SEARCH · Search USGS

Results for “Forest Ecosystems”

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

SourceResearch connectionFrom yearThrough year

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

At least 721 records · Page 40Linked to original sources

USGS2019

Negative impacts of summer heat on Sierra Nevada tree seedlings

Understanding the response of forests to climate change is important for predicting changes in biodiversity and ecosystem services, including carbon storage. Seedlings represent a key demographic stage in these responses, because seedling establishment is necessary for population persistence and spread, and because the conditions allowing seedlings to survive and grow are often more restrictive than those adults can tolerate. However, detailed long‐term data on the responses of individual seedlings to climatic variation are rare. Here, we analyze a decade of seedling growth and survival data collected in 25 long‐term plots located in Sequoia and Yosemite National Parks. The forest types represented range from lower‐elevation mixed conifer, to red fir‐dominated, to high‐elevation western white pine stands. Twelve species, including two oaks and ten conifers, are found across these plots. Survival and transition to larger size classes are modeled within a Bayesian framework as a function of species, size, fire, and various climate variables. We initially expected that precipitation‐related variables would have a strong effect on seedling survival and growth in this Mediterranean‐climate region and that some species might respond positively to higher temperatures if they are adapted to warmer low‐elevation areas or to higher‐than‐average temperatures if they are high‐elevation species whose growing seasons are limited by cold. However, we found that higher July maximum temperature or temperature anomalies were associated with lower survival and growth for most species, while precipitation and snow effects were weaker and more variable. Higher precipitation had a positive effect on survival of most species, but snow effects and precipitation effects on growth could be negative. Given the estimated climate responses, under potential future scenarios of higher summer temperatures and altered precipitation, most species are predicted to have lower survival and reduced growth. This is likely to favor species that have relatively high survival and growth and less negative responses to climatic shift (such as several of the pines) and perhaps lead to a more open forest structure—or potentially transition to non‐forest vegetation types where seedling recruitment does not keep pace with adult mortality.

California↗

USGS1997

Understory plant species composition in remnant stands along an urban-to-rural land-use gradient

We examined the understory species composition of 24 remnant forest stands along an urban-to-rural gradient in the metropolitan Milwaukee, Wisconsin region to determine the relationships between plant community composition, human disturbance, and contrasting types of land use along a gradient of urbanization. A significant difference was found in shrub species community composition among three contrasting land-use categories but no significant difference was found in herbaceous community composition. Significant differences in human activity existed among rural, urban, and urbanizing land-use categories, but this index of disturbance was not significantly correlated to gradients in species composition. All stands in this study had been subjected to various types of human activity and environmental disturbances in the past. Our data suggest that differences in the relative importance of understory species exist among stands but these differences may not be caused by the impacts of urbanization alone. Changes in the natural disturbance regime of this landscape, along with the impacts associated with urbanization, have led to an individualistic response in the compositional dynamics of forest stands.

Wisconsin↗

USGS2011

Divergence in forest-type response to climate and weather: Evidence for regional links between forest-type evenness and net primary productivity

Climate change is altering long-term climatic conditions and increasing the magnitude of weather fluctuations. Assessing the consequences of these changes for terrestrial ecosystems requires understanding how different vegetation types respond to climate and weather. This study examined 20 years of regional-scale remotely sensed net primary productivity (NPP) in forests of the northern Lake States to identify how the relationship between NPP and climate or weather differ among forest types, and if NPP patterns are influenced by landscape-scale evenness of forest-type abundance. These results underscore the positive relationship between temperature and NPP. Importantly, these results indicate significant differences among broadly defined forest types in response to both climate and weather. Essentially all weather variables that were strongly related to annual NPP displayed significant differences among forest types, suggesting complementarity in response to environmental fluctuations. In addition, this study found that forest-type evenness (within 8 × 8 km 2 areas) is positively related to long-term NPP mean and negatively related to NPP variability, suggesting that NPP in pixels with greater forest-type evenness is both higher and more stable through time. This is landscape- to subcontinental-scale evidence of a relationship between primary productivity and one measure of biological diversity. These results imply that anthropogenic or natural processes that influence the proportional abundance of forest types within landscapes may influence long-term productivity patterns.

Ecosystems↗

USGS2011

Setting limits: Using air pollution thresholds to protect and restore U.S. ecosystems

More than four decades of research provide unequivocal evidence that sulfur, nitrogen, and mercury pollution have altered, and will continue to alter, our nation's lands and waters. The emission and deposition of air pollutants harm native plants and animals, degrade water quality, affect forest productivity, and are damaging to human health. Many air quality policies limit emissions at the source but these control measures do not always consider ecosystem impacts. Air pollution thresholds at which ecological effects are observed, such as critical loads, are effective tools for assessing the impacts of air pollution on essential ecosystem services and for informing public policy. U.S. ecosystems can be more effectively protected and restored by using a combination of emissions-based approaches and science-based thresholds of ecosystem damage. Based on the results of a comprehensive review of air pollution thresholds, we conclude: ??? Ecosystem services such as air and water purification, decomposition and detoxification of waste materials, climate regulation, regeneration of soil fertility, production and biodiversity maintenance, as well as crop, timber and fish supplies are impacted by deposition of nitrogen, sulfur, mercury and other pollutants. The consequences of these changes may be difficult or impossible to reverse as impacts cascade throughout affected ecosystems. ??? The effects of too much nitrogen are common across the U.S. and include altered plant and lichen communities, enhanced growth of invasive species, eutrophication and acidification of lands and waters, and habitat deterioration for native species, including endangered species. ??? Lake, stream and soil acidification is widespread across the eastern United States. Up to 65% of lakes within sensitive areas receive acid deposition that exceeds critical loads. ??? Mercury contamination adversely affects fish in many inland and coastal waters. Fish consumption advisories for mercury exist in all 50 states and on many tribal lands. High concentrations of mercury in wildlife are also widespread and have multiple adverse effects. ??? Air quality programs, such as those stemming from the 1990 Clean Air Act Amendments, have helped decrease air pollution even as population and energy demand have increased. Yet, they do not adequately protect ecosystems from long-term damage. Moreover they do not address ammonia emissions. ??? A stronger ecosystem basis for air pollutant policies could be established through adoption of science-based thresholds. Existing monitoring programs track vital information needed to measure the response to policies, and could be expanded to include appropriate chemical and biological indicators for terrestrial and aquatic ecosystems and establishment of a national ecosystem monitoring network for mercury. The development and use of air pollution thresholds for ecosystem protection and management is increasing in the United States, yet threshold approaches remain underutilized. Ecological thresholds for air pollution, such as critical loads for nitrogen and sulfur deposition, are not currently included in the formal regulatory process for emissions controls in the United States, although they are now considered in local management decisions by the National Park Service and U.S. Forest Service. Ecological thresholds offer a scientifically sound approach to protecting and restoring U.S. ecosystems and an important tool for natural resource management and policy. ?? The Ecological Society of America.

Issues in Ecology↗

USGS2007

Use of multiple chemical tracers to define habitat use of Indo-Pacific mangrove crab, Scylla serrata (Decapoda: Portunidae)

The mangrove or mud crab, Scylla serrata, is an important component of mangrove fisheries throughout the Indo-Pacific. Understanding crab diets and habitat use should assist in managing these fisheries and could provide additional justification for conservation of the mangrove ecosystem itself. We used multiple chemical tracers to test whether crab movements were restricted to local mangrove forests, or extended to include adjacent seagrass beds and reef flats. We sampled three mangrove forests on the island of Kosrae in the Federated States of Micronesia at Lelu Harbor, Okat River, and Utwe tidal channel. Samples of S. serrata and likely food sources were analyzed for stable carbon (??13C), nitrogen (??15N), and sulfur (??34S) isotopes. Scylla serrata tissues also were analyzed for phosphorus (P), cations (K, Ca, Mg, Na), and trace elements (Mn, Fe, Cu, Zn, and B). Discriminant analysis indicated that at least 87% of the crabs remain in each site as distinct populations. Crab stable isotope values indicated potential differences in habitat use within estuaries. Values for ??13C and ??34S in crabs from Okat and Utwe were low and similar to values expected from animals feeding within mangrove forests, e.g., feeding on infauna that had average ??13C values near -26.5???. In contrast, crabs from Lelu had higher ?? 13C and ??34S values, with average values of -21.8 and 7.8???, respectively. These higher isotope values are consistent with increased crab foraging on reef flats and seagrasses. Given that S. serrata have been observed feeding on adjacent reef and seagrass environments on Kosrae, it is likely that they move in and out of the mangroves for feeding. Isotope mixing model results support these conclusions, with the greatest mangrove ecosystem contribution to S. serrata diet occurring in the largest mangrove forests. Conserving larger island mangrove forests (> 1 km deep) appears to support crab foraging activities. ?? 2007 Coastal and Estuarine Research Federation.

Estuaries and Coasts↗

USGS2010

The changing effects of Alaska’s boreal forests on the climate system

In the boreal forests of Alaska, recent changes in climate have influenced the exchange of trace gases, water, and energy between these forests and the atmosphere. These changes in the structure and function of boreal forests can then feed back to impact regional and global climates. In this manuscript, we examine the type and magnitude of the climate feedbacks from boreal forests in Alaska. Research generally suggests that the net effect of a warming climate is a positive regional feedback to warming. Currently, the primary positive climate feedbacks are likely related to decreases in surface albedo due to decreases in snow cover. Fewer negative feedbacks have been identified, and they may not be large enough to counterbalance the large positive feedbacks. These positive feedbacks are most pronounced at the regional scale and reduce the resilience of the boreal vegetation – climate system by amplifying the rate of regional warming. Given the recent warming in this region, the large variety of associated mechanisms that can alter terrestrial ecosystems and influence the climate system, and a reduction in the boreal forest resilience, there is a strong need to continue to quantify and evaluate the feedback pathways.

Alaska↗

USGS1997

Status of the Sierra Nevada: the Sierra Nevada Ecosystem Project

The Sierra Nevada ecosystem project was requested by Congress in the Conference Report for Interior and related Agencies 1993 Appropriation Act, which authorized funds for a scientific review of the remaining old growth in the national forests of the Sierra Nevada in California, and for a study of the entire Sierra Nevada ecosystem by an independent panel of scientists, with expertise in diverse areas related to this issue. This CD-ROM is a digital version of the set of reports titled 'Sierra Nevada Ecosystem Project, final report to Congress' published in paper form by the Centers for Water and Wildland Resources of the University of California, Davis.

Data Series↗

USGS1997

The frequency and intensity of Atlantic hurricanes and their influence on the structure of south Florida mangrove communities

Hurricanes are formidable forces that wreak havoc on society and nature alike. Mangrove ecosystems are especially vulnerable because they thrive in the intertidal zone of tropical regions where hurricanes originate and are most frequent. Because mangroves are found at the land-sea interface where hurricanes are often most intense, these coastal forests are subject to damage from both high wind and surge. Mangroves are also an important habitat for many colonial and migratory birds and other wildlife, along with being nursery grounds for our fisheries. The fate of mangrove habitat as influenced by hurricanes may be threatened in the future under a global warming environment that might yield more intense storms than have been previously observed. Simulation models of hurricane abiotics and mangrove community dynamics have been developed to evaluate the effects of hurricanes on mangrove habitat across the South Florida landscape. Model applications show that hurricane frequency and intensity have varied spatially across Florida’s lower peninsula over the last century of record. Hindcast simulations of actual hurricane tracks and conditions seem to account for the structural composition of modernday mangrove forests across South Florida. A recurrence interval of major storms every 30 years over the last century is the major factor controlling mangrove ecosystem dynamics in South Florida. Some climate change models predict an increase in hurricane intensity over the next century that may further alter the structure and composition of our mangrove ecosystems. Model results of climate change scenarios indicate that future mangrove forests are likely to be diminished in stature and perhaps include a higher proportion of red mangroves. This modeling approach offers the ability to assess decadal and longer time scale changes in hurricane behavior and its effects on community structure and distribution of important plant associations such as the fate of mangrove habitat.

Florida↗

USGS2017

Climate change may restrict dryland forest regeneration in the 21st century

The persistence and geographic expansion of dryland forests in the 21st century will be influenced by how climate change supports the demographic processes associated with tree regeneration. Yet, the way that climate change may alter regeneration is unclear. We developed a quantitative framework that estimates forest regeneration potential (RP) as a function of key environmental conditions for ponderosa pine, a key dryland forest species. We integrated meteorological data and climate projections for 47 ponderosa pine forest sites across the western United States, and evaluated RP using an ecosystem water balance model. Our primary goal was to contrast conditions supporting regeneration among historical, mid-21st century and late-21st century time frames. Future climatic conditions supported 50% higher RP in 2020–2059 relative to 1910–2014. As temperatures increased more substantially in 2060–2099, seedling survival decreased, RP declined by 50%, and the frequency of years with very low RP increased from 25% to 58%. Thus, climate change may initially support higher RP and increase the likelihood of successful regeneration events, yet will ultimately reduce average RP and the frequency of years with moderate climate support of regeneration. Our results suggest that climate change alone may begin to restrict the persistence and expansion of dryland forests by limiting seedling survival in the late 21st century.

Ecology↗

USGS2018

Conservation and restoration of mangroves: Global status, perspectives, and prognosis

Mangrove forests provide critical services around the globe to both human populations and the ecosystems they occupy. However, losses of mangrove habitat of more than 50% have been recorded in some parts of the world, and these losses are largely attributable to human activities. The importance of mangroves and the threats to their persistence have long been recognized, leading to actions taken locally, by national governments, and through international agreements for their protection. In this review, we explore the status of mangrove forests as well as efforts to protect them. We examine threats to the persistence of mangroves, consequences, and potential solutions for effective conservation. We present case studies from disparate regions of the world, showing that the integration of human livelihood needs in a manner that balances conservation goals can present solutions that could lead to long-term sustainability of mangrove forests throughout the world.

Ocean and Coastal Management↗

USGS2026

When is a parasite a problem?

A parasite’s perceived societal impact depends on the disease it causes and the perception of the affected host species. For instance, doctors and veterinarians have a mission to treat parasites that infect humans or that impact host species that have some utilitarian or aesthetic value for society. Marine scientists have different concerns than doctors. Although the number of parasites that marine scientists should be concerned about may vary, only 13% of parasites and 6% of host–parasite links might be considered “problematic” in a kelp forest food web. With regard to the many threats to marine ecosystems, these percentages suggest that most parasites and infectious diseases are inconsequential. A related issue is the common expectation that parasites and the impacts that they cause are increasing under stress as ocean environments across the globe degrade. Yet, reports of disease have not increased due to human impacts on the marine environment, where the factors that influence parasitism are more complex. Thus, the expectation that marine parasites create problems, and that the diseases they cause are getting worse, is more likely the exception than the rule.

Book chapter↗

USGS2020

Occurrence of a suite of stream-obligate amphibians in timberlands of Mendocino County, California, examined using environmental DNA

Stream-obligate amphibians are important indicators of ecosystem health in the Pacific Northwest, but distributional information to improve forest management is lacking in many regions. We analyzed archived DNA extracted from water samples in 60 pools in streams on private timberlands in Mendocino County, California, for 3 California Species of Special Concern—Coastal Tailed Frogs ( Ascaphus truei ), Foothill Yellow-legged Frogs ( Rana boylii ), and Southern Torrent Salamanders ( Rhyacotriton variegatus )—to better understand their distributions in the region. Detection probabilities for eDNA of Foothill Yellow-legged Frogs and Coastal Tailed Frogs were positively influenced by water temperature. eDNA occurrence for both frogs was affected by whether silt or organic matter was a dominant substrate in the sampled pool, and Foothill Yellow-legged Frog eDNA occurrence was also affected by water temperature. Foothill Yellow-legged Frog eDNA occurrence had a strong, positive association with water temperature, with occurrence unlikely below 14°C and very likely above 16°C, and a positive association with silt or organic substrates in pools, which was likely an indicator of higher-order stream reaches. In contrast, Coastal Tailed Frogs had a negative association with silt or organic substrates. Historical visual detections were generally congruent with findings using eDNA, but differences highlight important areas for further study. We did not detect Southern Torrent Salamanders using eDNA at any sites. Our study reinforces that ecological relationships of these species are varied, and shows the importance of maintaining the integrity of streams with diverse characteristics for conserving stream amphibians.

California↗

USGS2021

Tamm review: Postfire landscape management in frequent-fire conifer forests of the southwestern United States

The increasing incidence of wildfires across the southwestern United States (US) is altering the contemporary forest management template within historically frequent-fire conifer forests. An increasing fraction of southwestern conifer forests have recently burned, and many of these burned landscapes contain complex mosaics of surviving forest and severely burned patches without surviving conifer trees. These heterogeneous burned landscapes present unique social and ecological challenges. Severely burned patches can present numerous barriers to successful conifer regeneration, and often contain heavy downed fuels which have cascading effects on future fire behavior and conifer regeneration. Conversely, surviving forest patches are increasingly recognized for their value in postfire reforestation but often are overlooked from a management perspective. Here we present a decision-making framework for landscape-scale management of complex postfire landscapes that allows for adaptation to a warming climate and future fire. We focus specifically on historically frequent-fire forests of the southwestern US but make connections to other forest types and other regions. Our framework depends on a spatially-explicit assessment of the mosaic of conifer forest and severely burned patches in the postfire landscape, evaluates likely vegetation trajectories, and identifies critical decision points to direct vegetation change via manipulations of fuels and live vegetation. This framework includes detailed considerations for postfire fuels management (e.g., edge hardening within live forest patches and repeat burning) and for reforestation (e.g., balancing tradeoffs between intensive and extensive planting strategies, establishing patches of seed trees, spatial planning to optimize reforestation success, and improving nursery capacity). In a future of increasing fire activity in forests where repeated low- to moderate-severity fire is essential to ecosystem resilience, the decision-making framework developed here can easily be integrated with existing postfire management strategies to optimize allocation of limited resources and more actively manage burned landscapes.

Arizona, Colorado, New Mexico, Utah↗

USGS2022

Evolutionary ecology of fire

Fire has been an ecosystem process since plants colonized land over 400 million years ago. Many diverse traits provide a fitness benefit following fires, and these adaptive traits vary with the fire regime. Some of these traits enhance fire survival, while others promote recruitment in the postfire environment. Demonstrating that these traits are fire adaptations is challenging, since many arose early in the paleontological record, although increasingly better fossil records and phylogenetic analysis make timing of these trait origins to fire more certain. Resprouting from the base of stems is the most widely distributed fire-adaptive trait, and it is likely to have evolved under a diversity of disturbance types. The origins of other traits like serotiny, thick bark, fire-stimulated germination, and postfire flowering are more tightly linked to fire. Fire-adaptive traits occur in many environments: boreal and temperate forests, Mediterranean-type climate (MTC) shrublands, savannas, and other grasslands. MTC ecosystems are distinct in that many taxa in different regions have lost the resprouting ability and depend solely on postfire recruitment for postfire recovery. This obligate seeding mode is perhaps the most vulnerable fire-adaptive syndrome in the face of current global change, particularly in light of increasing anthropogenic fire frequency.

Annual Review of Ecology, Evolution, and Systemati↗

USGS2005

Effects of a clearcut on the net rates of nitrification and N mineralization in a northern hardwood forest, Catskill Mountains, New York, USA

The Catskill Mountains of southeastern New York receive among the highest rates of atmospheric nitrogen (N) deposition in eastern North America, and ecosystems in the region may be sensitive to human disturbances that affect the N cycle. We studied the effects of a clearcut in a northern hardwood forest within a 24-ha Catskill watershed on the net rates of N mineralization and nitrification in soil plots during 6 years (1994-1999) that encompassed 3-year pre- and post-harvesting periods. Despite stream NO3- concentrations that increased by more than 1400 ??mol l-1 within 5 months after the clearcut, and three measures of NO3- availability in soil that increased 6- to 8-fold during the 1st year after harvest, the net rates of N mineralization and nitrification as measured by in situ incubation in the soil remained unchanged. The net N-mineralization rate in O-horizon soil was 1- 2 mg N kg-1 day-1 and the net nitrification rate was about 1 mg N kg-1 day-1, and rates in B-horizon soil were only one-fifth to one-tenth those of the O-horizon. These rates were obtained in single 625 m2 plots in the clearcut watershed and reference area, and were confirmed by rate measurements at 6 plots in 1999 that showed little difference in N-mineralization and nitrification rates between the treatment and reference areas. Soil temperature increased 1 ?? 0.8??C in a clearcut study plot relative to a reference plot during the post-harvest period, and soil moisture in the clearcut plot was indistinguishable from that in the reference plot. These results are contrary to the initial hypothesis that the clearcut would cause net rates of these N-cycling processes to increase sharply. The in situ incubation method used in this study isolated the samples from ambient roots and thereby prevented plant N uptake; therefore, the increases in stream NO3- concentrations and export following harvest largely reflect diminished uptake. Changes in temperature and moisture after the clearcut were insufficient to measurably affect the net rates of N mineralization and nitrification in the absence of plant uptake. Soil acidification resulting from the harvest may have acted in part to inhibit the rates of these processes. ?? Springer 2005.

Biogeochemistry↗

USGS2024

Dynamic treeline and cryosphere response to pronounced mid-Holocene climatic variability in the US Rocky Mountains

Climate-driven changes in high-elevation forest distribution and reductions in snow and ice cover have major implications for ecosystems and global water security. In the Greater Yellowstone Ecosystem of the Rocky Mountains (United States), recent melting of a high-elevation (3,091 m asl) ice patch exposed a mature stand of whitebark pine ( Pinus albicaulis ) trees, located ~180 m in elevation above modern treeline, that date to the mid-Holocene (c. 5,950 to 5,440 cal y BP). Here, we used this subfossil wood record to develop tree-ring-based temperature estimates for the upper-elevation climate conditions that resulted in ancient forest establishment and growth and the subsequent regional ice-patch growth and downslope shift of treeline. Results suggest that mid-Holocene forest establishment and growth occurred under warm-season (May-Oct) mean temperatures of 6.2 °C (±0.2 °C), until a multicentury cooling anomaly suppressed temperatures below 5.8 °C, resulting in stand mortality by c. 5,440 y BP. Transient climate model simulations indicate that regional cooling was driven by changes in summer insolation and Northern Hemisphere volcanism. The initial cooling event was followed centuries later (c. 5,100 y BP) by sustained Icelandic volcanic eruptions that forced a centennial-scale 1.0 °C summer cooling anomaly and led to rapid ice-patch growth and preservation of the trees. With recent warming (c. 2000–2020 CE), warm-season temperatures now equal and will soon exceed those of the mid-Holocene period of high treeline. It is likely that perennial ice cover will again disappear from the region, and treeline may expand upslope so long as plant-available moisture and disturbance are not limiting.

Montana, Wyoming↗

USGS2007

Calibrating a forest landscape model to simulate frequent fire in Mediterranean-type shrublands

In Mediterranean-type ecosystems (MTEs), fire disturbance influences the distribution of most plant communities, and altered fire regimes may be more important than climate factors in shaping future MTE vegetation dynamics. Models that simulate the high-frequency fire and post-fire response strategies characteristic of these regions will be important tools for evaluating potential landscape change scenarios. However, few existing models have been designed to simulate these properties over long time frames and broad spatial scales. We refined a landscape disturbance and succession (LANDIS) model to operate on an annual time step and to simulate altered fire regimes in a southern California Mediterranean landscape. After developing a comprehensive set of spatial and non-spatial variables and parameters, we calibrated the model to simulate very high fire frequencies and evaluated the simulations under several parameter scenarios representing hypotheses about system dynamics. The goal was to ensure that observed model behavior would simulate the specified fire regime parameters, and that the predictions were reasonable based on current understanding of community dynamics in the region. After calibration, the two dominant plant functional types responded realistically to different fire regime scenarios. Therefore, this model offers a new alternative for simulating altered fire regimes in MTE landscapes. ?? 2007 Elsevier Ltd. All rights reserved.

Environmental Modelling and Software↗

USGS2001

Varied ecosystems need different fire protection

Covington states in his Commentary 1 that the open ponderosa pine forests of the western United States are "in widespread collapse" because fire suppression by humans has eliminated the low-intensity surface fire regime that maintained the open, park-like structure of these forests. He fears this will lead to an "unprecedented" crown fire regime that will eliminate forests.

Nature↗