Us Forest Service Southern Research Station

Clemson, United States

Us Forest Service Southern Research Station

Clemson, United States
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Steen D.A.,Joseph W. Jones Ecological Research Center | Steen D.A.,Auburn University | McClure C.J.W.,Auburn University | Brock J.C.,Joseph W. Jones Ecological Research Center | And 9 more authors.
Ecological Applications | Year: 2012

Habitat loss and degradation are thought to be the primary drivers of species extirpations, but for many species we have little information regarding specific habitats that influence occupancy. Snakes are of conservation concern throughout North America, but effective management and conservation are hindered by a lack of basic natural history information and the small number of large-scale studies designed to assess general population trends. To address this information gap, we compiled detection/nondetection data for 13 large terrestrial species from 449 traps located across the southeastern United States, and we characterized the land cover surrounding each trap at multiple spatial scales (250-, 500-, and 1000-m buffers). We used occupancy modeling, while accounting for heterogeneity in detection probability, to identify habitat variables that were influential in determining the presence of a particular species. We evaluated 12 competing models for each species, representing various hypotheses pertaining to important habitat features for terrestrial snakes. Overall, considerable interspecific variation existed in important habitat variables and relevant spatial scales. For example, kingsnakes (Lampropeltis getula) were negatively associated with evergreen forests, whereas Louisiana pinesnake (Pituophis ruthveni) occupancy increased with increasing coverage of this forest type. Some species were positively associated with grassland and scrub/shrub (e.g., Slowinski's cornsnake, Elaphe slowinskii) whereas others, (e.g., copperhead, Agkistrodon contortrix, and eastern diamond-backed rattlesnake, Crotalus adamanteus) were positively associated with forested habitats. Although the species that we studied may persist in varied landscapes other than those we identified as important, our data were collected in relatively undeveloped areas. Thus, our findings may be relevant when generating conservation plans or restoration goals. Maintaining or restoring landscapes that are most consistent with the ancestral habitat preferences of terrestrial snake assemblages will require a diverse habitat matrix over large spatial scales. © 2012 by the Ecological Society of America.

Drake J.E.,University of Illinois at Urbana - Champaign | Drake J.E.,Boston University | Gallet-Budynek A.,Boston University | Gallet-Budynek A.,French National Institute for Agricultural Research | And 19 more authors.
Ecology Letters | Year: 2011

The earth's future climate state is highly dependent upon changes in terrestrial C storage in response to rising concentrations of atmospheric CO2. Here we show that consistently enhanced rates of net primary production (NPP) are sustained by a C-cascade through the root-microbe-soil system; increases in the flux of C belowground under elevated CO2 stimulated microbial activity, accelerated the rate of soil organic matter decomposition and stimulated tree uptake of N bound to this SOM. This process set into motion a positive feedback maintaining greater C gain under elevated CO2 as a result of increases in canopy N content and higher photosynthetic N-use efficiency. The ecosystem-level consequence of the enhanced requirement for N and the exchange of plant C for N belowground is the dominance of C storage in tree biomass but the preclusion of a large C sink in the soil. © 2011 Blackwell Publishing Ltd/CNRS.

Smee D.L.,Texas A&M University-Corpus Christi | Sanchez J.A.,Texas A&M University-Corpus Christi | Diskin M.,Texas A&M University-Corpus Christi | Trettin C.,Us Forest Service Southern Research Station
Estuarine, Coastal and Shelf Science | Year: 2017

Climate change is altering the distribution of foundation species, with potential effects on organisms that inhabit these environments and changes to valuable ecosystem functions. In the Gulf of Mexico, black mangroves (Avicennia germinans) are expanding northward into salt marshes dominated by Spartina alterniflora (hereafter Spartina). Salt marshes are essential habitats for many organisms, including ecologically and economically important species such as blue crabs (Callinectes sapidus) and Penaeid shrimp (e.g., Penaeus aztecus), which may be affected by vegetation changes. Black mangroves occupied higher tidal elevations than Spartina, and Spartina was present only at its lowest tidal elevations in sites when mangroves were established. We compared nekton and infaunal communities within monoculture stands of Spartina that were bordered by mangroves to nearby areas where mangroves had not yet become established. Nekton and infaunal communities were significantly different in Spartina stands bordered by mangroves, even though salinity and temperature were not different. Overall abundance and biomass of nekton and infauna was significantly higher in marshes without mangroves, although crabs and fish were more abundant in mangrove areas. Black mangrove expansion as well as other ongoing vegetation shifts will continue in a warming climate. Understanding how these changes affect associated species is necessary for management, mitigation, and conservation. © 2017 Elsevier Ltd

Mattingly W.B.,University of Wisconsin - Madison | Mattingly W.B.,Eastern Connecticut State University | Orrock J.L.,University of Wisconsin - Madison | Collins C.D.,Colby College | And 4 more authors.
Oecologia | Year: 2014

Land-use legacies are known to shape the diversity and distribution of plant communities, but we lack an understanding of whether historical land use influences community responses to contemporary disturbances. Because human-modified landscapes often bear a history of multiple land-use activities, this contingency can challenge our understanding of land-use impacts on plant diversity. We address this contingency by evaluating how beta diversity (the spatial variability of species composition), an important component of regional biodiversity, is shaped by interactions between historical agriculture and prescribed fire, two prominent disturbances that are often coincident in terrestrial ecosystems. At three study locations spanning 450 km in the southeastern United States, we surveyed longleaf pine woodland understory plant communities across 232 remnant and post-agricultural sites with differing prescribed fire regimes. Our results demonstrate that agricultural legacies are a strong predictor of beta diversity, but the direction of this land-use effect differed among the three study locations. Further, although beta diversity increased with prescribed fire frequency at each study location, this effect was influenced by agricultural land-use history, such that positive fire effects were only documented among sites that lacked a history of agriculture at two of our three study locations. Our study not only highlights the role of historical agriculture in shaping beta diversity in a fire-maintained ecosystem but also illustrates how this effect can be contingent upon fire regime and geographic location. We suggest that interactions among historical and contemporary land-use activities may help to explain dissimilarities in plant communities among sites in human-dominated landscapes. © 2014, Springer-Verlag Berlin Heidelberg.

Brudvig L.A.,Michigan State University | Orrock J.L.,University of Wisconsin - Madison | Damschen E.I.,University of Wisconsin - Madison | Collins C.D.,Colby College | And 5 more authors.
PLoS ONE | Year: 2014

Ecological restoration is frequently guided by reference conditions describing a successfully restored ecosystem; however, the causes and magnitude of ecosystem degradation vary, making simple knowledge of reference conditions insufficient for prioritizing and guiding restoration. Ecological reference models provide further guidance by quantifying reference conditions, as well as conditions at degraded states that deviate from reference conditions. Many reference models remain qualitative, however, limiting their utility. We quantified and evaluated a reference model for southeastern U.S. longleaf pine woodland understory plant communities. We used regression trees to classify 232 longleaf pine woodland sites at three locations along the Atlantic coastal plain based on relationships between understory plant community composition, soils (which broadly structure these communities), and factors associated with understory degradation, including fire frequency, agricultural history, and tree basal area. To understand the spatial generality of this model, we classified all sites together and for each of three study locations separately. Both the regional and location-specific models produced quantifiable degradation gradients-i.e., progressive deviation from conditions at 38 reference sites, based on understory species composition, diversity and total cover, litter depth, and other attributes. Regionally, fire suppression was the most important degrading factor, followed by agricultural history, but at individual locations, agricultural history or tree basal area was most important. At one location, the influence of a degrading factor depended on soil attributes. We suggest that our regional model can help prioritize longleaf pine woodland restoration across our study region; however, due to substantial landscape-to-landscape variation, local management decisions should take into account additional factors (e.g., soil attributes). Our study demonstrates the utility of quantifying degraded states and provides a series of hypotheses for future experimental restoration work. More broadly, our work provides a framework for developing and evaluating reference models that incorporate multiple, interactive anthropogenic drivers of ecosystem degradation. © 2014 Brudvig et al.

Greenberg C.H.,Us Forest Service Southern Research Station | Forrest T.G.,University of North Carolina at Asheville | Waldrop T.,Us Forest Service Southern Research Station
Forest Science | Year: 2010

As part of the multidisciplinary National Fire and Fire Surrogate Study, we used drift fences with pitfall traps to determine how three fuel reduction treatments affected ground-dwelling macroarthropods in the southern Appalachian Mountains of North Carolina. Four experimental units, each > 14 ha, were contained within each of three replicate blocks. Treatments were (1) prescribed burning, (2) mechanical felling of shrubs and small trees, (3) mechanical felling + burning, and (4) untreated controls. Mechanical understory felling was conducted in winter 2001-2002, and prescribed burning was conducted in March 2003. Mechanical felling burning resulted in greater canopy openness compared with the other treatments as a result of hotter fires and elevated levels of subsequent tree mortality. Burning reduced leaf litter depth in both burned treatments by >80%. We captured 6,776 individual macroarthropods (460 g of dry biomass) within 22 identified orders and 59 identified families. Coleoptera and Hymenoptera were numerically dominant (27.3 and 25.9%, respectively); Lepidoptera larvae also were a dominant component of dry biomass (37%). We found no differences among treatments in the relative abundance or dry biomass of total ground-dwelling macroarthropods or within most orders; Hymenoptera (predominantly Formicidae) dry biomass was greater with mechanical felling burning than with mechanical felling. Total relative abundance and dry biomass were low in spring and higher in late summer. Our results indicate that prescribed burning and mechanical fuel reduction treatments conducted in winter or early spring have little impact on the community composition, relative abundance, or biomass of total arthropods or most arthropod orders and families, at least in the short term. However, because we did not use a killing agent, our trapping method probably undersampled macroarthropods that could climb or fly from traps, and results for those groups should be interpreted cautiously. Our study suggests that the fuel reduction methods studied may be used as a land management tool in upland hardwood forest with little effect on macroarthropod communities or the ground-dwelling arthropod prey base for vertebrates.

Veldman J.W.,University of Wisconsin - Madison | Brudvig L.A.,Michigan State University | Damschen E.I.,University of Wisconsin - Madison | Orrock J.L.,University of Wisconsin - Madison | And 2 more authors.
Journal of Vegetation Science | Year: 2014

Question: Human-altered disturbance regimes and agricultural land uses are broadly associated with reduced plant species diversity in terrestrial ecosystems. In this study, we seek to understand how fire frequency and agricultural land-use history influence savanna understorey plant diversity through complex relationships (i.e. indirect effects) among multiple biophysical variables. Location: Fort Bragg, NC, US, Savannah River Site, SC, US and Fort Stewart, GA, US. Methods: We use structural equation modelling (SEM) to evaluate the relationships among six groups of predictor variables and their influence on local-scale species richness in pine savannas at 256 sites from three locations in the southeastern USA. In the model, fire frequency and agricultural history are hypothesized to control richness through a combination of direct effects, and indirect effects mediated by resource availability, tree abundance, understorey plant abundance and the O horizon (litter and duff depth). Results: Frequent fires promote richness by limiting tree abundance, which increases understorey abundance and reduces the O horizon. Frequent fires also limit the O horizon independent of tree abundance. Of the total positive effect of fire on richness, 70% is attributable to reductions in the O horizon and 30% to reduced tree abundance. Agricultural history has a negative effect on richness through a positive correlation with tree abundance, which decreases understorey abundance and increases the O horizon. Agricultural history has a modest negative effect on richness by reducing resource availability as well as a strong direct negative effect (38% of the total effect) that is unrelated to other modelled variables. Conclusions: Through a multivariate framework and large-scale data set, this study unites and tests our understanding of the factors that control plant species diversity in a fire-dependent ecosystem. We show that the effects of fire frequency and agricultural history on richness are largely mediated through other ecosystem attributes, including vegetation structure (i.e. tree and understorey abundance), resource availability and the O horizon. Persistent, negative effects of agricultural history demonstrate the slow rates of savanna plant community recovery on post-agricultural land and highlight the conservation value of frequently burned savanna remnants. © 2014 International Association for Vegetation Science.

De Steven D.,Us Forest Service Southern Research Station | Sharitz R.R.,Savannah River Ecology Laboratory | Barton C.D.,University of Kentucky
Wetlands | Year: 2010

Depressional wetlands may be restored passively by disrupting prior drainage to recover original hydrology and relying on natural revegetation. Restored hydrology selects for wetland vegetation; however, depression geomorphology constrains the achievable hydroperiod, and plant communities are influenced by hydroperiod and available species pools. Such constraints can complicate assessments of restoration success. Sixteen drained depressions in South Carolina, USA, were restored experimentally by forest clearing and ditch plugging for potential crediting to a mitigation bank. Depressions were assigned to alternate revegetation methods representing desired targets of herbaceous and wet-forest communities. After five years, restoration progress and revegetation methods were evaluated. Restored hydroperiods differed among wetlands, but all sites developed diverse vegetation of native wetland species. Vegetation traits were influenced by hydroperiod and the effects of early drought, rather than by revegetation method. For mitigation banking, individual wetlands were assessed for improvement from pre-restoration condition and similarity to assigned reference type. Most wetlands met goals to increase hydroperiod, herb-species dominance, and wetland-plant composition. Fewer wetlands achieved equivalence to reference types because some vegetation targets were incompatible with depression hydroperiods and improbable without intensive management. The results illustrated a paradox in judging success when vegetation goals may be unsuited to system constraints. © Society of Wetland Scientists (Outside the USA) 2010.

Knoepp J.D.,Us Forest Service Southern Research Station | Vose J.M.,Us Forest Service Southern Research Station | Clinton B.D.,Us Forest Service Southern Research Station | Hunter M.D.,Us Forest Service Southern Research Station | Hunter M.D.,University of Georgia
Soil Science Society of America Journal | Year: 2011

Eastern hemlock [Tsuga canadensis (L.) Carrière] trees serve an important ecological role in riparian ecosystems in the Southern Appalachians. Significant hemlock mortality is occurring due to infestation by the hemlock woolly adelgid (HWA) (Adelges tsugae Annand), a non-native invasive pest. Our objective was to quantify the impacts of HWA and hemlock mortality on nutrient cycling pools and processes. In 2004, we established eight research plots in riparian areas with>50% basal area in hemlock and four reference plots in riparian areas without hemlock (hardwood). All hemlock plots were infested withHWA. In four of the hemlock plots, all hemlock trees were girdled to induce defoliation and rapid mortality. By fall 2006, there was 90 and 10% mortality in the girdled and nongirdled hemlock plots, respectively. Measurements included soil temperature and moisture, nutrient pools, N transformations, litterfall and forest floor amount and chemistry, and throughfall and soil solution chemistry. From 2004 to 2008, litterfall composition changed, withan initial increase in the hemlock needle percentage followed by a decline. Hemlock plots had cooler spring soil temperatures than hardwood plots. Hemlock plots had greater surface soil and forest floor total C than hardwood plots; soil C content did not change during the 4 yr of measurement. There were no differences in N mineralization rates or soil solution N concentrations among treatments. Differences between litterfall and forest floor nutrient contents in hemlock and hardwood plots suggest that as hemlocks are replaced by hardwood species, nutrient cycling rates and processes will be similar to hardwood reference plots. © Soil Science Society of America.

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