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At least 325 records · Page 18Linked to original sources
USGS2006

Temporal evolution of carbon budgets of the Appalachian forests in the U.S. from 1972 to 2000

Estimating dynamic terrestrial ecosystem carbon (C) sources and sinks over large areas is difficult. The scaling of C sources and sinks from the field level to the regional level has been challenging due to the variations of climate, soil, vegetation, and disturbances. As part of an effort to estimate the spatial, temporal, and sectional dimensions of the United States C sources and sinks (the U.S. Carbon Trends Project), this study estimated the forest ecosystem C sequestration of the Appalachian region (186,000 km 2 ) for the period of 1972–2000 using the General Ensemble Biogeochemical Modeling System (GEMS) that has a strong capability of assimilating land use and land cover change (LUCC) data. On 82 sampling blocks in the Appalachian region, GEMS used sequential 60 m resolution land cover change maps to capture forest stand-replacing events and used forest inventory data to estimate non-stand-replacing changes. GEMS also used Monte Carlo approaches to deal with spatial scaling issues such as initialization of forest age and soil properties. Ensemble simulations were performed to incorporate the uncertainties of input data. Simulated results show that from 1972 to 2000 the net primary productivity (NPP), net ecosystem productivity (NEP), and net biome productivity (NBP) averaged 6.2 Mg C ha −1 y −1 (±1.1), 2.2 Mg C ha −1 y −1 (±0.6), and 1.8 Mg C ha −1 y −1 (±0.6), respectively. The inter-annual variability was driven mostly by climate. Detailed C budgets for the year 2000 were also calculated. Within a total 148,000 km 2 forested area, average forest ecosystem C density was estimated to be 186 Mg C ha −1 (±20), of which 98 Mg C ha −1 (±12) was in biomass and 88 Mg C ha −1 (±13) was in litter and soil. The total simulated C stock of the Appalachian forests was estimated to be 2751 Tg C (±296), including 1454 Tg C (±178) in living biomass and 1297 Tg C (±192) in litter and soil. The total net C sequestration (i.e. NBP) of the forest ecosystem in 2000 was estimated to be 19.5 Tg C y −1 (±6.8).

Forest Ecology and Management↗
USGS2009

Windthrow and salvage logging in an old-growth hemlock-northern hardwoods forest

Although the initial response to salvage (also known as, post-disturbance or sanitary) logging is known to vary among system components, little is known about longer term forest recovery. We examine forest overstory, understory, soil, and microtopographic response 25 years after a 1977 severe wind disturbance on the Flambeau River State Forest in Wisconsin, USA, a portion of which was salvage logged. Within this former old-growth hemlock-northern hardwoods forest, tree dominance has shifted from Eastern hemlock (Tsuga canadensis) to broad-leaf deciduous species (Ulmus americana, Acer saccharum, Tilia americana, Populus tremuloides, and Betula alleghaniensis) in both the salvaged and unsalvaged areas. While the biological legacies of pre-disturbance seedlings, saplings, and mature trees were initially more abundant in the unsalvaged area, regeneration through root suckers and stump sprouts was common in both areas. After 25 years, tree basal area, sapling density, shrub layer density, and seedling cover had converged between unsalvaged and salvaged areas. In contrast, understory herb communities differed between salvaged and unsalvaged forest, with salvaged forest containing significantly higher understory herb richness and cover, and greater dominance of species benefiting from disturbance, especially Solidago species. Soil bulk density, pH, organic carbon content, and organic nitrogen content were also significantly higher in the salvaged area. The structural legacy of tip-up microtopography remains more pronounced in the unsalvaged area, with significantly taller tip-up mounds and deeper pits. Mosses and some forest herbs, including Athyrium filix-femina and Hydrophyllum virginianum, showed strong positive responses to this tip-up microrelief, highlighting the importance of these structural legacies for understory biodiversity. In sum, although the pathways of recovery differed, this forest appeared to be as resilient to the compound disturbances of windthrow plus salvage logging as to wind disturbance alone, by most vegetative measures.

Forest Ecology and Management↗
USGS2018

Bat community response to silvicultural treatments in bottomland hardwood forests managed for wildlife in the Mississippi Alluvial Valley

Silvicultural treatments (e.g., selective timber harvests) that are prescribed to promote wildlife habitat are intended to alter the physical structure of forests to achieve conditions deemed beneficial for wildlife. Such treatments have been advocated for management of bottomland hardwood forests on public conservation lands in the Mississippi Alluvial Valley. Although some songbirds respond positively to these management actions, and wildlife-forestry indirectly promotes bat prey availability, bat response is largely unknown. Forest structure may affect bat use of bottomland forests due to differences in foraging space or roost sites. We examined the effects of silvicultural treatments that were implemented to promote wildlife habitat on bat species activity. We conducted vegetation surveys and sampled insect biomass within 64 treated and 64 reference stands located on 15 public conservation areas in Arkansas, Louisiana, and Mississippi, USA. We examined the influence of vegetation metrics and insect biomass on acoustic detections of bats during passive nocturnal surveys in these stands. Detections of bat activity were similar between silviculturally treated stands and reference stands, indicating that both managed and reference stands provide habitat for generalist and forest interior bat species. Generalist bat species (e.g., evening bats, eastern red bats, and Seminole bats) were positively associated with increased insect biomass and the amount of dead wood within a stand. Basal area of large trees was positively associated with detection of tri-colored bats and bottomland specialists (Rafinesque’s big-eared bats and myotine bats). Conversely, acoustic detection of bats was negatively associated with increased vegetative density (i.e., clutter). Managers that implement silvicultural treatments to improve desired forest conditions for wildlife can provide habitat for both generalist and forest interior bat species by providing heterogeneous forest structure that includes dead wood, high basal area of large trees, high tree species diversity, and gaps that are sufficiently thinned to allow unimpeded flight by bats.

Arkansas, Louisiana, Mississippi↗
USGS2019

Influence of forest harvest severity and time since perturbation on conservation of North American birds

I calculated avian conservation scores, based on published quantitative assessment of bird presence (typically relative abundance) and regional Partners in Flight conservation concern score of each species. I related these avian conservation scores to severity of forest perturbation (i.e., % retention) and number of years since perturbation for forest stands within North America. I characterized avian response to perturbation by comparing avian conservation score on perturbed stands with that of paired unperturbed reference stands. Positive avian response to perturbation, representative of improved avian conservation status, was found when forest retention was >20% of coniferous forests or 25%–75% of hardwood forests. Positive avian response was greatest ~10 years after perturbation that retained 58% of conifer forests or 49% of hardwood forests. Increased avian conservation scores following perturbation may last for up to 23 years after perturbation but occur and diminish sooner with greater forest retention. Average annual avian response, over 23 years post-perturbation, was greatest when 30%–50% of hardwood stands were retained and when 50%–70% of conifer stands were retained.

Forest Ecology and Management↗
USGS2022

What is a stand? Assessing the variability of composition and structure in floodplain forest ecosystems across spatial scales in the Upper Mississippi River

The forest stand typically represents relatively homogenous forest conditions; the forest stand is generally the unit at which forest attributes are assessed, summarized, and subsequently managed. However, some ecosystems, such as the floodplain forests of the Upper Mississippi River (UMR), can exhibit high variability at fine spatial scales that can confound prescription development, implementation, and ultimate success of stand-level management actions. Here we assess how forest composition and structure vary within and across stand management units on the UMR and test at what spatial scale environmental variables relate to forest characteristics. We found that plot-level measures of composition, structure, and diversity were not well represented by site-level averages of these values. When basal area of all overstory species was combined, this variable was more closely related to “site” than to any of the environmental variables, but when analyzed by species, within-plot topographic variation (“microtopography”) was a significant positive predictor for both importance values of an individual species (swamp white oak ( Quercus bicolor Willd.)) as well as importance value of a specific group of species (oaks (Quercus spp.), bitternut hickory ( Carya cordiformis (Wangenh.) K. Koch), hackberry ( Celtis occidentalis L.), and American basswood ( Tilia americana L.)). This work highlights the challenges of using average stand conditions to summarize complex or heterogeneous systems and the need for flexibility and relaxed assumptions in defining management units in these forests.

Iowa, Minnesota, Wisconsin↗
USGS2023

Adjacent and downstream effects of forest harvest on the distribution and abundance of larval headwater stream amphibians in the Oregon Coast Range

Forest harvest is a primary landscape-scale management action affecting riparian forests. Although concerns about impacts of forest harvest on stream amphibians is generally limited to areas adjacent to harvest, there is a paucity of information regarding potential downstream effects of forest harvest on these species. We designed a before-after, control-impact (BACI) experiment to quantify potential impacts of clearcut logging that included 12-m buffers or smaller variable-width buffers on the distribution and abundance of headwater stream amphibians in adjacent and downstream areas. We sampled larval coastal tailed frogs ( Ascaphus truei ), coastal giant salamanders ( Dicamptodon tenebrosus ), and Columbia torrent salamanders ( Rhyacotriton kezeri ) across 3,915 sampling occasions that spanned 13 study reaches in 2008–2011 (pre-harvest) and 2013–2016 (post-harvest) as part of the Trask River Watershed Study in the Oregon Coast Range, U.S.A. We analyzed these data using occupancy models to estimate occupancy and (when possible) relative abundance, while accounting for various sources of imperfect detection. All species exhibited reduced occupancy adjacent to clearcuts with variable-width buffers (odds ratios [ORs] ranged = 0.24–0.48), and these negative impacts were not always diminished when increasing the buffer size to 12 m (ORs ranged = 0.20–3.56). Dicamptodon tenebrosus was the only species to have occupancy impacted in downstream areas, and this negative impact was related to clearcut logging with uniform 12-m buffers (OR = 0.60). This species was also the only species to have abundance negatively impacted by forest harvest in downstream areas (OR = 0.41 with uniform 12-m buffers, OR = 0.38 with variable-width buffers), albeit impacts to abundance were not evaluated for R. kezeri . Ascaphus truei abundance increased in areas downstream of clearcut logging with uniform 12-m buffers (OR = 2.92). Although we found the direction and magnitude of responses varied by species, our study confirms that clearcut logging can have negative impacts on amphibians that inhabit the adjacent stream areas. Perhaps more importantly, we also found that forest harvest can have negative effects on stream amphibians downstream of the harvested area and that increasing the buffer size to 12 m did not necessarily diminish these impacts in adjacent and downstream areas. Altogether, our study provides a nuanced picture of adjacent and downstream effects of forest harvest on three endemic headwater stream amphibians, and our findings demonstrate that forest management practices should consider downstream effects on aquatic taxa when assessing the impact of harvesting trees near headwater streams.

Oregon↗
USGS2021

Recent carbon storage and burial exceed historic rates in the San Juan Bay estuary peri-urban mangrove forests (Puerto Rico, United States)

Mangroves sequester significant quantities of organic carbon (C) because of high rates of burial in the soil and storage in biomass. We estimated mangrove forest C storage and accumulation rates in aboveground and belowground components among five sites along an urbanization gradient in the San Juan Bay Estuary, Puerto Rico. Sites included the highly urbanized and clogged Caño Martin Peña in the western half of the estuary, a series of lagoons in the center of the estuary, and a tropical forest reserve (Piñones) in the easternmost part. Radiometrically dated cores were used to determine sediment accretion and soil C storage and burial rates. Measurements of tree dendrometers coupled with allometric equations were used to estimate aboveground biomass. Estuary-wide mangrove forest C storage and accumulation rates were estimated using interpolation methods and coastal vegetation cover data. In recent decades (1970–2016), the highly urbanized Martin Peña East (MPE) site with low flushing had the highest C storage and burial rates among sites. The MPE soil carbon burial rate was over twice as great as global estimates. Mangrove forest C burial rates in recent decades were significantly greater than historic decades (1930–1970) at Caño Martin Peña and Piñones. Although MPE and Piñones had similarly low flushing, the landscape settings (clogged canal vs forest reserve) and urbanization (high vs low) were different. Apparently, not only urbanization, but site-specific flushing patterns, landscape setting, and soil fertility affected soil C storage and burial rates. There was no difference in C burial rates between historic and recent decades at the San José and La Torrecilla lagoons. Mangrove forests had soil C burial rates ranging from 88 g m –2 y –1 at the San José lagoon to 469 g m –2 y –1 at the MPE in recent decades. Watershed anthropogenic CO 2 emissions (1.56 million Mg C y –1 ) far exceeded the annual mangrove forest C storage rates (aboveground biomass plus soils: 17,713 Mg C y –1 ). A combination of maintaining healthy mangrove forests and reducing anthropogenic emissions might be necessary to mitigate greenhouse gas emissions in urban, tropical areas.

Puerto Rico↗
USGS2016

Regional differences in upland forest to developed (urban) land cover conversions in the conterminous U.S., 1973–2011

In this U.S. Geological Survey study of forest land cover across the conterminous U.S. (CONUS), specific proportions and rates of forest conversion to developed (urban) land were assessed on an ecoregional basis. The study period was divided into six time intervals between 1973 and 2011. Forest land cover was the source of 40% or more of the new urban land in 35 of the 84 ecoregions located within the CONUS. In 11 of these ecoregions this threshold exceeded in every time interval. When the percent of change, forest to urban, was compared to the percent of forest in each ecoregion, 58 ecoregions had a greater percent of change and, in six of those, change occurred in every time interval. Annual rates of forest to urban land cover change of 0.2% or higher occurred in 12 ecoregions at least once and in one ecoregion in all intervals. There were three ecoregions where the above conditions were met for nearly every time interval. Even though only a small number of the ecoregions were heavily impacted by forest loss to urban development within the CONUS, the ecosystem services provided by undeveloped forest land cover need to be quantified more completely to better inform future regional land management.

Conterminous United States↗
USGS2019

Northern forest winters have lost cold, snowy conditions that are important for ecosystems and human communities

Winter is an understudied but key period for the socio-ecological systems of northeastern North American forests. A growing awareness of the importance of the winter season to forest ecosystems and surrounding communities has inspired several decades of research, both across the northern forest and at other mid- and high-latitude ecosystems around the globe. Despite these efforts, we lack a synthetic understanding of how winter climate change may impact hydrological and biogeochemical processes and the social and economic activities they support. Here we take advantage of 100 years of meteorological observations across the northern forest region of the northeastern U.S. and eastern Canada to develop a suite of indicators that enable a cross-cutting understanding of 1) how winter temperatures and snow cover have been changing and 2) how these shifts may impact both ecosystems and surrounding human communities. We show that cold and snow-covered conditions have generally decreased over the past 100 years. These trends suggest positive outcomes for tree health as related to reduced fine root mortality and nutrient loss associated with winter frost but negative outcomes as related to the northward advancement and proliferation of forest insect pests. In addition to effects on vegetation, reductions in cold temperatures and snow cover are likely to have negative impacts on the ecology of the northern forest through impacts on water, soils, and wildlife. The overall loss of coldness and snow cover may also have negative consequences for logging and forest products, vector-borne diseases and human health, recreation and tourism, and cultural practices, which together represent important social and economic dimensions for the northern forest region. These findings advance our understanding of how our changing winters may transform the socio- ecological system of a region that has been defined by the contrasting rhythm of the seasons. Our research also identifies a trajectory of change that informs our expectations for the future as the climate continues to warm.

Ecological Applications↗
USGS2016

Total belowground carbon flux in subalpine forests is related to leaf area index, soil nitrogen, and tree height

In forests, total belowground carbon (C) flux (TBCF) is a large component of the C budget and represents a critical pathway for delivery of plant C to soil. Reducing uncertainty around regional estimates of forest C cycling may be aided by incorporating knowledge of controls over soil respiration and TBCF. Photosynthesis, and presumably TBCF, declines with advancing tree size and age, and photosynthesis increases yet C partitioning to TBCF decreases in response to high soil fertility. We hypothesized that these causal relationships would result in predictable patterns of TBCF, and partitioning of C to TBCF, with natural variability in leaf area index (LAI), soil nitrogen (N), and tree height in subalpine forests in the Rocky Mountains, USA. Using three consecutive years of soil respiration data collected from 22 0.38-ha locations across three 1-km 2 subalpine forested landscapes, we tested three hypotheses: (1) annual soil respiration and TBCF will show a hump-shaped relationship with LAI; (2) variability in TBCF unexplained by LAI will be related to soil nitrogen (N); and (3) partitioning of C to TBCF (relative to woody growth) will decline with increasing soil N and tree height. We found partial support for Hypothesis 1 and full support for Hypotheses 2 and 3. TBCF, but not soil respiration, was explained by LAI and soil N patterns ( r 2 = 0.49), and the ratio of annual TBCF to TBCF plus aboveground net primary productivity (ANPP) was related to soil N and tree height ( r 2 = 0.72). Thus, forest C partitioning to TBCF can vary even within the same forest type and region, and approaches that assume a constant fraction of TBCF relative to ANPP may be missing some of this variability. These relationships can aid with estimates of forest soil respiration and TBCF across landscapes, using spatially explicit forest data such as national inventories or remotely sensed data products.

Ecosphere↗
USGS2022

Trophic interactions and feedbacks maintain intact and degraded states of Hawaiian tropical forests

Feedbacks within ecosystems can lead to internal reinforcement of the current state providing ecosystem resilience. Often, multiple biotic interactions across trophic levels play a role in such feedbacks, yet these are generally studied independently, obscuring the relative importance of interactions among different factors. We look at various potential feedbacks in intact and degraded mesic forests on Hawaiʻi Island where managers have planted native Acacia koa (koa) trees in an attempt to jumpstart succession in former cattle pastures. These restoration forests, however, have not undergone secondary succession, instead maintaining a koa overstory with an exotic pasture grass understory. We contrasted different trophic level processes that influence the capacity for natural understory regeneration: feedbacks between bird-mediated seed rain and fruiting understory (“top-down”), as well as links between understory composition and microhabitats for native seed germination (“bottom-up”). We quantified bird-mediated seed rain under canopy trees along transects spanning intact, fragmented, and restoration forests. Along these transects, we established plots around focal overstory trees to measure abundance of fruiting understory species, ground cover (e.g., exotic grass, bryophyte), and obtained estimates of bird density to evaluate the contribution of each of these factors to seedling abundance. We also used a factorial seed addition/grass removal experiment to directly compare the influence of seed rain and germination substrate. We found evidence of both top-down and bottom-up feedbacks that reinforced the current state of each forest type. In the intact and fragmented forests, the combination of comparatively high seed rain and ample germination substrate is likely critical for maintaining a diverse forest system. In contrast, exotic grasses exhibit priority effects in restoration forests, inhibiting seed germination and effectively negating any benefits that could be derived from bird-mediated seed rain. Such internal reinforcement suggests that active, rather than passive, restoration would be beneficial to increase forest diversity in restoration areas.

Hawaii↗
USGS2019

Quantifying trends and uncertainty in prehistoric forest composition

Forest ecosystems in eastern North America were in flux over the last several thousand years, well before Euro-American land clearance and the 20th-century onset of anthropogenic climate change. However, the magnitude and uncertainty of prehistoric vegetation change have been difficult to quantify because of the multiple ecological, dispersal, and sedimentary processes that govern the relationship between forest composition and fossil pollen assemblages. Here we extend STEPPS, a Bayesian hierarchical spatio-temporal pollen-vegetation model, to estimate changes in forest composition in the upper Midwestern United States from about 2000 to 200 years ago. Using this approach, we identify areas of statistically and ecologically significant change. Between 2000 and 200 years ago, forest composition significantly changed across broad regions of north-central Wisconsin and Minnesota. Rates of compositional change varied spatially, and can be linked to previously reported events. The single largest change is the infilling of Tsuga canadensis in northern Wisconsin over the past 2000 years. Despite this range in-filling, the range limit of T. canadensis was largely stable, with modest expansion westward. The regional ecotone between temperate hardwood forests and northern mixed hardwood/conifer forests shifted southwestward by 15-20 km in Minnesota and Northwestern Wisconsin. Fraxinus, Ulmus, and other mesic hardwoods expanded in the Big Woods region of southern Minnesota. However, some areas showed no significant change, suggesting high complexity in the spatiotemporal patterns of past forest dynamics. The increasing density of paleoecological data networks and advances in statistical modeling approaches now enables the confident detection of subtle but significant changes in forest composition over the last 2000 years.

Minnesota, Wisconsin↗
USGS2021

The Robinson Forest environmental monitoring network: Long‐term evaluation of streamflow and precipitation quantity and stream‐water and bulk deposition chemistry in eastern Kentucky watersheds

The University of Kentucky (U KY) has owned Robinson Forest (37.460723° N, 83.158598° W) since 1923, conducting experiments crucial to understanding the environmental effects of land management in the region. Part of the management of Robinson Forest has been collection of environmental data, including precipitation quantity, bulk‐deposition chemistry, streamflow, stream‐water chemistry, and air and stream temperature. Over the years, these data have been collected and archived using various technologies and have been mostly inaccessible for research use – unedited and uncompiled, scattered across several spreadsheets and paper records. Through a partnership between the U.S. Geological Survey (USGS) and U KY, daily precipitation data for six stations and stream data from four watersheds in Robinson Forest have been compiled for 1971–2018, checked for transcription errors, and annotated for changes in methodologies. These data are available as a USGS data release at https://doi.org/10.5066/P9FPLG1O . Improved accessibility of this data set provides an important research resource for understanding water quality in minimally effected forests in the region. Preliminary results indicate that these data present a valuable opportunity to evaluate linkages among atmospheric deposition and stream chemistry, the effects of environmental policy, such as the Clean Air Act, and effects from nearby land disturbance in the form of surface mining. Furthermore, these data fill a geographic and physiographic gap in what is available to examine deposition and streamflow patterns over the last 45 years, supplementing those long‐term records of research sites in northern (e.g., Hubbard Brook Experimental Forest), central (e.g., Fernow Experimental Forest) and southern Appalachia (e.g., Coweeta Hydrologic Laboratory). As an oasis in the midst of significant surface mining activity, Robinson Forest presents a unique opportunity to understand environmental conditions characteristic of minimally disturbed forests similar to pre‐mining conditions in the Central Appalachian region.

Kentucky↗
USGS2015

Approaches to modeling landscape-scale drought-induced forest mortality

Drought stress is an important cause of tree mortality in forests, and drought-induced disturbance events are projected to become more common in the future due to climate change. Landscape Disturbance and Succession Models (LDSM) are becoming widely used to project climate change impacts on forests, including potential interactions with natural and anthropogenic disturbances, and to explore the efficacy of alternative management actions to mitigate negative consequences of global changes on forests and ecosystem services. Recent studies incorporating drought-mortality effects into LDSMs have projected significant potential changes in forest composition and carbon storage, largely due to differential impacts of drought on tree species and interactions with other disturbance agents. In this chapter, we review how drought affects forest ecosystems and the different ways drought effects have been modeled (both spatially and aspatially) in the past. Building on those efforts, we describe several approaches to modeling drought effects in LDSMs, discuss advantages and shortcomings of each, and include two case studies for illustration. The first approach features the use of empirically derived relationships between measures of drought and the loss of tree biomass to drought-induced mortality. The second uses deterministic rules of species mortality for given drought events to project changes in species composition and forest distribution. A third approach is more mechanistic, simulating growth reductions and death caused by water stress. Because modeling of drought effects in LDSMs is still in its infancy, and because drought is expected to play an increasingly important role in forest health, further development of modeling drought-forest dynamics is urgently needed.

Book chapter↗
USGS1996

Simulating secondary succession of elk forage values in a managed forest landscape, western Washington

Modern timber management practices often influence forage production for elk (Cervus elaphus) on broad temporal and spatial scales in forested landscapes. We incorporated site-specific information on postharvesting forest succession and forage characteristics in a simulation model to evaluate past and future influences of forest management practices on forage values for elk in a commercially managed Douglas fir (Pseudotsuga menziesii, PSME)-western hemlock (Tsuga heterophylla, TSHE) forest in western Washington. We evaluated future effects of: (1) clear-cut logging 0, 20, and 40% of harvestable stands every five years; (2) thinning 20-year-old Douglas fir forests; and (3) reducing the harvesting cycle from 60 to 45 years. Reconstruction of historical patterns of vegetation succession indicated that forage values peaked in the 1960s and declined from the 1970s to the present, but recent values still were higher than may have existed in the unmanaged landscape in 1945. Increased forest harvesting rates had little short-term influence on forage trends because harvestable stands were scarce. Simulations of forest thinning also produced negligible benefits because thinning did not improve forage productivity appreciably at the stand level. Simulations of reduced harvesting cycles shortened the duration of declining forage values from approximately 30 to 15 years. We concluded that simulation models are useful tools for examining landscape responses of forage production to forest management strategies, but the options examined provided little potential for improving elk forages in the immediate future.

Washington↗
USGS2005

Denitrification and N2O emission from forested and cultivated alluvial clay soil

Restored forested wetlands reduce N loads in surface discharge through plant uptake and denitrification. While removal of reactive N reduces impact on receiving waters, it is unclear whether enhanced denitrification also enhances emissions of the greenhouse gas N2O, thus compromising the water-quality benefits of restoration. This study compares denitrification rates and N2O:N2 emission ratios from Sharkey clay soil in a mature bottomland forest to those from an adjacent cultivated site in the Lower Mississippi Alluvial Valley. Potential denitrification of forested soil was 2.4 times of cultivated soil. Using intact soil cores, denitrification rates of forested soil were 5.2, 6.6 and 2.0 times those of cultivated soil at 70, 85 and 100% water-filled pore space (WFPS), respectively. When NO3 was added, N2O emissions from forested soil were 2.2 times those of cultivated soil at 70% WFPS. At 85 and 100% WFPS, N2O emissions were not significantly different despite much greater denitrification rates in the forested soil because N2O:N2 emission ratios declined more rapidly in forested soil as WFPS increased. These findings suggest that restoration of forested wetlands to reduce NO3 in surface discharge will not contribute significantly to the atmospheric burden of N2O. ?? Springer 2005.

Biogeochemistry↗
USGS2021

Riparian forests buffer the negative effects of cropland on macroinvertebrate diversity in lowland Amazonian streams

Riparian forests regulate stream ecosystems and biodiversity. Therefore, changes to riparian structure may threaten stream ecosystem function by triggering taxonomic and functional changes to aquatic communities. Because macroinvertebrate assemblages are sensitive to environmental changes, they can be effective indicators of stream integrity in disturbed landscapes. To assess the role of riparian forests in maintaining tropical stream communities in areas experiencing large-scale watershed disturbance, we quantified the taxonomic and functional response of stream macroinvertebrate communities to forest clearing in the southeastern Amazon’s agricultural frontier, a region experiencing widespread deforestation. Our results show that watershed deforestation can lead to significant changes in macroinvertebrate richness and community composition. We found a predominance of shredders in forested watersheds; scrapers in cropland watersheds with riparian forests; and collector-filterers in cropland watersheds without riparian forest buffers. Taxonomic composition was controlled by available organic material in forested watersheds and by periphyton in cropland sites regardless of whether they had a riparian buffer. Our results show that the clearing of riparian forests alters food sources supporting aquatic food webs, leading to ecosystem-level shifts through changes in light and temperature dynamics that affect aquatic communities in areas with intense land-use change such as the southeastern Amazon.

Tanguro Ranch↗
USGS2018

Influence of landscape structure, topography, and forest type on spatial variation in historical fire regimes, central Oregon, USA

Context In the interior Northwest, debate over restoring mixed-conifer forests after a century of fire exclusion is hampered by poor understanding of the pattern and causes of spatial variation in historical fire regimes. Objectives To identify the roles of topography, landscape structure, and forest type in driving spatial variation in historical fire regimes in mixed-conifer forests of central Oregon. Methods We used tree rings to reconstruct multicentury fire and forest histories at 105 plots over 10,393 ha. We classified fire regimes into four types and assessed whether they varied with topography, the location of fuel-limited pumice basins that inhibit fire spread, and an updated classification of forest type. Results We identified four fire-regime types and six forest types. Although surface fires were frequent and often extensive, severe fires were rare in all four types. Fire regimes varied with some aspects of topography (elevation), but not others (slope or aspect) and with the distribution of pumice basins. Fire regimes did not strictly co-vary with mixed-conifer forest types. Conclusions Our work reveals the persistent influence of landscape structure on spatial variation in historical fire regimes and can help inform discussions about appropriate restoration of fire-excluded forests in the interior Northwest. Where the goal is to restore historical fire regimes at landscape scales, managers may want to consider the influence of topoedaphic and vegetation patch types that could affect fire spread and ignition frequency.

Landscape Ecology↗