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At least 91 records · Page 5Linked to original sources
USGS2022

Local groundwater decline exacerbates response of dryland riparian woodlands to climatic drought

Dryland riparian woodlands are considered to be locally buffered from droughts by shallow and stable groundwater levels. However, climate change is causing more frequent and severe drought events, accompanied by warmer temperatures, collectively threatening the persistence of these groundwater dependent ecosystems through a combination of increasing evaporative demand and decreasing groundwater supply. We conducted a dendro-isotopic analysis of radial growth and seasonal (semi-annual) carbon isotope discrimination (Δ 13 C) to investigate the response of riparian cottonwood stands to the unprecedented California-wide drought from 2012 to 2019, along the largest remaining free-flowing river in Southern California. Our goals were to identify principal drivers and indicators of drought stress for dryland riparian woodlands, determine their thresholds of tolerance to hydroclimatic stressors, and ultimately assess their vulnerability to climate change. Riparian trees were highly responsive to drought conditions along the river, exhibiting suppressed growth and strong stomatal closure (inferred from reduced Δ 13 C) during peak drought years. However, patterns of radial growth and Δ 13 C were quite variable among sites that differed in climatic conditions and rate of groundwater decline. We show that the rate of groundwater decline, as opposed to climate factors, was the primary driver of site differences in drought stress, and trees showed greater sensitivity to temperature at sites subjected to faster groundwater decline. Across sites, higher correlation between radial growth and Δ 13 C for individual trees, and higher inter-correlation of Δ 13 C among trees were indicative of greater drought stress. Trees showed a threshold of tolerance to groundwater decline at 0.5 m year −1 beyond which drought stress became increasingly evident and severe. For sites that exceeded this threshold, peak physiological stress occurred when total groundwater recession exceeded ~3 m. These findings indicate that drought-induced groundwater decline associated with more extreme droughts is a primary threat to dryland riparian woodlands and increases their susceptibility to projected warmer temperatures.

California↗
USGS2025

Sapsucker wells as a keystone nutritional resource: Evaluating methods for detection of secondary sap consumers

North American sapsuckers are considered double keystone species because they (1) excavate nest cavities that are used by other birds, small mammals, and invertebrates, and (2) create and maintain sap wells, a temporary nutritional resource available to a variety of secondary consumers. Most previous reports of secondary sap consumption relied on human observers and were based on either brief or incidental observations. However, modern technology can greatly enhance observational techniques and provide additional insights into the functional, community-level importance of sap wells. We used visual surveys, camera traps, and environmental DNA (eDNA) to identify secondary consumers of sap from wells created by red-naped ( Sphyrapicus nuchalis ) and Williamson's ( S. thyroideus ) sapsuckers among three functional groups of shrubs and trees in south-central Colorado: shrub willows ( Salix spp.), Rocky Mountain maple ( Acer glabrum ), and conifer trees (Pinopsida). Camera traps and eDNA revealed additional sap-well visitors not identified from direct observations. Camera traps were effective for detecting nocturnal sap-well visitors such as small rodents as well as occasional diurnal visitors. Environmental DNA analyses corroborated findings from other methods and identified four additional taxa as possible sap consumers. The physiology of sap-well visitors, such as the ability to taste and assimilate compounds within sap, may aid in determining consumption versus contact when evaluating the results of eDNA analyses. Total vertebrate taxa detected using all 3 methods included 17 bird taxa in 10 families within 3 orders and 8 mammal taxa in 6 families within 4 orders. Shrub-willow sap wells attracted the most diverse vertebrate taxa (23), followed by Rocky Mountain maple (13) and conifer trees (10). Invertebrates in 13 families within 3 orders were observed feeding from sap wells during visual surveys. Because many secondary sap consumers perform ecological services such as pollination, seed dispersal, and pest control, the methods described here may aid in elucidating the importance of sap-well creators in supporting biodiversity and ecosystem functioning.

Colorado↗
USGS2017

Exudation rates and δ13C signatures of tree root soluble organic carbon in a riparian forest

Tree root exudation (TRE) of water soluble organic carbon (WSOC) is an important but under-assessed component of net primary production, and is thought to strongly influence rhizosphere biogeochemistry. Riparian systems in particular are often viewed as biogeochemical hot spots fueled partially by root exudate WSOC. However, TRE rates have not been previously reported for these systems. The δ 13 C signatures of exudates may provide important insights into plant physiology and inform isotope-based methods to identify sources of soil CO 2 fluxes, but this information is also generally lacking. In the present study, root exudate WSOC was collected in situ to assess both net exudation rates and exudate δ 13 C values in a temperate riparian forest. Net TRE rates were found to be most strongly related to a combination of tree species, root characteristics and net ecosystem exchange (Adj. R 2 = 0.73; p < 0.001). In contrast, exudate δ 13 C values were correlated to time-lagged vapor pressure deficit (Adj. R 2 = 0.21; p < 0.05) and air temperature (Adj. R 2 = 0.43; p < 0.05), suggesting a rapid transfer of photosynthate from the canopy to the rhizosphere. Extrapolation of mean net TRE rates (13 µmol C g root −1 day −1 ) from a root mass basis to the entire sampling area suggests that TRE may account for as much as 3% of net annual C uptake and represents an important input of organic matter to riparian soils. Our findings of predictable TRE rates and exudate δ 13 C values in the present study suggest that future studies examining δ 13 C values of different plant components, soil organic matter and respired soil CO 2 would benefit by accounting for the impact of root exudates.

Biogeochemistry↗
USGS2025

Chapter 6: Climate change, wildlife, and wildlife habitats in the Oregon Coast Range

Climate change is likely to have profound effects on wildlife species within the Oregon Coast Adaptation Partnership (OCAP) assessment area, although the direction and magnitude of effects are likely to vary across species. Increased mean and extreme temperatures, especially during summer, may cause shifts in plant and animal species ranges, reduce habitat for some temperature-sensitive wildlife, alter plant phenology and the timing of available food resources, and affect species interactions (e.g., predation, competition). Altered timing of precipitation, summer drought, loss of fog, increased flooding events, earlier snowmelt, and rising sea level may reduce plant productivity, increase tree mortality, shift plant species composition, and lead to reduced wildlife habitat and habitat quality for some forests, riparian areas, wetlands, meadows, estuaries, and beaches. In addition, increasing frequency and extent of wildfire and insect outbreaks may reduce the extent of late-successional forest, reduce habitat connectivity, and increase the spread of invasive species. The biggest change expected for the assessment area is an increase in area where climatic conditions favor coastal mixed forest and a large reduction in area favoring montane conifer forest. Although actual changes in forest types may not necessarily occur by the end of the 21st century, climate change may add physiological and behavioral stress to wildlife. Some wildlife species will be able to persist in place and adapt to new conditions; some may be able to migrate to find suitable habitat; and some may be greatly reduced or extirpated from the assessment area or even go extinct. Shifts in major tree and shrub species will play a major role in food, den, and cover availability for wildlife. Rising sea level will reduce low-elevation habitats along the coast. An increase in the frequency of high-severity weather events will increase frequency and magnitude of flooding, including debris flow events. Coupled with increased temperatures during summer, this may reduce or fragment important ecosystems for aquatic and semi-aquatic species. Evaluation of the vulnerabilities of nine wildlife species based on literature reviews suggests that each species has life-history attributes that can lead to resilience or vulnerability to climate change effects. Depending on long-term objectives, several broad adaptation strategies focus on protecting refugia, establishing redundant wildlife strongholds with large-scale connectivity, and promoting structural and biological complexity.

Oregon↗
USGS2019

Bioclimatic envelopes for individual demographic events driven by extremes: Plant mortality from drought and warming

The occurrence of plant species across the globe is largely constrained by climate. Ecologists use plant-climate relationships such as bioclimatic envelopes and related niche models to determine potential environmental conditions promoting probable species occurrence. Traditionally bioclimatic envelopes either exclude disturbance explicitly, or only include disturbance as infrequent and smaller scale processes, assuming that the net effect of climate parameters on key demographic processes predict longer-term equilibrial responses of biota. Due to increasing frequency and extent of extreme events associated with climate change, ecologists may need to increase focus on individual demographic events driven by environmental extremes such as widespread coral bleaching or large-scale tree die-off. An expanded focus on how extreme events catalyze individual demographic events would complement existing tools that predict long-term equilibrial biogeographic responses associated with long-term trends in climate. In many cases, extreme conditions (e.g. drought) are a necessary precursor for an abrupt demographic event (e.g. large-scale tree die-off) and the effects of extremes can be exacerbated by climatic trends (e.g. higher temperatures in combination with drought). Here, we highlight application of bioclimatic models for predicting individual demographic events. Defining the environmental conditions that precipitate demographic events such as widespread tree mortality is a necessary precursor for applying predictions to geographic space, and may require challenging biota with experiments that impose a combination of ecologically extreme conditions in one parameter and a shifting distribution in another (e.g. drought under higher temperatures). Currently data on conditions that drive individual demographic events associated with extremes are usually rare, aggregated across time, and/or correlative. We highlight this approach with a case study of drought-induced mortality in adult Pinus edulis trees that predicts a more than five-fold increase in frequency of die-off events under a global change scenario of high emissions. This general approach complements both traditional bioclimatic envelopes and more detailed physiological approaches currently being refined to address climate change challenges. Notably, this proposed approach could be developed for any climate condition or plant life stage, offering promise for improving predictions of individual demographic events that are rapidly altering ecosystems globally.

International Journal of Plant Sciences↗
USGS2014

Dendrochemical patterns of calcium, zinc, and potassium related to internal factors detected by energy dispersive X-ray fluorescence (EDXRF)

Energy dispersive X-ray fluorescence (EDXRF) provides highly sensitive and precise spatial resolution of cation content in individual annual growth rings in trees. The sensitivity and precision have prompted successful applications to forensic dendrochemistry and the timing of environmental releases of contaminants. These applications have highlighted the need to distinguish dendrochemical effects of internal processes from environmental contamination. Calcium, potassium, and zinc are three marker cations that illustrate the influence of these processes. We found changes in cation chemistry in tree rings potentially due to biomineralization, development of cracks or checks, heartwood/sapwood differentiation, intra-annual processes, and compartmentalization of infection. Distinguishing internal from external processes that affect dendrochemistry will enhance the value of EDXRF for both physiological and forensic investigations.

Chemosphere↗
USGS2016

Organic contamination in tree swallow ( Tachycineta bicolor ) nestlings at United States and binational great Lakes Areas of Concern

Contaminant exposure of tree swallows, Tachycineta bicolor , nesting in 27 Areas of Concern (AOCs) in the Great Lakes basin was assessed from 2010 to 2014 to assist managers and regulators in their assessments of Great Lakes AOCs. Contaminant concentrations in nestlings from AOCs were compared with those in nestlings from nearby non-AOC sites. Polychlorinated biphenyl (PCB) and polybrominated diphenyl ether concentrations in tree swallow nestling carcasses at 30% and 33% of AOCs, respectively, were below the mean concentration for non-AOCs. Polycyclic aromatic hydrocarbon (PAH) concentrations in nestling stomach contents and perfluorinated compound concentrations in nestling plasma at 67% and 64% of AOCs, respectively, were below the mean concentration for non-AOCs. Concentrations of PCBs in nestling carcasses were elevated at some AOCs but modest compared with highly PCB-contaminated sites where reproductive effects have been documented. Concentrations of PAHs in diet were sufficiently elevated at some AOCs to elicit a measurable physiological response. Among AOCs, concentrations of the perfluorinated compound perfluorooctane sulfonate in plasma were the highest on the River Raisin (MI, USA; geometric mean 330 ng/mL) but well below an estimated toxicity reference value (1700 ng/mL). Both PAH and PCB concentrations in nestling stomach contents and PCBs in carcasses were significantly correlated with concentrations in sediment previously reported, thereby reinforcing the utility of tree swallows to assess bioavailability of sediment contamination.

Environmental Toxicology and Chemistry↗
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↗
USGS2021

Ecological correlates of fecal corticosterone metabolites in female Greater Sage-Grouse (Centrococercus urophasianus)

Measurement of physiological responses can reveal effects of ecological conditions on an animal and correlate with demographic parameters. Ecological conditions for many animal species have deteriorated as a function of invasive plants and habitat fragmentation. Expansion of juniper (Juniperus spp.) trees and invasion of annual grasses into sagebrush (Artemisia spp.) ecosystems have contributed to habitat degradation for Greater Sage-Grouse (Centrococercus urophasianus (Bonaparte, 1827); hereafter, “Sage-Grouse”), a species of conservation concern throughout its range. We evaluated relationships between habitat use in a landscape modified by juniper expansion and annual grasses and corticosterone metabolite levels (stress responses) in feces (FCORTm) of female Sage-Grouse. We used remotely sensed data to estimate vegetation cover within hens’ home ranges and accounted for factors that influence FCORTm in other vertebrates, such as age and weather. We collected 36 fecal samples from 22 radio-collared hens during the brood-rearing season (24 May–26 July) in southwestern Idaho 2017–18. Concentrations of corticosterone increased with home range size but decreased with reproductive effort and temperature. The importance of home range size suggests that maintaining or improving habitats that promote smaller home ranges would likely facilitate a lower stress response by hens, which should benefit Sage-Grouse survival and reproduction.

Idaho↗
USGS2004

Nutrient controls on biocomplexity of mangrove ecosystems

Mangrove forests are important coastal ecosystems that provide a variety of ecological and societal services. These intertidal, tree-dominated communities along tropical coastlines are often described as “simple systems,” compared to other tropical forests with larger numbers of plant species and multiple understory strata; however, mangrove ecosystems have complex trophic structures, and organisms exhibit unique physiological, morphological, and behavioral adaptations to environmental conditions characteristic of the land-sea interface. Biogeochemical functioning of mangrove forests is also controlled by interactions among the microbial, plant, and animal communities and feedback linkages mediated by hydrology and other forcing functions. Scientists with the U.S. Geological Survey (USGS) at the National Wetlands Research Center are working to understand more fully the impact of nutrient variability on these delicate and important ecosystems.

Fact Sheet↗
USGS2019

Rapid broad-scale ecosystem changes and their consequences for biodiversity

Biodiversity contributes to and depends on ecosystem structure and associated function. Ecosystem structure, such as the amount and type of tree cover, influences fundamental abiotic variables such as near-ground incoming solar radiation (e.g., Royer et al. 2011), which in turn affects species and associated biodiversity (e.g., Trotter et al. 2008). In many systems, foundational, dominant, or keystone species (or species groups) are important in determining biodiversity, often because of their role in determining ecosystem structure. At spatial scales ranging from ecosystems to regions and larger, structural characteristics of vegetation or other structurally dominant organisms such as corals can influence species diversity, whether focused on alpha diversity (mean species diversity at the habitat level), beta diversity (differentiation among habitats), or gamma diversity (total species diversity across a landscape; Whittaker 1960). Climate change is projected to alter ecosystems at broad scales. In many cases, this will be due to extreme climate events such as droughts, floods and hurricanes, the effects of which can be rapid (IPCC 2012). Consequently, rapid broad-scale changes in ecosystems are of increasing concern. Climate change can directly affect species physiology, phenology, and distribution, as highlighted throughout this book (e.g. Citations to chapters in this volume to be added). Changes in one species can also affect other species (Cahill et al. 2013), particularly when dominant or co-dominant species that collectively provide habitat for other species are impacted (e.g. tree canopy architecture in many forest ecosystems; coral species via their reefs). Several rapid ecological changes have occurred at spatial scales that are sufficiently broad enough to represent biome changes (Gonzalez et al. 2010, Settele et al. 2014; Fig. 1 A). Rapid broad-scale changes differ from other patterns of vegetation dynamics in that they result in a “crash” in one or more populations (Breshears et al. 2008) over large areas of the affected region. Rapid broad-scale changes triggered by climate can include mega-fires; drought-triggered tree die-off and associated pest and pathogen outbreaks (Breshears et al. 2005, Safranyik et al. 2007); and hurricanes and wind-throw events (IPCC 2012, 2014). These rapid broad-scale changes can rapidly alter other factors such as resultant microclimate, which in turn can affect numerous other species and associated biodiversity (Royer et al. 2011; Fig. 1B). Many examples of broad-scale changes are documented in the paleoecology literature (Settele et al. 2014), although the temporal resolution at which those events can be resolved is relatively coarse (often centuries or longer). Such broad-scale changes documented in the paleoecology literature provide examples of types of change are likely to be of increasing concern in the future (Settele et al. 2014). Contemporary events have highlighted that broad-scale changes can occur rapidly (years or less; Breshears et al. 2005, Gonzalez et al. 2010, Settele et al. 2014). These rapid broad-scale changes will have important consequences for biodiversity beyond the direct impacts of climate change through the cascading effects associated with ecosystem structural and functional changes. The objective of this chapter is to alert readers to recent and projected rapid ecosystem changes and their potential consequences for biodiversity at ecosystem, landscape and regional scales.

Book chapter↗
USGS2007

Geographical and climatic limits of needle types of one- and two-needled pinyon pines

Aim: The geographical extent and climatic tolerances of one- and two-needled pinyon pines (Pinus subsect. Cembroides) are the focus of questions in taxonomy, palaeoclimatology and modelling of future distributions. The identification of these pines, traditionally classified by one- versus two-needled fascicles, is complicated by populations with both one- and two-needled fascicles on the same tree, and the description of two more recently described one-needled varieties: the fallax-type and californiarum-type. Because previous studies have suggested correlations between needle anatomy and climate, including anatomical plasticity reflecting annual precipitation, we approached this study at the level of the anatomy of individual pine needles rather than species. Location: Western North America. Methods: We synthesized available and new data from field and herbarium collections of needles to compile maps of their current distributions across western North America. Annual frequencies of needle types were compared with local precipitation histories for some stands. Historical North American climates were modelled on a c. 1-km grid using monthly temperature and precipitation values. A geospatial model (ClimLim), which analyses the effect of climate-modulated physiological and ecosystem processes, was used to rank the importance of seasonal climate variables in limiting the distributions of anatomical needle types. Results: The pinyon needles were classified into four distinct types based upon the number of needles per fascicle, needle thickness and the number of stomatal rows and resin canals. The individual needles fit well into four categories of needle types, whereas some trees exhibit a mixture of two needle types. Trees from central Arizona containing a mixture of Pinus edulis and fallax-type needles increased their percentage of fallax-type needles following dry years. All four needle types occupy broader geographical regions with distinctive precipitation regimes. Pinus monophylla and californiarum-type needles occur in regions with high winter precipitation. Pinus edulis and fallax-type needles are found in regions with high monsoon precipitation. Areas supporting californiarum-type and fallax-type needle distributions are additionally characterized by a more extreme May-June drought. Main conclusions: These pinyon needle types seem to reflect the amount and seasonality of precipitation. The single needle fascicle characterizing the fallax type may be an adaptation to early summer or periodic drought, while the single needle of Pinus monophylla may be an adaptation to summer-autumn drought. Although the needles fit into four distinct categories, the parent trees are sometimes less easily classified, especially near their ancestral Pleistocene ranges in the Mojave and northern Sonoran deserts. The abundance of trees with both one- and two-needled fascicles in the zones between P. monophylla, P. edulis and fallax-type populations suggest that needle fascicle number is an unreliable characteristic for species classification. Disregarding needle fascicle number, the fallax-type needles are nearly identical to P. edulis, supporting Little's (1968) initial classification of these trees as P. edulis var. fallax, while the californiarum-type needles have a distinctive morphology supporting Bailey's (1987) classification of this tree as Pinus californiarum.

Journal of Biogeography↗
USGS2024

Phylogenomics, male internal genitalia, a new species, and other notes on New World Stenopelmatus Jerusalem crickets (Orthoptera: Stenopelmatoidea: Stenopelmatini)

Based on past and expanded DNA sampling, the orthopteran families Stenopelmatidae and Anostostomatidae, as currently structured, are shown to be non-monophyletic. The splay-footed cricket genus Comicus is confirmed to be genetically distinct from all Stenopelmatidae. We add two specimens to our previously published phylogenetic tree for New World Stenopelmatus Jerusalem cricket species and report the first multilocus DNA recovery for S. ater from Costa Rica. Male internal genitalia may be of systematic value in Jerusalem crickets, but we believe they should be analyzed when in their unfolded, “physiologically functional” configuration, where morphological characters can be seen in more detail when compared to their preserved, folded state. We describe Stenopelmatus nuevoguatemalae n. sp. from Guatemala.

Zootaxa↗
USGS2016

A synthesis of radial growth patterns preceding tree mortality

Tree mortality is a key factor influencing forest functions and dynamics, but our understanding of the mechanisms leading to mortality and the associated changes in tree growth rates are still limited. We compiled a new pan-continental tree-ring width database from sites where both dead and living trees were sampled (2970 dead and 4224 living trees from 190 sites, including 36 species), and compared early and recent growth rates between trees that died and those that survived a given mortality event. We observed a decrease in radial growth before death in ca. 84% of the mortality events. The extent and duration of these reductions were highly variable (1–100 years in 96% of events) due to the complex interactions among study species and the source(s) of mortality. Strong and long-lasting declines were found for gymnosperms, shade- and drought-tolerant species, and trees that died from competition. Angiosperms and trees that died due to biotic attacks (especially bark-beetles) typically showed relatively small and short-term growth reductions. Our analysis did not highlight any universal trade-off between early growth and tree longevity within a species, although this result may also reflect high variability in sampling design among sites. The intersite and interspecific variability in growth patterns before mortality provides valuable information on the nature of the mortality process, which is consistent with our understanding of the physiological mechanisms leading to mortality. Abrupt changes in growth immediately before death can be associated with generalized hydraulic failure and/or bark-beetle attack, while long-term decrease in growth may be associated with a gradual decline in hydraulic performance coupled with depletion in carbon reserves. Our results imply that growth-based mortality algorithms may be a powerful tool for predicting gymnosperm mortality induced by chronic stress, but not necessarily so for angiosperms and in case of intense drought or bark-beetle outbreaks.

Global Change Biology↗
USGS2003

Physiological and morphological response patterns of Populus deltoides to alluvial groundwater

We examined the physiological and morphological response patterns of plains cottonwood [ Populus deltoides subsp. monilifera (Aiton) Eck.] to acute water stress imposed by groundwater pumping. Between 3 and 27 July 1996, four large pumps were used to withdraw alluvial groundwater from a cottonwood forest along the South Platte River, near Denver, Colorado, USA. The study was designed as a stand-level, split-plot experiment with factorial treatments including two soil types (a gravel soil and a loam topsoil over gravel), two water table drawdown depths (∼0.5 m and >1.0 m), and one water table control (no drawdown) per soil type. Measurements of water table depth, soil water potential (Ψ s ), predawn and midday shoot water potential (Ψ pd and Ψ md ), and D/H (deuterium/hydrogen) ratios of different water sources were made in each of six 600-m 2 plots prior to, during, and immediately following pumping. Two additional plots were established and measured to examine the extent to which surface irrigation could be used to mitigate the effects of deep drawdown on P. deltoides for each soil type. Recovery of tree water status following pumping was evaluated by measuring stomatal conductance ( g s ) and xylem water potential (Ψ xp ) on approximately hourly time steps from before dawn to mid-afternoon on 11 August 1996 in watered and unwatered, deep-drawdown plots on gravel soils. P. deltoides responded to abrupt alluvial water table decline with decreased shoot water potential followed by leaf mortality. Ψ pd and percent leaf loss were significantly related to the magnitude of water table declines. The onset and course of these responses were influenced by short-term variability in surface and ground water levels, acting in concert with physiological and morphological adjustments. Decreases in Ψ pd corresponded with increases in Ψ md , suggesting shoot water status improved in response to stomatal closure and crown dieback. Crown dieback caused by xylem cavitation likely occurred when Ψ pd reached −0.4 to −0.8 MPa. The application of surface irrigation allowed trees to maintain favorable water status with little or no apparent cavitation, even in deep-drawdown plots. Two weeks after the partial canopy dieback and cessation of pumping, g s and Ψ xp measurements indicated that water stress persisted in unwatered P. deltoides in deep-drawdown plots.

Environmental Management↗
USGS2018

Refining aging criteria for northern sea otters in Washington State

Measurement of skull ossification patterns is a standard method for aging various mammalian species and has been used to age sea otters Enhydra lutris from Russia, California, and Alaska. Cementum annuli counts have also been verified as an accurate aging method for sea otters in Alaska. In this study, we compared cementum annuli count results and skull ossification patterns as methods for aging the northern sea otter, E. l. kenyoni, in Washington State. We found significant agreement between the two methods, suggesting that either method could be used to age sea otters in Washington. We found that ossification of the squamosal–jugal suture at the ventral glenoid fossa can be used to differentiate male subadults from adults. To assist field biologists or others without access to cementum annuli or skull ossification analysis techniques, we analyzed a suite of morphologic, physiologic, and developmental characteristics to assess whether a set of these more easily accessible parameters could also predict age class. We identified tooth condition score, evidence of reproductive activity in females, and tooth eruption pattern as the most useful criteria for classifying sea otters in Washington. We created a simple decision tree based on characteristics accessible in the field or at necropsy, which can be used to reliably predict age class of Washington sea otters as determined by cementum annuli. These techniques offer field biologists and marine mammal stranding networks a replicable, cost-conscious methodology to gather useful biological information from sea otters.

Washington↗
USGS2012

Warming and the dependence of limber pine ( Pinus flexilis ) establishment on summer soil moisture within and above its current elevation range

Continued changes in climate are projected to alter the geographic distributions of plant species, in part by affecting where individuals can establish from seed. We tested the hypothesis that warming promotes uphill redistribution of subalpine tree populations by reducing cold limitation at high elevation and enhancing drought stress at low elevation. We seeded limber pine (Pinus flexilis) into plots with combinations of infrared heating and water addition treatments, at sites positioned in lower subalpine forest, the treeline ecotone, and alpine tundra. In 2010, first-year seedlings were assessed for physiological performance and survival over the snow-free growing season. Seedlings emerged in midsummer, about 5–8 weeks after snowmelt. Low temperature was not observed to limit seedling photosynthesis or respiration between emergence and October, and thus experimental warming did not appear to reduce cold limitation at high elevation. Instead, gas exchange and water potential from all sites indicated a prevailing effect of summer moisture stress on photosynthesis and carbon balance. Infrared heaters raised soil growing degree days (base 5 °C, p < 0.001) and August–September mean soil temperature ( p < 0.001). Despite marked differences in vegetation cover and meteorological conditions across sites, volumetric soil moisture content (θ) at 5–10 cm below 0.16 and 0.08 m 3 m -3 consistently corresponded with moderate and severe indications of drought stress in midday stem water potential, stomatal conductance, photosynthesis, and respiration. Seedling survival was greater in watered plots than in heated plots ( p = 0.01), and negatively related to soil growing degree days and duration of exposure to θ < 0.08 m 3 m -3 in a stepwise linear regression model ( p < 0.0001). We concluded that seasonal moisture stress and high soil surface temperature imposed a strong limitation to limber pine seedling establishment across a broad elevation gradient, including at treeline, and that these limitations are likely to be enhanced by further climate warming.

Colorado↗
USGS2021

Sap flow evidence of chilling injury and recovery in mangroves following a spring cold spell

Mangroves are periodically influenced in negative ways by non-freezing temperatures across their global sub-tropical range. However, physiological and morphological evidence of chilling influences to non-freezing chilling events has not been measured in field settings. In this study, we measured sap flow ( J s ) during such a chilling (but non-freezing) event in southern China and documented the reductions in J s and the recovery that ensued. We calculated tree water use (TWU) from J s measurements taken from thermal dissipation sap flow sensors on two mangrove species ( Sonneratia apetala and S. caseolaris ). This chilling event significantly injured the mangrove trees in the form of leaf scorch and massive defoliation. Diurnal variations of stem J s of both species were altered significantly after chilling. On the day of the chilling event, J s of S. caseolaris was reduced from the daily maximum of 44.1 g H 2 O m −2 s −1 to 0 immediately after chilling, which lasted throughout the remainder of the day. In contrast, S. apetala showed a certain low-temperature tolerance, while still maintaining an adequate transpiration rate after chilling, indicative of a more resilient hydraulic transport system to low temperatures. The sap flow data collected revealed substantial evidence for acute water conservation during low-temperature events, perhaps ameliorating low-temperature damage. Hence, the responses of some mangrove species with high sensitivity to low, but non-freezing, temperature (such as S. caseolaris ) may indicate that mangroves possess adaptive whole-tree strategies to cold temperature.

Trees: Structure and Function↗