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USGS2026

Identifying headwater streams across the conterminous United States

Headwater streams play critical roles in hydrologic and biogeochemical processes and functions, yet their spatial distribution and land cover context remain poorly understood at continental scales, and no dedicated geospatial dataset exists. Building from a high-resolution conterminous United States (CONUS) hydrography network dataset, we quantified the spatial extent, density, and upstream catchment characteristics of headwater stream segments across the CONUS. We identified approximately 8.4 million kilometers of headwater streams, finding that 77% of the total stream network consists of headwaters, nearly double the total length represented in prior estimates. Stream density varied fivefold across regions, from < 1 km·km −2 in arid basins to > 5 km·km −2 in humid, forested areas. Over 73% of the CONUS landmass drains from headwater streams. The majority of headwater stream length occurred in forested and cultivated catchments across the CONUS, while substantial regional differences were evident for headwater stream distribution in other land cover classes (for example, wetlands, urban areas, shrublands, and herbaceous-dominated catchments). The dedicated and novel geospatial dataset, HELiOS (HEadwater streams and Low-Order Systems) is introduced for management and research use. The HELiOS dataset provides the first continental-scale, high-resolution characterization of headwater streams, offering new insights and opportunities for hydrologic modeling, ecological assessments, and environmental policy.

conterminous United States↗

USGS2010

Emerging dragonfly diversity at small Rhode Island (U.S.A.) wetlands along an urbanization gradient

Natal habitat use by dragonflies was assessed on an urban to rural land-use gradient at a set of 21 wetlands, during two emergence seasons (2004, 2005). The wetlands were characterized for urbanization level by using the first factor from a principal components analysis combining chloride concentration in the wetland and percent forest in the surrounding buffer zone. Measurements of species diversity and its components (species richness and evenness) were analyzed and compared along the urbanization gradient, as were distributions of individual species. Dragonfly diversity, species richness, and evenness did not change along the urbanization gradient, so urban wetlands served as natal habitat for numerous dragonfly species. However, several individual species displayed strong relationships to the degree of urbanization, and most were more commonly found at urban sites and at sites with fish. In contrast, relatively rare species were generally found at the rural end of the gradient. These results suggest that urban wetlands can play important roles as dragonfly habitat and in dragonfly conservation efforts, but that conservation of rural wetlands is also important for some dragonfly species.

Urban Ecosystems↗

USGS1997

Flood dependency of cottonwood establishment along the Missouri River, Montana, USA

Flow variability plays a central role in structuring the physical environment of riverine ecosystems. However, natural variability in flows along many rivers has been modified by water management activities. We quantified the relationship between flow and establishment of the dominant tree (plains cottonwood, Populus deltoides subsp. monilifera ) along one of the least hydrologically altered alluvial reaches of the Missouri River: Coal Banks Landing to Landusky, Montana. Our purpose was to refine our understanding of how local fluvial geomorphic processes condition the relationship between flow regime and cottonwood recruitment. We determined date and elevation of tree establishment and related this information to historical peak stage and discharge over a 112-yr hydrologic record. Of the excavated trees, 72% were established in the year of a flow >1400 m 3 /s (recurrence interval of 9.3 yr) or in the following 2 yr. Flows of this magnitude or greater create the necessary bare, moist establishment sites at an elevation high enough to allow cottonwoods to survive subsequent floods and ice jams. Almost all cottonwoods that have survived the most recent flood (1978) were established >1.2 m above the lower limit of perennial vegetation (active channel shelf). Most younger individuals were established between 0 and 1.2 m, and are unlikely to survive over the long term. Protection of riparian cottonwood forest along this National Wild and Scenic section of the Missouri River depends upon maintaining the historical magnitude, frequency, and duration of floods >1400 m 3 /s. Here, a relatively narrow valley constrains lateral channel movement that could otherwise facilitate cottonwood recruitment at lower flows. Effective management of flows to promote or maintain cottonwood recruitment requires an understanding of locally dominant fluvial geomorphic processes.

Montana↗

USGS2018

Shrubland carbon sink depends upon winter water availability in the warm deserts of North America

Global-scale studies suggest that dryland ecosystems dominate an increasing trend in the magnitude and interannual variability of the land CO 2 sink. However, such model-based analyses are poorly constrained by measured CO 2 exchange in open shrublands, which is the most common global land cover type, covering ∼14% of Earth’s surface. Here we evaluate how the amount and seasonal timing of water availability regulate CO 2 exchange between shrublands and the atmosphere. We use eddy covariance data from six US sites across the three warm deserts of North America with observed ranges in annual precipitation of ∼100–400mm, annual temperatures of 13–18°C, and records of 2–8 years (33 site-years in total). The Chihuahuan, Sonoran and Mojave Deserts present gradients in both mean annual precipitation and its seasonal distribution between the wet-winter Mojave Desert and the wet-summer Chihuahuan Desert. We found that due to hydrologic losses during the wettest summers in the Sonoran and Chihuahuan Deserts, evapotranspiration (ET) was a better metric than precipitation of water available to drive dryland CO 2 exchange. In contrast with recent synthesis studies across diverse dryland biomes, we found that NEP could not be directly predicted from ET due to wintertime decoupling of the relationship between ecosystem respiration (R eco ) and gross ecosystem productivity (GEP). Ecosystem water use efficiency (WUE=GEP/ET) did not differ between winter and summer. Carbon use efficiency (CUE=NEP/GEP), however, was greater in winter because R eco returned a smaller fraction of carbon to the atmosphere (23% of GEP) than in summer (77%). Combining the water-carbon relations found here with historical precipitation since 1980, we estimate that lower average winter precipitation during the 21st century reduced the net carbon sink of the three deserts by an average of 6.8TgC yr 1 . Our results highlight that winter precipitation is critical to the annual carbon balance of these warm desert shrublands.

Agricultural and Forest Meteorology↗

USGS2024

Need and vision for global medium-resolution Landsat and Sentinel-2 data products

Global changes in climate and land use are threatening natural ecosystems, biodiversity, and the ecosystem services people rely on. This is why it is necessary to track and monitor spatiotemporal change at a level of detail that can inform science, management, and policy development. The current constellation of multiple Landsat and Sentinel-2 satellites collecting imagery at predominantly ≤ "> ≤ 30-m spatial resolution affords an opportunity for the generation of global medium- resolution products every few days. Our goal is to both identify the information needs and provide direction towards the generation of a suite of global, high-level, systematically-generated, medium-resolution products designed for both management and science. Our vision builds on the success of the NASA MODIS/VIIRS product suite, while recognizing the unique strengths of medium-resolution satellite data given their higher spatial resolution and longer time series. We propose a suite of 13 essential products that enable the characterization of the current state and changes in the biosphere, cryosphere, and hydrosphere, and would fill information needs identified by the Committee on Earth Observation Satellites for the Global Climate Observing System and the Global Terrestrial Observing System, by the National Research Council of the US National Academies in the decadal survey, and by others. These products are: land cover, land cover change, burned area, forest loss, vegetation indices, phenology, dynamic habitat indices, albedo, land surface temperature, snow cover, ice extent, surface water extent, and evapotranspiration. Furthermore, we provide a list of desirable products poised for addition to the essential products (e.g., crop type, emissivity, and ice sheet velocity). Lastly, we suggest aspirational products requiring further algorithm development (e.g., forest structure and crop yield). For the identified essential products, algorithms are in place, making it feasible to begin generating products systematically. These products should be accompanied by quality and accuracy assessments undertaken following consensus protocols. Five decades after the first Landsat satellite, and two decades after the MODIS products were first produced, it is time now for readily available, standardized, and consistent high-level products built upon medium-resolution imagery, thereby fulfilling the promise and the vision that inspired the Landsat program since its inception.

Remote Sensing of Environment↗

USGS2016

Atmospheric inputs of organic matter to a forested watershed: Variations from storm to storm over the seasons

The objectives of this study were to determine the quantity and chemical composition of precipitation inputs of dissolved organic carbon (DOC) to a forested watershed; and to characterize the associated temporal variability. We sampled most precipitation that occurred from May 2012 through August 2013 at the Susquehanna Shale Hills Critical Zone Observatory (Pennsylvania, USA). Sub-event precipitation samples (159) were collected sequentially during 90 events; covering various types of synoptic meteorological conditions in all climatic seasons. Precipitation DOC concentrations and rates of wet atmospheric DOC deposition were highly variable from storm to storm, ranging from 0.3 to 5.6 mg C L −1 and from 0.5 to 32.8 mg C m −2 h −1 , respectively. Seasonally, storms in spring and summer had higher concentrations of DOC and more optically active organic matter than in winter. Higher DOC concentrations resulted from weather types that favor air advection, where cold frontal systems, on average, delivered more than warm/stationary fronts and northeasters. A mixed modeling statistical approach revealed that factors related to storm properties, emission sources, and to the chemical composition of the atmosphere could explain more than 60% of the storm to storm variability in DOC concentrations. This study provided observations on changes in dissolved organic matter that can be useful in modeling of atmospheric oxidative chemistry, exploring relationships between organics and other elements of precipitation chemistry, and in considering temporal changes in ecosystem nutrient balances and microbial activity.

Atmospheric Environment↗

USGS2003

Historic range of variability in landscape structure in subalpine forests of the Greater Yellowstone Area, USA

A measure of the historic range of variability (HRV) in landscape structure is essential for evaluating current landscape patterns of Rocky Mountain coniferous forests that have been subjected to intensive timber harvest. We used a geographic information system (GIS) and FRAGSTATS to calculate key landscape metrics on two ???130,000-ha landscapes in the Greater Yellowstone Area, USA: one in Yellowstone National Park (YNP), which has been primarily shaped by natural fires, and a second in the adjacent Targhee National Forest (TNF), which has undergone intensive clearcutting for nearly 30 years. Digital maps of the current and historical landscape in YNP were developed from earlier stand age maps developed by Romme and Despain. Maps of the TNF landscape were adapted from United States Forest Service Resource Information System (RIS) data. Key landscape metrics were calculated at 20-yr intervals for YNP for the period from 1705-1995. These metrics were used to first evaluate the relative effects of small vs. large fire events on landscape structure and were then compared to similar metrics calculated for both pre- and post-harvest landscapes of the TNF. Large fires, such as those that burned in 1988, produced a structurally different landscape than did previous, smaller fires (1705-1985). The total number of patches of all types was higher after 1988 (694 vs. 340-404 before 1988), and mean patch size was reduced by almost half (186 ha vs. 319-379 ha). The amount of unburned forest was less following the 1988 fires (63% vs. 72-90% prior to 1988), yet the number of unburned patches increased by nearly an order of magnitude (230 vs. a maximum of 41 prior to 1988). Total core area and mean core area per patch decreased after 1988 relative to smaller fires (???73,700 ha vs. 87,000-110,000 ha, and 320 ha vs. 2,123 ha, respectively). Notably, only edge density was similar (17 m ha-1 after 1988) to earlier landscapes (9.8-14.2 m ha-1). Three decades of timber harvesting dramatically altered landscape structure in the TNF. Total number of patches increased threefold (1,481 after harvest vs. 437 before harvest), and mean patch size decreased by ???70% (91.3 ha vs. 309 ha). None of the post-harvest landscape metrics calculated for the TNF fell within the HRV as defined in YNP, even when the post-1988 landscape was considered. In contrast, pre-harvest TNF landscape metrics were all within, or very nearly within, the HRV for YNP While reference conditions such as those identified by this study are useful for local and regional landscape evaluation and planning, additional research is necessary to understand the consequences of changes in landscape structure for population, community, ecosystem, and landscape function.

Landscape Ecology↗

USGS2009

Carbon cycling under 300 years of land use change: importance of the secondary vegetation sink

We have developed a dynamic land model (LM3V) able to simulate ecosystem dynamics and exchanges of water, energy, and CO 2 between land and atmosphere. LM3V is specifically designed to address the consequences of land use and land management changes including cropland and pasture dynamics, shifting cultivation, logging, fire, and resulting patterns of secondary regrowth. Here we analyze the behavior of LM3V, forced with the output from the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model AM2, observed precipitation data, and four historic scenarios of land use change for 1700-2000. Our analysis suggests a net terrestrial carbon source due to land use activities from 1.1 to 1.3 GtC/a during the 1990s, where the range is due to the difference in the historic cropland distribution. This magnitude is substantially smaller than previous estimates from other models, largely due to our estimates of a secondary vegetation sink of 0.35 to 0.6 GtC/a in the 1990s and decelerating agricultural land clearing since the 1960s. For the 1990s, our estimates for the pastures' carbon flux vary from a source of 0.37 to a sink of 0.15 GtC/a, and for the croplands our model shows a carbon source of 0.6 to 0.9 GtC/a. Our process-based model suggests a smaller net deforestation source than earlier bookkeeping models because it accounts for decelerated net conversion of primary forest to agriculture and for stronger secondary vegetation regrowth in tropical regions. The overall uncertainty is likely to be higher than the range reported here because of uncertainty in the biomass recovery under changing ambient conditions, including atmospheric CO 2 concentration, nutrients availability, and climate. Copyright 2009 by the American Geophysical Union.

Global Biogeochemical Cycles↗

USGS2023

Soil and geomorphic patterns within relict charcoal hearths could represent unique ecosystem niches

Hearths used for 19th and 20th century charcoal manufacturing have been found to have unique plant communities or to produce unique growth characteristics for some species but not others. Given known differences in hearth morphology, within hearth physical and chemical differences may exist and result in unique ecologic niches. We examined soil stratigraphy across 8 relict charcoal hearths (RCH) and control soils on different landforms near a 19th century furnace complex (Greenwood Furnace, northcentral Appalachians USA). Soils were analyzed for particle size, total and trace elements, and fertility. Platform creation resulted in soils from upslope RCH positions mixed with subsurface materials on the downslope side to create a stabilized platform. The thin, uniform thickness of charcoal surface horizons (Ac) suggests that RCHs were not used more than once for charcoal manufacturing or that charcoal was always removed very efficiently. While rubification of soil or rock from high heat was seen in 6 of 8 sites sampled, it was not extensive across sampled areas of any one hearth, which suggests hearth use may not have frequent, hot enough, or spatially disparate. Soil fertility characteristics change within RCHs but also by landscape position. Downslope RCH positions are enriched in some parameters compared to control soils (total C, Mehlich 3 Mg, Ca, and Aquia Regia digestion Mn) and that enrichment often is from the surface downward. Downslope enrichment within RCH soils may have occurred from charcoal and released ions, slope erosion and accumulation, or transportation of constructed materials during RCH creation. Landscape position may accentuate or mute soil chemistry differences. Greenwood Furnace RCHs have unique patterns of chemistry, which could result in unique niches for flora and maybe fauna within RCH. Future research should more closely investigate whether hearths support unique species assemblages and how they may play a role in enhancing today’s forest biodiversity.

Pennsylvania↗

USGS2022

Effects of prescribed fire on prenesting movements of wild turkeys in Arkansas

The restoration of historic disturbance regimes is an increasingly common management strategy to conserve disturbance-dependent communities and species, and enhance resilience of ecosystems to climate change or plant and animal invasions. However, the reintroduction of frequent and wide-scale disturbance may have unexpected consequences on species that are accustomed to an environment absent of frequent disturbance. Implementation of frequent prescribed fire for community restoration has coincided with population declines of eastern wild turkeys ( Meleagris gallopavo silvestris ) in the Ozark Highlands of Arkansas. We investigated whether there was evidence of linkage between wild turkey movement behavior and habitat use and the widespread use of prescribed fire that began in 2002 and continued through the end of our study in 2013. We fitted 67 female wild turkeys with satellite transmitters in 2012 and 2013 on the White Rock Ecosystem Restoration Area to estimate annual and seasonal home ranges and examine pre-nesting habitat use at multiple spatial scales. Home range was larger for adults in 2013 (4,750 ha, SE = 946.2, n = 12) than in 2012 (2,703 ha, SE = 283.4, n = 19). Mean pre-nesting ranges for adults were 1,633 ha (SE = 238.9, n = 23) in 2012 and 1,118 ha (SE = 158.8, n = 18) in 2013, smaller than those of sub-adults, 1,761 ha (SE = 581.2, n = 3) in 2012 and 5,576 ha (SE = 2260, n = 8) in 2013. Habitat selection analyses for the pre-nesting period indicated that wild turkeys used locations with more variability in canopy cover and vegetation height and in smaller patch sizes than expected based on availability. However, female wild turkeys selected nesting cover that had more variability in canopy cover and vegetation height but in larger patches. Differences in sub-adults and adult home and seasonal ranges suggest that other factors such as density dependence or social hierarchy could be driving movements as opposed to prescribed fire application. Wild turkey females selected variable vegetation structure during the pre-nesting and nesting periods with characteristics that could be a result of frequent prescribed fire or forest succession. However, we documented no direct evidence these characteristics or other aspects of the prescribed fire program were causing wild turkey population declines.

Arkansas↗

USGS2023

The sands of time: Predicting sea level rise impacts to barrier island habitats

Coastal beach ecosystems support critical habitat for numerous species and are vulnerable to sea level rise. Sand beaches are spatially and temporally dynamic, making it difficult to accurately predict future habitat loss – estimates that are crucial as species are being assessed for protection. We mapped sand beach habitat on 12 focal barrier islands and low-lying beaches off the Gulf Coast of Florida, USA using two methods for comparison - a remotely sensed land cover and hand-digitized aerial imagery that was collected concurrently with digital elevation data. We then compared estimates of beach habitat lost to sea level rise between the two methods and compared this sensitivity to control mangrove islands. Predictions suggest that most of the beach habitat in our study areas will be underwater within the next century. These beaches represent critical nesting habitat for vulnerable vertebrate species such as the snowy plover ( Charadrius nivosus ) and the loggerhead turtle ( Caretta caretta ). Importantly, we found that for some islands, using remotely sensed land cover data led us to under- or over-estimate the amount of beach habitat lost to sea level rise relative to the digitized data because of the temporal mismatch between land cover and elevation data. In contrast, we found relatively little difference between methods in the amount of mangrove forest lost to sea level rise on nearby control islands. We suggest that using land cover data collected at the same time as elevation data can produce more accurate predictions of beach habitat inundation from sea level rise.

Florida↗

USGS2023

New indicators of ecological resilience and invasion resistance to support prioritization and management in the sagebrush biome, United States

Ecosystem transformations to altered or novel ecological states are accelerating across the globe. Indicators of ecological resilience to disturbance and resistance to invasion can aid in assessing risks and prioritizing areas for conservation and restoration. The sagebrush biome encompasses parts of 11 western states and is experiencing rapid transformations due to human population growth, invasive species, altered disturbance regimes, and climate change. We built on prior use of static soil moisture and temperature regimes to develop new, ecologically relevant and climate responsive indicators of both resilience and resistance. Our new indicators were based on climate and soil water availability variables derived from process-based ecohydrological models that allow predictions of future conditions. We asked: (1) Which variables best indicate resilience and resistance? (2) What are the relationships among the indicator variables and resilience and resistance categories? (3) How do patterns of resilience and resistance vary across the area? We assembled a large database ( n = 24,045) of vegetation sample plots from regional monitoring programs and derived multiple climate and soil water availability variables for each plot from ecohydrological simulations. We used USDA Natural Resources Conservation Service National Soils Survey Information, Ecological Site Descriptions, and expert knowledge to develop and assign ecological types and resilience and resistance categories to each plot. We used random forest models to derive a set of 19 climate and water availability variables that best predicted resilience and resistance categories. Our models had relatively high multiclass accuracy (80% for resilience; 75% for resistance). Top indicator variables for both resilience and resistance included mean temperature, coldest month temperature, climatic water deficit, and summer and driest month precipitation. Variable relationships and patterns differed among ecoregions but reflected environmental gradients; low resilience and resistance were indicated by warm and dry conditions with high climatic water deficits, and moderately high to high resilience and resistance were characterized by cooler and moister conditions with low climatic water deficits. The new, ecologically-relevant indicators provide information on the vulnerability of resources and likely success of management actions, and can be used to develop new approaches and tools for prioritizing areas for conservation and restoration actions.

Frontiers in Ecology and Evolution↗

USGS2024

Benthic community metrics track hydrologically stressed mangrove systems

Mangrove restoration efforts have increased in order to help combat their decline globally. While restoration efforts often focus on planting seedlings, underlying chronic issues, including disrupted hydrological regimes, can hinder restoration success. While improving hydrology may be more cost-effective and have higher success rates than planting seedlings alone, hydrological restoration success in this form is poorly understood. Restoration assessments can employ a functional equivalency approach, comparing restoration areas over time with natural, reference forests in order to quantify the relative effectiveness of different restoration approaches. Here, we employ the use of baseline community ecology metrics along with stable isotopes to track changes in the community and trophic structure and enable time estimates for establishing mangrove functional equivalency. We examined a mangrove system impacted by road construction and recently targeted for hydrological restoration within the Rookery Bay National Estuarine Research Reserve, Florida, USA. Samples were collected along a gradient of degradation, from a heavily degraded zone, with mostly dead trees, to a transition zone, with a high number of saplings, to a full canopy zone, with mature trees, and into a reference zone with dense, mature mangrove trees. The transition, full canopy, and reference zones were dominated by annelids, gastropods, isopods, and fiddler crabs. Diversity was lower in the dead zone; these taxa were enriched in 13 C relative to those found in all the other zones, indicating a shift in the dominant carbon source from mangrove detritus (reference zone) to algae (dead zone). Community-wide isotope niche metrics also distinguished zones, likely reflecting dominant primary food resources (baseline organic matter) present. Our results suggest that stable isotope niche metrics provide a useful tool for tracking mangrove degradation gradients. These baseline data provide critical information on the ecosystem functioning in mangrove habitats following hydrological restoration.

Florida↗

USGS2011

Linking habitat quality with trophic performance of steelhead along forest gradients in the South Fork Trinity River Watershed, California

We examined invertebrate prey, fish diet, and energy assimilation in relation to habitat variation for steelhead Oncorhynchus mykiss (anadromous rainbow trout) and rainbow trout in nine low-order tributaries of the South Fork Trinity River, northern California. These streams spanned a range of environmental conditions, which allowed us to use bioenergetics modeling to determine the relative effects of forest cover, stream temperature, season, and fish age on food consumption and growth efficiency. Evidence of seasonal shifts in reliance on aquatic versus terrestrial food sources was detected among forest cover categories and fish ages, although these categories were not robust indicators of O. mykiss condition and growth efficiency. Consumption estimates were generally less than 20% of maximum consumption, and fish lost weight in some streams during summer low-flow conditions when stream temperatures exceeded 15°C. Current 100-year climate change projections for California threaten to exacerbate negative growth patterns and may undermine the productivity of this steelhead population, which is currently not listed as endangered or threatened. To demonstrate the potential effect of global warming on fish growth, we ran three climate change scenarios in two representative streams. Simulated temperature increases ranging from 1.4°C to 5.5°C during the summer and from 1.5°C to 2.9C during the winter amplified the weight loss; estimated average growth for age-1 fish was 0.4–4.5 times lower than normal (low to high estimated temperature increase) in the warm stream and 0.05–0.8 times lower in the cool stream. We conclude that feeding rate and temperature during the summer currently limit the growth and productivity of steelhead and rainbow trout in low-order streams in the South Fork Trinity River basin and predict that climate change will have detrimental effects on steelhead growth as well as on macroinvertebrate communities and stream ecosystems in general.

Transactions of the American Fisheries Society↗

USGS2017

Variability of dissolved organic carbon in precipitation during storms at the Shale Hills Critical Zone Observatory

Organic compounds are removed from the atmosphere and deposited to the earth's surface via precipitation. In this study, we quantified variations of dissolved organic carbon (DOC) in precipitation during storm events at the Shale Hills Critical Zone Observatory, a forested watershed in central Pennsylvania (USA). Precipitation samples were collected consecutively throughout the storm during 13 events, which spanned a range of seasons and synoptic meteorological conditions, including a hurricane. Further, we explored factors that affect the temporal variability by considering relationships of DOC in precipitation with atmospheric and storm characteristics. Concentrations and chemical composition of DOC changed considerably during storms, with the magnitude of change within individual events being comparable or higher than the range of variation in average event composition among events. While some previous studies observed that concentrations of other elements in precipitation typically decrease over the course of individual storm events, results of this study show that DOC concentrations in precipitation are highly variable. During most storm events concentrations decreased over time, possibly as a result of washing out of the below-cloud atmosphere. However, increasing concentrations that were observed in the later stages of some storm events highlight that DOC removal with precipitation is not merely a dilution response. Increases in DOC during events could result from advection of air masses, local emissions during breaks in precipitation, or chemical transformations in the atmosphere that enhance solubility of organic carbon compounds. This work advances understanding of processes occurring during storms that are relevant to studies of atmospheric chemistry, carbon cycling, and ecosystem responses.

Pennsylvania↗

USGS2011

Salvage logging versus the use of burnt wood as a nurse object to promote post-fire tree seedling establishment

Intense debate surrounds the effects of post-fire salvage logging (SL) versus nonintervention policies on forest regeneration, but scant support is available from experimental studies. We analyze the effect of three post-fire management treatments on the recruitment of a serotinous pine ( Pinus pinaster ) at a Mediterranean mountain. Treatments were applied 7 months after the fire and differ in the degree of intervention, ranging from “no intervention” (NI, all trees left standing) to “partial cut plus lopping” (PCL, felling most of the trees, cutting the main branches, and leaving all the biomass in situ without mastication), and “SL” (felling and piling the logs, and masticating the woody debris). Seedling survival after 3 years was the highest in PCL (47.3% versus 38.7% in SL). This was associated with the amelioration of microclimatic conditions under the scattered branches, which reduced radiation and soil temperature while increasing soil moisture. Seedling density after 2 years was approximately 5.5 times higher in PCL than in SL, as in SL a large fraction of seedlings was lost as a consequence of mechanized mastication. The NI treatment showed the lowest seedling survival (17.3%). Nevertheless, seedling density was similar to SL. Seedling growth scarcely differed among treatments. Our results show that branches left onsite acted as nurse objects that improved key microclimatic conditions for seedling recruitment. This creates a facilitative interaction ideal for seedling establishment in moisture-deficient ecosystems, as it provides the benefit of a shading overstory but without underground competition.

Restoration Ecology↗

USGS2014

Temporal variability of carbon and nutrient burial, sediment accretion, and mass accumulation over the past century in a carbonate platform mangrove forest of the Florida Everglades.

The objective of this research was to measure temporal variability in accretion and mass sedimentation rates (including organic carbon (OC), total nitrogen (TN), and total phosphorous (TP)) from the past century in a mangrove forest on the Shark River in Everglades National Park, USA. The 210 Pb Constant Rate of Supply model was applied to six soil cores to calculate annual rates over the most recent 10, 50, and 100 year time spans. Our results show that rates integrated over longer timeframes are lower than those for shorter, recent periods of observation. Additionally, the substantial spatial variability between cores over the 10 year period is diminished over the 100 year record, raising two important implications. First, a multiple-decade assessment of soil accretion and OC burial provides a more conservative estimate and is likely to be most relevant for forecasting these rates relative to long-term processes of sea level rise and climate change mitigation. Second, a small number of sampling locations are better able to account for spatial variability over the longer periods than for the shorter periods. The site average 100 year OC burial rate, 123 ± 19 (standard deviation) g m -2 yr -1 , is low compared with global mangrove values. High TN and TP burial rates in recent decades may lead to increased soil carbon remineralization, contributing to the low carbon burial rates. Finally, the strong correlation between OC burial and accretion across this site signals the substantial contribution of OC to soil building in addition to the ecosystem service of CO 2 sequestration.

Florida↗

USGS2021

The response of streams in the Adirondack region of New York to projected changes in sulfur and nitrogen deposition under changing climate

Modeling studies project that in the future surface waters in the northeast US will continue to recover from acidification over decades following reductions in atmospheric sulfur dioxide and nitrogen oxides emissions. However, these studies generally assume stationary climatic conditions over the simulation period and ignore the linkages between soil and surface water recovery from acid deposition and changing climate, despite fundamental impacts to watershed processes and comparable time scales for both phenomena. In this study, the integrated biogeochemical model PnET-BGC was applied to two montane forest watersheds in the Adirondack region of New York, USA to evaluate the recovery of surface waters from historical acidification in response to possible future changes in climate and atmospheric sulfur and nitrogen deposition. Statistically downscaled climate scenarios on average project warmer temperatures and greater precipitation for the Adirondack by the end of the century. Model simulations suggest under constant climate, acid-sensitive Buck Creek would gain 12.8 μeq L −1 of acid neutralizing capacity (ANC) by 2100 from large reductions in deposition, whereas acid insensitive Archer Creek is projected to gain 7.9 μeq L −1 of ANC. However, climate change could limit those improvements in acid-base status. Under climate change, a negative offset relative to the ANC increases with no climate change are projected for both streams by 2100. In acid-insensitive Archer Creek the negative offset (−8.5 μeq L −1 ) was large enough that ANC is projected to decrease by −0.6 μeq L −1 , whereas in acid-sensitive Buck Creek, the negative offset (−0.4 μeq L −1 ) resulted in a slight decline of the projected future ANC increase to 12.4 μeq L −1 . Calculated target loads for 2150 for both sites decreased when future climate change was considered in model simulations, which suggests further reductions in acid deposition may be necessary to restore ecosystem structure and function under a changing climate.

New York↗