnerability and/or ecological value, providing an important compliment to a prioritization scheme based largely on risk to structures. Our results highlight the importance of considering ecological and social factors when implementing wildfire mitigation treatments and provide actionable guidance for integrating these considerations into existing prioritizations. Read the free Plain Language Summary for this article on the Journal blog.

Beyond the well‐established benefits of wildlife road crossings and associated infrastructure—improving driver safety, reducing animal mortality, reconnecting habitats—there is another important but often underappreciated benefit: supporting wildlife and ecosystems in adapting to climate change. We explore this potential by (1) synthesizing the literature surrounding climate adaptation and wildlife crossings, (2) presenting a case study on how crossings support shifting animal migrations, and (3) describing key considerations for incorporating climate information into crossing prioritizations. Among other climate‐adaptive benefits, research suggests crossings can support species range shifts and protect access to resources even as drought and human development compromise that access. Our case study outlines an approach for prioritizing crossing locations most likely to support animal migration both today and into the future. By accounting for such dynamics, wildlife crossings can be a cost‐effective tool that protects wildlife as well as motorists and enhances the resilience of infrastructure and ecosystems in a changing world.

Individual growth can exert strong control on population dynamics but is constrained by resource acquisition rates. Difficulty in accurately quantifying resource availability over large spatial extents and at high temporal frequencies often limits attempts to understand the extent to which resources limit individual growth. Daily estimates of stream metabolism, including gross primary productivity (GPP), are increasingly available but have not, to our knowledge, been linked to fish growth. Here we examine how environmental variables such as GPP, water temperature, turbidity, and high-flow releases from a dam are linked to spatiotemporal variation in the growth of flannelmouth sucker (Catostomus latipinnis) in the Colorado River within the Grand Canyon. We fit state-space growth models to 6 years of mark–recapture data collected in four river reaches spanning 300 river kilometers. Consistent with past research in this system, we find that all four environmental variables influence growth in length of a native primary consumer fish. GPP and temperature have a positive influence on growth, while turbidity and high-flow events have a negative influence. Water temperature is the dominant driver of spatiotemporal variation in growth, while the link between high-frequency GPP and fish growth is relatively novel. Fish growth is likely to be linked to stream metabolism in other systems where overall productivity, not the quality of primary producers, limits the food webs that support fish growth.

Abstract Unprecedented rates of climate change and biodiversity loss have galvanized efforts to expand protected areas (PAs) globally. However, limited spatial overlap between the most important landscapes for mitigating climate change and those with the highest value for biodiversity may impede efforts to simultaneously address both issues through new protections. At the same time, there is a need to understand how lands with high conservation value align with existing patterns of land management, both public and private, which will inform strategies for developing new conservation areas. To address these challenges, we developed three composite indices to identify the highest conservation value lands across the conterminous United States (CONUS) and Alaska, drawing on a suite of key ecological and environmental indicators. Two indices characterize the most important conservation lands for addressing climate change (based on climate accessibility, climate stability, and total carbon storage) and biodiversity (based on species richness, ecological integrity, and ecological connectivity), while a third, combined index simultaneously addresses both conservation challenges. We found that existing PAs in the United States have relatively low overlap with the highest conservation value lands, regardless of the index used (10%–13% in CONUS, 27%–34% in Alaska), suggesting limited effectiveness of current protections but substantial opportunity for expanding conservation into high‐value, unprotected areas. In unprotected landscapes, the highest value lands for addressing climate change generally diverged from those identified as most important for protecting biodiversity (22%–38% overlap, depending on index and geography). Our combined index reconciled these spatial trade‐offs through high overlap with both the climate and biodiversity indices (66%–72%). Of the unprotected high conservation value lands identified by each of our three indices, we found ≥70% are privately managed in CONUS, while 16%–27% are privately managed in Alaska, underscoring the need to engage private landowners and land trusts in efforts to substantially increase the total footprint of conservation lands in the United States. Our findings highlight the importance of balancing climate and biodiversity objectives when identifying new lands for conservation and provide guidance on where to target new protections to simultaneously address both goals. To facilitate planning using the indices, we developed an interactive web application.

Data from long‐term monitoring programs, such as the US Fish and Wildlife Service (USFWS) line distance sampling (LDS) program for Mojave desert tortoises (Gopherus agassizii), are increasingly being used in new ways to elucidate trends in population dynamics. We used the USFWS LDS data in a novel way to generate range‐wide predictions of occupancy, colonization, and local extinction rates from 2001 to 2018. We developed a dynamic occupancy model to answer fundamental questions posed by Bureau of Land Management personnel regarding how G. agassizii are distributed across the landscape over space and time. We transformed the LDS data into detection/nondetection data and constructed a Bayesian dynamic occupancy model using several time‐varying (e.g., temperature, precipitation, normalized difference vegetation index, fire, and a proxy for invasive grasses) and static covariates (e.g., soil properties, topography, distance to roads, distance to urban areas) hypothesized to influence G. agassizii occupancy dynamics. We estimated that over the entire time series (2001–2018) the probability of G. agassizii occupancy is declining in over one quarter (26%) of the range, largely in the northeastern part of the range, but that from 2011 to 2018, 77% of the range has a declining trend. Drawing on these model outputs, we developed an interactive, web‐based tool for exploring trends in dynamic occupancy across the species range, allowing users to focus on areas of management interest or concern.

Despite frequently being implicated in species declines, agricultural lands may nonetheless play an important role in connecting wildlife populations by serving as movement corridors or stopover sites between areas of high-quality habitat. For many North American bird species, agricultural intensification over the past half century has substantially impacted populations, yet recent studies have noted the potential for supporting avian biodiversity on agricultural lands through the promotion of functional connectivity. To support avian conservation efforts on agricultural lands across the United States, we used publicly available data from eBird to quantify and map the effects of agriculture on habitat suitability (using random forest models) and functional connectivity (via circuit theory) for three focal species that have experienced agriculture-linked declines or range contractions in recent decades: Greater Sage-grouse (Centrocercus urophasianus), American Black Duck (Anas rubripes), and Bobolink (Dolichonyx oryzivorus). Our analysis drew on novel, remotely sensed estimates of agricultural management intensity to quantify the effects of management practices on avian habitat and movement, revealing complex, species-specific relationships between agriculture and habitat value for the three focal species. Rangelands and croplands exhibited relatively high connectivity values for Greater Sage-grouse and Bobolink, respectively, mirroring these species’ strong habitat preferences for open sagebrush and cultivated grasslands. By contrast, American Black Duck migratory connectivity was low on all agricultural cover types. Mapping our model results across each species’ geographic range in the U.S. revealed key areas for agricultural management action to preserve high-quality habitat and connectivity, and we link these spatial recommendations to government incentive programs that can be used to increase wildlife-friendly management on U.S. agricultural lands.

Depending on management practices, agricultural lands can either pose substantial barriers to the movement of native species or can support landscape connectivity by linking areas of high-quality habitat. Balancing connectivity and sustainable food production on agricultural lands is critical to conservation in the conterminous United States (CONUS) where agriculture makes up close to half of total land area. However, limited guidance exists on where to target conservation resources to maximize benefits for native species and food security. To quantify the potential contribution of agricultural lands to the movement of organisms, we developed a novel method for estimating agricultural management intensity (based on remotely sensed temporal variation in vegetation cover on croplands and pastures) and incorporated these estimates into a CONUS-wide, circuit-theory based model of ecological flow connectivity. We then combined our connectivity results with data on the productivity, versatility, and resilience of agricultural lands (PVR) to identify conservation opportunities that support both biodiversity and food production. The highest levels of connectivity on agricultural lands occurred on relatively unmodified rangelands and on cropland and pasture in close proximity to large amounts of natural land cover. Mapping connectivity and PVR across CONUS revealed 10.2 Mha of agricultural lands (2.7%) with high value for both connectivity and food production, as well as large amounts of agricultural land (>140 Mha in total) with high value for either cultivation or supporting biodiversity (e.g., through ecological restoration). Drawing on these findings, we provide recommendations on the types of conservation approaches most suitable for a given agricultural system and link these recommendations to specific government incentive programs. To help facilitate conservation planning based on our results, we have developed an interactive web application, allowing users to visualize the spatial data developed here within their regions of interest.

Wind energy is a growing source of renewable energy with a 3-fold increase in use globally over the last decade. However, wind turbines cause bat mortality, especially for migratory species. The southwest United States has high bat species diversity and is an important area for migratory species, although little is known about their seasonal distribution. To examine potential risk to bats in areas proposed for wind energy development, we characterized bat occupancy spatially and temporally across northern Arizona, identifying use during summer when bats are reproductively active and fall during the migratory season. Our objectives were to determine occupancy of migratory species and species of greatest conservation need and develop a probability of occupancy map for species to identify areas of potential conflict with wind energy development. We selected 92 sites in 10 clusters with potential for development and used acoustic detectors to sample bats in the summer and fall of 2016 and 2017 for 6 nights per site per year. We predicted response of migratory bat species and species of special concern to 9 landscape variables using Program MARK. During summer, higher densities of forest on the landscape resulted in a higher probability of occupancy of migratory species such as hoary bats (Lasiurus cinereus), silver-haired bats (Lasionycteris noctivagans), big free-tailed bats (Nyctinomops macrotis), and species of conservation need such as spotted bats (Euderma maculatum). During the fall, higher concentration of valleys on the landscape predicted occupancy of hoary bats, big free-tailed bats, and spotted bats. High bat occupancy in the fall was also associated with higher elevation and close proximity to forests. We recommend that wind turbines be placed in open, flat grasslands away from forested landscapes and concentrations of valleys or other topographic variation.

Freshwater ecosystems are facing a deepening biodiversity crisis. Developing robust indicators to assess ecological integrity across large spatial scales and identifying the specific threats and pathways of impairment are thus critically needed if we are to inform freshwater conservation strategies. Here we present the first comprehensive threat assessment across the Colorado River Basin – one of the largest and most endangered river basins in North America – using a spatial framework accounting for the wide range of human activities (land uses, transportation infrastructure, exploitative activities, water withdrawals), pathways (local footprint, overland runoff, upstream cumulative effects), and spatial extent of influence (valley bottom, catchment and river network) known to affect the ecological integrity of riverine ecosystems. We quantified and mapped 69 individual threat indices with geospatial tools for each permanent, ephemeral, and intermittent stream segment within the Basin, encompassing a total of >1,067,700 river kilometers. We further aggregated these indices into components of water quality (diffuse and point-source pollution), hydrology (flow regulation/uses and climate change), and physical system (connectivity and geomorphology). To demonstrate the potential of our framework to inform spatial planning decision processes, we examined the typical combinations of threats experienced by different hydrologic areas and stream segment types, identified candidate watersheds for habitat restoration and enhancement where hotspots of biodiversity and threat overlapped, and assessed the associations between threat indices and in situ measurements of ecological integrity describing a suite of biological (benthic macroinvertebrate, fish), chemical (total nitrogen load, water conductivity), hydrological (flow alteration) and physical indicators (streambed stability, instream habitat complexity). Our assessment highlights clear disparities in term of overall degree of threat that result from different combinations and contributions of individual stressors, with different priorities emerging for perennial versus intermittent or ephemeral stream segments, and between the upper and lower parts of the Basin. Importantly, we showed that our threat indices were generally correlated with biological, chemical, hydrological and physical indicators of ecological integrity they were intended to capture. In addition to its implications for the conservation and management of the highly imperiled Colorado River Basin, our case study illustrates how multi-faceted threat mapping can be used to assess the ecological integrity of riverine ecosystems in the absence of spatially extensive in situ measurements.