USGS Science⌕ Search

SEARCH · USGS Science

Results for “Challenge”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,441 records · Page 80Linked to original sources
USGS2017

A rapid assessment method to estimate the distribution of juvenile Chinook Salmon in tributary habitats using eDNA and occupancy estimation

Identification and protection of water bodies used by anadromous species are critical in light of increasing threats to fish populations, yet often challenging given budgetary and logistical limitations. Noninvasive, rapid‐assessment, sampling techniques may reduce costs and effort while increasing species detection efficiencies. We used an intrinsic potential (IP) habitat model to identify high‐quality rearing habitats for Chinook Salmon Oncorhynchus tshawytscha and select sites to sample throughout the Chena River basin, Alaska, for juvenile occupancy using an environmental DNA (eDNA) approach. Water samples were collected from 75 tributary sites in 2014 and 2015. The presence of Chinook Salmon DNA in water samples was assessed using a species‐specific quantitative PCR (qPCR) assay. The IP model predicted over 900 stream kilometers in the basin to support high‐quality (IP ≥ 0.75) rearing habitat. Occupancy estimation based on eDNA samples indicated that 80% and 56% of previously unsampled sites classified as high or low IP (IP < 0.75), respectively, were occupied. The probability of detection ( p ) of Chinook Salmon DNA from three replicate water samples was high ( p = 0.76) but varied with drainage area (km 2 ). A power analysis indicated high power to detect proportional changes in occupancy based on parameter values estimated from eDNA occupancy models, although power curves were not symmetrical around zero, indicating greater power to detect positive than negative proportional changes in occupancy. Overall, the combination of IP habitat modeling and occupancy estimation provided a useful, rapid‐assessment method to predict and subsequently quantify the distribution of juvenile salmon in previously unsampled tributary habitats. Additionally, these methods are flexible and can be modified for application to other species and in other locations, which may contribute towards improved population monitoring and management.

Alaska↗
USGS2018

Assessing angler effort, catch, and harvest and the efficacy of a use-estimation system on a multi-lake fishery in middle Georgia

Creel surveys are valuable tools in recreational fisheries management. However, multiple‐impoundment fisheries of complex spatial structure can complicate survey designs and pose logistical challenges for management agencies. Marben Public Fishing Area in Mansfield, GA is a multi‐impoundment fishery with many access points, and these features prevent or complicate use of traditional on‐site contact methods such as standard roving‐ or access‐point designs because many anglers may be missed during the survey process. Therefore, adaptation of a traditional survey method is often required for sampling this special case of multi‐lake fisheries to develop an accurate fishery profile. Accordingly, a modified non‐uniform probability roving creel survey was conducted at the Marben PFA during 2013 to estimate fishery characteristics relating to fishing effort, catch, and fish harvest. Monthly fishing effort averaged 7,523 angler‐hours (h) (SD = 5,956) and ranged from 1,301 h (SD = 562) in December to 21,856 h (SD = 5909) in May. A generalized linear mixed model was used to determine that angler catch and harvest rates were significantly higher in the spring and summer (all p < 0.05) than in the other seasons, but did not vary by fishing location. Our results demonstrate the utility of modifying existing creel methodology for monitoring small, spatially complex, intensely managed impoundments that support quality recreational fisheries and provide a template for the assessment and management of similar regional fisheries.

Georgia↗
USGS2021

Evaluating fish rescue as a drought adaptation strategy using a life cycle modeling approach for imperiled coho salmon

Projected intensification of drought as a result of climate change may reduce the capacity of streams to rear fish, exacerbating the challenge of recovering salmonid populations listed under the Endangered Species Act. Without management intervention, some stocks will likely go extinct as stream drying and fragmentation reduce juvenile survival to unsustainable levels. To offset drought‐related mortality, fish rescue programs have proliferated, whereby juvenile salmonids are captured and transferred to off‐site rearing facilities. However, the efficacy of this potential conservation tool remains poorly understood. We developed a life cycle model to examine the implications of fish rescue on the abundance of Coho Salmon Oncorhynchus kisutch across serial life stages. The simulation model examines scenarios with varying quantities of rescued fish, time in captivity, drought severity, and reduced smolt‐to‐adult return rates. Our results indicate that fish rescue can increase the abundance of adults and lower extinction risk, particularly for fish held in captivity for a full year. However, fish rescue can also decrease the abundance of adults and increase extinction risk if fish are held only for summer and there is limited winter habitat. We found that when fish rescue did increase returns, it functioned more like a stock enhancement program than a drought mitigation tool and it would likely lead to consecutive generations of captive rearing, which has been shown to have negative effects on fitness. We translated our model into an R Shiny application ( https://shiny.wdfw‐fish.us/CohoPopulationDynamics/ ) that allows users to explore how fish rescue affects Coho Salmon population dynamics through customized parameterization of the model to represent different systems or different assumptions about the effects of fish rescue.

North American Journal of Fisheries Management↗
USGS2022

Suppression of invasive fish in the west: Synthesis and suggestions for improvement

Reservoirs are ubiquitous features on the landscape of the western United States. Although reservoirs provide numerous benefits (e.g., irrigation, flood control, hydropower, recreational use), these systems are often a concern from an ecological perspective. Reservoirs support fisheries primarily composed of nonindigenous sport fishes that may become invasive and negatively influence recipient ecosystems. Furthermore, reservoirs alter adjacent riverine habitats, further increasing the threat of invasive fishes to aquatic systems. As such, most western natural resource management agencies focus considerable effort on managing the threat of invasive fish species. Unfortunately, controlling invasive fish is expensive and rarely effective because of a lack of clear objectives, appropriate fishing mortality, and long-term commitment. In an effort to improve management of invasive fish in the western United States, we reviewed existing literature to identify the steps necessary to effectively suppress these species. Specifically, we provide guidance on defining achievable objectives, assessing feasibility, evaluating success, and improving the efficiency of invasive fish suppression. This iterative approach provides managers with a framework to effectively address the challenge of suppressing invasive fish in the western United States.

North American Journal of Fisheries Management↗
USGS2023

Conservation at the nexus of niches: Multidimensional niche modeling to improve management of Prairie Chub

Objective A central challenge in applied ecology is understanding how organisms are spatially and temporally distributed and how management might be tailored to maintain or restore species distributions. The niche concept is central to understanding species distributions, but the diversity of niche definitions requires that multiple dimensions be considered. For example, the Grinnellian niche concept focuses on environmental conditions that allow species to persist, the Eltonian niche concept stresses the influence of biotic interactions, and the fundamental niche concept considers both abiotic and biotic environmental features to define spaces that organisms could occupy. Methods We combined abiotic ( A ), biotic ( B ), and movement ( M ) information (collectively, BAM model) to map the multidimensional niche of Prairie Chub Macrhybopsis australis , a regionally endemic freshwater fish currently under review for listing under the Endangered Species Act. We estimated A using remotely sensed environmental riverscape variables, B using the spatial distribution of a hybridization zone between Prairie Chub and Shoal Chub M. hyostoma , and M using data from a mark–recapture study. Result The BAM model estimated the spatial extent of multiple niches, including the Grinnellian ( A ; extent = 944 km of river), Eltonian ( B ; 2974 km), and fundamental niche (overlap of A + B ; 645 km) niches. When A , B , and M components were combined, the estimated extent of the Prairie Chub niche was 645 km. Conclusion Our work shows that the realized, multidimensional niche of Prairie Chub includes medium to large rivers with high habitat connectivity in the upper–middle Red River basin upstream of the distribution of Shoal Chub. The current Prairie Chub distribution could be maintained by preventing further habitat fragmentation and maintaining the environmental gradient separating Prairie Chub from Shoal Chub. Expansion of the species distribution may be possible through restoration of longitudinal fluvial connectivity.

North American Journal of Fisheries Management↗
USGS2024

Fish size structure analysis via ordination: A visualization aid

Objective Visual aids like length-frequency histograms are widely used to examine fish population status and trends; however, comparing multiple histograms simultaneously becomes cumbersome and inefficient. Complicating matters further, overlaying covariates on histograms to highlight connections with length frequencies can be challenging. An alternative, and the subject of this Perspective, is to display length distributions as an ordination using similarity indexes; in many cases, this allows for improved visual organization and representation of relationships with covariates. Methods I review the application of ordination methods for analysis of size structures using alternative visualizations that may facilitate the identification of connections that are concealed when analyzing a series of histograms. After a brief introduction to similarity indexes, types of ordinations, and sample sizes, I examine four case studies to illustrate size structure analysis via similarity indices: (1) unconstrained ordination to identify “bass-crowded” populations in a set of 34 small fishing lakes, (2) unconstrained ordination to evaluate the effect of three consecutive length limits on a Largemouth Bass Micropterus nigricans population over a span of 28 years, (3) constrained ordination to assess the relationships between fish community size structure and in-lake and off-lake environmental descriptors in 30 oxbow lakes, and (4) constrained ordination to identify what aspects of Largemouth Bass size structure were related to six types of reservoir habitats. Result Size structure analysis via similarity indexes enabled the exploration of extensive length-frequency data. It is important to acknowledge that ordinations serve solely as a visual aid for assessing size structure—no statistical testing is involved. Conclusion Ordination techniques and software are advancing at a quick pace, holding great promise for the future of size structure analysis via similarity indices.

North American Journal of Fisheries Management↗
USGS2025

National Park Service staff perspectives on how climate change affects visitor use

1. Many public lands, including those managed by the U.S. National Park Service(NPS), have the purpose of conserving natural and cultural resources and providing opportunities for visitors to recreate in and enjoy these areas. Achieving this mission becomes more challenging as drought, flooding, increasing temperatures and other climatic change effects are impacting NPS lands and visitors and affecting factors such as visitation, recreation access and health and safety among other aspects of park operations. 2. However, the literature lacks insights from staff dealing with on-the-ground climate impacts to visitor use. To address this gap, we held semi-structured interviews with 63 staff from 31 NPS units across the United States (U.S.) to better understand the effects of climate change on visitor use. We qualitatively analysed the interviews using both deductive and inductive methods to identify key themes. 3. Interview participants consistently noted that climate change is already affecting visitor use at their parks. For instance, increasing temperatures are negatively affecting both staff and visitor safety at parks nationwide, whereas all coastal parks within our sample are already experiencing impacts from sea-level rise or more frequent and severe coastal storms and hurricanes. Other impacts include reduced recreational access, damaged infrastructure and cultural resources and diminished visitor experiences due to fire and smoke. 4. Similarly, concerns about future impacts often revolved around the health and safety of visitors and staff—particularly related to wildfire and smoke, water quality and availability, and increased heat—and climate change forever altering parks. 5. Our research shows staff in parks and protected areas are noticing effects of climate change on visitor use; some of these impacts have not been previously documented in the scientific literature. Study results highlight future visitor use management research needs and key topics to consider for visitor use planning processes.

People and Nature↗
USGS2022

Measured efficacy, bioaccumulation, and leaching of a transfluthrin-based insecticidal paint: A case study with a nuisance, nonbiting aquatic insect

BACKGROUND Pest management professionals will require a diverse, adaptive abatement toolbox to combat advanced challenges from disease vector and nuisance insect populations. Designed for post-application longevity, insecticidal paints offer extended residual effects on targeted insect pest populations; a measured understanding of active ingredient bioavailability over time is valuable to fully assess treatment efficacy and potential environmental risks. This study was initiated because a nuisance net-spinning caddisfly, Smicridea fasciatella , is lowering the quality of life for riverfront residents at the type locality. RESULTS We tested the efficacy and potential mobility of a transfluthrin-based paint (a.i. 0.50%), comparing the impacts of UV exposure and substrate texture over time. Direct UV exposure decreased efficacy (β ± S.E. = 0.008 ± 0.001, P < 0.001) and a coarse texture maintained greater efficacy (β ± S.E. = −3.7 ± 1.3, P = 0.004) over time. Notably, the coarse texture + indirect UV treatment maintained 100% mortality after 240 days. UV exposure and substrate texture did not have a significant impact on leachate concentrations over time, and successive immersion tests indicated a two-phase emission pattern. Bioaccumulation increased with time on the cuticle of dead adult S. fasciatella ; after 24 h of direct exposure the concentration of transfluthrin was 25.3 ± 0.9 ng/caddisfly with a maximum concentration of 345 ng/caddisfly after 7 days. CONCLUSION Our predictions were validated with measured, time-dependent impacts on efficacy, leachability, and bioaccumulation. Because of the mobility of active ingredient in the environment, insecticidal paints merit low-impact protocols to improve public health outcomes and environmental safety. © 2022 Society of Chemical Industry.

Pest Management Science↗
USGS2020

Quantifying and mapping inundation regimes within a large river‐floodplain ecosystem for ecological and management applications

Spatial information on the distribution of ecosystem patterns and processes can be a critical component of designing and implementing effective management programs in river‐floodplain ecosystems. For example, translating how flood pulses detected within a stream gauge record are spatially manifested across a river‐valley bottom can be used to evaluate whether the current distribution of physical conditions has the potential to support priority habitats or if intervention is needed to meet desired goals. The size and complexity of large river‐floodplain systems can make mapping inundation dynamics a challenging task. We used a geospatial model to simulate 40 years (1972–2011) of daily surface‐water inundation depths for 11,331 km 2 of the Upper Mississippi River System floodplain. We identified discrete inundation events at each 4‐m × 4‐m pixel in the model as sequential days of submergence. We then quantified and mapped four aspects of inundation regime – event frequency, duration, magnitude, and timing – for each pixel. The spatial distribution of inundation regime attributes varied within and among multiple levels of river organization, including navigation pools and geomorphic reaches, but only event timing exhibited a strong down‐river trend. Non‐linear relations among inundation attributes and their geospatial distributions likely reflect complex interactions among topographic, hydrologic, and anthropogenic constraints on flooding dynamics. Together, our results reveal spatial gradients in inundation dynamics not captured by hydrologic data alone. Characterizing such diversity in inundation dynamics is important for testing hypotheses about ecological processes, developing models of ecosystem functions, and informing management actions.

Illinois, Indiana, Iowa, Minnesota, Missouri, Wisc↗
USGS2022

High resolution spatiotemporal patterns of flow at the landscape scale in montane non-perennial streams

Intermittent and ephemeral streams in dryland environments support diverse assemblages of aquatic and terrestrial life. Understanding when and where water flows provide insights into the availability of water, its response to external controlling factors, and potential sensitivity to climate change and a host of human activities. Knowledge regarding the timing of drying/wetting cycles can also be useful to map critical habitats for species and ecosystems that rely on these temporary water sources. However, identifying the locations and monitoring the timing of streamflow and channel sediment moisture remains a challenging endeavor. In this paper, we analyzed daily conductivity from 37 sensors distributed along 10 streams across an arid mountain front in Arizona (United States) to assess spatiotemporal patterns in flow permanence, defined as the timing and extent of water in streams. Conductivity sensors provide information on surface flow and sediment moisture, supporting a stream classification based on seasonal flow dynamics. Our results provide insight into flow responses to seasonal rainfall, highlighting stream reaches very reactive to rainfall versus those demonstrating more stable streamflow. The strength of stream responses to precipitation are explored in the context of surficial geology. In summary, conductivity data can be used to map potential stream habitat for water-dependent species in both space and time, while also providing the basis upon which sensitivity to ongoing climate change can be evaluated.

Arizona↗
USGS2024

How low is too low? Partnering with stakeholders and managers to define ecologically based low-flow thresholds in a perennial temperate river

Managing aquatic ecosystems for people and nature can be improved by collaboration among scientists, managers, decision-makers, and other stakeholders. Many collaborative and interdisciplinary approaches have been developed to address the management of freshwater ecosystems; however, there are still barriers to overcome. We worked as part of a regional stakeholder group comprising municipal water utility operators, conservation organizations, academic partners, and other stakeholders to understand the effects of low-flow and drought on ecological functions of the upper Flint River, Georgia (USA), a free-flowing river important for municipal water supply, recreation, and native biota. We used published literature and locally targeted studies to identify quantitative flow targets that could be used to inform water management and drought planning. Drawing from principles of Translational Ecology, we relied on an iterative process to develop information needs for the group and maintained communication and engagement throughout data collection, analysis, and synthesis. We identified three quantitative flow benchmarks to evaluate the ecological impacts of drought in the river. The results were valuable to both the water utilities represented in the working group and State regional water planning, which is used to guide water management strategies and permitting for the basin. We identified principles that were important for the successful engagement in the working group and helped to overcome the challenge of working across sectors and without direct authority guiding the implementation of our work. Interdisciplinary work and creative solutions are crucial to plan for and adapt to greater pressure on our water resources.

River Research and Applications↗
USGS2024

Wood you believe it? Experimental addition of nonnative wood enhances instream habitat for native dryland fishes

Flow alteration and riparian vegetation encroachment are causing habitat simplification with severe consequences for native fishes. To assess the effectiveness of enhancing simplified habitat in a large dryland river, we experimentally added invasive wood at 19 paired treatment and reference (no wood added) subreaches (50–100 m) within the main channel of the San Juan River. Using a before-after-control-impact design, we sampled fishes and macroinvertebrates, and quantified habitat complexity. After wood addition, total native fish densities were 2.2× higher in treatments compared with references, whereas total nonnative fish densities exhibited no response. Macroinvertebrate densities were 6.8× higher, and habitat complexity increased in treatments. Counts of geomorphic features in treatments increased from 1 to a maximum of 11 following wood addition, while the number of features in references remained unchanged. Wood addition has potential to instigate natural riverine processes, ultimately enhancing native fish habitat by increasing macroinvertebrate densities and habitat complexity in dryland rivers. Water overallocation and increasing aridity will continue to challenge efforts to improve habitat conditions with environmental flows alone, and managers might consider integrating non-flow alternatives like addition of abundant, invasive wood to reduce habitat simplification.

New Mexico, Utah↗
USGS2024

Spatio-temporal distribution of adult Pacific lamprey Entosphenus tridentatus relative to habitat fragmentation

Pacific lamprey ( Entosphenus tridentatus ), a fish species native to the Pacific Northwest (USA), have distinctive cultural and ecological value but determining their spatial and temporal distribution is challenging due to a general lack systematic monitoring. In this study, we used counts of Pacific lamprey redds to model the probability of occurrence and abundance of Pacific lamprey based on environmental covariates including artificial barriers, assuming higher predicted lamprey redds translates to more suitable spawning habitats. Using generalized linear mixed zero-inflated models, results suggest that Pacific lamprey abundance was generally lower in high gradient streams, further from the ocean. Stream reaches with warmer spring water temperatures and greater historical median spring flows supported higher abundances. Lamprey occurrence was primarily influenced by spring water temperatures and distance from the ocean. We further observed that when streams warm beyond 18°C, confidence intervals around the abundance estimates widen and zero-inflation increases, indicating a decrease in occurrence. One objective of the study was to recommend where barrier removal or restoration should be prioritized to increase passage and thus access to upstream habitats. We considered artificial barriers to primarily influence the probability of occurrence through access. The barrier variable in this model had a negative effect on the probability of lamprey occurrence, but it was not a strong predictor in the model. While we are not able to suggest specific locations that would most benefit barrier removal or improvement based on these model results, we can identify the watersheds with a higher probability to support Pacific lamprey and provide potential additional habitats by improving habitat connectivity. Focusing restoration and/ or removal of barriers on watersheds in the Mid-South region of the Oregon Coast (i.e., Alsea, Siuslaw, Coos, Coquille, and Sixes rivers) with higher habitat suitability could prioritize use of limited funds, increase the probability of benefiting Pacific lamprey, and potentially other native lampreys and migratory (e.g., salmon, steelhead; Oncorhynchus ) species. Although this manuscript focuses on the Oregon Coast region, the methods are transferrable to other regions where Pacific lamprey are present.

Oregon↗
USGS2024

Implementation of controlled floods for sediment management on the Colorado River in Grand Canyon under aridification

In addition to supplying water for agriculture, cities, and industry, the Colorado River traverses the Colorado Plateau, including several of the most unique and valued National Parks and Recreation Areas in the United States. Although the water needs of these landscapes were not considered at the time water allocations were first negotiated, these needs were recognized in subsequent legislation and policy. Management goals address a range of aquatic and riparian resources, including fine sediment (sand, silt, and clay) which, in Grand Canyon, is important for ecological, cultural, and recreational resources. Over ~30 years, stakeholders, resource managers, and scientists collectively developed operational strategies for sediment management to meet goals outlined by an adaptive management program. However, prolonged drought, or “aridification,” resulting in declining runoff and the lowest reservoir storage elevations in decades has challenged those strategies. The paradigm for sustainable sediment management relies on (1) sand accumulation on the bed of the Colorado River during periods of sediment-rich tributary floods from summer/fall thunderstorms, and (2) dam-released controlled (artificial) floods, referred to as High-Flow Experiments (HFEs), to redistribute the accumulated sand to rebuild eroded bar and floodplain deposits. The management protocol, which specifies narrowly defined sand accumulation periods and HFE implementation windows, is based on implementing HFEs in late fall during the period of greatest sediment enrichment, before higher winter releases for hydropower erode the accumulated sand from the riverbed. Low dam releases associated with drought, however, have changed the pattern of sand accumulation and low reservoir elevations have prevented HFE implementation in the defined window. An alternative strategy for HFE planning and implementation was tested opportunistically in April 2023 following lower-than-normal winter dam releases. We present findings from this HFE indicating that sand enrichment and sandbar building equaled or exceeded that of HFEs conducted under the established management protocol. These findings show that management goals for sediment under conditions of prolonged drought may be achievable but will likely require substantial changes in dam management strategies.

Arizona↗
USGS2026

Development and assessment of fluorescent-dyed, preserved invasive grass carp (Ctenopharyngodon idella) eggs as surrogates for live eggs in transport and dispersal control experiments

Invasive species such as grass carp ( Ctenopharyngodon idella ) pose substantial ecological threats to North American freshwater ecosystems. Understanding their early life stage behavior is critical for management efforts. From spawning to hatching, invasive carp eggs must remain suspended in the water column while drifting downstream for the best chance of survival. This highly vulnerable life stage is a potential target for population control to reduce recruitment. However, studying egg transport and potential dispersal control techniques is challenging, because the availability of live eggs and time period for experimentation are extremely limited. Additionally, accurately replicating the physical characteristics and transport mechanisms of fish eggs using surrogates in laboratory and field studies is not trivial. This study presents a novel method to create fluorescein-dyed, preserved grass carp eggs as surrogates for live eggs in transport and dispersal control experiments. This technique enables year-round studies of grass carp egg transport, offering managers a reliable tool for developing and testing dispersal control and passive sampling methods for invasive carp eggs. In this study, we rehydrate and dye preserved grass carp eggs in varying concentrations of aqueous fluorescein for a range of rehydration times, evaluate dye retention and egg visibility under ultraviolet light (UV-A), and measure diameters and settling velocities for comparison with live eggs. Eggs rehydrated in 0.100 g per liter fluorescein for 30 min maintain adequate brightness for up to 40 min in mixed conditions and exhibit mean settling velocities and densities similar to live eggs, making them ideal for laboratory experiments using quantitative imaging techniques.

River Research and Applications↗
USGS2026

Non-physical barrier design and environmental conditions alter routing and survival of juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Sacramento-San Joaquin River Delta

Pacific salmon face substantial challenges when migrating through anthropogenically modified river systems, such as the Sacramento-San Joaquin River Delta (the Delta). Non-physical behavioral barriers, such as the bioacoustic fish fence (BAFF), are one potential solution for guiding fish away from hazards without obstructing water flow. However, the effectiveness of these technologies depends on abiotic and biotic conditions. In the Delta, a BAFF was deployed at Georgiana Slough in 2011, 2012, and 2024 to deter juvenile Chinook salmon ( Oncorhynchus tshawytscha ) from migrating into the interior Delta, a region associated with lower survival than the mainstem Sacramento River. We leveraged nine years of acoustic telemetry data to evaluate BAFF performance across flow conditions and two BAFF designs (2011/2012 vs. 2024), and to assess the BAFF's contribution to improving through-Delta survival. The BAFF reduced routing into Georgiana Slough from 26.5% without a barrier to 8.9% in 2011/2012 and 15.9% in 2024. In general, routing into Georgiana Slough increased with the proportion of flow entering the channel during periods without a BAFF and during the 2024 deployment but remained constant during the 2011/2012 deployment. Additionally, BAFF effectiveness declined with increasing input flow. Ultimately, reduced routing into Georgiana Slough during the 2024 BAFF deployment resulted in an increase in estimated through-Delta survival between 0.2 and 1.6 percentage points depending on release group. Our results provide valuable insights into the role of non-physical barriers in complex river systems and inform future management strategies for protecting migrating juvenile Chinook salmon in the Sacramento-San Joaquin River Delta.

California↗
USGS2019

UAV-derived estimates of forest structure to inform ponderosa pine forest restoration

Restoring forest ecosystems has become an increasingly high priority for land managers across the American West. Millions of hectares of forest are in need of drastic yet strategic reductions in density (e.g., basal area). Meeting the restoration and management goals requires quantifying metrics of vertical and horizontal forest structure, which has relied upon field‐based measurements, manned airborne or satellite remote sensing datasets. We used unmanned aerial vehicle (UAV ) image‐derived Structure‐from‐Motion (SfM) models and high‐resolution multispectral orthoimagery in this study to quantify vertical and horizontal forest structure at both the fine‐ (<4 ha) and mid‐scales (4–400 ha) across a forest density gradient. We then used these forest structure estimates to assess specific objectives of a forest restoration treatment. At the fine‐scale, we found that estimates of individual tree height and canopy diameter were most accurate in low‐density conditions, with accuracies degrading significantly in high‐density conditions. Mid‐scale estimates of canopy cover and forest density followed a similar pattern across the density gradient, demonstrating the effectiveness of UAV image‐derived estimates in low‐ to medium‐density conditions as well as the challenges associated with high‐density conditions. We found that post‐treatment conditions met a majority of the prescription objectives and demonstrate the UAV image application in quantifying changes from a mechanical thinning treatment. We provide a novel approach to forest restoration monitoring using UAV ‐derived data, one that considers varying density conditions and spatial scales. Future research should consider a more spatially extensive sampling design, including different restoration treatments, as well as experimenting with different combinations of equipment, flight parameters, and data processing workflows.

Western United States↗
USGS2020

Ultra‐high‐resolution mapping of biocrusts with Unmanned Aerial Systems

Biological soil crusts (biocrusts) occur in drylands globally where they support ecosystem functioning by increasing soil stability, reducing dust emissions and modifying soil resource availability (e.g. water, nutrients). Determining biocrust condition and extent across landscapes continues to present considerable challenges to scientists and land managers. Biocrusts grow in patches, cover vast expanses of rugged terrain and are vulnerable to physical disturbance associated with ground‐based mapping techniques. As such, remote sensing offers promising opportunities to map and monitor biocrusts. While satellite‐based remote sensing has been used to detect biocrusts at relatively large spatial scales, few studies have used high‐resolution imagery from Unmanned Aerial Systems (UAS) to map fine‐scale patterns of biocrusts. We collected sub‐centimeter, true color 3‐band imagery at 10 plots in sagebrush and pinyon‐juniper woodland communities in a semiarid ecosystem in the southwestern US and used object‐based image analysis (OBIA) to segment and classify the imagery into maps of light and dark biocrusts, bare soil, rock and various vegetation covers. We used field data to validate the classifications and assessed the spatial distribution and configuration of different classes using fragmentation metrics. Map accuracies ranged from 46 to 77% (average 65%) and were higher in pinyon‐juniper (average 70%) versus sagebrush (average 60%) plots. Biocrust classes showed generally high accuracies at both pinyon‐juniper plots (average dark crust = 70%; light crust = 80%) and sagebrush plots (average dark crust = 69%; light crust = 77%). Point cloud density, sun elevation and spectral confusion between vegetation cover explained some differences in accuracy across plots. Spatial analyses of classified maps showed that biocrust patches in pinyon‐juniper plots were generally larger, more aggregated and contiguous than in sagebrush plots. Pinyon‐juniper plots also had greater patch richness and a lower Shannon evenness index than sagebrush plots, suggesting greater soil cover heterogeneity in this plant community type.

Utah↗