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USGS2020

Local to landscape-level controls of water fluxes through Hawaiian forests: Effects of invasive animals and plants on soil infiltration capacity across substrate and moisture gradients

Given the potential effect of invasive plants and animals to water fluxes through forests, the invasive-driven degradation of native ecosystems is a topic of great concern for many downstream land and water managers. The infiltration rate determines the partitioning between runoff and infiltration into soil in Hawaiian forests and beyond. Thus, to explore the ecohydrological effects of plant and animal invasion in mesic and wet forests in Hawaii, we measured soil infiltration capacity in multiple fenced (i.e., ungulate-free)/unfenced and native/invaded forest sites along moisture and substrate age gradients across the islands of Hawai‘i and Kaua‘i. We also characterized forest composition and structure and soil characteristics at these sites to assess the direct and vegetation-mediated impacts of invasive species on infiltration capacity. Infiltration capacity is highly variable across forested sites and the wider landscape. Much of this variability is determined by a complex set of soil, vegetation, and disturbance factors that affect infiltration capacity at the immediate surrounding of measurement plots. Consequently, the effect of any given factor can be masked by variability in other factors. However, by controlling for variability in soil and vegetation conditions at a local plot level, we found that the presence of invasive species in forests has complex and sometimes non-intuitive effects on infiltration. Our final models showed that invasive ungulates negatively affect soil infiltration capacity consistently across the wide moisture and substrate age gradients considered. Additionally, because several soil characteristics known to be affected by ungulates were associated with local infiltration rates (e.g., soil organic matter, bare soil cover, soil depth), the long-term secondary effects of high ungulate densities in Hawaiian forests may be higher than effects observed in this study. These results provide clear evidence for land managers that ungulate control efforts likely improve ecohydrologic function to mesic and wet forest systems critical to protecting downstream and nearshore resources and maintaining groundwater recharge. Compared to ungulate effects, the effect of invasive plants on water infiltration capacity in Hawaiian forests appeared much more complex. In general, elements of forest structure including increased canopy, understory and floor cover, greater presence of large roots, and lower grass and bare soil covers were positively associated with water infiltration. Whether native or not, a plant species’ potential to alter infiltration rates in Hawaiian forests was likely to depend on its physiognomy and how it affects forest community structure. For instance, while the cover of native dominant tree ‘ōhi‘a, Metrosideros polymorpha, was found to be positively associated with infiltration capacity (perhaps as an indicator of overall forest integrity), invasive Himalayan ginger, Hedychium gardnerianum, was also positively correlated with infiltration capacity, possibly due to preferential flow channels created by the presence of large root mats. Few studies have conducted comprehensive integrated ecological and hydrological sampling in forests of high conservation value. While we show there are large benefits to understanding how conservation efforts may help shape water fluxes, we also found that the commonly used study design for infiltration studies used here and elsewhere (i.e., adjacent paired sites) could be modified to provide more accurate effects of invasion in future studies for ecosystems in Hawaii and beyond.

Hawaii↗

USGS2012

The effect of increasing salinity and forest mortality on soil nitrogen and phosphorus mineralization in tidal freshwater forested wetlands

Tidal freshwater wetlands are sensitive to sea level rise and increased salinity, although little information is known about the impact of salinification on nutrient biogeochemistry in tidal freshwater forested wetlands. We quantified soil nitrogen (N) and phosphorus (P) mineralization using seasonal in situ incubations of modified resin cores along spatial gradients of chronic salinification (from continuously freshwater tidal forest to salt impacted tidal forest to oligohaline marsh) and in hummocks and hollows of the continuously freshwater tidal forest along the blackwater Waccamaw River and alluvial Savannah River. Salinification increased rates of net N and P mineralization fluxes and turnover in tidal freshwater forested wetland soils, most likely through tree stress and senescence (for N) and conversion to oligohaline marsh (for P). Stimulation of N and P mineralization by chronic salinification was apparently unrelated to inputs of sulfate (for N and P) or direct effects of increased soil conductivity (for N). In addition, the tidal wetland soils of the alluvial river mineralized more P relative to N than the blackwater river. Finally, hummocks had much greater nitrification fluxes than hollows at the continuously freshwater tidal forested wetland sites. These findings add to knowledge of the responses of tidal freshwater ecosystems to sea level rise and salinification that is necessary to predict the consequences of state changes in coastal ecosystem structure and function due to global change, including potential impacts on estuarine eutrophication.

Biogeochemistry↗

USGS2010

Resilience of Alaska’s boreal forest to climatic change

This paper assesses the resilience of Alaska’s boreal forest system to rapid climatic change. Recent warming is associated with reduced growth of dominant tree species, plant disease and insect outbreaks, warming and thawing of permafrost, drying of lakes, increased wildfire extent, increased postfire recruitment of deciduous trees, and reduced safety of hunters traveling on river ice. These changes have modified key structural features, feedbacks, and interactions in the boreal forest, including reduced effects of upland permafrost on regional hydrology, expansion of boreal forest into tundra, and amplification of climate warming because of reduced albedo (shorter winter season) and carbon release from wildfires. Other temperature-sensitive processes for which no trends have been detected include composition of plant and microbial communities, long-term landscape-scale change in carbon stocks, stream discharge, mammalian population dynamics, and river access and subsistence opportunities for rural indigenous communities. Projections of continued warming suggest that Alaska’s boreal forest will undergo significant functional and structural changes within the next few decades that are unprecedented in the last 6000 years. The impact of these social–ecological changes will depend in part on the extent of landscape reorganization between uplands and lowlands and on policies regulating subsistence opportunities for rural communities.

Alaska↗

USGS2021

Plant community succession following ungulate exclusion in a temperate rainforest

Ecosystem structure and processes of coastal temperate rainforests of the Pacific Northwest are thought to be strongly influenced by herbivory primarily of Roosevelt elk ( Cervus elaphus roosevelti ) and secondarily of Columbian black-tailed deer ( Odocoileus hemionus columbianus ). Two large (0.5-ha) exclosures were built in old-growth coniferous rainforest communities in Olympic National Park, Washington, during 1979 to study these effects. Cover of shrubs, ferns, herbs, and graminoids and numbers of tree seedlings were described over 36 yr. Results show a sequence following ungulate exclusion of early release of shrubs, ferns, and herbs followed by eventual dominance of shrubs as other vegetation layers become shaded. Short-term responses of individual species reflected functional traits related to ability to avoid or tolerate herbivory. Over the longer term, effects reflected changing competitive relationships among vegetation layers and other ecosystem dynamics such as the provision of fallen trees in the appropriate decay class to serve as establishment substrate for tree seedlings. In aggregate, vegetation composition shifted after 36 yr from a system dominated by herbaceous cover with a major graminoid component to one dominated by shrubs (5- to 6-fold absolute increase) and ferns (5–7% increase in absolute cover), less absolute herb cover (15–20% loss), and almost no graminoids (<1.5% cover remaining in any plot) after 36 yr. These changes represented a substantial loss in plant community diversity with a loss of 46 of 74 species. Elk abundance outside of the exclosures began to decline in the 1990s leading to parallel changes in plant community trajectories outside of exclosures to those initially seen inside. While this suggests plant community responses inside the exclosures were also driven by elk exclusion, the strength of this response depends on elk abundance.

Washington↗

USGS2015

Linking carbon and water limitations to drought-induced mortality of Pinus flexilis seedlings

Survival of tree seedlings at high elevations has been shown to be limited by thermal constraints on carbon balance, but it is unknown if carbon relations also limit seedling survival at lower elevations, where water relations may be more important. We measured and modeled carbon fluxes and water relations in first-year Pinus flexilis seedlings in garden plots just beyond the warm edge of their natural range, and compared these with dry-mass gain and survival across two summers. We hypothesized that mortality in these seedlings would be associated with declines in water relations, more so than with carbon-balance limitations. Rather than gradual declines in survivorship across growing seasons, we observed sharp, large-scale mortality episodes that occurred once volumetric soil-moisture content dropped below 10%. By this point, seedling water potentials had decreased below −5 MPa, seedling hydraulic conductivity had decreased by 90% and seedling hydraulic resistance had increased by >900%. Additionally, non-structural carbohydrates accumulated in aboveground tissues at the end of both summers, suggesting impairments in phloem-transport from needles to roots. This resulted in low carbohydrate concentrations in roots, which likely impaired root growth and water uptake at the time of critically low soil moisture. While photosynthesis and respiration on a leaf area basis remained high until critical hydraulic thresholds were exceeded, modeled seedling gross primary productivity declined steadily throughout the summers. At the time of mortality, modeled productivity was insufficient to support seedling biomass-gain rates, metabolism and secondary costs. Thus the large-scale mortality events that we observed near the end of each summer were most directly linked with acute, episodic declines in plant hydraulic function that were linked with important changes in whole-seedling carbon relations.

Tree Physiology↗

USGS2015

Darcy’s law predicts widespread forest mortality under climate warming

Drought and heat-induced tree mortality is accelerating in many forest biomes as a consequence of a warming climate, resulting in a threat to global forests unlike any in recorded history . Forests store the majority of terrestrial carbon, thus their loss may have significant and sustained impacts on the global carbon cycle . We use a hydraulic corollary to Darcy ’ s law, a core principle of vascular plant physiology , to predict characteristics of plants that will survive and die during drought under warmer future climates. Plants that are tall with isohydric stomatal regulation, low hydraulic conductance, and high leaf area are most likely to die from future drought stress. Thus, tall trees of old-growth forests are at the greatest risk of loss, which has ominous implications for terrestrial carbon storage. This application of Darcy ’ s law indicates today ’ s forests generally should be replaced by shorter and more xeric plants, owing to future warmer droughts and associated wildfires and pest attacks. The Darcy ’ s corollary also provides a simple, robust framework for informing forest management interventions needed to promote the survival of current forests. Given the robustness of Darcy ’ s law for predictions of vascular plant function, we conclude with high certainty that today ’ s forests are going to be subject to continued increases in mortality rates that will result in substantial reorganization of their structure and carbon storage.

Nature Climate Change↗

USGS2019

Assessment of the impacts of image signal-to-noise ratios in impervious surface mapping

Medium spatial resolution satellite images are frequently used to characterize thematic land cover and a continuous field at both regional and global scales. However, high spatial resolution remote sensing data can provide details in landscape structures, especially in the urban environment. With upgrades to spatial resolution and spectral coverage for many satellite sensors, the impact of the signal-to-noise ratio (SNR) in characterizing a landscape with highly heterogeneous features at the sub-pixel level is still uncertain. This study used WorldView-3 (WV3) images as a basis to evaluate the impacts of SNR on mapping a fractional developed impervious surface area (ISA). The point spread function (PSF) from the Landsat 8 Operational Land Imager (OLI) was used to resample the WV3 images to three different resolutions: 10 m, 20 m, and 30 m. Noise was then added to the resampled WV3 images to simulate different fractional levels of OLI SNRs. Furthermore, regression tree algorithms were incorporated into these images to estimate the ISA at different spatial scales. The study results showed that the total areal estimate could be improved by about 1% and 0.4% at 10-m spatial resolutions in our two study areas when the SNR changes from half to twice that of the Landsat OLI SNR level. Such improvement is more obvious in the high imperviousness ranges. The root-mean-square-error of ISA estimates using images that have twice and two-thirds the SNRs of OLI varied consistently from high to low when spatial resolutions changed from 10 m to 20 m. The increase of SNR, however, did not improve the overall performance of ISA estimates at 30 m.

Remote Sensing↗

USGS2024

Despite regional variation, Gymnorhinus cyanocephalus (Pinyon Jay) densities generally increase with local pinyon–juniper cover and heterogeneous ground cover

Traditionally, local-scale habitat-relationship models are developed over small spatial extents, limiting model transferability and inference outside the study area. Thus, habitat managers frequently lack fine-scale information regarding the influence of vegetation composition and structure on site suitability or species abundance. Gymnorhinus cyanocephalus (Pinyon Jay) represents one declining species for which managers have limited information regarding the influence that vegetation composition and structure have on abundance at broad scales. To address this need, we developed a hierarchical Bayesian abundance model using summertime bird and vegetation data collected under the Integrated Monitoring in Bird Conservation Regions program to explain jay abundance as a function of local conditions. Our G. cyanocephalus abundance model allowed abundance relationships with pinyon pine ( Pinus edulis and P. monophylla ) and juniper ( Juniperus spp.) to vary by ecoregion, thereby accounting for potential regional differences in habitat associations. We found G. cyanocephalus abundance was generally positively associated with pinyon pine and juniper cover; however, habitat relationships varied by ecoregion. Additionally, we found positive associations between jay abundance and grass cover, sagebrush cover, and percent bare ground. Our results agree with prior research suggesting mechanical removal of pinyon pine and juniper trees for sagebrush restoration or fuel treatments may negatively affect G. cyanocephalus . Managers wishing to reduce pinyon and juniper tree cover without negatively affecting G. cyanocephalus may benefit from targeting sites where both large-scale distribution models and our local habitat relationships suggest G. cyanocephalus are likely to occur in low numbers. Additionally, our modeled relationships indicate restoration that increases grass cover, sagebrush cover, and bare ground, while maintaining pinyon and (or) juniper cover, may lead to increased local densities of G. cyanocephalus .

Ornithological Applications↗

USGS2015

Evaluating connection of aquifers to springs and streams, Great Basin National Park and vicinity, Nevada

Federal agencies that oversee land management for much of the Snake Range in eastern Nevada, including the management of Great Basin National Park by the National Park Service, need to understand the potential extent of adverse effects to federally managed lands from nearby groundwater development. As a result, this study was developed (1) to attain a better understanding of aquifers controlling groundwater flow on the eastern side of the southern part of the Snake Range and their connection with aquifers in the valleys, (2) to evaluate the relation between surface water and groundwater along the piedmont slopes, (3) to evaluate sources for Big Springs and Rowland Spring, and (4) to assess groundwater flow from southern Spring Valley into northern Hamlin Valley. The study focused on two areas—the first, a northern area along the east side of Great Basin National Park that included Baker, Lehman, and Snake Creeks, and a second southern area that is the potential source area for Big Springs. Data collected specifically for this study included the following: (1) geologic field mapping; (2) drilling, testing, and water quality sampling from 7 test wells; (3) measuring discharge and water chemistry of selected creeks and springs; (4) measuring streambed hydraulic gradients and seepage rates from 18 shallow piezometers installed into the creeks; and (5) monitoring stream temperature along selected reaches to identify places of groundwater inflow. The Snake Range was formed by a generally normal-faulted uplift, where late Proterozoic and Cambrian siliciclastic rocks and metamorphic rocks are present at the highest altitudes and younger Paleozoic carbonate rocks are exposed along the flanks. The consolidated rocks are intruded by Jurassic to Tertiary age plutons, which are most common between the Lehman and Snake Creek drainage basins. Older Cenozoic rocks, including Oligocene volcanic rocks and Miocene sedimentary rocks, crop out locally and fill the basins that underlie Snake, Spring, and Hamlin Valleys. Younger Tertiary and Quaternary sedimentary (basin-fill) deposits overlie the older Cenozoic rocks. The rocks and deposits can be divided into three distinct aquifers. These aquifers include (1) basin-fill aquifers that consist of the permeable parts of the Cenozoic basin fill and some fractured or jointed Cenozoic volcanic rocks, (2) an upper carbonate-rock aquifer that consists of upper Paleozoic carbonate rocks overlying a regionally extensive middle Paleozoic siliciclastic confining unit, and (3) a lower carbonate-rock aquifer that consists of lower Paleozoic carbonate rocks. Secondary openings created by faults, shear zones, fractures, and, in the carbonate rocks, karst solution features, largely determine the water-transmitting properties of the volcanic- and carbonate-rock aquifers. The basin-fill aquifers are composed of a wide variety of rock types and have highly variable hydraulic properties. The three aquifers are stratigraphically and structurally heterogeneous, causing large variations in the ability to store and transmit water. The aquifers are separated by confining units in some areas and are in contact with each other in other areas, yet function as a single, composite aquifer system. Basin-fill aquifers most often overlie or adjoin the lower and upper carbonate-rock aquifers. Baker, Lehman and Snake Creek drainage basins were divided into five hydrologic zones on the basis of climate, geology, and topography. The five zones, from highest to lowest altitudes, are the mountain-upland, karst-limestone, upper-piedmont, lower-piedmont, and valley-lowland zones. The primary hydrologic connection between the mountain-upland and the valley-lowland zones is streamflow. Much of the streamflow from the mountain-upland zone is generated above tree line. Groundwater flow increases in the karst-limestone zone because of increased permeability caused by dissolution, which results in increased streamflow losses. Most of the increased groundwater flow is to springs near faults that form the boundary with the upper-piedmont zone. Thus, groundwater flow from the karst-limestone zone to the upper-piedmont zone was only 10 percent of the combined flow of streams and springs that exit the karst-limestone zone. About 60 percent of the water flowing from Rowland Spring in the Lehman Creek drainage basin was from streamflow losses along Baker Creek. The remaining flow from Rowland Spring comes from local recharge in the karst-limestone zone. In the upper-piedmont zone, the water table by Baker, Lehman and Snake Creeks was near the water level in the creeks for several hundred feet downstream from the karst-limestone zone. Water levels in piezometers along Snake Creek downstream from its confluence with Spring Creek were far below the streambed, indicating gravity drainage beneath this section of the creek. Estimated vertical hydraulic conductivity along a 3-mile reach of Snake Creek downstream of this confluence was 0.5 foot per day, which was an order of magnitude less than that estimated for Baker and Lehman Creeks. The low vertical hydraulic conductivity in the streambed along the lower reaches of Snake Creek results from chemical precipitation of calcite caused by off-gassing of carbon dioxide derived from springs at the end of the karst-limestone zone. The younger alluvial deposits thicken rapidly across faults that form the upper boundary of the lower-piedmont zone. The absence of springs or groundwater flow to the creeks upstream of these faults indicates they are not a complete barrier to groundwater flow. The water table was shallow in the valley-lowland zone in the Baker and Lehman Creek drainage basins, whereas the water table was more than 50 feet below land surface in the Snake Creek drainage basin. In contrast to thick basin fill in the valley-lowland zone in the Baker and Lehman Creek drainage basins, fractured and karst limestone underlie basin fill at relatively shallow depths in Snake Creek drainage basin. The underlying limestone acts as a drain for groundwater in the basin fill beneath Snake Creek. A groundwater divide in southern Spring Valley south of Baking Powder Flat separates groundwater flow to the flat from southeastward flow into northern Hamlin Valley. Groundwater flow from southern Spring Valley south of the groundwater divide into northern Hamlin Valley was estimated to range from 6,000 to 11,000 acre-feet per year. This groundwater does not flow to Big Springs in southern Snake Valley; rather, the source of water to Big Springs is groundwater recharge in the Big Spring Wash drainage basin and in nearby smaller drainage basins at the south end of the Snake Range. Groundwater flow from southern Spring Valley continues through the western side of Hamlin Valley before being directed northeast toward the south end of Snake Valley. This flow is constrained by southward-flowing groundwater from Big Spring Wash and northward-flowing groundwater beneath central Hamlin Valley. The redirection to the northeast corresponds to a narrowing of the width of flow in southern Snake Valley caused by a constriction formed by a steeply dipping middle Paleozoic siliciclastic confining unit exposed in the flanks of the mountains and hills on the east side of southern Snake Valley and shallowly buried beneath basin fill in the valley. The narrowing of groundwater flow could be responsible for the large area where groundwater flows to springs or is lost to evapotranspiration between Big Springs in Nevada and Pruess Lake in Utah.

Nevada↗

USGS2004

Using lidar and effective LAI data to evaluate IKONOS and Landsat 7 ETM+ vegetation cover estimates in a ponderosa pine forest

Structural and functional analyses of ecosystems benefit when high accuracy vegetation coverages can be derived over large areas. In this study, we utilize IKONOS, Landsat 7 ETM+, and airborne scanning light detection and ranging (lidar) to quantify coniferous forest and understory grass coverages in a ponderosa pine ( Pinus ponderosa ) dominated ecosystem in the Black Hills of South Dakota. Linear spectral mixture analyses of IKONOS and ETM+ data were used to isolate spectral endmembers (bare soil, understory grass, and tree/shade) and calculate their subpixel fractional coverages. We then compared these endmember cover estimates to similar cover estimates derived from lidar data and field measures. The IKONOS-derived tree/shade fraction was significantly correlated with the field-measured canopy effective leaf area index (LAI e ) ( r 2 =0.55, p <0.001) and with the lidar-derived estimate of tree occurrence ( r 2 =0.79, p <0.001). The enhanced vegetation index (EVI) calculated from IKONOS imagery showed a negative correlation with the field measured tree canopy effective LAI and lidar tree cover response ( r 2 =0.30, r =−0.55 and r 2 =0.41, r =−0.64, respectively; p <0.001) and further analyses indicate a strong linear relationship between EVI and the IKONOS-derived grass fraction ( r 2 =0.99, p <0.001). We also found that using EVI resulted in better agreement with the subpixel vegetation fractions in this ecosystem than using normalized difference of vegetation index (NDVI). Coarsening the IKONOS data to 30 m resolution imagery revealed a stronger relationship with lidar tree measures ( r 2 =0.77, p <0.001) than at 4 m resolution ( r 2 =0.58, p <0.001). Unmixed tree/shade fractions derived from 30 m resolution ETM+ imagery also showed a significant correlation with the lidar data ( r 2 =0.66, p <0.001). These results demonstrate the power of using high resolution lidar data to validate spectral unmixing results of satellite imagery, and indicate that IKONOS data and Landsat 7 ETM+ data both can serve to make the important distinction between tree/shade coverage and exposed understory grass coverage during peak summertime greenness in a ponderosa pine forest ecosystem.

Remote Sensing of Environment↗

USGS2018

Quantifying functional connectivity: The role of breeding habitat, abundance, and landscape features on range‐wide gene flow in sage‐grouse

Functional connectivity, quantified using landscape genetics, can inform conservation through the identification of factors linking genetic structure to landscape mechanisms. We used breeding habitat metrics, landscape attributes, and indices of grouse abundance, to compare fit between structural connectivity and genetic differentiation within five long‐established Sage‐Grouse Management Zones (MZ) I‐V using microsatellite genotypes from 6,844 greater sage‐grouse ( Centrocercus urophasianus ) collected across their 10.7 million‐km 2 range. We estimated structural connectivity using a circuit theory‐based approach where we built resistance surfaces using thresholds dividing the landscape into “habitat” and “nonhabitat” and nodes were clusters of sage‐grouse leks (where feather samples were collected using noninvasive techniques). As hypothesized, MZ‐specific habitat metrics were the best predictors of differentiation. To our surprise, inclusion of grouse abundance‐corrected indices did not greatly improve model fit in most MZs. Functional connectivity of breeding habitat was reduced when probability of lek occurrence dropped below 0.25 (MZs I, IV) and 0.5 (II), thresholds lower than those previously identified as required for the formation of breeding leks, which suggests that individuals are willing to travel through undesirable habitat. The individual MZ landscape results suggested terrain roughness and steepness shaped functional connectivity across all MZs. Across respective MZs, sagebrush availability (<10%–30%; II, IV, V), tree canopy cover (>10%; I, II, IV), and cultivation (>25%; I, II, IV, V) each reduced movement beyond their respective thresholds. Model validations confirmed variation in predictive ability across MZs with top resistance surfaces better predicting gene flow than geographic distance alone, especially in cases of low and high differentiation among lek groups. The resultant resistance maps we produced spatially depict the strength and redundancy of range‐wide gene flow and can help direct conservation actions to maintain and restore functional connectivity for sage‐grouse.

Evolutionary Applications↗

USGS2011

Forecasting climate change impacts to plant community composition in the Sonoran Desert region

Hotter and drier conditions projected for the southwestern United States can have a large impact on the abundance and composition of long-lived desert plant species. We used long-term vegetation monitoring results from 39 large plots across four protected sites in the Sonoran Desert region to determine how plant species have responded to past climate variability. This cross-site analysis identified the plant species and functional types susceptible to climate change, the magnitude of their responses, and potential climate thresholds. In the relatively mesic mesquite savanna communities, perennial grasses declined with a decrease in annual precipitation, cacti increased, and there was a reversal of the Prosopis velutina expansion experienced in the 20th century in response to increasing mean annual temperature (MAT). In the more xeric Arizona Upland communities, the dominant leguminous tree, Cercidium microphyllum, declined on hillslopes, and the shrub Fouquieria splendens decreased, especially on south- and west-facing slopes in response to increasing MAT. In the most xeric shrublands, the codominant species Larrea tridentata and its hemiparasite Krameria grayi decreased with a decrease in cool season precipitation and increased aridity, respectively. This regional-scale assessment of plant species response to recent climate variability is critical for forecasting future shifts in plant community composition, structure, and productivity.

Sonoran Desert↗

USGS2026

Population densities and trends of landbirds in the National Park of American Samoa

The National Park of American Samoa (NPSA), which protects some of the most intact tropical rainforest in the South Pacific, is exposed to recurring, intense tropical cyclones, including Tropical Cyclone Gita in 2018. In combination with other anthropogenic pressures, cyclones represent a potential source of disturbance to landbird populations, particularly native frugivorous and seed-dispersing species. Long-term monitoring provides a means to evaluate population trajectories following disturbance events and to identify potential management gaps. Landbird surveys were conducted in the Tutuila and Taʻū units of NPSA in 2011, 2018, and 2023 using point-transect distance sampling, with vegetation composition and structure quantified at each sampling station. Species-specific detection functions were fitted to count data to estimate densities by unit, with variance estimated using bootstrap procedures. Comparisons of 2018 and 2023 density estimates using two-sample z-tests indicated that changes in most landbird populations were inconclusive. Since 2018, increases in density were observed for the Pacific Imperial Pigeon ( Ducula pacifica ) and Crimson-crowned Fruit Dove ( Ptilinopus porphyraceus ) on Tutuila, while decreases were observed for the Pacific Kingfisher ( Todiramphus sacer ) on Tutuila, and for the Polynesian Wattled Honeyeater ( Foulehaio carunculatus ), Polynesian Starling ( Aplonis tabuensis ), and Samoan Starling ( Aplonis atrifusca ) on Taʻū. The Many-colored Fruit Dove ( Ptilinopus perousii ) remained rare in both units, and the Manuʻa Shrikebill (Clytorhynchus vitiensis powelli) was narrowly distributed on Taʻū, with insufficient detections of either species to estimate density. The cryptic Spotless Crake ( Zapornia tabuensis ) was detected only in 2018. Changes in tree canopy cover and height did not exhibit patterns clearly associated with a major disturbance event and likely reflected differences in sampling frames among surveys. Invasive non-native plants, most notably Miconia crenata , were widespread in both units. Although many landbird populations in NPSA remain abundant, inference from current monitoring is constrained by limited information on vital rates and species-specific responses to invasive species, disease, habitat change, and extreme weather. As climate change is projected to increase tropical cyclone intensity in the South Pacific, sustained monitoring and targeted management will be important for understanding and conserving landbird populations in American Samoa.

National Park of American Samoa, Ta'u, Tutuila↗

USGS2007

A hypothesis about factors that affect maximum stream temperatures across montane landscapes

Temperature is an important variable structuring lotic biotas, but little is known about how montane landscapes function to determine stream temperatures. We developed an a priori hypothesis that was used to predict how watershed elements would interact to affect stream temperatures. The hypothesis was tested in a series of path analyses using temperature data from 26 sites on second-order to fourth-order streams across a fifth-order Rocky Mountain watershed. Based on the performance of the first hypothesis, two revised versions of the hypothesis were developed and tested that proved to be more accurate than the original hypothesis. The most plausible of the revised hypotheses accounted for 82 percent of the variation in maximum stream temperature, had a predicted data structure that did not deviate from the empirical data structure, and was the most parsimonious. The final working hypothesis suggested that stream temperature maxima were directly controlled by a large negative effect from mean basin elevation (direct effect = -0.57, p < 0.01) and smaller effects from riparian tree abundance (direct effect = -0.28, p = 0.03), and cattle density (direct effect = 0.24, p = 0.05). Watershed slope, valley constraint, and the abundance of grass across a watershed also affected temperature maxima, but these effects were indirect and mediated through cattle density and riparian trees. Three variables included in the a priori hypothesis - watershed aspect, stream width, and watershed size - had negligible effects on maximum stream temperatures and were omitted from the final working hypothesis.

Idaho, Wyoming↗

USGS2019

Jump-starting coastal wetland restoration: A comparison of marsh and mangrove foundation species

During coastal wetland restoration, foundation plant species play a critical role in creating habitat, modulating ecosystem functions, and supporting ecological communities. Following initial hydrologic restoration, foundation plant species can help stabilize sediments and jump-start ecosystem development. Different foundation species, however, have different traits and environmental tolerances. To understand how these traits and tolerances impact restoration trajectories, there is a need for comparative studies among foundation species. In subtropical and tropical climates, coastal wetland restoration practitioners can sometimes choose between salt marsh and/or mangrove foundation species. Here, we compared the early life history traits and environmental tolerances of two foundation species: (1) a salt marsh grass (Spartina alterniflora), and (2) a mangrove tree (Avicennia germinans). In an 18-month study of a recently-restored coastal wetland in southeastern Louisiana (USA), we examined growth and survival along an elevation gradient and compared expansion and recruitment rates. We found that the rapid growth, expansion, and recruitment rates of the salt marsh grass make it a better species for quickly establishing ecological structure at suitable elevations. The slower growth, limited expansion, and lower recruitment of the mangrove species show its limited capacity for immediate structural restoration, especially in areas where it co-occurs with perennial salt marsh foundation species. Our findings suggest that the structural attributes needed in recently-restored areas (e.g., erosion control, vegetation structure) can be achieved more quickly using fast-growing foundation marsh species. Following salt marsh grass establishment, mangroves can then be used to further assist ecosystem development. This work highlights how appropriate foundation species can help jump-start ecosystem development to meet restoration objectives.

Restoration Ecology↗

USGS2011

Wildfires alter rodent community structure across four vegetation types in southern California, USA

We surveyed burned and unburned plots across four habitat reserves in San Diego County, California, USA, in 2005 and 2006, to assess the effects of the 2003 wildfires on the community structure and relative abundance of rodent species. The reserves each contained multiple vegetation types (coastal sage scrub, chaparral, woodland, and grassland) and spanned from 250 m to 1078 m in elevation. Multivariate analyses revealed a more simplified rodent community structure in all burned habitats in comparison to unburned habitats. Reduction in shrub and tree cover was highly predictive of changes in post-fire rodent community structure in the burned coastal sage scrub and chaparral habitats. Reduction in cover was not predictive for the less substantially burned woodlands and grasslands, for which we hypothesized that interspecific competition played a greater role in post-fire community structure. Across vegetation types, generalists and open habitat specialists typically increased in relative abundance, whereas closed habitat specialists decreased. We documented significant increases in relative abundance of the deer mouse ( Peromyscus maniculatus Wagner) and Dulzura kangaroo rat ( Dipodomys simulans Merriam). In contrast, we found significant decreases in relative abundance for the California mouse ( Peromyscus californicus Gambel), San Diego pocket mouse ( Chaetodipus fallax Merriam), desert woodrat ( Neotoma lepida Thomas), and brush mouse ( Peromyscus boylii Baird). Currently, our research program involves assessment of whether habitat conservation plans (HCPs) in southern California provide long-term protection to HCP covered species, as well as preserve ecosystem function. The scenario of increased wildfires needs to be incorporated into this assessment. We discuss our results in relation to management and conservation planning under a future scenario of larger and more frequent wildfires in southern California.

California↗

USGS2008

Contrasting rainfall generated debris flows from adjacent watersheds at Forest Falls, southern California, USA

Debris flows are widespread and common in many steeply sloping areas of southern California. The San Bernardino Mountains community of Forest Falls is probably subject to the most frequently documented debris flows in southern California. Debris flows at Forest Falls are generated during short-duration high-intensity rains that mobilize surface material. Except for debris flows on two consecutive days in November 1965, all the documented historic debris flows have occurred during high-intensity summer rainfall, locally referred to as 'monsoon' or 'cloudburst' rains. Velocities of the moving debris range from about 5??km/h to about 90??km/h. Velocity of a moving flow appears to be essentially a function of the water content of the flow. Low velocity debris flows are characterized by steep snouts that, when stopped, have only small amounts of water draining from the flow. In marked contrast are high-velocity debris flows whose deposits more resemble fluvial deposits. In the Forest Falls area two adjacent drainage basins, Snow Creek and Rattlesnake Creek, have considerably different histories of debris flows. Snow Creek basin, with an area about three times as large as Rattlesnake Creek basin, has a well developed debris flow channel with broad levees. Most of the debris flows in Snow Creek have greater water content and attain higher velocities than those of Rattlesnake Creek. Most debris flows are in relative equilibrium with the geometry of the channel morphology. Exceptionally high-velocity flows, however, overshoot the channel walls at particularly tight channel curves. After overshooting the channel, the flows degrade the adjacent levee surface and remove trees and structures in the immediate path, before spreading out with decreasing velocity. As the velocity decreases the clasts in the debris flows pulverize the up-slope side of the trees and often imbed clasts in them. Debris flows in Rattlesnake Creek are relatively slow moving and commonly stop in the channel. After the channel is blocked, subsequent debris flows cut a new channel upstream from the blockage that results in the deposition of new debris-flow deposits on the lower part of the fan. Shifting the location of debris flows on the Rattlesnake Creek fan tends to prevent trees from becoming mature. Dense growths of conifer seedlings sprout in the spring on the late summer debris flow deposits. This repeated process results in stands of even-aged trees whose age records the age of the debris flows. ?? 2007.

Geomorphology↗

USGS2025

Vegetation community monitoring: Forest structure in Klamath Network parks

The Klamath Network, comprising six national park units in northern California and southern Oregon, initiated a vegetation monitoring protocol in 2011 to discern ecologically significant vegetation trends in these parks. The premise of the protocol is that multivariate analyses of species composition data is the most robust means for early detection of vegetation change over time. Here, we present these community metrics based on our sampling efforts from 2011 to 2019. Observations from the first sampling event (2011–2013) were used to establish baseline conditions for the vegetation communities. Observations from subsequent sampling in 2014–2019 were used to identify potential temporal variation in forest structure across habitat types and parks. Park landscapes were categorized into three strata: matrix (low- to mid-elevation upland habitats), riparian (within 10 m of a perennial stream), and high-elevation (above a predefined elevation, park-specific). At the onset of the network’s vegetation monitoring protocol, 241 permanent plots were established at random locations across the three strata. We present summary statistics from three repeated samplings (2011–2019) of each plot, describing variation in forest structure across broad habitat types and parks. Observable differences in forest structure aligned with expected productivity gradients across the parks. Measures of forest structure (vegetation cover, stem density, basal area, tree heights, height to live crown, shrub cover, and surface fuels) were generally higher in mesic sites, compared to sites located in more arid, continental climates. Differences across sampling frames also followed this general pattern of productivity. Matrix and riparian sampling frames had similar ranges of values in most cases, while high elevation sites had relatively lower stem density, basal area, shrub cover, fuels, and recruitment. Notably, we observed a relative lack of change in forest structure over time. This is not surprising given the relatively short (six-year) timespan of observations in each park. The fourth set of Klamath Network surveys (2021–2023) is likely to show substantial changes in vegetation cover and forest structure, particularly for parks that have recently experienced major fires. Continued long-term vegetation monitoring is crucial for understanding ecosystem responses to a rapidly changing world. This report on vegetation composition is the second in a series; upcoming reports will analyze structure and function, aiming to detect spatiotemporal trends.

California, Oregon↗