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At least 1,009 records · Page 56Linked to original sources

USGS2019

Three-dimensional partitioning of resources by congeneric forest predators with recent sympatry

Coexistence of ecologically similar species can be maintained by partitioning along one or more niche axes. Three-dimensional structural complexity is central to facilitating resource partitioning between many forest species, but is underrepresented in field-based studies. We examined resource selection by sympatric northern spotted owls (Strix occidentalis caurina), a threatened species under the US Endangered Species Act, and nonnative barred owls (S. varia) in western Oregon, USA to explore the relative importance of canopy heterogeneity, vertical complexity of forest, and abiotic features to resource selection and identify potential differences that may facilitate long-term coexistence. We predicted that within home range selection of understory densities, measured with airborne lidar, would differ between species based on proportional differences in arboreal and terrestrial prey taken by each owl species. We used discrete choice models and telemetry data from 41 spotted owls and 38 barred owls monitored during 2007–2009 and 2012–2015. Our results suggested that while both species used tall canopy areas more often than low canopy areas, spotted owls were more commonly found in areas with lower tree cover, more developed understory, and steeper slopes. This is the first evidence of fine-scale partitioning based on structural forest properties by northern spotted owls and barred owls.

Oregon↗

USGS2002

Overwinter survival of neotropical migratory birds in early-successional and mature tropical forests

Many Neotropical migratory species inhabit both mature and earty-successional forests on their wintering grounds, yet comparisons of survival rates between habitats are lacking. Consequently, the factors affecting habitat suitability for Neotropical migrants and the potential effects of tropical deforestation on migrants are not well understood. We estimated overwinter survival and capture probabilities of Wood Thrush ( Hylochichla mustelina ), Ovenbird ( Seiurus aurocapillus ), Hooded Warbler ( Wilsonia citrina ), and Kentucky Warbler ( Oporornis formosus ) inhabiting two common tropical habitat types, mature and early-successional forest. Our results suggest that large differences (for example, ratio of survival rates (γ) ≤ 0.85) in overwinter survival between these habitats do not exist for any of these species. Age ratios did not differ between habitats, but males were more common in forest habitats and females more common in successional habitats for Hooded Warblers and Kentucky Warblers. Future research on overwinter survival should address the need for age- and sex-specific survival estimates before we can draw strong conclusions regarding winter habitat suitability. Our estimates of overwinter survival extrapolated to annual survival rates that were generally lower than previous estimates of annual survival of migratory birds. Capture probability differed between habitats for Kentucky Warblers, but our results provide strong evidence against large differences in capture probability between habitats for Wood Thrush, Hooded Warblers, and Ovenbirds. We found no temporal or among-site differences in survival or capture probability for any of the four species. Additional research is needed to examine the effects of winter habitat use on survival during migration and between-winter survival.

Conservation Biology↗

USGS1996

Remote sensing of forest fire severity and vegetation recovery

Burned forested areas have patterns of varying burn severity as a consequence of various topographic, vegetation, and meteorological factors. These patterns are detected and mapped using satellite data. Other ecological information can be abstracted from satellite data regarding rates of recovery of vegetation foliage and variation of burn severity on different vegetation types. Middle infrared wavelengths are useful for burn severity mapping because the land cover changes associated with burning increase reflectance in this part of the electromagnetic spectrum. Simple stratification of Landsat Thematic Mapper data define varying classes of burn severity because of changes in canopy cover, biomass removal, and soil chemical composition. Reasonable maps of burn severity are produced when the class limits of burn severity reflectance are applied to the entire satellite data. Changes in satellite reflectance over multiple years reveal the dynamics of vegetation and fire severity as low burn areas have lower changes in reflectance relative to high burn areas. This results as a consequence of how much the site was altered due to the burn and how much space is available for vegetation recovery. Analysis of change in reflectance across steppe, riparian, and forested vegetation types indicate that fires potentially increase biomass in steppe areas, while riparian and forested areas are slower to regrow to pre-fire conditions. This satellite-based technology is useful for mapping severely burned areas by exploring the ecological manifestations before and after fire.

International Journal of Wildland Fire↗

USGS2025

Dynamic and context-dependent keystone species effects in kelp forests

Sea otters are an iconic keystone predator that can maintain kelp forests by preying on grazing invertebrates such as sea urchins. However, the effects of sea otters on kelp forests vary over their geographic range. Here, we analyze two 30-y datasets on kelp forest communities during the reintroduction of sea otters along the west coast of Vancouver Island, BC, Canada, and around San Nicolas Island, CA. We developed a community model to estimate species interactions as dynamic rates, varying with community state. We find evidence of a classic trophic cascade off Vancouver Island; the arrival of otters quickly led to depletion of urchins and recovery of kelp. However, this cascade was muted around San Nicolas Island, with otters, urchins, and kelp all coexisting at intermediate densities for multiple years. Our models show that this difference came from a pulse of strong otter impacts on urchins following recolonization off Vancouver Island, but not off San Nicolas Island. The mean effects of otters on urchins and urchins on kelp were not stronger in the north, indicating that interaction dynamics and not average interaction strength are key to explaining differences in community trajectories. We also find stronger multistep interaction chains in the south, arising from competitive interactions that indirectly buffered otter effects. These findings shed light on long-standing hypotheses about how interspecific interactions can alter the function of keystone species across community contexts. More broadly, we show how community change can be more accurately predicted by considering dynamic interaction strengths.

Proceedings of the National Academy of Sciences↗

USGS1998

Higher temporal variability of forest breeding bird communities in fragmented landscapes

Understanding the relationship between animal community dynamics and landscape structure has become a priority for biodiversity conservation. In particular, predicting the effects of habitat destruction that confine species to networks of small patches is an important prerequisite to conservation plan development. Theoretical models that predict the occurrence of species in fragmented landscapes, and relationships between stability and diversity do exist. However, reliable empirical investigations of the dynamics of biodiversity have been prevented by differences in species detection probabilities among landscapes. Using long-term data sampled at a large spatial scale in conjunction with a capture-recapture approach, we developed estimates of parameters of community changes over a 22-year period for forest breeding birds in selected areas of the eastern United States. We show that forest fragmentation was associated not only with a reduced number of forest bird species, but also with increased temporal variability in the number of species. This higher temporal variability was associated with higher local extinction and turnover rates. These results have major conservation implications. Moreover, the approach used provides a practical tool for the study of the dynamics of biodiversity.

Proceedings of the National Academy of Sciences↗

USGS2017

Urban forest management in New England: Towards a contemporary understanding of tree wardens in Massachusetts communities

In the New England states, tree wardens are local officials responsible for the preservation, maintenance and stewardship of municipal public trees. This study explores the emerging professional challenges, duties and responsibilities of tree wardens, from the subject’s point of view, by conducting in-person, semi-structured qualitative research interviews with 50 tree wardens throughout Massachusetts. Many of the findings corroborate previous literature, including that tree wardens are typically housed in a municipal department (often public works or highway), that tree wardens routinely interact with a wide variety of local organisations (representatives from other municipal departments, community volunteer associations) and that as community size increases, tree wardens typically have access to a greater pool of resources to carry out urban forest management. A newer finding is that the subject of urban forest health arose as a topic of great importance for tree wardens, as nearly all interviewees ( n = 49) indicated that they monitor for urban forest pests and that they would like further continuing education concerning this subject.

Massachusetts↗

USGS2020

A random forest approach for bounded outcome variables

Random forests have become an established tool for classication and regres- sion, in particular in high-dimensional settings and in the presence of non-additive predictor-response relationships. For bounded outcome variables restricted to the unit interval, however, classical modeling approaches based on mean squared error loss may severely suer as they do not account for heteroscedasticity in the data. To address this issue, we propose a random forest approach for relating a beta dis- tributed outcome to a set of explanatory variables. Our approach explicitly makes use of the likelihood function of the beta distribution for the selection of splits dur- ing the tree-building procedure. In each iteration of the tree-building algorithm it chooses one explanatory variable in combination with a split point that maximizes the log-likelihood function of the beta distribution with the parameter estimates de- rived from the nodes of the currently built tree. Results of several simulation studies and an application using data from the U.S.A. National Lakes Assessment Survey demonstrate the properties and usefulness of the method, in particular when com- pared to random forest approaches based on mean squared error loss and parametric regression models.

Journal of Computational and Graphical Statistics↗

USGS2025

Population trends of native and non-native forest birds on the island of Molokai, Hawaii

Hawaiʻi’s avifauna has undergone profound changes over the past 1,000 years, with many endemic bird species driven to extinction and non-native introductions reshaping forest ecosystems. On the island of Molokaʻi, habitat degradation and the introduction of mosquito-borne disease, mainly avian malaria ( Plasmodium relictum ), have caused extinctions and severe declines in native forest bird populations. To assess these changes, point-transect distance sampling surveys were initiated in 1979 and 1980 and repeated six times, most recently in 2021, covering a 3,527 ha area. This study analyzes species composition, population densities, abundances, and long-term trends for species with sufficient detections using log-linear regression. Since 1979–1980, a total of 17 non-native and 3 native species were detected across all six surveys. The non-native Warbling White-eye ( Zosterops japonicus ) had the highest density and abundance in every survey, while abundance of Red-billed Leiothrix ( Leiothrix lutea ) significantly trended upward. The Japanese Bush Warbler ( Horornis diphone ) irrupted in the survey area, increasing in abundance by more than 99% since 1979–1980. Among native species, ʻApapane ( Himatione sanguinea ) populations increased by 33%, while Hawaiʻi ʻAmakihi ( Chlorodrepanis virens ) declined by 78% from their peak in 1995. Federally threatened ʻIʻiwi ( Drepanis coccinea ), highly susceptible to avian malaria, have not been recorded on Molokaʻi since 2010, and the endemic Olomaʻo ( Myadestes lanaiensis ) has not been detected since 1980 and is possibly extinct. Our results underscore the ongoing conservation crisis for Molokaʻi’s forest birds and the continued vulnerability of native birds to disease and habitat loss.

Hawaii↗

USGS1990

Survival rates of birds of tropical and temperate forests: Will the dogma survive?

Survival rates of tropical forest birds are widely assumed to be high relative to the survival rates of temperate forest birds. Much life-history theory is based on this assumption despite the lack of empirical data to support it. We provide the first detailed comparison of survival rates of tropical and temperate forest birds based on extensive data bases and modern capture-recapture models. We find no support for the conventional wisdom. Because clutch size is only one component of reproductive rate, the frequently assumed, simple association between clutch size and adult survival rates should not necessarily be expected. Our results emphasize the need to consider components of fecundity in addition to clutch size when comparing the life histories of tropical and temperate birds and suggest similar considerations in the development of vertebrate life-history theory.

American Naturalist↗

USGS2019

Soil chemistry, and not short-term (1–2 year) deer exclusion, explains understory plant occupancy in forests affected by acid deposition

The loss of species diversity and plant community structure throughout the temperate deciduous forests of North America have often been attributed to overbrowsing by white-tailed deer ( Odocoileus virginanus ). Slow species recovery following removal from browsing, or reduction in deer density, has been termed a legacy effect of past deer herbivory. However, vegetation legacy effects have also coincided with changes to soil chemistry throughout the north-eastern USA. In this paper, we assess the viability of soil chemistry (i.e. pH, extractable nutrients and extractable metals) and other factors (topography, light, overstory basal area and location) as alternative explanations for a lack of vegetation recovery. We compared the relative effects of soil chemistry, site conditions and short-term (1–2 year) deer exclusion on single-species occupancy probabilities of 10 plant taxa common to oak-hickory forests in central Pennsylvania. We found detection for all modelled species was constant and high ( ⁠ p ^ "> p ^ p^ > 0.65), and occupancy probability of most taxa was best explained by at least one soil chemistry parameter. Specifically, ericaceous competing vegetation was more likely to occupy acidic (pH < 3.5), base cation-poor (K < 0.20 cmol c kg −1 ) sites, while deer-preferred plants were less likely to occur when soil manganese exceeded 0.1 cmol c kg −1 . Short-term deer exclusion did not explain occupancy of any plant taxon, and site conditions were of nominal importance. This study demonstrates the importance of soil chemistry in shaping plant community composition in the north-central Appalachians, and suggests soil as an alternative, or additional, explanation for deer vegetation legacy effects. We suggest that the reliance on phyto-indicators of deer browsing effects may overestimate the effects of browsing if those species are also limited by unfavourable soil conditions. Future research should consider study designs that address the complexity of deer forest interactions, especially in areas with complex site-vegetation histories.

Pennsylvania↗

USGS2021

Long‐term surveys support declines in early‐season forest plants used by bumblebees

Populations of bumble bees and other pollinators have declined over the past several decades due to numerous threats, including habitat loss and degradation. However, we can rarely investigate the role of resource loss due to a lack of detailed long‐term records of forage plants and habitats. We use 22‐year repeated surveys of more than 262 sites located in grassland, forest, and wetland habitats across Illinois, USA to explore how the abundance and richness of bumble bee food plants have changed over the period of decline of the endangered rusty patched bumble bee ( Bombus affinis ). We document a decline in abundance of bumble bee forage plants in forest understories, which our phenology analysis suggests provide the primary nectar and pollen sources for foundress queens in spring, a critical life stage in bumble bee demography. By contrast, the per‐unit area abundance of food plants in primarily midsummer‐flowering grassland and wetland habitats has not declined. However, the total area of grasslands has declined across the region resulting in a net loss of grassland resources. Synthesis and applications . Our results suggest a decline in spring‐flowering forest understory plants is a previously unappreciated bumble bee stressor, compounding factors like agricultural intensification, novel pathogen exposure, and grassland habitat loss. These findings emphasize the need for greater consideration of habitat complementarity in bumble bee conservation. We conclude that continued loss of early‐season floral resources may add additional stress to critical life stages of bumble bees and limit restoration efforts if not explicitly considered in pollinator conservation.

Illinois↗

USGS2017

Growth strategies and threshold responses to water deficit modulate effects of warming on tree seedlings from forest to alpine

1.Predictions of upslope range shifts for tree species with warming are based on assumptions of moisture stress at lower elevation limits and low temperature stress at high elevation limits. However, recent studies have shown that warming can reduce tree seedling establishment across the entire gradient from subalpine forest to alpine via moisture limitation. Warming effects also vary with species, potentially resulting in community shifts in high elevation forests. 2.We examined the growth and physiology underlying effects of warming on seedling demographic patterns. We evaluated dry mass (DM), root length, allocation above- and belowground, and relative growth rate (RGR) of whole seedlings, and their ability to avoid or endure water stress via water-use efficiency and resisting turgor loss, for Pinus flexilis, Picea engelmannii and Pinus contorta seeded below, at, and above treeline in experimentally warmed, watered, and control plots in the Rocky Mountains, USA. We expected that growth and allocation responses to warming would relate to moisture status and that variation in drought tolerance traits would explain species differences in survival rates. 3.Across treatments and elevations, seedlings of all species had weak turgor-loss resistance, and growth was marginal with negative RGR in the first growth phase (-0.01 to -0.04 g/g/d). Growth was correlated with soil moisture, particularly in the relatively small-seeded P. contorta and P. engelmannii. P. flexilis, known to have the highest survivorship, attained the greatest DM and longest root but was also the slowest growing and most water-use-efficient. This was likely due to its greater reliance on seed reserves. Seedlings developed 15% less total DM, 25% less root DM, and 11% shorter roots in heated compared to unheated plots. Higher temperatures slightly increased DM, root length and RGR where soils were wettest, but more strongly decreased these variables under drier conditions. 4.Synthesis: The surprising heat-inhibition of tree seedling establishment at the cold edge of forests appears to have a physiological basis: newly germinated seedlings have poor moisture stress tolerance, which appears related to marginal initial growth and heavy reliance on seed reserves. Variation in these attributes among tree species at treeline helps explain their different climate responses.

Journal of Ecology↗

USGS2022

Watershed-scale liming reveals the short- and long-term effects of pH on the forest soil microbiome and carbon cycling

Soil microbial community composition routinely correlates with pH, reflecting both direct pH effects on microbial physiology and long-term biogeochemical feedbacks. We used two watershed-scale liming experiments to identify short- (2 years) and long-term (25 years) changes in the structure and function of bacterial and fungal communities in organic horizons (O e and O a ) of acid forest soils. Liming increased soil pH, extractable calcium, and soil carbon stocks, reduced biomass-specific respiration, and caused major changes in the soil microbiome in the short and long term. More taxa responded to liming in the short term (70%) than in the long term (30%), with most showing consistent directional responses at both sites. The ratio of change in relative abundance between limed and reference sites was twofold higher at the long than the short-term site, indicating that the effects of liming grew over time. Liming impacts were most pronounced in fungi, as steep declines of dominant ectomycorrhizal fungi ( Cenococcum and Russula ) occurred at both sites. Liming favoured neutrophilic bacteria over acidophilic populations according to estimated environmental pH optima. Collectively, these results demonstrate that a liming-induced change of one pH unit has an immediate and persistent effect on the structure and function of microbial communities in acid forest soils. The corresponding suppression of respiration indicates that anthropogenic alterations of soil pH, as driven by acid deposition or liming, can affect forest floor C stocks due to pH-driven shifts in community structure.

New York↗

USGS2019

Reduced soil macropores and forest cover reduce warm-season baseflow below ecological thresholds in the upper Delaware River Basin

We examined the impacts of changes in land cover and soil conditions on the flow regime of the upper Delaware River Basin using the Water Availability Tool for Environmental Resources (WATER). We simulated flows for two periods, circa 1600 and 1940, at three sites using the same temperature and precipitation conditions: the East Branch (EB), West Branch (WB), and mainstem Delaware River at Callicoon, NY. The 1600 period represented pristine forest and soils. The 1940 period included reduced forest cover, increased agriculture, and degraded soils with reduced soil macropore fractions. A model-sensitivity test examined the impact of soil macropore and land cover change separately. We assessed changes in flow regimes between the 1600 and 1940 periods using a variety of flow statistics, including established ecological limits of hydrologic alteration (ELOHA) thresholds. Reduced forest soil macropore fraction significantly reduced summer and fall base flows. The 1940 period had significantly lower Q50 flows (50% exceedance) than the 1600 period, as well as summer and fall Q90 and Q75-90 flows below the ELOHA thresholds. The 1- to 7-day minimum flows were also lower for the 1940 period, by 17% on the mainstem. 1940 flows were 6% more likely than the 1600 period to fall below the low-flow threshold for federally endangered dwarf wedgemussel (Alasmidonta heterodon) habitat. In contrast, the 1940 period had higher flows than the 1600 period from late fall to early winter.

New York, Pennsylvania↗

USGS2022

Flood regimes alter the role of landform and topographic constraint on functional diversity of floodplain forests

Understanding patterns of species coexistence is a fundamental challenge in ecology. The physical environment is believed to play an important role, influencing patterns of dispersal and biotic interactions across space and time. Floodplain forest species are presumed to interact strongly with their environment, as evidenced by pronounced spatial variation in forest composition associated with flood-driven abiotic constraints. Questions of how, and to what degree, fine-scale heterogeneity interacts with broad-scale hydrogeomorphology to influence patterns of functional composition remain unresolved. We examined how functional diversity (i.e. richness and range of functional traits) and ecological strategies (i.e. functional trait combinations) of floodplain forest communities varied across regional and local gradients of flooding in a northern temperate region of the United States of America. We found functional diversity of woody overstory species varied across hydrogeomorphic settings and that different settings altered associations between functional diversity and both the relative elevation above and proximity to rivers. Ecological strategies shifted over local gradients of relative elevation and distance to channel with different magnitudes and directions depending on the broader hydrogeomorphic context. We found evidence that interactions among flood regimes and landform position impose different levels of functional constraint. These results indicate patterns of community assembly are not easily discerned from landform type or position alone, but rather from filtering that operates and interacts with biota over multiple spatial scales. Our results imply that it is important to characterize flood dynamics in ways that can be clearly linked to ecological processes and that treatment of floodplain landforms as transferable units across river-valley segments is problematic, even within a single basin.

Ecography↗

USGS2020

Forests do not limit bumble bee foraging movements in a montane meadow complex

1. Understanding the roles of habitat fragmentation and resource availability in shaping animal movement are integral for promoting species persistence and conservation. For insects like bumble bees, their movement patterns affect the survival and reproductive potential of their colonies as well as the pollen flow of plant species. However, our understanding of their mobility or the impact of putative barriers in natural environments is limited due to the technical difficulties of studying wild populations. 2. We used genetic mark-recapture to estimate the foraging distance, resource use, and site connectivity of two bumble bee species in a montane meadow complex composed of open meadows within a matrix of forest. 3. There was no evidence that forests or changes in landcover function as barriers to the fine‐scale movement for either species. Substantially greater colony‐specific foraging distances were found for Bombus vosnesenskii (maximum: 1867 m) compared to Bombus bifarius (maximum: 362 m). Despite this difference in absolute range, both species were detected across putative forest barriers at frequencies expected by uninhibited movement. Siblings separated by greater distances were more likely to be foraging on different floral species, potentially suggesting a resource‐based motivation for movement. 4. These results suggest that bumble bee foraging patterns are influenced by species-specific differences in movement capacity, with little influence of matrix composition between resource patches. They also support the perspective that habitat conservation for bumble bees should prioritize providing abundant and diverse patches of resources within species-specific movement radii with less emphasis on matrix composition.

Ecological Entomology↗

USGS2013

Climatic stress increases forest fire severity across the western United States

Pervasive warming can lead to chronic stress on forest trees, which may contribute to mortality resulting from fire-caused injuries. Longitudinal analyses of forest plots from across the western US show that high pre-fire climatic water deficit was related to increased post-fire tree mortality probabilities. This relationship between climate and fire was present after accounting for fire defences and injuries, and appeared to influence the effects of crown and stem injuries. Climate and fire interactions did not vary substantially across geographical regions, major genera and tree sizes. Our findings support recent physiological evidence showing that both drought and heating from fire can impair xylem conductivity. Warming trends have been linked to increasing probabilities of severe fire weather and fire spread; our results suggest that warming may also increase forest fire severity (the number of trees killed) independent of fire intensity (the amount of heat released during a fire).

Ecology Letters↗

USGS2016

A review of the relationships between drought and forest fire in the United States

The historical and pre-settlement relationships between drought and wildfire are well documented in North America, with forest fire occurrence and area clearly increasing in response to drought. There is also evidence that drought interacts with other controls (forest productivity, topography, fire weather, management activities) to affect fire intensity, severity, extent, and frequency. Fire regime characteristics arise across many individual fires at a variety of spatial and temporal scales, so both weather and climate—including short- and long-term droughts—are important and influence several, but not all, aspects of fire regimes. We review relationships between drought and fire regimes in United States forests, fire-related drought metrics and expected changes in fire risk, and implications for fire management under climate change. Collectively, this points to a conceptual model of fire on real landscapes: fire regimes, and how they change through time, are products of fuels and how other factors affect their availability (abundance, arrangement, continuity) and flammability (moisture, chemical composition). Climate, management, and land use all affect availability, flammability, and probability of ignition differently in different parts of North America. From a fire ecology perspective, the concept of drought varies with scale, application, scientific or management objective, and ecosystem.

Global Change Biology↗