@article{spence_leggett_2024, title={A pilot program to expand career opportunities in conservation for students of color}, url={https://doi.org/10.1002/nse2.20136}, DOI={10.1002/nse2.20136}, abstractNote={Abstract}, journal={Natural Sciences Education}, author={Spence, Porché L. and Leggett, Zakiya H.}, year={2024}, month={Jun} }
 @article{rodgers_scanga_st juliana_tietjen_honea_byrne_leggett_middendorf_2024, title={Four-Dimensional Ecology Education (4DEE) for everyone: teaching ecology to non-majors}, volume={5}, ISSN={["1540-9309"]}, DOI={10.1002/fee.2749}, abstractNote={Originally developed for application to ecology courses for undergraduate majors, the Four‐Dimensional Ecology Education (4DEE) Framework offers possibilities for adaptation to courses with ecology content for many other audiences. Recognizing the extraordinary range of classroom contexts and constraints, we developed some general, flexible recommendations and approaches to guide instructors in adapting the 4DEE Framework for an array of non‐major audiences and classroom context needs. Our hope is that 4DEE‐aligned courses for non‐majors will provide these students with greater appreciation of ecology and inspire them to use their knowledge to address many critical environmental issues in their personal and professional lives. Many of our recommendations likely apply to natural science, engineering, and math majors as well. We encourage more ecologists to embrace teaching non‐majors courses as a response to the urgent need to improve ecological literacy for everyone.}, journal={FRONTIERS IN ECOLOGY AND THE ENVIRONMENT}, author={Rodgers, Vikki L. and Scanga, Sara E. and St Juliana, Justin R. and Tietjen, Erica S. and Honea, Jon M. and Byrne, Loren B. and Leggett, Zakiya H. and Middendorf, George}, year={2024}, month={May} }
 @article{korhonen_panwar_henderson_fernholz_leggett_meyer_bhuta_2024, title={Gaps in diversity representation and data insufficiencies in the U.S. forest sector workforce analysis}, volume={15}, ISSN={["2666-7193"]}, url={https://doi.org/10.1016/j.tfp.2023.100486}, DOI={10.1016/j.tfp.2023.100486}, abstractNote={When comprehensive and accurate data on diversity and representation is available, it significantly enhances our understanding of business challenges, thereby bolstering policy decisions and strategy formulation across all organizational tiers. Using the U.S. forest sector as a case study, we illustrate that there are significant gaps in diversity and representation within the private forest sector, particularly in terms of gender and race. These disparities exist across various domains and categories, including different forest industries, job roles, and business ownership structures. Our analysis brings to light the inadequacies of the current workforce data, emphasizing their limitations in keeping pace with the changing socio-economic landscape. We examine these areas of oversight and emphasize the profound implications they have for guiding both research and practices aimed at cultivating a sustainable and inclusive workforce.}, journal={TREES FORESTS AND PEOPLE}, author={Korhonen, Jaana and Panwar, Rajat and Henderson, Jesse and Fernholz, Kathryn and Leggett, Zakiya and Meyer, Eliza and Bhuta, Arvind A. R.}, year={2024}, month={Mar} }
 @article{barnes_parajuli_leggett_suchoff_2023, title={Assessing the financial viability of growing industrial hemp with loblolly pine plantations in the southeastern United States}, volume={6}, ISSN={["2624-893X"]}, DOI={10.3389/ffgc.2023.1148221}, abstractNote={Industrial hemp (Cannabis sativa L. <0.3% THC), a non-psychoactive chemotype of cannabis, was reclassified and made legal for growing across the United States under the 2018 Farm Bill. Given that resources, knowledge, and interest for this novel crop are expanding rapidly, we explored the possibility of intercropping industrial hemp for fiber with loblolly pine (Pinus taeda) plantations, one of the most commercially widespread tree species in the southern United States. Following a previous greenhouse study confirming hemp’s ability to grow in pine-influenced soils, we examined the financial feasibility of this potential agroforestry system. We simulated the loblolly pine tree growth information using PTAEDA 4.0, a growth and yield model, and collected the enterprise budget data on hemp productivity, operating and fixed costs, and prices from various sources. Based on the capital budgeting analyses, results suggest that pine-hemp intercropping can yield higher economic returns –at least 25% higher net present value—than the conventional monoculture loblolly pine plantation. The early rotation cash flow and the complimentary benefits can result in a more financially viable loblolly pine plantation under the intercropping scenario. While new research continues to advance further with field trials and other analyses, this study provides valuable insights into the current market conditions and productivity level of industrial hemp cultivation that need to be addressed for hemp intercropping to succeed as an economically viable agroforestry investment.}, journal={FRONTIERS IN FORESTS AND GLOBAL CHANGE}, author={Barnes, Thomas and Parajuli, Rajan and Leggett, Zakiya and Suchoff, David}, year={2023}, month={May} }
 @article{height_martin_leggett_2023, title={Call for environmental justice amplification among ecology scholars and practitioners: A Black Ecology perspective}, url={https://doi.org/10.1002/bes2.2039}, DOI={10.1002/bes2.2039}, abstractNote={Abstract}, journal={The Bulletin of the Ecological Society of America}, author={Height, Tatiana C. and Martin, Katherine L. and Leggett, Zakiya H.}, year={2023}, month={Jan} }
 @article{woods_leggett_miriti_2023, title={The intersections of identity and persistence for retention in ecology and environmental biology with personal narratives from Black women}, url={https://doi.org/10.1080/10899995.2022.2154935}, DOI={10.1080/10899995.2022.2154935}, abstractNote={Abstract Ecology and environmental (EE) biology has low representation of Black Indigenous and People of Color (BIPOC). Degree completion and career placement in EE often fail due to poor consideration of the intersections among student lived experiences and the academic support, peer community support, mentoring, and leadership development that they receive. The demographic composition of these disciplines, which are situated within the geosciences, differs from the composition of the broader society and will continue to do so until biases associated with the dominant culture are remedied. Lack of diverse representation leaves young people of color unable to visualize themselves in EE careers, which contributes to their not pursuing EE programs, majors, and career placement. As Black ecologists, we share narratives that include lessons gained from our individual journeys through undergraduate, graduate, and postdoctoral positions emphasizing experiences that supported our successful recruitment into our current academic positions. Throughout, we emphasize intersections of identity and persistence in EE. We assert that colorblind interventions to promote diverse participation in EE will be inadequate to affect meaningful increases in BIPOC participation. We highlight the value of diverse mentors, institutional support, and institutional commitment to diversity across multiple institutions. Additionally, we offer recommendations in support of BIPOC student retention in EE and the geosciences. Increasing diversity in EE will involve reassessment of how ecologists and environmental biologists are defined, interventions that support BIPOC retention at all career stages, and critical assessment of cultural biases in EE education and field experiences.}, journal={Journal of Geoscience Education}, author={Woods, Natasha N. and Leggett, Zakiya H. and Miriti, Maria N.}, year={2023}, month={Jul} }
 @article{arenas_spence_nilon_leggett_2022, title={Diversifying the Field of Forestry Through a Graduate Fellowship Program: A Pilot Study on the Expectations of Students of Color}, volume={8}, ISSN={["1938-3746"]}, url={https://doi.org/10.1093/jofore/fvac024}, DOI={10.1093/jofore/fvac024}, abstractNote={Abstract}, journal={JOURNAL OF FORESTRY}, author={Arenas, Aaron A. and Spence, Porche L. and Nilon, Charles H. and Leggett, Zakiya H.}, year={2022}, month={Aug} }
 @article{dick_gardner_frene_heitman_sucre_leggett_2022, title={Forest floor manipulation effects on the relationship between aggregate stability and ectomycorrhizal fungi}, volume={505}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2021.119873}, abstractNote={Forest floor and mineral soil manipulations influence the soil biogeochemical properties important for loblolly pine (Pinus taeda L.) tree growth. The impacts of forest floor manipulations on soil aggregate stability and the presence of ectomycorrhizal fungi (EMF), was assessed to elucidate the relationship between EMF abundance and aggregate stability. The study site consists of a 14-year-old loblolly pine plantation managed by Weyerhaeuser Company in the Lower Coastal Plain, approximately 8 miles east of New Bern, North Carolina, USA. The soil samples were collected from the top 7.62 cm of each soil treatment which includes three levels of forest floor retention: removed, control, and doubled and two levels of forest floor mixing with the mineral soil: mixed and unmixed. Ectomycorrhizal fungi abundance was evaluated by ester-linked fatty acid methyl ester analysis and microbial community functionality was assessed by acid-phosphatase activity measurement. Aggregate stability was assessed using the aggregate mean weight diameter approach. Results indicate that the forest floor manipulations had no significant impact on aggregate stability and EMF abundance. However, a positive relationship between EMF abundance and aggregate stability was identified. Removing the forest floor resulted in a soil bulk density increase of 0.18 g cm−3 compared to doubling the forest floor. Our results demonstrate that some mineral soil properties recover relatively quickly from forest floor manipulations. The study informs forest managers interested in how soil responds to forest floor manipulation and the interaction between EMF and aggregate stability.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Dick, David L. and Gardner, Terrence G. and Frene, Juan P. and Heitman, Joshua L. and Sucre, Eric B. and Leggett, Zakiya H.}, year={2022}, month={Feb} }
 @article{shively_cook_maier_garcia_albaugh_campoe_leggett_2022, title={Readily available resources across sites and genotypes result in greater aboveground growth and reduced fine root production in Pinus taeda}, volume={521}, ISSN={["1872-7042"]}, url={http://europepmc.org/abstract/AGR/IND607837981}, DOI={10.1016/j.foreco.2022.120431}, abstractNote={Fine roots serve as the primary interface between trees and the soil, and they are dynamic in their response to environmental conditions.Among many functions, they are principle in gathering nutrients and water, and they constitute a major component of the tree.Their overall contribution to soil carbon flux is not well understood, nor is the effect of site and genotype on their dynamics, and these factors are crucial to understanding nutrient cycles and tree growth under variable conditions.This study evaluated how the fine root dynamics of loblolly pine (Pinus taeda L.) might be different between genotypes and on different sites.Three loblolly pine plantations were established, two in 2009 in North Carolina (NC) and Virginia (VA), and one in 2011 in Brazil (BR).Root biomass was estimated with soil cores across the three sites and between two genotypes in 2020.Seasonal and annual fine root production was measured at the NC and VA sites over the 12th growing season using ingrowth cores.The trees in BR that were two years younger were much larger than those in NC and VA and had more fine root biomass at initial sampling than those in NC, despite similar levels of fertility.Meanwhile, fine root production rates decreased with higher rates of aboveground productivity across all measured plots in NC and VA.These results indicate that (1) standing fine root biomass may be related to environmental conditions that are not easily manipulated, which could inform modeling of carbon cycles, and (2) in these intensively managed plots, sufficient resources were available to allow for increased aboveground growth despite lower rates of fine root production, which supports the employment of these intensive silvicultural practices.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Shively, Timothy J. and Cook, Rachel and Maier, Chris A. and Garcia, Kevin and Albaugh, Timothy J. and Campoe, Otavio and Leggett, Zakiya}, year={2022}, month={Oct} }
 @article{minick_leggett_sucre_fox_strahm_2021, title={Bioenergy production effects on SOM with depth of loblolly pine forests on Paleaquults in southeastern USA}, volume={27}, ISSN={["2352-0094"]}, DOI={10.1016/j.geodrs.2021.e00428}, abstractNote={Managed loblolly pine (P. taeda L.) forests comprise a major land-use across the “wood basket” of the southeastern US. Lower coastal plain loblolly pine forests can enhance carbon (C) storage in fast-growing vegetation and soils, representing a significant opportunity to manage these forests for improved soil health through an understanding of soil C and nitrogen (N) storage. Furthermore, these forests have unrealized potential to produce biomass for emerging bioenergy markets. Despite this, very little is known about how intensified management (herbaceous bioenergy production) of these forests influences short-term soil organic C (SOC) and soil organic N (SON) pools in surface and subsurface soil horizons. The field site was located in the Lower Coastal Plain of North Carolina, USA in which trees were planted in bedded (e.g., raised) rows (bed) and intercropped with or without switchgrass (P. virgatum L.) between the bedded rows of trees (interbed). Soils were collected from four depths (0–5, 5–15, 15–30, and 30–45 cm) and two locations (bed and interbed regions) and fractionated into light and heavy mineral-associated SOC and SON pools using a sequential density fractionation technique. Bulk soil SOC and SON concentration as well as C:N ratio decreased with depth for both treatments, while 15N became enriched. Free and occluded lighter fractions (< 1.65 g cm−3) had higher SOC and SON concentration (~45% C and ~ 1.15% N) compared to medium (1.65–2.00 g cm−3) and heavy (> 2.00 g cm−3) fractions. At the 0–5 cm depth in interbeds, SOC and SON were concentrated in the free light fraction (~45%), but transitioned to being concentrated in the heaviest mineral-associated fraction at the 15–30 (~55%) and 30–45 (~70%) cm depth. The 15N analysis of density fractions indicated progressive enrichment with increasing density, suggesting increasing incorporation of microbially-derived products into stable mineral-associated soil organic matter (SOM) pools. In the pine-switchgrass treatment, SOC and SON concentrations were higher in the light and medium fractions in beds and interbeds compared to the pine only treatment, particularly at the 30–45 cm depth. The C:N ratio in the pine-switchgrass treatment was higher compared to the pine only treatment indicating inputs of new plant-derived organic matter. Furthermore, the δ13C stable isotope signature was enriched in both the occluded light fraction (1.65 g cm−3) and the mineral-associated fraction (1.65–1.85 g cm−3). Our results suggest that switchgrass intercropping is contributing to the early buildup of SOM in particulate and mineral-associated SOM pools possibly through additions of new root-derived organic matter and the positive effect on soil microbial activity through priming of microbes.}, journal={GEODERMA REGIONAL}, author={Minick, Kevan J. and Leggett, Zakiya H. and Sucre, Eric B. and Fox, Thomas R. and Strahm, Brian D.}, year={2021}, month={Dec} }
 @article{cooper_hawn_larson_parrish_bowser_cavalier_dunn_haklay_gupta_jelks_et al._2021, title={Inclusion in citizen science: The conundrum of rebranding}, volume={372}, ISSN={0036-8075 1095-9203}, url={http://dx.doi.org/10.1126/science.abi6487}, DOI={10.1126/science.abi6487}, abstractNote={Does replacing the term “citizen science” do more harm than good?}, number={6549}, journal={Science}, publisher={American Association for the Advancement of Science (AAAS)}, author={Cooper, C.B. and Hawn, C. and Larson, L.R. and Parrish, J.K. and Bowser, G. and Cavalier, D. and Dunn, R.R. and Haklay, M. and Gupta, K. and Jelks, N.O. and et al.}, year={2021}, month={Jun}, pages={1386–1388} }
 @article{bakken_forrester_mladenoff_leggett_juzwik_jetton_2021, title={Mortality patterns following a hickory decline event - Is density reduction key to maintaining bitternut hickory?}, volume={485}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2021.118956}, abstractNote={Bitternut hickory (Carya cordiformis (Wangenh.) K. Koch) is an important component of many hardwood forest systems in the northern hardwood forests of the Lake States. Extensive mortality of the species was observed in a long-term field experimental site in a second growth northern hardwood forest of Wisconsin between 2010 and 2016. We quantified and documented the characteristics of the mortality, investigated the relationship between bitternut hickory density and mortality patterns, and assessed the persistence of hickory regeneration. The presence of a pathogenic fungus (Ceratocystis smalleyi Johnson and Harrington) and hickory bark beetle (Scolytus quadrispinosus Say) were identified as the main cause of mortality in other instances of hickory decline during a similar time period in the Midwest and Northeast. We investigated the role of these agents through post hoc analysis. Tree surveys of mapped stems ≥10 cm dbh conducted periodically from 2005 to 2016 indicated mortality of hickory rose sharply to 35% year−1 from 2010 to 2016. This is a substantial increase in mortality relative to the dominant species at the site (Acer saccharum Marshall, Tilia americana L., and Fraxinus spp.) which was 1.11% year−1 in the same time period. Mortality rates were higher in larger stems (≥20 cm dbh) than smaller stems (10 < 20 cm dbh). Additional analyses evaluated whether mortality rates were affected by localized species composition, using the proportion of hickory stems among neighboring trees. Proportion of hickory stems, diameter, and crown class proved to be statistically important in predicting mortality in individual hickory stems. The density of hickory regeneration in the <30 cm tall height class decreased from 2010 to 2016. Overall the bitternut hickory population significantly declined, especially the larger sized trees, and this decline will have lasting consequences on the persistence of the species in the area. Potential management actions for mitigating impacts of such rapid hickory decline events, mainly selective thinning, are discussed. Methods for maintaining this co-occurring species is increasingly important as several other codominant species in northern hardwood forests are also decreasing.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Bakken, K. A. and Forrester, J. A. and Mladenoff, D. J. and Leggett, Z. and Juzwik, J. and Jetton, R. M.}, year={2021}, month={Apr} }
 @article{riley_goller_leggett_lewis_ciccone_dunn_2020, title={Catalyzing rapid discovery of gold-precipitating bacterial lineages with university students}, volume={8}, ISSN={2167-8359}, url={http://dx.doi.org/10.7717/peerj.8925}, DOI={10.7717/peerj.8925}, abstractNote={Intriguing and potentially commercially useful microorganisms are found in our surroundings and new tools allow us to learn about their genetic potential and evolutionary history. Engaging students from different disciplines and courses in the search for microbes requires an exciting project with innovative but straightforward procedures and goals. Here we describe an interdisciplinary program to engage students from different courses in the sampling, identification and analysis of the DNA sequences of a unique yet common microbe, Delftia spp. A campus-wide challenge was created to identify the prevalence of this genus, able to precipitate gold, involving introductory level environmental and life science courses, upper-level advanced laboratory modules taken by undergraduate students (juniors and seniors), graduate students and staff from the campus. The number of participants involved allowed for extensive sampling while undergraduate researchers and students in lab-based courses participated in the sample processing and analyses, helping contextualize and solidify their learning of the molecular biology techniques. The results were shared at each step through publicly accessible websites and workshops. This model allows for the rapid discovery of Delftia presence and prevalence and is adaptable to different campuses and experimental questions.}, number={4}, journal={PeerJ}, publisher={PeerJ}, author={Riley, N. and Goller, C.C. and Leggett, Z.H. and Lewis, D. and Ciccone, K. and Dunn, R.R.}, year={2020}, month={Apr}, pages={e8925} }
 @article{sealey_beasley_halsey_schell_leggett_yitbarek_harris_2020, title={Human Dimensions: Raising Black Excellence by Elevating Black Ecologists Through Collaboration, Celebration, and Promotion}, volume={101}, url={http://dx.doi.org/10.1002/bes2.1765}, DOI={10.1002/bes2.1765}, abstractNote={Briana A. Sealey , DeAnna E. Beasley , Samniqueka J. Halsey , Christopher J. Schell , Zakiya H. Leggett , Senay Yitbarek, and Nyeema C. Harris Department of Integrative Biology, J.T. Patterson Laboratories Building, 2415 Speedway, Austin, Texas 78712 USA Department of Biology, Geology, and Environmental Science, University of Tennessee at Chattanooga, 215 Holt Hall, Dept. 2653, Chattanooga, Tennessee 37403 USA School of Natural Resources, University of Missouri-Columbia, 1111 E. Rollin Street, Columbia, Missouri 65201 USA School of Interdisciplinary Arts and Sciences, 1900 Commerce St., Tacoma, Washington 98405 USA Department of Forestry and Environmental Resources, North Carolina State University, 2800 Faucette Dr., Raleigh, North Carolina 27607 USA Department of Biology, The University of North Carolina, Chapel Hill, North Carolina 27599-3280 USA Applied Wildlife Ecology Lab, Ecology and Evolutionary Biology, University of Michigan, 1105 N. University Ave, Ann Arbor, Michigan 48109 USA}, number={4}, journal={The Bulletin of the Ecological Society of America}, publisher={Wiley}, author={Sealey, Briana A. and Beasley, DeAnna E. and Halsey, Samniqueka J. and Schell, Christopher J. and Leggett, Zakiya H. and Yitbarek, Senay and Harris, Nyeema C.}, year={2020}, month={Oct} }
 @article{cacho_youssef_shi_chescheir_skaggs_tian_leggett_sucre_nettles_arellano_2019, title={Impacts on soil nitrogen availability of converting managed pine plantation into switchgrass monoculture for bioenergy}, volume={654}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2018.11.133}, abstractNote={Biofuels derived from lignocellulosic materials is one of the options in addressing issues on climate change and energy independence. One of the most promising bioenergy crops is switchgrass (Panicum virgatum L.), particularly in North America. Future advancement in large-scale conversion of lignocellulosic feedstocks and relatively more competitive price for biomass and other economic advantages could lead to landowners opting to venture on switchgrass monoculture (SWITCH) in lieu of loblolly pine monoculture (PINE). Therefore, we investigated the conversion of previously managed loblolly pine stand into SWITCH in eastern North Carolina, U.S.A. on soil N availability. Treatments included PINE, SWTICH, and mature loblolly pine stand (REF). Each treatment was replicated three times on 0.8 ha plots drained by open ditches dug 1.0–1.2 m deep and spaced at 100 m. Rates of net N mineralization (Nm) and nitrification (Nn) at the top 20 cm were measured using sequential in-situ techniques in 2011 and 2012 (the 3rd and 4th years of establishment, respectively) along with a one-time laboratory incubation. On average, PINE, SWITCH, and REF can have field net Nm rates up to 0.40, 0.34 and 0.44 mg N·kg soil−1·d−1, respectively, and net Nn rates up to 0.14, 0.08 and 0.10 mg N·kg soil−1·d−1, respectively. Annually, net Nm rates ranged from 136.98 to 167.21, 62.00 to 142.61, and 63.57 to 127.95 kg N·ha−1, and net Nn rates were 56.31–62.98, 16.45–30.45, 31.99–32.94 kg N·ha−1 in PINE, SWITCH, and REF, respectively. Treatment effect was not significant on field Nm rate (p = 0.091). However, SWITCH significantly reduced nitrate-N production (p < 0.01). Overall, results indicated that establishment of SWITCH on poorly drained lands previously under PINE is less likely to significantly impact total soil N availability and potentially has minimum N leaching losses since soil mineral N under this system will be dominated by ammonium-N.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Cacho, Julian F. and Youssef, Mohamed A. and Shi, Wei and Chescheir, George M. and Skaggs, R. Wayne and Tian, Shiying and Leggett, Zakiya H. and Sucre, Eric B. and Nettles, Jami E. and Arellano, Consuelo}, year={2019}, month={Mar}, pages={1326–1336} }
 @article{cacho_youssef_chescheir_wayne skaggs_appelboom_leggett_sucre_nettles_arellano_2018, title={Effects of forest-based bioenergy feedstock production on shallow groundwater quality of a drained forest soil}, volume={631-632}, ISSN={0048-9697}, url={http://dx.doi.org/10.1016/J.SCITOTENV.2018.03.020}, DOI={10.1016/J.SCITOTENV.2018.03.020}, abstractNote={Managed forests in southern U.S. are a potential source of lignocellulosic biomass for biofuel production. Changes in management practices to optimize biomass production may impact the quality of waters draining to nutrient-sensitive waters in coastal plain regions. We investigated shallow groundwater quality effects of intercropping switchgrass (Panicum virgatum L.) with managed loblolly pine (Pinus taeda L.) to produce bioenergy feedstock and quality sawtimber in a poorly drained soil of eastern North Carolina, U.S.A. Treatments included PINE (traditional pine production), PSWITCH (pine-switchgrass intercropped), SWITCH (switchgrass monoculture) and REF (mature loblolly pine stand). Each treatment was replicated three times on 0.8 ha plots drained by parallel-open ditches, 1.0–1.2 m deep and 100 m apart. Water samples were collected monthly or more frequently after fertilizer application. Water samples were analyzed for organic nitrogen (ON), ammonium N (NH4+- N), and nitrite+nitrate N (NO3−+ NO2−- N), ortohophosphate phosphorus (OP), and total organic carbon (TOC). Overall, PSWITCH did not significantly affect shallow groundwater quality relative to PINE and SWITCH. ON, NO3−+ NO2−- N, and TOC concentrations in PSWITCH, PINE and SWITCH were substantially elevated during the two years after tree harvest and site establishment. The elevated nutrient concentrations at the beginning of the study were likely caused by a combination of rapid organic matter decomposition of the abundant supply of post-harvest residues, warming of exposed soil surfaces and reduction of plant nutrient uptake that can occur after harvesting, and pre-plant fertilization. Nutrient concentrations returned to background levels observed in REF during the third year after harvest.}, journal={Science of The Total Environment}, publisher={Elsevier BV}, author={Cacho, Julian F. and Youssef, Mohamed A. and Chescheir, George M. and Wayne Skaggs, R. and Appelboom, Timothy W. and Leggett, Zakiya H. and Sucre, Eric B. and Nettles, Jami E. and Arellano, Consuelo}, year={2018}, month={Aug}, pages={13–22} }
 @article{cacho_youssef_shi_chescheir_skaggs_tian_leggett_sucre_nettles_arellano_2018, title={Impacts of forest-based bioenergy feedstock production on soil nitrogen cycling}, volume={419-420}, ISSN={0378-1127}, url={http://dx.doi.org/10.1016/J.FORECO.2018.04.002}, DOI={10.1016/J.FORECO.2018.04.002}, abstractNote={We investigated impacts of simultaneous production of biomass for biofuel and quality timber on soil nitrogen (N) cycling in a poorly drained forest soil of eastern North Carolina, U.S.A. Treatments included traditional loblolly pine (PINE) and pine-switchgrass intercropping (PSWITCH). Treatments were replicated three times on 0.8 ha plots drained by parallel open ditches which were 1.2 m deep and spaced 100 m apart. Net N mineralization (Nm) and nitrification (Nn) rates were measured in the field using sequential in-situ technique over two years with multiple measurements in each year and laboratory by incubating soil samples for one-, two-, eight-, and thirteen weeks. Soil incubation in-situ or sample collection for laboratory incubation was conducted at nine sampling points within a 30 × 40 m subplot at each plot center and 20 cm from the soil surface. Soil samples were composited by location including near tree (NT), between two trees on the same bed (BT), and in the middle of four trees on two adjacent beds (M4T). Composite samples from NT and BT were categorized as tree-bed (BED), while those from M4T were grouped as interbed (INT). Field results showed that total soil N availability and its temporal variations over two years were not significantly affected by PSWITCH. However, it significantly reduced Nn rates, particularly in the INT. The plot-level mean Nm rates in PINE were 0.21 and 0.26 mg N·kg soil−1 d−1, while in PSWITCH they were 0.10 and 0.21 mg N kg soil−1 d−1 in 2011 and 2012, respectively. The plot-level mean Nn rates in PINE were 0.09 and 0.10 mg N kg soil−1 d−1 in 2011 and 2012, respectively, while in PSWITCH they remained at 0.03 mg N kg soil−1 d−1 across these two years. At the INT, mean Nn rates in PINE were 0.11 and 0.12 mg N kg soil−1 d−1 in 2011 and 2012, respectively, while in PSWITCH, Nn rate remained at 0.02 mg N kg soil−1 d−1 over two years. Laboratory results indicated that change in litter quality inputs (changing from mixed species to switchgrass) in the INT did not significantly affect Nm rates. Results of this study contributed to a better understanding of the changes in soil N cycling due to loblolly pine-switchgrass interactions, which is important in sustainable nutrient management of this new land use. Further, the results suggested that growing switchgrass as intercrop to managed loblolly pine has positive water quality implication since ammonium N is less mobile in soil than nitrate N.}, journal={Forest Ecology and Management}, publisher={Elsevier BV}, author={Cacho, Julian F. and Youssef, Mohamed A. and Shi, Wei and Chescheir, George M. and Skaggs, R. Wayne and Tian, Shiying and Leggett, Zakiya H. and Sucre, Eric B. and Nettles, Jami E. and Arellano, Consuelo}, year={2018}, month={Jul}, pages={227–239} }
 @article{minick_leggett_sucre_fox_strahm_2017, title={Soil and Aggregate-Associated Carbon in a Young Loblolly Pine Plantation}, volume={182}, ISSN={0038-075X}, url={http://dx.doi.org/10.1097/ss.0000000000000215}, DOI={10.1097/ss.0000000000000215}, abstractNote={ABSTRACT In order to assess the carbon (C) footprint of forest-based bioenergy systems, it is necessary to quantify soil C storage. This study addressed effects of intercropping loblolly pine (Pinus taeda L.) with switchgrass (Panicum virgatum L.) for wood and bioenergy production on soil C storage in coastal North Carolina, USA. Spaces between rows of bedded pine were intercropped with switchgrass or contained native vegetative regrowth after site preparation. Two years after switchgrass establishment, soils were collected from beds and interbeds of each treatment, and C concentration and &dgr;13C were measured in bulk soils and aggregate fractions. Soil C concentration, soil C density (Mg ha−1), and aggregate-associated C were lower in pine beds adjacent to switchgrass compared with pines adjacent to native regrowth. In the greater than 2,000-&mgr;m aggregate size class, 11% of C was derived from new pine inputs in beds of the pine-switchgrass treatment compared to the pine-native treatment. These results indicate that increased belowground C flow in pine beds adjacent to switchgrass may be driving breakdown soil C. In the pine-switchgrass intercropping treatment, a greater percentage of aggregates (by weight and C content) was found in the 2,000- to 250-&mgr;m size class of both beds and interbeds, suggesting that this aggregate size class is sensitive to management. This study provides a baseline analysis of C storage under different management scenarios in pine forests and for investigating long-term (10+ years) impacts. Although presence of switchgrass reduced soil C over the short term, bioenergy intercropping may still be pragmatic from an economical and land-use diversification view point.}, number={7}, journal={Soil Science}, publisher={Ovid Technologies (Wolters Kluwer Health)}, author={Minick, Kevan J. and Leggett, Zakiya H. and Sucre, Eric B. and Fox, Thomas R. and Strahm, Brian D.}, year={2017}, month={Nov}, pages={1} }
 @article{shrestha_seiler_strahm_sucre_leggett_2016, title={Soil CO2 Efflux and Root Productivity in a Switchgrass and Loblolly Pine Intercropping System}, volume={7}, ISSN={["1999-4907"]}, DOI={10.3390/f7100221}, abstractNote={Switchgrass intercropped with loblolly pine plantations can provide valuable feedstock for bioenergy production while providing ancillary benefits like controlling competing vegetation and enhancing soil C. Better understanding of the impact of intercropping on pine and switchgrass productivity is required for evaluating the long-term sustainability of this agroforestry system, along with the impacts on soil C dynamics (soil CO2 efflux; RS). RS is the result of root respiration (RA) and heterotrophic respiration (RH), which are used to estimate net C ecosystem exchange. We measured RS in intercropped and monoculture stands of loblolly pine (Pinus taeda L.) and switchgrass (Panicum virgatum L.). The root exclusion core technique was used to estimate RA and RH. The results showed pure switchgrass had significantly higher RS rates (July, August and September), root biomass and length relative to intercropped switchgrass, while there were no significant changes in RS and roots between intercropped and monoculture loblolly pine stands. A significant decrease in switchgrass root productivity in the intercropped stands versus monoculture stands could account for differences in the observed RS. The proportions of RS attributed to RA in the intercropped stand were 31% and 22% in the summer and fall respectively, indicating that the majority of the RS was heterotrophic-driven. Ancillary benefits provided by planting switchgrass between unutilized pine rows can be considered unless the goal is to increase switchgrass production.}, number={10}, journal={FORESTS}, author={Shrestha, Paliza and Seiler, John R. and Strahm, Brian D. and Sucre, Eric B. and Leggett, Zakiya H.}, year={2016}, month={Oct} }
 @article{strickland_leggett_sucre_bradford_2015, title={Biofuel intercropping effects on soil carbon and microbial activity}, volume={25}, ISSN={1051-0761}, url={http://dx.doi.org/10.1890/14-0285.1}, DOI={10.1890/14-0285.1}, abstractNote={Biofuels will help meet rising demands for energy and, ideally, limit climate change associated with carbon losses from the biosphere to atmosphere. Biofuel management must therefore maximize energy production and maintain ecosystem carbon stocks. Increasingly, there is interest in intercropping biofuels with other crops, partly because biofuel production on arable land might reduce availability and increase the price of food. One intercropping approach involves growing biofuel grasses in forest plantations. Grasses differ from trees in both their organic inputs to soils and microbial associations. These differences are associated with losses of soil carbon when grasses become abundant in forests.}, number={1}, journal={Ecological Applications}, publisher={Wiley}, author={Strickland, Michael S. and Leggett, Zakiya H. and Sucre, Eric B. and Bradford, Mark A.}, year={2015}, month={Jan}, pages={140–150} }
 @inproceedings{hatten_sucre_leggett_mack_roberts_dewey_strahm_2015, place={Asheville, NC}, title={Explaining the apparent resiliency of loblolly pine plantation to organic matter removal}, number={SRS–203.}, booktitle={Proceedings of the 17th biennial southern silvicultural research conference}, publisher={U.S. Department of Agriculture, Forest Service, Southern Research Station}, author={Hatten, J.A. and Sucre, E. and Leggett, Z.H. and Mack, J. and Roberts, S. and Dewey, J. and Strahm, B.}, year={2015}, pages={237–243} }
 @article{cacho_youssef_chescheir_skaggs_leggett_sucre_nettles_arellano_2015, title={Impacts of switchgrass-loblolly pine intercropping on soil physical properties of a drained forest}, volume={58}, DOI={10.13031/trans.58.11238}, abstractNote={Intercropping switchgrass ( L.) with managed loblolly pine ( L.) has been proposed as an alternative source of bioenergy feedstock that does not require conversion of agricultural cropland. Different management practices may alter soil physical properties (SPP), which could influence productivity, hydrologic and biogeochemical processes. Therefore, we investigated the effect of switchgrass-loblolly pine intercropping on the SPP of a poorly drained forest soil in eastern North Carolina using three management regimes: young loblolly pine stand (PINE), switchgrass-pine intercropping (PSWITCH), and a 38-year-old loblolly pine stand (REF). Measurements of SPP were conducted before and after the third annual harvesting operation using intact soil cores taken from three points within each of three replicated plots and at three depths: 0-15 cm, 15-30 cm, and 30-45 cm. Pre- and post-harvest values of SPP in PSWITCH were not significantly different. Compared to PINE, changes in bulk density and in both total porosity and saturated hydraulic conductivity in PSWITCH were significant only in the top 30 and 15 cm of soil, respectively. Volume drained and drainable porosity in PSWITCH decreased significantly at water table depths ≤45 cm. Cumulative effects of V-shearing for switchgrass seedbed preparation and the first and second harvest operations may have caused structural changes to the surface soil layer in PSWITCH that subsequently resulted in the measured differences in SPP between PSWITCH and PINE. We suggest that soil disturbance should be minimized during field operations to lessen the adverse effects on SPP, and models used to quantify impacts of management practices and land use change on the hydrology and biogeochemistry of managed forests should consider SPP changes caused by management regimes.}, number={6}, journal={Transactions of the ASABE}, author={Cacho, J. F. and Youssef, M. A. and Chescheir, G. M. and Skaggs, R. W. and Leggett, Zakiya H and Sucre, E. B. and Nettles, J. E. and Arellano, C.}, year={2015}, pages={1573–1583} }
 @article{minick_strahm_fox_sucre_leggett_2015, title={Microbial nitrogen cycling response to forest-based bioenergy production}, volume={25}, ISSN={1051-0761}, url={http://dx.doi.org/10.1890/14-1745.1}, DOI={10.1890/14-1745.1}, abstractNote={Concern over rising atmospheric CO2 and other greenhouse gases due to fossil fuel combustion has intensified research into carbon‐neutral energy production. Approximately 15.8 million ha of pine plantations exist across the southeastern United States, representing a vast land area advantageous for bioenergy production without significant land‐use change or diversion of agricultural resources from food production. Furthermore, intercropping of pine with bioenergy grasses could provide annually harvestable, lignocellulosic biomass feedstocks along with production of traditional wood products. Viability of such a system hinges in part on soil nitrogen (N) availability and effects of N competition between pines and grasses on ecosystem productivity. We investigated effects of intercropping loblolly pine (Pinus taeda) with switchgrass (Panicum virgatum) on microbial N cycling processes in the Lower Coastal Plain of North Carolina, USA. Soil samples were collected from bedded rows of pine and interbed space of two treatments, composed of either volunteer native woody and herbaceous vegetation (pine–native) or pure switchgrass (pine–switchgrass) in interbeds. An in vitro 15N pool‐dilution technique was employed to quantify gross N transformations at two soil depths (0–5 and 5–15 cm) on four dates in 2012–2013. At the 0–5 cm depth in beds of the pine–switchgrass treatment, gross N mineralization was two to three times higher in November and February compared to the pine–native treatment, resulting in increased NH4+ availability. Gross and net nitrification were also significantly higher in February in the same pine beds. In interbeds of the pine–switchgrass treatment, gross N mineralization was lower from April to November, but higher in February, potentially reflecting positive effects of switchgrass root‐derived C inputs during dormancy on microbial activity. These findings indicate soil N cycling and availability has increased in pine beds of the pine–switchgrass treatment compared to those of the pine–native treatment, potentially alleviating any negative effects of N competition between pine and switchgrass. We expect that reduced soil C in the pine–switchgrass treatment, effects of pine and switchgrass rooting on soil C availability, and plant N demand are major factors influencing soil N transformations. Future research should examine rooting architecture in intercropped systems and the effects on soil microbial communities and function.}, number={8}, journal={Ecological Applications}, publisher={Wiley}, author={Minick, Kevan J. and Strahm, Brian D. and Fox, Thomas R. and Sucre, Eric B. and Leggett, Zakiya H.}, year={2015}, month={Dec}, pages={2366–2381} }
 @article{blazier_clason_liechty_leggett_sucre_roberts_krapfl_vance_2015, title={Nitrogen and Carbon of Switchgrass, Loblolly Pine, and Cottonwood Biofuel Production Systems in the Southeast United States}, volume={61}, ISSN={0015-749X}, url={http://dx.doi.org/10.5849/forsci.14-016}, DOI={10.5849/forsci.14-016}, abstractNote={Switchgrass has favorable characteristics as a biofuel feedstock, and it may be feasibly grown on sites currently forested or retired from agricultural production. It is ecologically important to understand the impacts of establishing and managing switchgrass on site nutrient cycling. Four studies conducted in the southeast United States tested switchgrass as a bioenergy crop grown in monoculture, in alley cropping systems, and as an alternative to conventional agricultural rotations. Each trial included comparisons of switchgrass with the prevailing land uses. In each trial, nitrogen mineralization (Nmin), nitrification (Nnit), microbial biomass carbon (Cmic), microbial activity, and labile carbon were measured because of their sensitivity to management practices that alter soil nutrient cycling. In all studies of loblolly pine and switchgrass, switchgrass was apparently the dominant substrate source for C mic , and N min increased when juvenile loblolly pine was isolated with herbicide as the sole vegetation. However, Cmic and Nmin of loblolly pine-switchgrass alley cropping systems were similar to those observed in conventional juvenile loblolly pine plantation conditions. In a trial of converting former agricultural fields into switchgrass or cottonwood biofuel plantations, this conversion reduced Nnit, and therefore the potential for nitrogen losses compared with those for a soybean-sorghum rotation typical for such sites.}, number={3}, journal={Forest Science}, publisher={Oxford University Press (OUP)}, author={Blazier, Michael A. and Clason, Terry R. and Liechty, Hal O. and Leggett, Zakiya H. and Sucre, Eric B. and Roberts, Scott D. and Krapfl, Kurt and Vance, Eric D.}, year={2015}, month={Jun}, pages={522–534} }
 @article{dimov_howard_leggett_sucre_weninegar_2015, title={Removal of Organic Matter from the Forest Floor in Loblolly Pine Plantations Increased Ground-Layer Richness and Diversity 16 Years after Treatment}, volume={61}, ISSN={0015-749X}, url={http://dx.doi.org/10.5849/forsci.13-151}, DOI={10.5849/forsci.13-151}, abstractNote={Forest floor organic matter (forest floor, understory, and slash material) often serves as an indicator of soil quality and contributes to soil productivity.Silvicultural activities can affect this layer through common manipulations of slash on the forest floor.Few studies examine the long-term effects of changes in the organic matter on the ground-layer vegetation (below 1.4 m tall).We investigated the impact of forest floor organic matter manipulation after 16 years in a loblolly pine (Pinus taeda L.) plantation.We examined the cover, richness, diversity, and biomass of the ground-layer vegetation.Twelve 0.16 ha plots were established in a randomized complete block design following clearcutting of the previous 33-year-old plantation.The three treatments were: control (leaving unaltered), removing, and doubling the forest floor and slash material.In each plot, we established 15 1 m 2 subplots.Ground-layer diversity in the doubled treatment was less than in the other treatments.Similarly, plant richness, total plant cover, and the cover of herbaceous, graminoid, and woody species were all significantly greater in the removed treatment.The removal of organic matter overall increased the understory richness, cover, and diversity but had a negative effect on stand yield compared to the doubled treatment and no effect compared to the control.}, number={3}, journal={Forest Science}, publisher={Oxford University Press (OUP)}, author={Dimov, Luben D. and Howard, Kmberly J. and Leggett, Zakiya H. and Sucre, Eric B. and Weninegar, Loretta L.}, year={2015}, month={Jun}, pages={554–558} }
 @article{albaugh_albaugh_heiderman_leggett_stape_king_katherine p. o'neill_king_2014, title={Evaluating changes in switchgrass physiology, biomass, and light-use efficiency under artificial shade to estimate yields if intercropped with Pinus taeda L.}, volume={88}, ISSN={["1572-9680"]}, DOI={10.1007/s10457-014-9708-3}, number={3}, journal={AGROFORESTRY SYSTEMS}, author={Albaugh, Janine M. and Albaugh, Timothy J. and Heiderman, Ryan R. and Leggett, Zakiya and Stape, Jose L. and King, Kyle and Katherine P. O'Neill and King, John S.}, year={2014}, month={Jun}, pages={489–503} }
 @article{albaugh_domec_maier_sucre_leggett_king_2014, title={Gas exchange and stand-level estimates of water use and gross primary productivity in an experimental pine and switchgrass intercrop forestry system on the Lower Coastal Plain of North Carolina, USA}, volume={192}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2014.02.013}, abstractNote={Despite growing interest in using switchgrass (Panicum virgatum L.) as a biofuel, there are limited data on the physiology of this species and its effect on stand water use and carbon (C) assimilation when grown as a forest intercrop for bioenergy. Therefore, we quantified gas exchange rates of switchgrass within intercropped plots and in pure switchgrass plots during its second growing season in an intensively managed loblolly pine (Pinus taeda L.) plantation in North Carolina. Switchgrass physiology was characterized over the growing season from June to October 2010 in terms of photosynthesis (μmol m−2 s−1), stomatal conductance (mmol m−2 s−1), and assimilation responses to photosynthetic photon flux density and intercellular carbon dioxide concentration (CO2). We then used a process-based model of the soil–plant–atmosphere continuum to scale leaf-level gas exchange data to provide estimates of pine and switchgrass stand-level water use (mm) and carbon exchange (g C m−2) over a three-year period. Peak switchgrass photosynthesis (32.7 ± 0.9 μmol m−2 s−1) and stomatal conductance (252 ± 12 mmol m−2 s−1) rates were measured in July, with minimum values (18.7 ± 1.4 μmol m−2 s−1 and 104 ± 6 mmol m−2 s−1, respectively) recorded at the end of the growing season (October). Switchgrass gas exchange and parameter estimates from the light- and CO2 response curves did not vary between treatments. However, gas exchange values differed significantly between measurement dates. Model predictions of stand-level transpiration ranged from 287 to 431 mm year−1 for pine and from 245 to 296 mm year−1 for switchgrass. Annual C exchange for loblolly pine ranged from 1165 to 1903 g m−2 compared to 1386 to 1594 g m−2 for switchgrass. At this stage of stand development, no effect of intercropping was evident and there was no effect of distance from the nearest pine row on any switchgrass gas exchange variable measured. However, we anticipate that as this intercropped system develops over time, competition for resources such as light, water or nitrogen may change, with the potential to impact switchgrass physiology and biomass production.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Albaugh, Janine M. and Domec, Jean-Christophe and Maier, Chris A. and Sucre, Eric B. and Leggett, Zakiya H. and King, John S.}, year={2014}, month={Jul}, pages={27–40} }
 @article{minick_strahm_fox_sucre_leggett_zerpa_2014, title={Switchgrass intercropping reduces soil inorganic nitrogen in a young loblolly pine plantation located in coastal North Carolina}, volume={319}, ISSN={0378-1127}, url={http://dx.doi.org/10.1016/J.FORECO.2014.02.013}, DOI={10.1016/J.FORECO.2014.02.013}, abstractNote={As biofuel production continues to increase, so will demand for forests to provide sources of biomass feedstocks. Intensively managed loblolly pine (Pinus taeda L.) plantations cover 15.8 million ha of the southeastern United States. Intercropping of switchgrass (Panicum virgatum L.) within loblolly pine stands offers an opportunity to use interbed space to produce an herbaceous biomass feedstock. Furthermore, removal of post-harvest woody residues could act as another forest-based biomass feedstock. Understanding how managing forests for biofuel production influences soil nitrogen (N) cycling and availability is crucial given the critical role N plays in terrestrial ecosystem productivity. Therefore, our objective was to study effects of harvest residue removal and pine-switchgrass intercropping on soil extractable NH4+ and NO3-. We used a randomized complete block design, consisting of four blocks of seven plots (0.8 ha) established in the summer of 2008 on a recently harvested 34-year-old loblolly pine plantation in the Lower Coastal Plain of North Carolina, USA. Ion exchange membranes were deployed in the top 10 cm of mineral soil starting in June 2009 and replaced continuously every 4–6 weeks through December 2011. Presence of switchgrass significantly reduced soil extractable NH4+ and NO3-, amounting to a total reduction of 39% and 60%, respectively, over the course of the timeframe (30 months) of this study. There was evidence that intercropping of switchgrass increased extractable NO3- in the adjacent pine bed, although this result was only found in the final 6 months of the study. Presence or absence of harvest residues and/or interbed pines in the interbeds generally had no effect on soil inorganic N pools. These results indicate that switchgrass production effectively utilized inorganic N during a time when mineral N supply was greater than N demand by loblolly pines. Assessment of the long-term effects of switchgrass intercropping on soil nutrient cycling and availability and pine health and productivity will be essential to determine environmental and economic sustainability of intercropping.}, journal={Forest Ecology and Management}, publisher={Elsevier BV}, author={Minick, Kevan J. and Strahm, Brian D. and Fox, Thomas R. and Sucre, Eric B. and Leggett, Zakiya H. and Zerpa, Jose L.}, year={2014}, month={May}, pages={161–168} }
 @article{mack_hatten_sucre_roberts_leggett_dewey_2014, title={The effect of organic matter manipulations on site productivity, soil nutrients, and soil carbon on a southern loblolly pine plantation}, volume={326}, ISSN={0378-1127}, url={http://dx.doi.org/10.1016/J.FORECO.2014.04.008}, DOI={10.1016/J.FORECO.2014.04.008}, abstractNote={Forest harvesting intrinsically removes organic matter and associated nutrients; these exports may impact soil productivity and soil carbon stores of managed forests. This study examined the effect of manipulating forest floor and harvest residue inputs on nutrient availability and carbon content in the context of intensive forest management. Treatments were applied 15 years prior to this study and included removal and addition of forest floor and harvest residues, and a reference. We examined stand volume, litterfall, root biomass and foliar N and P at year 14 or 15. Soil moisture and temperature (0–10 cm) and available N and P in the O and 0–20 cm depths were measured once per month during year 15. Soil carbon and nitrogen were measured on whole soils as well as two density fractions in the O-horizon, 0–20, 20–40, and 40–60 cm soil depths at year 15. In general, many of the initial responses found by an earlier study (age 10) have dissipated. Standing volume in the added treatment was 31% higher than the removed, but no significant difference was found between the removed and reference treatments. The added treatment resulted in higher concentrations of N in the light and heavy density fractions of the 0–20 cm depth, which led to higher mass of N in both of these fractions. The added treatment had the greatest whole soil heavy fraction N mass. There were no differences in available N in the O-horizon or 0–20 cm depth as tested using ion exchange membranes; however available P was significantly lower in the O-horizon of the removed treatment (37% lower than the reference). Bole volume was correlated with some measures of total and available N and P in the O and 0–20 cm soil horizons, suggesting that increases in growth found in the added treatment were a result of additional nutrients. There were no significant differences between C concentration or mass of the 0–20 cm or 20–40 cm soil depths between the treatments; however the added treatment had significantly more (51% more than the reference) carbon at the 40–60 cm soil depth. The added treatment had a significantly higher C:N relative to the reference in the 20–40 cm (21.0 and 14.5, respectively) and 40–60 cm (18.0 and 11.4, respectively) depths, suggesting that relatively fresh, undegraded organic matter had enriched this depth. This additional carbon sequestered at depth could contribute to a long-term soil carbon pool. The results of this study suggest that higher intensity use, such as forest floor removal and whole tree harvest, of these forests may not impact long term productivity at this site with typical soil nutrient status; however, more research is necessary to determine the mechanism(s) of this resilience.}, journal={Forest Ecology and Management}, publisher={Elsevier BV}, author={Mack, Jason and Hatten, Jeff and Sucre, Eric and Roberts, Scott and Leggett, Zakiya and Dewey, Janet}, year={2014}, month={Aug}, pages={25–35} }
 @article{ridley_jager_clark_efroymson_kwit_landis_leggett_miller_2013, title={Debate: Can Bioenergy Be Produced in a Sustainable Manner That Protects Biodiversity and Avoids the Risk of Invaders?}, volume={94}, ISSN={0012-9623}, url={http://dx.doi.org/10.1890/0012-9623-94.3.277}, DOI={10.1890/0012-9623-94.3.277}, abstractNote={Weighing contrasting evidence is an integral element of science (Osborne 2010). The dominant forum for doing this and for scientific exchange in general is the peer-review and publication process. It tends to be slow because of the time required to conduct critical reviews. Rapid exchange and discourse, in the form of a live debate, can also move science forward. Whether fast or slow, debate and discourse are particularly important in sustainability research when novel human activities with unknown consequences are introduced. For example, whether bioenergy can become a sustainable future source of energy is a contentious issue. Topics of disagreement include the relative importance of different aspects of sustainability, regional variation in benefits, the validity of methods used to perform environmental assessments, choices of sustainability targets, and the reliability of sustainability certification (Acosta-Michlik et al. 2011, Jorgensen and Andersen 2012). We held a modified Oxford-style debate at the 2012 ESA Annual Meeting in Portland, Oregon. Here, we summarize the key arguments advanced by opposing debate positions on the thesis that Producing bioenergy can be sustainable for habitat availability and biodiversity and can avoid the risk of new invaders. We gauged audience reactions to arguments made by representatives of both sides. We highlight the salient uncertainties in the debate, describe effective rhetorical strategies, and discuss purposes and appropriate contexts for scientific debate in general. We invited two experts to support and two to oppose the above thesis. Experts were asked to develop compelling arguments to support their assigned positions, which did not necessarily represent their actual views. We polled the audience on their a priori support for the thesis using real-time polling software, SMS Poll (www.smspoll.net). The software permitted up to 50 votes via text or web interface, representing roughly half of the ~100-member audience. The two sides alternated delivering main arguments within a seven-minute time limit, supported by published literature. After each speaker, we informally polled the audience regarding support for the speaker's position. Main arguments were followed by three minutes of rebuttal, allowing each expert to counter opposing arguments. We conducted an identical online poll after the debate to determine whether arguments swayed opinions. We concluded by soliciting both oral questions and written comments from the audience. First, biofuels will replace a portion of fossil fuels, thereby avoiding associated large-scale biodiversity impacts from seismic exploration lines, drilling, and transporting petroleum and gasoline (Parish et al. 2012). Second, bioenergy feedstocks will not necessarily be grown as monocultures; cultivation of mixtures of native grassland perennials or algal communities is possible. Even where the feedstock is a single species, it can be managed so that other species are nearby. Moreover, diverse communities used as biofuel feedstocks can have significant environmental benefits other than biodiversity, such as a high energy return on investment, reduced net greenhouse gas emissions, and low agrochemical pollution (Tilman et al. 2006). Stockenreiter et al. (2012) found that lipid production is higher in more diverse microalgal communities. Including fish can, in theory, stabilize algal cultivation ponds by keeping zooplankton consumers of algae low (Smith et al. 2010). 1) Grow crops on low-diversity lands. Plant diversity increases if perennial grasses or trees displace monoculture crops or brownfields. Aquatic biodiversity may be enhanced if highly fertilized crops are displaced. Algal biofuels can be produced on brownfields or paved areas. 2) Maintain structural complexity. Complexity of vegetation structure is related to biodiversity, and bioenergy crops can be managed to promote this. Moser et al. (2002) recommend maintaining a diversity of forest ages. Dhondt et al. (2007) found that the number of bird species on plantations with mixed ages of coppice willow and poplar was comparable to that in shrublands and successional fields. Wintering raptors preferred hybrid poplar plantations to adjacent habitat types in Oregon (Moser and Hilpp 2003). Small mammals preferred 1–3 year old hybrid poplar plantations with abundant understory to older plantations (Moser et al. 2002). Murray et al. (2003) recommended interspersing nonharvested switchgrass fields with harvested fields to support more grassland birds. 3) Select species as feedstocks to avoid invasion risk. Invasiveness is a combination of invasive potential of species and invasibility of the native community. Some species used as feedstocks have broad geographic ranges. For example, switchgrass is native to most of North America east of the Rocky Mountains. Switchgrass and the nonnative giant Miscanthus, a sterile hybrid, have been tested and found not to be invasive in dryland regions of California (Barney et al. 2012). Most species of eukaryotic microalgae and cyanobacteria being proposed as algal feedstocks are cosmopolitan and native, already inhabiting many water bodies. The use of saltwater algae in inland environments and use of freshwater algae near coasts can lower invasion risk. Clearly, there are ways to manage biofuel feedstocks that will support biodiversity conservation and reduce invasion risk. Commercial-scale bioenergy production threatens habitat availability for many organisms in ways that are unlikely to be easily mitigated. For example, meeting federally mandated renewable fuel targets could require harvest of biomass from hundreds of millions of hectares of agricultural lands, forest, and uncultivated lands set aside for conservation (e.g., Conservation Reserve Program lands). Increased harvest will reduce habitat availability for critical taxa for a variety of reasons. In a recent meta-analysis, Fletcher et al. (2011) conclude that "vertebrate diversity and abundance are generally lower in biofuel crop habitats than in non-crop habitats these crops may replace." Bioenergy production in agricultural landscapes will require placing marginal lands that currently provide habitat into production. Meehan et al. (2010) conclude that producing annual bioenergy crops in marginal lands will lead to up to a 65% loss of avian richness across 20% of the Midwest. Moreover, conversion of marginal lands will exacerbate other threats to wildlife, including pesticide use. For example, loss of noncrop habitat reduces natural pest suppression, resulting in increased pesticide use in agricultural crops (Meehan et al. 2010). Harvest in forest systems changes forest structure (Littlefield and Keeton 2012) and reduces coarse and fine woody debris. Extraction of fine woody debris might reduce this key habitat component by up to 45%, affecting over 280 species (Dahlberg et al. 2011). Finally, industrialization of bioenergy production will cause each region to converge to the most efficient bioenergy crop, reducing habitat diversity to the detriment of many species. Intensification of bioenergy production will inexorably lead to losses of biodiversity and ecosystem services. In agriculture, crop yields have been increased by using more fertilizers and pesticides, planting monocultures, and decreasing landscape complexity, which has resulted in local species extirpations (Kleijn et al. 2009). Functional diversity is also being lost (Flynn et al. 2009), raising the specter of system collapse. Similarly, intensification in managed forests is reducing biodiversity and associated ecosystem services. Moreover, as the value of wood increases, forested lands will be converted to fastgrowing species that support fewer species (Flaspohler and Webster 2011). Despite good intentions to diversify working landscapes, powerful economic and social forces will undoubtedly favor intensified bioenergy production systems with concomitant losses in biodiversity and ecosystem services. Production of biomass feedstock and conservation of biodiversity are not mutually exclusive. Empirical evidence from forested systems shows that common best practices maintain biodiversity in working landscapes. Of course, potential effects are largely dictated by spatial scale, landscape composition, and individual species response (Efroymson et al. 2013). A series of meta-analyses (Riffell et al. 2011a, b, Verschuyl et al. 2011) examined possible impacts of biofuel feedstock production on forest biodiversity. A review of 68 studies concluded that (1) response varied by taxa and production system; (2) most taxa responded positively to thinning; (3) reduction of coarse woody debris may negatively impact some birds, but effects on other taxa were equivocal; (4) short-rotation woody crops may negatively affect birds and small mammals, but responses are variable and addition of shrubby habitat types on some landscapes may be beneficial; and (5) if woody biomass removal is <70–95% of experimental removals, impacts on overall biodiversity may be minimal. Related to point 5, it is uneconomical to eliminate most woody debris through forest residual harvest (see retention levels cited in Riffell et al. [2011a]). Additionally, harvest in a forested landscape would occur on a very small proportion of land in any given year, minimizing negative effects. Another opportunity for feedstock production in managed forests is intercropping an herbaceous crop between rows of planted pine (Fig. 1a). Although more work is needed (Riffell et al. 2012), recent results show similar plant diversity between traditional planted pine stands and those intercropped with switchgrass (155 plant species), a diverse breeding bird community (54 species) in intercropped stands, and negligible effects on rodent and herptile communities. Early results indicate that intercropping may not substantially affect the diverse plant and wildlife communities associated with planted pine in a sawtimber rotation. (a) Switchgrass intercropped in a pine plantation of Lenoir County, North Carolina. Photo credit: Jessica Homyack, (b) Miscanthus sinensis escaped from horticultural plantings in central Kentucky. Photo credit: Lauren Quinn. Implementation of science-based, best management practices (BMPs) (e.g., buffer strips and streamside management zones) and protecting unique ecological communities and those with threatened and endangered species can effectively retain elements of native biodiversity in commodity-based landscapes. Additionally, in most landscapes, not every acre will be available for biomass production. This mixture of land uses may increase habitat heterogeneity and promote higher biodiversity. Retaining key habitat elements (e.g., snags) is a practical solution to maintain biodiversity in managed landscapes. Using portions of some landscapes for intensive biomass feedstock production may alleviate pressures on other managed lands, thus conserving wildlife habitat and biodiversity at larger spatial scales. Finally, bioenergy production may provide landowners with economic incentive to maintain forest and/ or agricultural landscapes. This will reduce one of the largest threats to privately owned rural and wild landscapes: urbanization. The large-scale land use and landscape changes necessary to meet U.S. government-mandated benchmarks for renewable bioenergy (McDonald et al. 2009) will likely promote invasiveness. Reduced landscape heterogeneity in "new" areas of large-scale monoculture plantings increases susceptibility to invasion (Hoffman et al. 1995), particularly by introduced and weedy plants that take advantage of changed environmental conditions (Simberloff 2008). More notably, biomass feedstocks themselves are candidates for invasive spread (Fig. 1b); their establishment from seed in altered low-competition environments (Barney et al. 2012) and invasive spread has already been documented (Buddenhagen et al. 2009). At the forefront of the issue of invasibility is the fear that biomass feedstocks have many traits associated with invasiveness, including C4 photosynthesis, long canopy duration, few-to-no known pests or diseases, rapid growth and belowground partitioning of nutrients early in the growing season, and high water use efficiency (Raghu et al. 2006). Some of these same traits are targets of genetic improvement efforts, and others are not compromised at the expense of improvements in biomass (Rogers et al. 2012). Indeed, risk assessments to predict weediness and invasiveness of biomass feedstocks (e.g., Cousens 2008) are a necessary and precautionary step before widespread cultivation (e.g., Buddenhagen et al. 2009, Gordon et al. 2011). Genes and propagules can spread into surrounding areas in many ways. For alien plants used as biomass feedstocks, "effective" seed dispersal will be necessary for invasive spread. For native feedstocks and alien feedstocks with reproductively compatible relatives, successful pollination provides another avenue along which agronomic genes spread. Introgression of agronomic and transgenes into wild and compatible populations has been documented (Watrud et al. 2004). To reduce likelihood of invasive spread, sterile varieties of feedstocks must be developed (Quinn et al. 2010), which has proven difficult. Our opponents argued that Fletcher et al. (2011) conclude that biodiversity and abundance are generally lower in biofuel crops than in the noncrop areas they replace. This evidence is based on row crops, pine, and poplar. But the same authors acknowledge lack of evidence to make that claim for second-generation crops like switchgrass. Meehan et al. (2010) analyzed expansion of corn and soybean for bioenergy onto marginal land in the Midwest, but they also say, "In contrast, replacement of annual with diverse perennial bioenergy crops (e.g., mixed grasses and forbs) is expected to bring increases in avian richness between 12% and 207% across 20% of the region, and possibly aid the recovery of several species of conservation concern." Similarly, arguments about agricultural intensification are not likely to apply to perennial crops because these require much lower nutrient and pesticide supplements. Species selection, modification, landscape design, and monitoring will help mitigate risk of species invasiveness. Measured changes in biodiversity and how those changes are interpreted will depend on context (Efroymson et al. 2013), including focal species, region and previous land use, land management, and scale of measurement. The "increased risk of invasion" argument put forward has been challenged on two main fronts. First, polycultures have been championed over monocultures. How bioenergy crops are grown will likely be a function of biomass yield and economics. Limited research in this area shows that monocultures produce higher yields than polycultures and make the most sense from an economic perspective (Griffith et al. 2011). Thus, monocultures will be the norm. Second, feedstock species put forward as less likely to pose invasive risks included cosmopolitan algae and crops that are either native or that were not shown to be invasive in case studies. Algae production, especially in open systems, is ripe with risk. Biofuel "type" strains of algae, cosmopolitan or not, may pose invasive threats to aquatic systems and public waterways (Wilkie et al. 2011). As for species specifically mentioned as not being invasive, the same case study used to illustrate this also showed that switchgrass is capable of establishing by seed in disturbed, lowcompetition areas outside its native range (Barney et al. 2012). Finally, using bioenergy crop plants native to a particular region does not necessarily lower invasion risk. On the contrary, introgression into native populations of conspecifics or other compatible relatives may well be applicable for some bioenergy feedstocks (Kwit and Stewart 2012). Our opponents used definitive language to imply that reduced habitat and biodiversity would be a "foregone conclusion" following widespread biofuel feedstock production. However, both presenters fail to acknowledge that, to date, science-based data are very limited, especially at larger spatial scales. Their arguments also ignore effective strategies for mitigating potential negative effects such as landscape planning and BMPs. The presenters do not acknowledge that most large forest landowners adhere to sustainable forestry standards, which have metrics for protection of unique ecological communities, sensitive species, provision of wildlife habitat, and management of invasive species. Additionally, positive or negative impacts of biomass system establishment will depend completely on landscape context, and responses by individual species and communities will be varied. Further, it has been argued that biofuel production equates with "habitat loss" when, in many cases, it is actually "habitat change." This distinction is important; any habitat change will positively impact some species and negatively impact others. Our opponents also generalize that changes in forest structure will be necessarily negative, when this is not the case (e.g. Riffell et al. 2011a, Verschuyl et al. 2011). Due to differing landowner objectives and other factors, it is probable that establishment of short-rotation woody crops will only comprise portions of landscapes, and that positive and/or negative effects on biodiversity will be dependent on landscape context. Additionally, short-rotation pine forests support local and regional biodiversity (e.g., Miller et al. 2009), and the general supposition that this must lead to reduced biodiversity is flawed. The supporters of the thesis suggest that bioenergy production and maintenance of habitat availability and biodiversity are not mutually exclusive; they argue that there may even be opportunities for synergies. They suggest that additional research can be conducted and BMPs applied to achieve optimal bioenergy systems. I find this position to be very optimistic. Although we certainly need to be optimistic, as scientists we might also ask what is the probability that such favorable outcomes will be achieved? Our opponents repeatedly used qualifications including, "can," "may," "might," and "could" when describing aspects of a sustainable bioenergy future. Given their uncertainty, we might look to the track records of the two major industry players in commercial bioenergy production in the United States: agriculture and forestry. Both already operate within an extensive framework of federal and state regulation. Both have also shared the ideal of "sustainable management" for at least three decades. And yet examples abound where ideals do not match realities. In agriculture, data show that farmers regularly apply excess fertilizer to corn. Although we have multiple BMPs to prevent this, agricultural pollution of surface and groundwater is common. Similarly, in forest management, decades of research has been conducted to develop and implement BMPs (e.g., thinning schedules and riparian buffer zones), and yet in some places we continue to struggle with fire-prone landscapes with degraded water quality. What makes us optimistic that research and policy can help us avoid similar outcomes for an expanding bioenergy industry? As a society, we are about to embark on an experimental shift in land use at a grand scale. These changes, caused by commercialization of bioenergy production systems, will impact hundreds of millions of hectares of diverse landscapes across North America. We hope to manage this shift with thoughtful legislation, wise regulation, and cooperation of individual land owners and industry leaders whose longterm interests truly do lie in developing and implementing sustainable approaches. Unfortunately, we are not as optimistic as our opponents that this will easily be achieved, but the question remains: What might we as ecologists do to tip the balance in favor of sustainable otcomes? Comparison of pre- and post-debate electronic polling of 50 audience members showed no significant difference in opinion before and after the debate (Table 1; χ2 = 1.989, P = 0.158). Although this did not represent a probability sample, it included nearly half of the audience. This test assumes independence, but we note that accounting for autocorrelation never increases power. If we had been able to obtain repeated measures by tracking the votes by individual, we could have used a more powerful test suitable for nonindependent data. Voting after each speaker showed that all arguments presented were supported by most audience members (Table 2). We received written comments from 15 audience members. Some of those who agreed with the thesis expressed a need to maintain optimism about energy alternatives to fossil fuels. Those who disagreed echoed debaters' arguments about the poor track record of industries (agriculture, forestry) and the high likelihood of energy crop invasions. Others in disagreement cited evidence not presented during the debate; one emphasized that sustainable bioenergy will not be achievable because of soil quality deterioration. General comments on the debate format included suggestions to better define the terms and scope of the debate at the outset, and to provide more time for audience questions and feedback. Our live, formal debate focused on a thesis that was sufficiently broad to permit a variety of perspectives and arguments from scientists. Each side addressed elements of the thesis to support their stance, selectively presenting evidence and arguments deemed to be compelling. The content and rhetorical style used by each participant was selected to persuade the audience. For instance, the first argument presented by the supporting side highlighted algae production in some locations as a way to avoid species loss and invasion; this point was not forcefully countered by the opposing side. The other main argument presented by the supporting side drew from research on forest bioenergy systems. The side opposing the thesis cited historical evidence by analogy with agronomic systems, voicing doubt that biodiversity would be maintained in bioenergy systems. This debater used the first person pronoun "we" rhetorically to sway the audience as ecologists and members of society. Both sides highlighted uncertainties in opposing arguments. The audience responded positively to arguments as shown in the results of the middebate hand votes (Table 2). Our debate clarified what aspects of bioenergy and biodiversity remain uncertain and what hypotheses could be tested to reduce scientific uncertainty. Key uncertainties included: (1) invasive potential of alternative feedstocks in different situations; (2) magnitude (area) of land conversion from bioenergy; (3) which land uses (i.e., urban vs. marginal vs. agricultural) will be replaced by each feedstock; (4) qualitative and quantitative effects of alternative bioenergy management practices on ecosystems; and (5) whether the cost of implementing ecologically sustainable management practices will be low enough. Research to clarify these questions will help to reduce uncertainty with respect to the broad thesis. Formal debate is an efficient means of facilitating scientific discourse at meetings because it capitalizes on the presence of experts, promotes lively and interactive exchange of scientific information, and deliberately intersperses contrasting points of view on controversial topics (Table 3). Theory tenacity is dangerous to good science. Alternating between arguments for and against the thesis counteracts our tendency to seek out information that conforms to our previously held beliefs (Sarewitz 2004). Immediate feedback between ideas and counter-arguments leads to more efficient progress toward a shared assessment of the likelihood that elements of a thesis are true, and what aspects remain uncertain. Ideally, this clarification will guide research in directions that will reduce scientific uncertainty. With the advent of electronic publishing, we are seeing even more direct public discourse between researchers in written formats; some journals publish articles, comments, and author responses simultaneously. Professional societies have an opportunity to enhance scientific exchange by directly engaging their membership through live dialogue and debate at their meetings. This has been done at the Society of Environmental Toxicology and Chemistry and the Entomological Society of America conferences. In the latter case, students participate in debate, which helps to develop professional scientists with important critical thinking skills (Osborne 2010). The debate format also has drawbacks (Table 3). Formal debate tends to polarize positions, thereby causing more complex dimensions or nuances to be lost. One way to recover these facets is by engaging the audience in a post-debate question-and-answer session. Debate can lower scientific credibility if it is felt that debaters are advancing particular interests by selectively representing a body of knowledge or exaggerating scientific certainty. Further, the debate format is not suitable for all situations. For example, it is less interesting to debate topics with overwhelming scientific support for one side. Debate is also a poor choice for communicating uncertainty to nonscientists, who may consider scientific results to be absolute and exact truths (Rabinovich and Morton 2012). We nevertheless strongly support live debate as a communication tool for scientific meetings. This debate grew out of a U.S. Department of Energy (DOE) workshop on the DOE BioEnergy Technologies Office (BETO) Billion Ton-2 study, which was held at Oak Ridge National Laboratory (ORNL), organized by Virginia Dale in the fall of 2011. H. Jager and R. Efroymson were supported by the DOE BETO at ORNL, which is managed by UT-Battelle, LLC, for the DOE under contract DE-AC05-00OR22725. Participation by D. Landis was supported by the DOE Great Lakes Bioenergy Research Center (BER Office of Science DE-FC02-07ER64494) and BETO (DE-AC05-76RL01830). We thank Natalie Griffiths and Peter Schweizer for assistance. Disclaimer: This article does not represent the official views of the U.S. Environmental Protection Agency or of BETO.}, number={3}, journal={Bulletin of the Ecological Society of America}, publisher={Wiley}, author={Ridley, Caroline E. and Jager, Henriette I. and Clark, Christopher M. and Efroymson, Rebecca A. and Kwit, Charles and Landis, Douglas A. and Leggett, Zakiya H. and Miller, Darren A.}, year={2013}, month={Jul}, pages={277–290} }
 @article{king_ceulemans_albaugh_dillen_domec_fichot_fischer_leggett_sucre_trnka_et al._2013, title={The Challenge of Lignocellulosic Bioenergy in a Water-Limited World}, volume={63}, ISSN={["1525-3244"]}, DOI={10.1525/bio.2013.63.2.6}, abstractNote={It is hoped that lignocellulosic sources will provide energy security, offset carbon dioxide enrichment of the atmosphere, and stimulate the development of new economic sectors. However, little is known about the productivity and sustainability of plant cell-wall energy industries. In this study, we used 16 global circulation models to project the global distribution of relative water availability in the coming decades and summarized the available data on the water-use efficiency of tree- and grass-based bioenergy systems. The data on bioenergy water use were extremely limited. Productivity was strongly correlated with water-use efficiency, with C4 grasses having a distinct advantage in this regard. Our analysis of agro climatic drivers of bioenergy productivity suggests that relative water availability will be one of the most important climatic changes to consider in the design of bioenergy systems.}, number={2}, journal={BIOSCIENCE}, author={King, John S. and Ceulemans, Reinhart and Albaugh, Janine M. and Dillen, Sophie Y. and Domec, Jean-Christophe and Fichot, Regis and Fischer, Milan and Leggett, Zakiya and Sucre, Eric and Trnka, Mirek and et al.}, year={2013}, month={Feb}, pages={102–117} }
 @inproceedings{leggett_sucre_2012, place={New Orleans, LA}, title={Evaluating the impact of switchgrass intercropping in loblolly pine plantations on long-term soil productivity}, booktitle={Proceedings from Sun Grant National Conference: Science for Biomass Feedstock Production and Utilization}, author={Leggett, Z.H. and Sucre, E.B.}, year={2012} }
 @article{albaugh_sucre_leggett_domec_king_2012, title={Evaluation of intercropped switchgrass establishment under a range of experimental site preparation treatments in a forested setting on the Lower Coastal Plain of North Carolina, USA}, volume={46}, DOI={10.1016/j.biombioe.2012.06.029}, abstractNote={There is growing interest in using switchgrass (Panicum virgatum L.) as a biofuel crop and for its potential to sequester carbon. However, there are limited data on the establishment success of this species when grown as a forest intercrop in coastal plain settings of the U.S. Southeast. Therefore, we studied establishment success of switchgrass within experimental intercropped plots and in pure switchgrass plots in an intensively managed loblolly pine (Pinus taeda) plantation in eastern North Carolina. Pine trees were planted in the winter of 2008, and switchgrass was planted in the summer of 2009. Establishment success of switchgrass was measured over the growing season from May to October 2010, and quantified in terms of percent cover, height (cm), tiller density (number of tillers m−2), leaf area index and biomass (Mg ha−1). At the end of the growing season, pure switchgrass plots were taller than the intercropped treatments (114 ± 2 cm versus 98 ± 1 cm, respectively), but no significant treatment effects were evident in the other variables measured. Switchgrass biomass across all treatments increased from 2.65 ± 0.81 Mg ha−1 in 2009 to 4.14 ± 0.45 Mg ha−1 in 2010. There was no significant effect of distance from the pine row on any switchgrass growth parameters. However, we anticipate a shading effect over time that may limit switchgrass growth as the pines approach stand closure.}, journal={Biomass and Bioenergy}, author={Albaugh, J. M. and Sucre, E. B. and Leggett, Zakiya H and Domec, J. C. and King, J. S.}, year={2012}, pages={673–682} }
 @inproceedings{nettles_leggett_2012, place={New Orleans, LA}, title={Extent and distribution of sustainable intensive forest biofuel practices}, booktitle={Proceedings from Sun Grant National Conference: Science for Biomass Feedstock Production and Utilization}, author={Nettles, J.E. and Leggett, ZH}, year={2012} }
 @article{blazier_clason_vance_leggett_sucre_2012, title={Loblolly Pine Age and Density Affects Switchgrass Growth and Soil Carbon in an Agroforestry System}, volume={58}, ISSN={0015-749X}, url={http://dx.doi.org/10.5849/forsci.11-052}, DOI={10.5849/forsci.11-052}, abstractNote={: Global interest in biomass-based fossil fuel substitutes is increasing, creating needs for new crops and cropping systems that will expand biofuel production. In the southeastern United States, an alley cropping agroforestry management system in which switchgrass is cultivated between rows of loblolly pine is being explored. Such a system could produce an annually harvested, high-yield energy crop, wood waste for biofuel production, conventional forest products, and environmental services such as soil carbon (C) sequestration. The objectives of this study were to determine the effects of loblolly pine age (juvenile, mid-rotation, and late-rotation) and loblolly pine density (no trees, low density, and high density) on switchgrass and loblolly pine growth and soil characteristics (microbial biomass C and activity, labile C, and total soil C) linked to carbon sequestration and site productivity. Switchgrass ground coverage was greater in loblolly pine alleys than in open conditions in 2 of the 3 years of this study, but switchgrass biomass was lower in loblolly pine alleys than in open conditions in the mid-rotation stand. Switchgrass in alleys was associated with greater labile C, respiration, and microbial biomass and activity in soil compared with that in loblolly pine plantations with intensive suppression of understory. F OR . S CI . 58(5):485–496.}, number={5}, journal={Forest Science}, publisher={Oxford University Press (OUP)}, author={Blazier, Michael A. and Clason, Terry R. and Vance, Eric D. and Leggett, Zakiya and Sucre, Eric B.}, year={2012}, month={Oct}, pages={485–496} }
 @inproceedings{albaugh_domec_maier_sucre_leggett_king_2012, place={New Orleans, LA}, title={Water relations and productivity in an intercropped pine-switchgrass study examining biofuel production in North Carolina, USA}, booktitle={Proceedings from Sun Grant National Conference: Science for Biomass Feedstock Production and Utilization}, author={Albaugh, J.M. and Domec, J. and Maier, C.A. and Sucre, E.B. and Leggett, Z.H. and King, J.S.}, year={2012} }
 @inbook{nettles_youssef_cacho_grace_leggett_sucre_2011, place={Oxfordshire, UK}, title={The water quality and quantity effects of biofuel operations in pine plantations of the southeastern US}, number={Publication 348}, booktitle={Water Quality: Current Trends and Expected Climate Change Impacts}, publisher={IAHS Press}, author={Nettles, J. and Youssef, M. and Cacho, J. and Grace, J. and Leggett, Z.H. and Sucre, E.}, editor={Peters, N.E. and Krysanova, V. and Lepisto, A. and Prasad, R. and Thomas, M. and Wilby, R. and Zandarya, S.Editors}, year={2011}, pages={115–122} }
 @article{sanchez_carter_leggett_2009, title={Loblolly pine growth and soil nutrient stocks eight years after forest slash incorporation}, volume={257}, ISSN={0378-1127}, url={http://dx.doi.org/10.1016/j.foreco.2008.12.016}, DOI={10.1016/j.foreco.2008.12.016}, abstractNote={Incorporation of forest slash during stand establishment is proposed as a means of increasing soil carbon and nutrient stocks. If effective, the increased soil carbon and nutrient status may result in increased aboveground tree growth. Eight years after study installation, the impact of forest slash incorporation into the soil on soil carbon and nutrient stocks, foliar nutrients and loblolly pine growth are examined on mineral and organic sites on the North Carolina Lower Coastal Plain. Treatments include leaving forest slash on the surface and flat planting (control); V-shear and bedding (conventional), mulch forest slash followed by bedding (strip mulch) and mulch forest slash and till into the soil followed by bedding (strip mulch till). After eight years, mulching and/or tillage did not have a significant impact (p > 0.05) on soil bulk density or soil chemical properties (pH, cation exchange capacity, soil nutrients). Additionally, neither tree foliar nutrients nor stand volume were significantly impacted. However, significant effects were observed for soil phosphorus contents and stand volume between the control plots and the other treatment plots. For example, the mean stand volumes on the mineral site were 24.49 ± 1.28, 38.16 ± 2.90, 44.59 ± 3.07 and 46.96 ± 2.74 m3 ha−1 for the control, conventional, strip mulch and strip mulch till plots. These observations are more likely due to the effect of bedding rather than mulching or tillage of the forest slash. These results are consistent for the mineral and the organic sites. Considering the greater expense to install the mulch and tillage treatments, the lack of a treatment effect on soil carbon and nutrient stocks and tree growth does not justify these treatments on these sites.}, number={5}, journal={Forest Ecology and Management}, publisher={Elsevier BV}, author={Sanchez, Felipe G. and Carter, Emily A. and Leggett, Zakiya H.}, year={2009}, month={Feb}, pages={1413–1419} }
 @article{leggett_kelting_2006, title={Fertilization effects on carbon pools in loblolly pine plantations on two upland sites}, volume={70}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2003.0232}, abstractNote={A study was conducted in loblolly pine (Pinus taeda L.) plantations on sandy and clayey upland sites, with and without the addition of 250 kg ha−1 of diammonium phosphate (DAP) applied at planting, to estimate the effects of fertilization on ecosystem C storage. Soil C pools were inventoried before planting and in the 11th year of stand development. Tree inventory data were used to convert stand volume to accumulated biomass. During the 11 yr of stand development, total ecosystem C increased by 24.2 Mg ha−1 on average across sites, averaging 2.2 Mg C ha−1 yr−1 Fertilization increased accretion by 25.3 Mg ha−1, or 2.3 Mg C ha−1 yr−1, with the majority of increase (65%) occurring in biomass. The clayey site averaged 64% more total ecosystem C than the sandy site. With the exception of a 12 Mg ha−1 loss in mineral soil C for the 10‐ to 20‐cm depth in nonfertilized (control) plots on the sandy site, soil C in the surface 20 cm did not change during the 11 yr of stand development, suggesting that the mineral soil C is a minor sink in these aggrading pine plantations. The loss in mineral soil C observed in control plots on the sandy site may be explained by the macroporosity of this coarse‐textured sandy soil creating an environment conducive to oxidation and in turn optimal for respiration and C losses following site preparation, and a disadvantaged opportunity for C accumulation owing to higher soil temperatures. Fertilization may have improved the opportunity for C accumulation on the plots having been fertilized on the sandy site in early years by creating a cooler soil as a result of more rapid canopy closure and forest floor accumulation.}, number={1}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Leggett, ZH and Kelting, DL}, year={2006}, pages={279–286} }
 @article{sanchez_leggett_sankar_2005, title={Analyzing water soluble soil organics as trifluoroacetyl derivatives by liquid state proton nuclear magnetic resonance}, volume={36}, ISSN={["1532-2416"]}, DOI={10.1080/00103620500304150}, abstractNote={Abstract In forested ecosystems, water soluble organics play an important role in soil processes including carbon and nutrient turnover, microbial activity and pedogenesis. The quantity and quality (i.e., chemistry) of these materials is sensitive to land management practices. Monitoring alterations in the chemistry of water soluble organics resulting from land management practices is difficult because of the complexity and low concentration of these compounds. A procedure is described in which the water soluble organics are quantitatively derivatized with trifluoroacetic anhydride and then analyzed by liquid state proton nuclear magnetic resonance (1H NMR). The procedure was applied to sample amounts as low as 0.03 mg from the forest floor and root exudates. The root exudate samples were dominated by aliphatic compounds with relatively few O‐alkyl, olefinic and aromatic compounds. The chemistry of the samples originating from the forest floor differed dramatically with soil texture and treatment combinations.}, number={19-20}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Sanchez, FG and Leggett, ZH and Sankar, S}, year={2005}, pages={2793–2805} }
 @phdthesis{leggett_2004, place={Raleigh, NC}, title={Carbon storage and transport in fertilized loblolly pine (Pinus taeda, L.) plantations on upland sandy and clayey soils}, school={Department of Forestry. North Carolina State University}, author={Leggett, Z.H.}, year={2004} }
 @article{verchot_holmes_mulon_groffman_lovett_2001, title={Gross vs net rates of N mineralization and nitrification as indicators of functional differences between forest types}, volume={33}, ISSN={0038-0717}, url={http://dx.doi.org/10.1016/s0038-0717(01)00095-5}, DOI={10.1016/s0038-0717(01)00095-5}, abstractNote={Floristic species composition and differences in litter quality between species are the primary factors controlling N mineralization in forest ecosystems. Generalizations about species effects on N cycling are based on measurements of net rates of mineralization and nitrification. However, there have been few tests on the ability of these measurements to reflect the mechanistic complexity underlying the species effects. The objectives of this study are to: (1) determine whether differences in net mineralization and net nitrification rates between stands of different species composition are due to differences in gross rates of mineralization, nitrification, and microbial consumption; (2) determine whether field and laboratory assays of net mineralization and nitrification are useful indicators of internal N dynamics; and (3) test the hypothesis that microbial immobilization increases with rates of mineralization and nitrification. We measured net rates of mineralization and nitrification in the field and in the laboratory, and gross rates of mineralization, nitrification and microbial consumption in different stands at two sites in eastern New York State. The results indicated that vegetation type was not always a robust indicator of N cycling differences between ecosystems. At one site there was no difference in net mineralization (P<0.05) between oak and maple stands, and no nitrification in either forest type. We attributed this lack of conformity to expected patterns to either differences in soil moisture regimes resulting from landscape position, forest floor disturbance by earthworms, or influences of previous land-use. At the second site, both beech and maple stands showed significantly greater rates of net nitrification than oak stands (P<0.05) and beech had significantly greater (P<0.05) rates of net mineralization than both maple and oak. Gross rates of mineralization, nitrification and microbial consumption were very high and often exceeded net rates by an order of magnitude. Gross rates were not good indicators of differences between forest types and in most cases we did not find differences in gross rates between stands where we found differences in net rates. We found a strong relationship between microbial consumption of NH4+ or NO3− and gross rates of mineralization or nitrification (R2=0.83 and R2=0.52, respectively).}, number={14}, journal={Soil Biology and Biochemistry}, publisher={Elsevier BV}, author={Verchot, L.V and Holmes, Z and Mulon, L and Groffman, P.M and Lovett, G.M}, year={2001}, month={Nov}, pages={1889–1901} }
 @phdthesis{holmes_2000, place={Durham, NC}, title={Leaching loss of chemical elements from decomposing logs of loblolly pine (Pinus taeda, L.)}, school={Duke University}, author={Holmes, Z.}, year={2000} }