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At least 595 records · Page 33Linked to original sources

USGS2000

Managers' summary - Ecological studies of the Pryor Mountain Wild Horse Range, 1992-1997

Ecological Studies of the Pryor Mountain Wild Horse Range, 1992-1997 provides a synthesis of key findings of landscape-scale, interdisciplinary studies of the effects of wild horses and native ungulates on a rugged, mountain ecosystem. This is perhaps the most comprehensive study of a wild horse herd conducted. This was a complex study and one involving a truly interagency approach. Six agencies either provided input to research priority setting, funding, or both. The agencies included the Bureau of Land Management, National Park Service, U.S. Geological Survey, Montana Department of Fish, Wildlife and Parks, Wyoming Game and Fish Department, and U.S. Forest Service. The major research direction and effort came from the U.S. Geological Survey and Natural Resources Ecology Lab, Colorado State University with Montana State University and the University of Kentucky also participating. Ungulate monitoring was conducted by the U.S. Geological Survey, Biological Resources Division, Bureau of Land Management, Billings Field Office and the Montana Fish and Wildlife Parks, with funding by Bighorn Canyon National Recreation Area. Many other individuals and groups were involved and deserve credit. The report printing was made possible with funds from the Bureau of Land Management, Wild Horse and Burro Program, Washington Office. This report was prepared by the Information Management Project, Midcontinent Ecological Science Center, U.S. Geological Survey.

Montana, Wyoming↗

USGS2017

Simulation of rapid ecological change in Lake Ontario

Lower trophic level processes are integral to proper functioning of large aquatic ecosystems and have been disturbed in Lake Ontario by various stressors including exotic species. The invasion of benthic habitats by dreissenid mussels has led to systemic changes and native faunal declines. Size-dependent physiological rates, spatial differences and connectivity, competition, and differential population dynamics among invertebrate groups contributed to the change and system complexity. We developed a spatially explicit, individual-based mechanistic model of the benthic ecosystem in Lake Ontario, with coupling to the pelagic system, to examine ecosystem dynamics and effects of dreissenid mussel invasion and native fauna losses. Benthic organisms were represented by functional groups; filter-feeders (i.e., dreissenid mussels), surface deposit-feeders (e.g., native amphipod Diporeia spp.), and deposit-feeders (e.g., oligochaetes and other burrowers). The model was stable, represented ecological structure and function effectively, and reproduced observed effects of the mussel invasion. Two hypotheses for causes of Diporeia loss, competition or disease-like mortality, were tested. Simple competition for food did not explain observed declines in native surface deposit-feeders during the filter-feeder invasion. However, the elevated mortality scenario supports a disease-like cause for loss of the native amphipod, with population changes in various lake areas and altered benthic biomass transfers. Stabilization of mussel populations and possible recovery of the native, surface-deposit feeding amphipod were predicted. Although further research is required on forcing functions, model parameters, and natural conditions, the model provides a valuable tool to help managers understand the benthic system and plan for response to future disruptions.

Lake Ontario↗

USGS2005

Nutritional condition of elk in rocky mountain national park

We tested the hypothesis that elk in Rocky Mountain National Park (RMNP) were at ecological carrying capacity by determining herd-specific levels of nutritional condition and fecundity. Ingesta-free body fat levels in adult cows that were lactating were 10.6% (s = 1.7; range = 6.2-15.4) and 7.7% (s = 0.5; range = 5.9-10.1) in November 2001 for the Horseshoe and Moraine Park herds, respectively. Cows that were not lactating were able to accrue significantly more body fat: 14.0% (s = 1.1; range = 7.7-19.3) and 11.5% (s = 0.8; range = 8.6-15.1) for the Horseshoe and Moraine Park herds, respectively. Cow elk lost most of their body fat over winter (April 2002 levels were 3.9% [s = 0.4] and 2.9% [s = 0.4] for the Horseshoe and Moraine Park herds, respectively). Nutritional condition indicated that both Horseshoe Park and Moraine Park elk were well below condition levels elk can achieve on very good-excellent nutrition (i.e., >15% body fat; Cook et al. 2004) and were comparable to other free-ranging elk populations. However, condition levels were higher than those expected at a "food-limited" carrying capacity, and a proportion of elk in each herd were able to achieve condition levels indicative of very good-excellent nutrition. Elk in RMNP are likely regulated and/or limited by a complex combination of density-independent (including significant heterogeneity in forage conditions across RMNP's landscape) and density-dependent processes, as condition levels contradict a simple density-dependent model of a population at ecological carrying capacity.

Western North American Naturalist↗

USGS2009

Water uptake and nutrient concentrations under a floodplain oak savanna during a non-flood period, lower Cedar River, Iowa

Floodplains during non-flood periods are less well documented than when flooding occurs, but non-flood periods offer opportunities to investigate vegetation controls on water and nutrient cycling. In this study, we characterized water uptake and nutrient concentration patterns from 2005 to 2007 under an oak savanna located on the floodplain of the Cedar River in Muscatine County, Iowa. The water table ranged from 0.5 to 2.5 m below ground surface and fluctuated in response to stream stage, plant water demand and rainfall inputs. Applying the White method to diurnal water table fluctuations, daily ET from groundwater averaged more than 3.5 mm/day in June and July and approximately 2 mm/day in May and August. Total annual ET averaged 404 mm for a growing season from mid-May to mid-October. Savanna groundwater concentrations of nitrate-N, ammonium-N, and phosphate-P were very low (mean <0.18, <0.14, <0.08 mg/l, respectively), whereas DOC concentrations were high (7.1 mg/l). Low concentrations of N and P were in contrast to high nutrient concentrations in the nearby Cedar River, where N and P averaged 7.5 mg/ l and 0.13, respectively. In regions dominated by intensive agriculture, study results document valuable ecosystem services for native floodplain ecosystems in reducing watershed-scale nutrient losses and providing an oasis for biological complexity. Improved understanding of the environmental conditions of regionally significant habitats, including major controls on water table elevations and water quality, offers promise for better management aimed at preserving the ecology of these important habitats. Copyright ?? 2009 John Wiley & Sons, Ltd.

Hydrological Processes↗

USGS2002

The effects of partial cutting on stand structure and growth of western hemlock-Sitka spruce stands in southeast Alaska

The effects of partial cutting on species composition, new and residual-tree cohorts, tree size distribution, and tree growth was evaluated on 73 plots in 18 stands throughout southeast Alaska. These partially cut stands were harvested 12-96 years ago, when 16-96% of the former stand basal area was removed. Partial cutting maintained stand structures similar to uncut old-growth stands, and the cutting had no significant effects on tree species composition. The establishment of new-tree cohorts was positively related to the proportion of basal-area cut. The current stand basal area, tree species composition, and stand growth were significantly related to trees left after harvest (p < 0.001). Trees that were 20-80 cm dbh at the time of cutting had the greatest tree-diameter and basal-area growth and contributed the most to stand growth. Diameter growth of Sitka spruce and western hemlock was similar, and the proportion of stand basal-area growth between species was consistent for different cutting intensities. Concerns about changing tree species composition, lack of spruce regeneration, and greatly reduced stand growth and vigor with partial cuts were largely unsubstantiated. Silvicultural systems based on partial cutting can provide rapidly growing trees for timber production while maintaining complex stand structures with mixtures of spruce and hemlock trees similar to oldgrowth stands.

Forest Ecology and Management↗

USGS2019

Ecological interventions to prevent and manage zoonotic pathogen spillover

Spillover of a pathogen from a wildlife reservoir into a human or livestock host requires the pathogen to overcome a hierarchical series of barriers. Interventions aimed at one or more of these barriers may be able to prevent the occurrence of spillover. Here, we demonstrate how interventions that target the ecological context in which spillover occurs (i.e. ecological interventions) can complement conventional approaches like vaccination, treatment, disinfection and chemical control. Accelerating spillover owing to environmental change requires effective, affordable, durable and scalable solutions that fully harness the complex processes involved in cross-species pathogen spillover.

Philosophical Transactions of the Royal Society B:↗

USGS2016

Sea lamprey avoid areas scented with conspecific tissue extract in Michigan streams

Three in-stream experiments were conducted to determine whether sea lamprey, Petromyzon marinus L., tissue extract (alarm cue) and 2-phenylethylamine hydrochloride (PEA HCl, a putative predator cue) influenced the distribution of migrating adult sea lamprey. Experiments evaluated sea lamprey movement when an odour was applied to (1) a tributary of a larger stream; and (2) half of a stream channel. Fewer sea lamprey entered the tributary and side of the river scented with sea lamprey tissue extract compared to the control treatment. Sea lamprey did not avoid the tributary and side of the river scented with PEA HCl. A final laboratory experiment found no difference in the avoidance response of sea lamprey to PEA HCl mixed with river water vs PEA HCl mixed with water from Lake Huron. As such, the lack of sea lamprey response to PEA HCl in the stream was unlikely to have been caused by the presence of the river water. Rather, the difference between laboratory and field results may be attributed to the complexity of the physical environment.

Michigan↗

USGS2011

Towards sustainable groundwater use: Setting long-term goals, backcasting, and managing adaptively

The sustainability of crucial earth resources, such as groundwater, is a critical issue. We consider groundwater sustainability a value‐driven process of intra‐ and intergenerational equity that balances the environment, society, and economy. Synthesizing hydrogeological science and current sustainability concepts, we emphasize three sustainability approaches: setting multigenerational sustainability goals, backcasting, and managing adaptively. As most aquifer problems are long‐term problems, we propose that multigenerational goals (50 to 100 years) for water quantity and quality that acknowledge the connections between groundwater, surface water, and ecosystems be set for many aquifers. The goals should be set by a watershed‐ or aquifer‐based community in an inclusive and participatory manner. Policies for shorter time horizons should be developed by backcasting, and measures implemented through adaptive management to achieve the long‐term goals. Two case histories illustrate the importance and complexity of a multigenerational perspective and adaptive management. These approaches could transform aquifer depletion and contamination to more sustainable groundwater use, providing groundwater for current and future generations while protecting ecological integrity and resilience.

Ground Water↗

USGS2011

Predator-induced demographic shifts in coral reef fish assemblages

In recent years, it has become apparent that human impacts have altered community structure in coastal and marine ecosystems worldwide. Of these, fishing is one of the most pervasive, and a growing body of work suggests that fishing can have strong effects on the ecology of target species, especially top predators. However, the effects of removing top predators on lower trophic groups of prey fishes are less clear, particularly in highly diverse and trophically complex coral reef ecosystems. We examined patterns of abundance, size structure, and age-based demography through surveys and collection-based studies of five fish species from a variety of trophic levels at Kiritimati and Palmyra, two nearby atolls in the Northern Line Islands. These islands have similar biogeography and oceanography, and yet Kiritimati has ∼10,000 people with extensive local fishing while Palmyra is a US National Wildlife Refuge with no permanent human population, no fishing, and an intact predator fauna. Surveys indicated that top predators were relatively larger and more abundant at unfished Palmyra, while prey functional groups were relatively smaller but showed no clear trends in abundance as would be expected from classic trophic cascades. Through detailed analyses of focal species, we found that size and longevity of a top predator were lower at fished Kiritimati than at unfished Palmyra. Demographic patterns also shifted dramatically for 4 of 5 fish species in lower trophic groups, opposite in direction to the top predator, including decreases in average size and longevity at Palmyra relative to Kiritimati. Overall, these results suggest that fishing may alter community structure in complex and non-intuitive ways, and that indirect demographic effects should be considered more broadly in ecosystem-based management.

PLoS ONE↗

USGS2005

Remote sensing sensitivity to fire severity and fire recovery

The paper examines fundamental ways that geospatial data on fire severity and recovery are influenced by conditions of the remote sensing. Remote sensing sensitivities are spatial, temporal and radiometric in origin. Those discussed include spatial resolution, the sampling time of year, and time since fire. For standard reference, sensitivities are demonstrated with examples drawn from an archive of burn assessments based on one radiometric index, the differenced Normalized Burn Ratio. Resolution determines the aggregation of fire effects within a pixel ( alpha variation ), hence defining the detected ecological response, and controlling the ability to determine patchiness and spatial distribution of responses throughout a burn ( beta variation ). As resolution decreases, alpha variation increases, extracting beta variation from the complexity of the whole burn. Seasonal timing impacts the radiometric quality of data in terms of transmittance, sun angle, and potential for enhanced contrast between responses within burns. Remote sensing sensitivity can degrade during many fire seasons when snow, incomplete burning, hazy conditions, low sun angles, or extended drought are common. Time since fire ( lag timing ) most notably shapes severity detection through the first-order fire effects evident in survivorship and delayed mortality that emerge by the growth period after fire. The former effects appear overly severe at first, but diminish, as burned vegetation remains viable. Conversely, the latter signals vegetation that appears healthy at first, but is damaged by heat to the extent that it soon dies. Both responses can lead to either over- or under-estimating severity, respectively, depending on fire behavior and pre-fire composition unique to each burned area. Based on implications of such sensitivities, three sampling intervals for short-term burn severity are identified; rapid , initial , and extended assessment , sampled within ca. two weeks, two months, and depending on the ecotype, from three months to one year after fire, respectively. Jointly, remote sensing conditions and the way burns are studied yield different tendencies for data quality and information content that impact the objectives and hypotheses that can be studied. Such considerations can be commonly overlooked, but need to be incorporated especially in comparative studies, and to build long-term reference databases on fire severity and recovery.

Conference Paper↗

USGS2016

Ecological requirements for pallid sturgeon reproduction and recruitment in the Missouri River—A synthesis of science, 2005 to 2012

This report is intended to synthesize the state of the scientific understanding of pallid sturgeon ecological requirements to provide recommendations for future science directions and context for Missouri River restoration and management decisions. Recruitment of pallid sturgeon has been low to non-existent throughout its range. Emerging understanding of the genetic structure of pallid sturgeon populations sets a broad framework for species and river management decisions, including decisions about managing the future genetic diversity of the species, but also decisions about where and what type of river restoration actions will be effective for subpopulations of this highly migratory species. Adult pallid sturgeon may migrate hundreds of kilometers (km) to spawn and their progeny may disperse even greater distances downstream as drifting free embryos. As a result of their complex life history pallid sturgeon naturally exploit a wide range of habitats during their life cycles. The construction of dams and reservoirs has fragmented habitats and may have shifted Missouri River subpopulations downstream. Research has not identified one primary biological or ecological constraint that appears to limit populations of the pallid sturgeon. With the present (2013) state of knowledge many life stages and life-stage transitions cannot be ruled out as contributing to recruitment failure. Biological opinions in 2000 (and amended in 2003) presented the dominant hypotheses for recruitment failure that existed at that time. Emphasis was on the role of the flow regime, specifically spring flow pulses (“spring rises”), to condition spawning substrate and cue reproductive aggregations and migrations, and on low flows and additional slow, shallow-water area to serve as rearing habitat for age-0 to juvenile pallid sturgeon. Studies on spawning habitat dynamics have documented that habitat patches selected for spawning by fish in the Lower Missouri River (Missouri River downstream from Gavins Point Dam to the confluence with the Mississippi River) are dominantly on outside, revetted bends in the deepest, fastest, and most turbulent water. Studies in more natural habitat on the Yellowstone River have documented spawning in convergent flow in the middle of the channel on discrete patches of gravel within a sand-dominated channel, an arrangement that may be more effective in attracting aggregations of reproductive fish compared to the nearly continuous revetment on the Lower Missouri River. Pallid sturgeon spawn in the spring and early summer during periods of increasing day length. Water temperature consistently exerts a threshold effect for spawning at 16–18 °C. In addition, the role of water temperature is indicated by pauses and reversals in upstream migrations that have been associated with cold weather fronts that create a transient decrease in water temperature. From 2005 to 2012 on the Lower Missouri River, no obvious relations between flow pulses and fish movements and spawning behaviors have been apparent. However, pallid sturgeon tracking at the Upper Missouri–Yellowstone confluence indicates that in most years, most telemetered pallid sturgeon migrate out of the Missouri River and into the Yellowstone River in the June–July timeframe in association with the spring pulse. This pattern was disrupted in 2011 when a high flow pulse with warm temperatures and high turbidity emanated from the Milk River, followed by record releases from Fort Peck Dam, and 36–39 percent of the telemetered population migrated up the Upper Missouri. This result supports the hypothesis that sufficiently large flow pulses may trigger migration and aggregation but it is not clear that functional pulses are within reservoir management authorities. Notably, a pallid sturgeon free embryo was captured on the Upper Missouri River in 2011 and another single, genetically confirmed embryo was captured on the Yellowstone River in 2012. Research on free-embryo drift has indicated the potential for hundreds of miles of downstream dispersal. Lack of distance to accommodate the extended downstream dispersal period of free embryos on the Upper Missouri and Yellowstone Rivers is the predominant hypothesis for recruitment failure in the upper basin. Long drift distances in the Lower Missouri River may be responsible for shifting Lower Missouri River sub-populations further into the Middle Mississippi River. Physical understanding of drift processes indicates that mean velocities could be slowed through decreased discharges or increased channel hydraulic radius (width and topographic diversity) to reduce free-embryo dispersal distances. In addition, the probability that free embryos are transported into and retained in channel-margin habitats is theoretically amenable to channel re-engineering that would increase cross-channel secondary currents in bends or channel expansions. Considerable uncertainty persists, however, about whether extended drift of Lower Missouri River larvae is responsible for recruitment failure. If drift distance is limiting, it is important to discern whether it would be advisable to retain larvae within the Missouri River, and where along the river restoration projects should be placed to optimize survival and growth of age-0 and juvenile sturgeon. Longitudinal differences in female pallid sturgeon fecundity lend support to the hypothesis that recruitment failure may be due, in part, to fish having insufficient nutrition to produce the numbers of gametes needed for the population to grow, perhaps because of simultaneous declines in prey-fish populations and their habitats. Establishing a chain of causality from habitat decline, to prey-fish populations, to sturgeon diets, to sturgeon fecundity, and to pallid sturgeon population growth presents a considerable scientific challenge. In addition to the dominant hypotheses relating pallid sturgeon populations to changes in flow regime and channel morphology, other factors have been identified that might be sources of stress and contribute to recruitment failure. Among these are water quality and contaminants. Ambient water-quality monitoring on the Missouri River has demonstrated summer episodes when dissolved oxygen dips below 5 milligrams per liter, a threshold that may be stressful especially to age-0 and juvenile sturgeon. Documented cases of intersex in shovelnose and pallid sturgeon indicate that agricultural and municipal sources of endocrine disrupting chemicals also may have a role in pallid sturgeon recruitment failure. Scientific understanding of the ecological requirements of pallid sturgeon has increased almost exponentially in the last two decades, and efforts are now turning from understanding fundamental biology of the species to quantifying how population dynamics relate to potential management actions. Progress in developing the science needed to inform management actions on the Missouri River may benefit from continuation of monitoring of reproductive cycles, reproductive movements, growth, and survival of telemetry tagged adults, increased emphasis on focused, complementary field and laboratory studies of factors influencing early life history, implementation of studies to resolve the role of food limitations in growth, survival, and reproductive condition, and implementation of studies designed specifically to parameterize models linking management to populations.

Missouri River↗

USGS2024

Chapter 24 - Resilience-based challenges and opportunities for fisheries management in Anthropocene rivers

Few pristine rivers remain worldwide, as they are among the most anthropogenically modified ecosystems. We suggest the geomorphology , hydrology and ecology of Anthropocene rivers are fundamentally different from historical natural rivers. These changes challenge conventional fisheries management practices, suggesting the tools supporting fisheries management may require expansion so that strategies match the scope and scale of present-day problems. We believe that resilience-thinking concepts offer substantial benefits for fisheries managers in Anthropocene rivers. When viewing resilience as a property of an ecosystem, the focus should be increasing the capacity of the system to self-organise and adapt to withstand regime shifts from internal and external disturbances. As an approach, a resilience-based perspective favours managing for sustainability and stewardship of fisheries by placing an emphasis on enhancing the capacity of complex systems to cope with dynamic change. Three case studies presented herein use resilience thinking to highlight challenges and opportunities for fisheries management in Anthropocene rivers from Europe, North America and Australia. Ultimately, a resilience approach to fisheries management emphasises increasing the ecological, institutional and societal capacities to deal with change, whether those changes be hydroclimatic, geomorphic, biological or social, to sustain desirable subsistence, recreational and commercial fisheries.

Book chapter↗

USGS2018

Consequences of gas flux model choice on the interpretation of metabolic balance across 15 lakes

Ecosystem metabolism and the contribution of carbon dioxide from lakes to the atmosphere can be estimated from free-water gas measurements through the use of mass balance models, which rely on a gas transfer coefficient ( k ) to model gas exchange with the atmosphere. Theoretical and empirically based models of k range in complexity from wind-driven power functions to complex surface renewal models; however, model choice is rarely considered in most studies of lake metabolism. This study used high-frequency data from 15 lakes provided by the Global Lake Ecological Observatory Network (GLEON) to study how model choice of k influenced estimates of lake metabolism and gas exchange with the atmosphere. We tested 6 models of k on lakes chosen to span broad gradients in surface area and trophic states; a metabolism model was then fit to all 6 outputs of k data. We found that hourly values for k were substantially different between models and, at an annual scale, resulted in significantly different estimates of lake metabolism and gas exchange with the atmosphere.

Inland Waters↗

USGS2026

Beyond pro-vs-anti hatchery: A typology of fishing community perceptions of salmonid hatcheries in Oregon

Objectives: Pacific salmon and steelhead hatcheries are central to fisheries management along the West Coast of North America, yet they remain a source of persistent controversy. While often framed in binary terms of pro- or anti-hatchery, public perspectives are more nuanced. Methods: We conducted 18 in-depth interviews with members of Oregon’s non-tribal fishing communities, including recreational anglers, professional fishers, non-governmental organizations, hatchery workers, and policymakers, to explore perceptions of salmonid hatcheries. Results: We developed a typology of perceptions of salmonid hatcheries in Oregon, identifying five distinct belief-based types, which we label Advocates, Reformers, Balancers, Skeptics, and Restorers. These types differed in how they evaluated hatcheries’ social and ecological impacts, governance legitimacy, and management acceptability. While Advocates and Reformers emphasized hatcheries’ social, economic, cultural, and ecological benefits, Skeptics and Restorers prioritized minimizing ecological harm and questioned hatchery effectiveness. Balancers acknowledged both social benefits and ecological risks, supporting context-specific management. All groups articulated different meanings of the term “wild,” suggesting that different perspectives across typologies may exacerbate fundamental miscommunications. Conclusion: Our findings highlight the complexity of stakeholder views and the limitations of binary framings. We suggest that tailored communication and engagement strategies, informed by typologies, may foster more inclusive and productive dialogue in hatchery policy and management.

Oregon↗

USGS2009

The decline of North American freshwater fishes

North America has a broad array of freshwater ecosystems because of the continent's complex geography and geological history. Within a multitude of habitats—that include streams, large rivers, natural lakes, springs, and wetlands—rich assemblages of fishes reside, representing diverse taxonomic groups with unique ecological requirements. They face an unprecedented conservation crisis. 1 In the last few decades, the proportion of inland fishes of North America, which are considered imperiled or extinct, increased from 20 to 40%. 2 Although extinctions have occurred, many species and populations are declining in range size and abundance. The fish biota of the continent as a whole remains diverse; however, we can take action to stem any further declines.

ActionBioscience↗

USGS2012

Ungulate management in national parks of the United States and Canada

Enabling legislation—that which gives appropriate officials the authority to implement or enforce the law—impacts management of ungulates in national parks of Canada and the United States (U.S.). The initial focus of such legislation in both countries centered on preserving natural and culturally significant areas for posterity. Although this objective remains primary, philosophies and practices have changed. A Canadian vision for ungulate management emerged during the latter half of the 20th century to protect and maintain or restore the ecological integrity of representative samples of the country’s 39 distinct landscapes, and to include provisions for traditional hunting and fishing practices representative of past cultural impacts on the environment. The current ungulate management approach in the U.S. relies on natural (ecological) processes, as long as normal conditions are promoted and there is no impairment of natural resources. Emphasizing natural processes as the basis has been a challenge because ecosystem dynamics are complex and management is multi-jurisdictional. Additionally, natural regulation typically will not prevent ungulates from reaching and sustaining densities that are incompatible with preservation or restoration of native flora and fauna, natural processes, or historical landscapes.

The Wildlife Society Technical Review↗

USGS2006

Mapping new terrain climate change and America’s West: Anticipating challenges to western mountain ecosystems and resources

Climate variability and sustained change presage far-reaching transformations across America’s West, an expanse dominated by immense mountain ranges and interspersed with important urban centers. These mountains provide the region’s life blood—water that courses through its streams and runs out its faucets, power that fuels its industries and lights its cities, and natural resources that feed its economy and provide many of its jobs. The West is a land where life is written in water—from vast ranchlands and farmlands, to large densely populated urban areas—and the communities of the West are intricately tied to it. Why should we be concerned about how climate change is affecting the mountains? Despite their imposing grandeur and apparent fortitude, the mountains contain highly sensitive environments that support delicately balanced physical and natural systems. A warming of only a few degrees has major implications for mountain regions—for the integrity of the seasonal snowpack, the extensive forests that western mountains support, and for the people who make their home there. Such changes are already affecting water supply, energy availability, fire severity, and recreational opportunities. Continuing climate change may significantly alter the western landscape, where one encounters distinct ecological communities as successive layers from the lowlands to the high peaks. Each of these ecosystems has specific requirements for temperature and precipitation. As climate variability increases and global warming continues, complex changes in montane plant and animal communities will occur, increasing vulnerability of species to dramatic shifts in distribution and local extinctions.

Report↗

USGS2011

Effects of nitrogen deposition and empirical nitrogen critical loads for ecoregions of the United States

Human activity in the last century has led to a significant increase in nitrogen (N) emissions and atmospheric deposition. This N deposition has reached a level that has caused or is likely to cause alterations to the structure and function of many ecosystems across the United States. One approach for quantifying the deposition of pollution that would be harmful to ecosystems is the determination of critical loads. A critical load is defined as the input of a pollutant below which no detrimental ecological effects occur over the long-term according to present knowledge. The objectives of this project were to synthesize current research relating atmospheric N deposition to effects on terrestrial and freshwater ecosystems in the United States, and to estimate associated empirical N critical loads. The receptors considered included freshwater diatoms, mycorrhizal fungi, lichens, bryophytes, herbaceous plants, shrubs, and trees. Ecosystem impacts included: (1) biogeochemical responses and (2) individual species, population, and community responses. Biogeochemical responses included increased N mineralization and nitrification (and N availability for plant and microbial uptake), increased gaseous N losses (ammonia volatilization, nitric and nitrous oxide from nitrification and denitrification), and increased N leaching. Individual species, population, and community responses included increased tissue N, physiological and nutrient imbalances, increased growth, altered root : shoot ratios, increased susceptibility to secondary stresses, altered fire regime, shifts in competitive interactions and community composition, changes in species richness and other measures of biodiversity, and increases in invasive species. The range of critical loads for nutrient N reported for U.S. ecoregions, inland surface waters, and freshwater wetlands is 1-39 kg N.ha -1.yr -1, spanning the range of N deposition observed over most of the country. The empirical critical loads for N tend to increase in the following sequence for different life forms: diatoms, lichens and bryophytes, mycorrhizal fungi, herbaceous plants and shrubs, and trees. The critical load approach is an ecosystem assessment tool with great potential to simplify complex scientific information and communicate effectively with the policy community and the public. This synthesis represents the first comprehensive assessment of empirical critical loads of N for major ecoregions across the United States. ?? 2011 by the Ecological Society of America.

Ecological Applications↗