Browsing by Author "O'Rourke, Megan E."

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    Archetype models upscale understanding of natural pest control response to land-use change
    Alexandridis, Nikolaos; Marion, Glenn; Chaplin-Kramer, Rebecca; Dainese, Matteo; Ekroos, Johan; Grab, Heather; Jonsson, Mattias; Karp, Daniel S.; Meyer, Carsten; O'Rourke, Megan E.; Pontarp, Mikael; Poveda, Katja; Seppelt, Ralf; Smith, Henrik G.; Walters, Richard J.; Clough, Yann; Martin, Emily A. (Wiley, 2022-06)
    Control of crop pests by shifting host plant availability and natural enemy activity at landscape scales has great potential to enhance the sustainability of agriculture. However, mainstreaming natural pest control requires improved understanding of how its benefits can be realized across a variety of agroecological contexts. Empirical studies suggest significant but highly variable responses of natural pest control to land-use change. Current ecological models are either too specific to provide insight across agroecosystems or too generic to guide management with actionable predictions. We suggest obtaining the full benefit of available empirical, theoretical, and methodological knowledge by combining trait-mediated understanding from correlative studies with the explicit representation of causal relationships achieved by mechanistic modeling. To link these frameworks, we adapt the concept of archetypes, or context-specific generalizations, from sustainability science. Similar responses of natural pest control to land-use gradients across cases that share key attributes, such as functional traits of focal organisms, indicate general processes that drive system behavior in a context-sensitive manner. Based on such observations of natural pest control, a systematic definition of archetypes can provide the basis for mechanistic models of intermediate generality that cover all major agroecosystems worldwide. Example applications demonstrate the potential for upscaling understanding and improving predictions of natural pest control, based on knowledge transfer and scientific synthesis. A broader application of this mechanistic archetype approach promises to enhance ecology's contribution to natural resource management across diverse regions and social-ecological contexts.
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    Assessing the conservation value and food system impacts of high tunnels
    Foust-Meyer, Nathaniel (Virginia Tech, 2015-07-09)
    There is growing demand for food grown and sold locally, but climate often limits supply. High tunnels can often overcome these limitations. In order to encourage local availability and production of specialty crops the Natural Resource Conservation Service (NRCS) has launched the Seasonal High Tunnel initiative. This cost-share program provides farmers with a high tunnel intended to encourage the availability of locally grown fresh produce. Using mixed-methods research this thesis examines the social, economic, and conservation impacts of the NRCS high tunnel program. We have run a county by county negative binomial regression of the NRCS high tunnel distribution biophysical, socio-demographic, and market driven factors. Additionally, 7 vegetable farms throughout Virginia were visited during the 2014 growing season to compare high tunnel and field grown cucumbers (Cucumis sativus) and tomatoes (Solanum lycopersicum). Additional detail about high tunnel production and food distribution was obtained with a survey of Virginia high tunnel growers. Survey respondents indicate that the majority of their high tunnel produce is sold within 100 miles of their farm. Regression results indicate that the NRCS high tunnel program is benefiting areas where the availability of local food is high, but may be neglecting areas with historically underserved communities. Our field results show that yield and the yield per pesticide application dividend were higher in high tunnel production of both cucumber and tomato. Therefore, we conclude that, high tunnels meet conservation goals different than the ones outlined by the NRCS. The NRCS high tunnel program is promoting the expansion of local food availability. However, work remains to clarify conservational benefits and to ensure that all communities have equal access to the fresh produce they provide.
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    Assessing the relationships between pollinator-friendly plantings and birds, bats and white-tailed deer on farms in the Coastal Plain of Virginia and Maryland
    Berge, Earle Johnathan (Virginia Tech, 2020-11-30)
    Pollinator-friendly wildflower and native grass plantings are increasingly incentivized by state and federal agencies to improve ecosystem services provided by pollinating insects on farmland. However, the potential ecosystem service benefits, or even disservices, of pollinator-friendly plantings relative to wildlife, such as resident, migratory, and nesting birds (e.g., wild turkey (Meleagris gallopavo)), resident and migratory bats, and white-tailed deer (Odocoileus virginianus) are of interest to both landowners and conservation managers. First, we studied bird species diversity, presence, density, and nesting on farms planted with and without pollinator-friendly plantings to evaluate the potential value of these plantings to bird-related values, such as cultural, recreational, and pest-regulating ecosystem services. Second, we quantified bat relative activity through recorded echolocation calls and explored how relative nightly activity varied across common cover types on a farm, by survey year, and by maternity (May-August) versus non-maternity season (September-April). Third, we determined whether white-tailed deer and wild turkey camera trap success and occupancy differed between farms with and without pollinator-friendly farmscaped plots, evaluated along with their relationships to percent cover of natural, developed, crop, and water habitats within 1 km of surveyed farms. We conducted bird point counts across 20 farms on the Eastern Shore of Virginia and Maryland and the city of Virginia Beach, VA during the Spring and Fall of 2017 and 2018. We searched for bird nests in pollinator-friendly plots during the summers of 2017 and 2018. There were no differences in alpha diversity, defined as the number of species per farm per survey period, between control and pollinator farms in either Spring or Fall. We did find differences in species evenness on farms during Spring surveys, as measured by Simpson's index, with pollinator farms having a higher mean Simpson's index. When examining factors relating to presence/absence of our 15 modeled bird species out of 110 species detected on farms, landscape-level cover types were influential in 14 species and presence of pollinator plots was influential for 5 species. After stratification of density estimates by control and pollinator farm study sites, we found that during Spring surveys, the blue jay (Cyanocitta cristata) and Carolina wren (Thryothorus ludovicianus) had lower density on pollinator farms. In the Fall, the blue grosbeak (Passerina caerulea) had higher density on pollinator farms. We found nesting in the pollinator-friendly plots by red-winged blackbirds (Agelaius phoeniceus; n=7). These nests were placed in locations within the pollinator plots with higher forb coverage than random points in the same plots without nests. We estimated the presence and relative activity of bats in 4 cover types, including forest trail, a forested pond edge, a crop field on forest edge, and a farmscaped wildflower plot, on the Eastern Shore Agricultural Research Extension Center in Painter, Virginia, from April 2017- November 2019 using acoustic detectors. Of total detections, 20.11% were identified as big brown bat (Eptesicus fuscus), 17.97% evening bat (Nycticeius humeralis), 15.35% silver-haired bat (Lasionycteris noctivagans), 7.11% eastern red bats (Lasiurus borealis), 3.66% hoary bats (Lasiurus cinereus), 3.1% little brown bat (Myotis lucifugus), and 1.38% tricolored bat (Perimyotis subflavus). Relative activity measured by calls per night varied by cover type, with relative activity highest for all 7 species in the crop field-forest edge and water-forest edge cover types as compared to pollinator plot and forest trail cover types during the maternity season (May-August). All 7 bat species were recorded in the pollinator plot cover type; of the 8,877 calls in pollinator plots, 26.07% were silver-haired bat, 25.21% eastern red bats, 23.78% evening bat, 9.32% hoary bats, 9.11% little brown bat, 5.42% big brown bat, and 1.09% tricolored bat. We used camera trap surveys to measure white-tailed deer and wild turkey occupancy across 20 farms on the Eastern Shore of Virginia and in the city of Virginia Beach, Virginia during the Spring and Fall of 2017 and 2018. Of all wild species photographed, white-tailed deer were most abundant (TS, # captures/100 nights) each survey season, however this varied season to season (Spring 2017 = 98.44 TS, Fall 2017 = 106.01 TS, Spring 2018 = 80.52 TS, Fall 2018 = 99.71 TS). Wild turkey total survey camera trap success was low compared to deer and other wildlife (4.51 TS), and also varied seasonally (Spring 2017 = 1.73 TS, Fall 2017 = 1.50 TS, Spring 2018 = 7.63 TS, Fall 2018 = 5.95 TS). White-tailed deer were detected at all survey locations at least once, and the occupancy of deer decreased as the percentage of developed land within 1km of a farm increased in each survey season. The factors relating to wild turkey occupancy varied by season. In Spring 2017, wild turkey occupancy increased as the percent of natural cover within 1 km of a farm increased. In Spring 2018, wild turkey occupancy decreased as the percent of developed land within 1 km increased. However, landscape variables did not influence wild turkey occupancy in the Fall seasons; rather in Fall 2018 we found that wild turkey occupancy decreased as camera trap success of farm machinery being used increased. Overall, wild turkey had a fairly low presence on all survey sites with an occupancy ranging from 0.18-0.53%, and no clear relationship to explain the change in survey season to season or year to year. Based on these results, pollinator plot presence or absence was not found to influence detection or occupancy of either of these target game species. Rather, other factors, mainly landscape-scale features, were found to have the largest influence on both species' occupancy and presence. Our study is one of just a few in North America to demonstrate some potential benefits of pollinator-friendly plantings to multiple different wildlife species with cultural, recreational, and insect-regulating ecosystem service benefits to landowners. Generally, birds, bats, and our focal game species' presence relied on surrounding landscape variables and forest-edge configurations more than the presence of pollinator friendly plantings. This is probably in part due to the small size of our pollinator plots. We recommend that future work explore potentially increasing the size of pollinator plot plantings or placing pollinator plantings in locations on the landscape with the most surrounding natural area, and least development, to maximize the benefits of this resource to diverse wildlife species with home ranges that are often larger than any one farm.
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    Biology of Chauliognathus spp. (Hentz) (Coleoptera: Cantharidae) in Virginia agroecosystems
    Catron, Katlyn Amos (Virginia Tech, 2021-05-17)
    Chauliognathus pensylvanicus (De Geer) and C. marginatus (Fabr.) are two of the most common species of cantharid beetles observed in agroecosystems in Virginia. Despite their widespread abundance and early recognition and description in the 1700s, little is known about their phenology and ecological role in agricultural systems. Immatures have been recorded feeding upon soft-bodied insects such as lepidopteran larvae, and adults frequently visit flowering plants, where they eat nectar and/or pollen. Beyond those observations, relatively little is known about these species, which are conspicuous elements on and around farms, though there is considerable potential for their use as pollinators and predators in a biological pest control context. I employed a phenological study to determine the period of C. marginatus activity in Southwestern Virginia, and found adults active on a variety of flowers from mid-May to late July. On these flowers, they spent a large percentage of their day mating or feeding, with significant differences in the percentage of beetles participating in behaviors based on time of day and beetle sex, but not based on month. The majority of C. marginatus observations occurred on narrowleaf mountain mint (Pycnanthemum tenuifolium Schrad.), poison hemlock (Conium maculatum L.), and wild bergamot (Monarda fistulosa L.). I also used a community science-based approach to evaluate the usage of host plants and flower colors by C. marginatus and C. pensylvanicus. Chauliognathus marginatus utilized white flowers more than expected based on their potential availability, while C. pensylvanicus utilized yellow flowers over all other flower colors and more than expected based on their potential availability. Communities of flowers available to and observed with C. marginatus and C. pensylvanicus differed significantly at the family and genus levels. Laboratory bioassays supported these conclusions regarding C. pensylvanicus color preference, but not C. marginatus color preference. Lastly, because of their susceptibility to nontarget chemical exposure in agroecosystems, I tested the efficacy of both organic and conventional vegetable insecticides against C. marginatus adults. The highest mortality was seen in the acetamiprid, flupyridifurone, sulfoxaflor, and imidacloprid treatments, which reached 97-100% mortality at two days after treatment. High mortality (60-97% two days after treatment) was also seen in the organic treatments containing azadirachtins, pyrethrins, and Chromobacterium subtsugae strain PRAA4-1T. Mortality in the Burkholderia spp. strain A396 and spinosad treatments was not significantly different from that of the controls, however, control mortality was relatively high in both assays.
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    Can Beef Be Bee-Friendly?  Using Native Warm-Season Grasses and Wildflowers in Pastures to Conserve Bees
    Wagner, Jennie Faith (Virginia Tech, 2020-05-29)
    Over the past several decades, native and managed bee populations have decreased in the United States and worldwide. Although bee decline is attributable to several factors, habitat loss is the primary driver. Simultaneously, cattle producers in the eastern U.S. rely primarily on cool-season forages that peak in biomass production in late spring, leading to a lack of forage in the summer months and increasing the costs of cattle production. Seeding pastures with a mix of native warm-season grasses and native wildflowers could increase forage availability while also increasing available resources for bees. In this study, a mix of three native warm-season grasses (NWSGs) and 15 wildflower species was planted at the Virginia Tech Shenandoah Valley Agricultural Research and Extension Center (SVAREC). The objectives of this project were to document the establishment and species composition of NWSG + wildflower pasture mixtures, compare the attractiveness of wildflowers and weedy species to bees, and compare the bee community between NWSG + wildflower pastures and more typical cool-season grass pastures. The wildflowers in the NWSG + wildflower pastures dominated over grasses. All wildflower species that established were attractive to bees, as were some weedy species. The NWSG + wildflower treatments had the highest abundance of bees collected, with an average of 14.8 bees collected per pasture per sampling date in 2018, and an average of 12.4 bees collected per pasture per sampling date in 2019. These results indicate that with modification of establishment methods so that more grasses are present, this pasture system could be beneficial from both a cattle production and bee conservation standpoint.
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    Case Study on a Container Gardening Program:  Can Home Food Production Impact Community Food Security in Rural Appalachia?
    Dobson, Elizabeth Rose (Virginia Tech, 2016-06-29)
    Home gardening has historically been a subsistence or supplemental form of food procurement worldwide and promoted as a food security project in times of economic hardship. Qualitative research was used to investigate container gardening's potential to provide the impetus for further agricultural activities within low-income, low-food-access, rural Appalachian Virginia, thereby impacting community food security, food choices of individuals, and the local food system. Ethnography and phenomenology methodologies were used through the lens of community-engaged research, and the lived experiences of participants were recognized as valid representations of food insecurity. Semi-structured interviews with fourteen participating households revealed program involvement was deeply connected to previous food production experiences and fueled by existing interest in home gardening. Containers were valued as providing alternative modes to continue a meaningful practice, specifically mitigating challenges of limited mobility for the elderly. As rural areas are experiencing an outmigration of young people and struggling social services, container gardening could be utilized as a low-cost culturally appropriate mental- and nutritional-health service for the rural elderly. Similar initiatives should begin with appreciative inquiry into existing perceptions, values, assets, and potentials within a target community. Through preliminary investigation, needs and barriers can be acknowledged and community-identified solutions can be implemented through culturally sensitive program development. With the existing impetus for home gardening in the region, program expansion could potentially impact food security and the local food system. Overall, this case study serves to further endorse a public effort to support home food production in rural areas of the United States.
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    Conservation Wildflower Plantings Do Not Enhance On-Farm Abundance of Amblyomma americanum (Ixodida: Ixodidae)
    McCullough, Christopher T.; Angelella, Gina M.; O'Rourke, Megan E. (MDPI, 2020-09-09)
    Planting wildflowers is a commonly suggested measure to conserve pollinators. While beneficial for pollinators, plots of wildflowers may be inadvertently performing an ecosystem disservice by providing a suitable habitat for arthropod disease vectors like ticks. The lone star tick, Amblyomma americanum (L.), is a medically important tick species that might be able to utilize wildflower plantings as a suitable habitat. In this two-year study, ticks were sampled using dry ice baited traps from wildflower plots, weedy field margins, and forested areas to determine if wildflower plantings were increasing the on-farm abundance of A. americanum. Abiotic and biotic environmental variables were also measured to better understand which factors affect A. americanum abundance. We found no more A. americanum in wildflower plots than in weedy field margins. Forested areas harbored the greatest number of A. americanum sampled. The height of the vegetation in the sampled habitats was a significant factor in determining A. americanum abundance. Depending on the sampled habitat and life stage, this relationship can be positive or negative. The relationship with vegetation height may be related to the behavior of the white-tailed deer and the questing success of A. americanum. Overall, wildflower plots do not pose an increased risk of exposure to A. americanum on farms.
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    Crop pests and predators exhibit inconsistent responses to surrounding landscape composition
    Karp, Daniel S.; O'Rourke, Megan E. (NAS, 2018-06-11)
    The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies.
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    Diverse landscapes but not wildflower plantings increase marketable crop yield
    McCullough, Christopher; Grab, Heather; Angelella, Gina; Karpanty, Sarah M.; Samtani, Jayesh; Olimpi, Elissa M.; O'Rourke, Megan E. (Elsevier, 2022-11)
    Biodiversity-friendly farming practices may create a win-win scenario for biodiversity and crop production by supporting ecosystem services to agriculture. On-farm wildflower plantings and conserving semi-natural habitat surrounding farms are two such practices that focus on the integration of non-crop components into production systems at the local and landscape scale, respectively. Here, we examine the impact of these practices on the regulating services of biological control and pollination, as well as the provisioning service of crop yield in four crops replicated across 22 farms in two US states. Wildflower plantings had no effect on pollination while their influence on pest control was both dependent on the landscape context and inconsistent across crops. In contrast, farms surrounded by higher amounts of semi-natural habitat had consistently higher marketable yields for all four crops. Our findings suggest a need to account for non-production values of wildflower plantings as they provide fewer direct production benefits than surrounding semi-natural habitats.
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    The effects of wildflower plots and diverse landscapes on ecosystem services, bee communities, and on-farm tick abundance
    McCullough, Christopher T. (Virginia Tech, 2020-06-03)
    Conservation of natural habitats and planting wildflower plots are two commonly promoted tactics to enhance pollination services and biological control of crop pests, which are ecosystem services that can improve agricultural outputs. There are several programs at various levels of government in the United States that landowners can use to defray the costs of implementing these conservation strategies. Studies of European Agricultural Environmental Schemes have shown these tactics to have positive outcomes for crop production. However, real-world applications of cost-sharing programs have not been evaluated in the United States on pollination services and biological control. Furthermore, these tactics may inadvertently perform ecosystem disservices, like increasing crop pests or creating habitat for disease vectors. In this study, we evaluated the effects of natural habit and wildflower plots on biological control, pollination services, bee communities, and tick populations in Eastern Virginia and Maryland. This research was conducted on 22 farms. 10 of these farms had wildflower plots that were designed by Natural Resource Conservation Service personnel, and implemented by cooperating farmers. Collards, strawberries, tomatoes, and squash were used as model systems. We measured pest density, sentinel egg predation, crop damage, seed pollination, biomass production, marketable crop yield, sampled the bee community, and recorded tick abundance in wildflower plots. Many of the measures of biological control and pollination services had idiosyncratic results in regards to the wildflower plots and natural habit in the landscape. However, the proportion of high quality yield for all four crops increased with increasing natural habitat in the landscape. Bee communities between sites with and without wildflower plots were not different. Bee abundance did increase at wildflower sites when natural habitat comprised a certain proportion of the habitat around the site. Ticks were sampled from wildflower plantings, but not in greater abundance compared to field margins. In this study, the effects of wildflower plots were overshadowed by the landscape effects of natural habitat. Government personnel that oversee these programs may need to consider the surrounding landscape when helping implement on-farm conservation measure like wildflower plots. Such measures, do not perform an ecosystem disservice in regards to ticks.
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    Evaluating methods to establish biodiverse pasturelands with native grasses and wildflowers
    Ghajar, Shayan M.; Wagner, Jennie F.; O'Rourke, Megan E.; Tracy, Benjamin F. (University of Wisconsin Press, 2022)
    Virginia’s pasturelands are dominated by tall fescue (Schedonorus arundinaceus (Schreb.) Dumort., nom. cons. [Poaceae]), a competitive, non-native grass. Tall fescue has limited value for wildlife and insect pollinators, and it can pose issues for livestock if infected with an endophyte that produces a toxic alkaloid. Potential exists for developing more biodiverse pasturelands that would help reduce problems associated with tall fescue while increasing ecosystem services associated with improved wildlife and pollinator habitat. Native warmseason grasses (NWSG) and wildflowers (WF) have potential forage and conservation benefits; however, more research is needed to determine effective strategies that land managers can use to establish these species. This article summarizes 4 field experiments designed to evaluate establishment methods for NWSG and WF in tall fescue pasturelands. Experiments were established from 2016 to 2020 in central and western Virginia. Three evaluated preemergent imazapic herbicide applications while the fourth evaluated other methods, including glyphosate application, glyphosate combined with raking, prescribed fire, and tillage, to establish NWSG and WF. In the 3 experiments evaluating imazapic applications, the herbicide consistently suppressed wildflowers, with the exception of Rudbeckia hirta L. (Asteraceae), Desmanthus illinoensis (Michx.) MacMill. ex B.L. Rob. & Fernald (Fabaceae), Coreopsis lanceolata L. (Asteraceae), and Leucanthemum vulgare Lam. (Asteraceae). In the fourth experiment, tillage was the most effective method to establish wildflowers. Overall, we found imazapic can improve NWSG establishment, but suppresses most WF species tested in this environment. Methods to achieve more consistent WF establishment are needed if adoption of more biodiverse pasturelands becomes a future management goal.
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    Evaluating the interactions of crop management, carbon cycling, and climate using Earth system modeling and remote sensing
    Graham, Michael William (Virginia Tech, 2019-08-27)
    Crop management practices, such as soil tillage and crop residue management, are land management activities with potentially large impacts on carbon (C) cycling and climate at the global scale. Improvements in crop management practices, such as conservation tillage or 'no-till' (NT), have been proposed as climate change mitigation measures because such practices may alter C cycles through increased sequestration of soil C in agricultural soils. Despite their potential importance, regional to global scale data are lacking for many crop management practices, and few studies have evaluated the potential impact of the full range of crop management practices on C cycling and climate at the global scale. However, monitoring of crop management practices is crucial for assessing spatial variations in management intensity and informing policy decisions. Inclusion of crop management practices in Earth system models used for assessing global climate is a key requirement for evaluating the overall effects of different crop management practices on C cycling and their potential to mitigate climate change. Studies in this dissertation seek to address these issues by: (1) evaluating the efficacy of remote sensing methods for monitoring differences in soil tillage and crop residue management practices in Iowa; (2) incorporating soil tillage practices into an Earth system model and assessing the potential for soil C sequestration and climate change mitigation through adoption of NT practices; (3) assessing the historical impact of including the full range of crop management practices (residue harvest, grain harvest, soil tillage, irrigation, and fertilization) on changes in C cycling associated with land use and land cover change (LULCC) to crops in an Earth system model. The remote sensing study found that performance of the minimum Normalized Difference Tillage Index (minNDTI) method for assessing differences in tillage and residue management was below average compared to previous studies, even when using imagery from both Landsat 8 and Sentinel-2A sensors. Accurate assessment of these practices using minNDTI was hindered by issues with image quality and inability to obtain sufficient cloud-free, time series imagery during the critical planting window. Remote sensing research aimed at obtaining regional to global scale data on tillage and residue management practices is likely to continue to face these issues in the future, but further research should incorporate additional sensors and assess the efficacy of the minNDTI method for multiple locations and years. Adoption of NT practices in the Community Land Model, which is the land component of the Community Earth System Model, resulted in a cumulative soil C sequestration of 6.6 – 14.4 Pg C from 2015 – 2100 under a future climate change scenario (Representative Concentration Pathway 8.5), and cumulative soil C sequestration was equal to approximately one year of present-day fossil fuel emissions. Adjusting for areas where NT is already practiced had minor impacts on cumulative soil C storage, reducing gains in soil C from NT adoption by 0.4 – 0.9 Pg C globally. These results indicate that soil C sequestration and potential for climate change mitigation through NT may be more limited than has been anticipated elsewhere. Soil C sequestration via NT adoption was highest in temperate regions of developed countries with high initial soil C contents, indicating these areas should be targeted for NT adoption. Simulating the full range of crop management practices in the Community Land Model resulted in an increase in C emissions due to LULCC of 29 – 38 Pg C compared to scenarios with generic crops and model defaults. Individual crop management practices with the largest impact on LULCC emissions were crop residue harvest (18 Pg C), followed by grain harvest (9 Pg C) and soil tillage (5 Pg C). Although implementation of crop residue harvest and soil tillage was extreme in this study, these results imply that Earth system models may underestimate emissions from LULCC by excluding the full range of crop management practices. Studies in this dissertation corroborate the importance of crop management practices for C cycling and climate, but further research on these management practices is needed in terms of data collection, improving process-level understanding, and inclusion of these practices in Earth system models.
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    A global synthesis reveals biodiversity-mediated benefits for crop production
    Dainese, Matteo; Martin, Emily A.; Aizen, Marcelo A.; Albrecht, Matthias; Bartomeus, Ignasi; Bommarco, Riccardo; Carvalheiro, Luisa G.; Chaplin-Kramer, Rebecca; Gagic, Vesna; Garibaldi, Lucas A.; Ghazoul, Jaboury; Grab, Heather; Jonsson, Mattias; Karp, Daniel S.; Kennedy, Christina M.; Kleijn, David; Kremen, Claire; Landis, Douglas A.; Letourneau, Deborah K.; Marini, Lorenzo; Poveda, Katja; Rader, Romina; Smith, Henrik G.; Tscharntke, Teja; Andersson, Georg K. S.; Badenhausser, Isabelle; Baensch, Svenja; Bezerra, Antonio Diego M.; Bianchi, Felix J. J. A.; Boreux, Virginie; Bretagnolle, Vincent; Caballero-Lopez, Berta; Cavigliasso, Pablo; Cetkovic, Aleksandar; Chacoff, Natacha P.; Classen, Alice; Cusser, Sarah; da Silva e Silva, Felipe D.; de Groot, G. Arjen; Dudenhoeffer, Jan H.; Ekroos, Johan; Fijen, Thijs; Franck, Pierre; Freitas, Breno M.; Garratt, Michael P. D.; Gratton, Claudio; Hipolito, Juliana; Holzschuh, Andrea; Hunt, Lauren; Iverson, Aaron L.; Jha, Shalene; Keasar, Tamar; Kim, Tania N.; Kishinevsky, Miriam; Klatt, Bjorn K.; Klein, Alexandra-Maria; Krewenka, Kristin M.; Krishnan, Smitha; Larsen, Ashley E.; Lavigne, Claire; Liere, Heidi; Maas, Bea; Mallinger, Rachel E.; Martinez Pachon, Eliana; Martinez-Salinas, Alejandra; Meehan, Timothy D.; Mitchell, Matthew G. E.; Molina, Gonzalo A. R.; Nesper, Maike; Nilsson, Lovisa; O'Rourke, Megan E.; Peters, Marcell K.; Plecas, Milan; Potts, Simon G.; Ramos, Davi de L.; Rosenheim, Jay A.; Rundlof, Maj; Rusch, Adrien; Saez, Agustin; Scheper, Jeroen; Schleuning, Matthias; Schmack, Julia M.; Sciligo, Amber R.; Seymour, Colleen; Stanley, Dara A.; Stewart, Rebecca M.; Stout, Jane C.; Sutter, Louis; Takada, Mayura B.; Taki, Hisatomo; Tamburini, Giovanni; Tschumi, Matthias; Viana, Blandina F.; Westphal, Catrin; Willcox, Bryony K.; Wratten, Stephen D.; Yoshioka, Akira; Zaragoza-Trello, Carlos; Zhang, Wei; Zou, Yi; Steffan-Dewenter, Ingolf (AAAS, 2019-10)
    Human land use threatens global biodiversity and compromises multiple ecosystem functions critical to food production. Whether crop yield-related ecosystem services can be maintained by a few dominant species or rely on high richness remains unclear. Using a global database from 89 studies (with 1475 locations), we partition the relative importance of species richness, abundance, and dominance for pollination; biological pest control; and final yields in the context of ongoing land-use change. Pollinator and enemy richness directly supported ecosystem services in addition to and independent of abundance and dominance. Up to 50% of the negative effects of landscape simplification on ecosystem services was due to richness losses of service-providing organisms, with negative consequences for crop yields. Maintaining the biodiversity of ecosystem service providers is therefore vital to sustain the flow of key agroecosystem benefits to society.
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    High tunnels for local food systems: Subsidies, equity, and profitability
    Foust-Meyer, Nathaniel; O'Rourke, Megan E. (2015)
    High tunnels are expanding opportunities to increase local food production in the midst of a globalized food system. They can overcome biophysical growing constraints by buffering temperatures to extend the growing season and shelter crops from extreme weather events. In 2010, the U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) began subsidizing the purchase of high tunnels. However, many questions remain about the factors influencing participation in the program and its impacts. Using mixed-methods research, this paper assesses the biophysical, market, and socio-demographic factors influencing NRCS high tunnel adoption in the U.S. and examines how food production in high tunnels affects farmers, consumers, and the local food movement. Results show that the number of NRCS high tunnels per county increased in relation to a mixture of biophysical (high latitude, proximity to the coast, small average farm size, and high percent of farmland in vegetable production), market (high direct-to-consumer sales, good access to grocery stores, and high median household income), and socio-demographic (high percentage of nonwhite population, metropolitan counties with more than 250,000 people, and adjacent urban counties with fewer than 20,000 people) factors. According to our survey of Virginia high tunnel growers, high tunnel produce is largely sold locally (within 50 miles or 80 km of production) and marketed direct-to-consumers in Virginia. Many growers in Virginia who would not have purchased a high tunnel without NRCS support plan to purchase additional high tunnels in the future even without a subsidy. High tunnels are an emerging part of the U.S. local food movement, but work remains to ensure that their benefits reach all sectors of U.S. society.
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    Honey bee hives decrease wild bee abundance, species richness, and fruit count on farms regardless of wildflower strips
    Angelella, Gina M.; McCullough, Christopher T.; O'Rourke, Megan E. (2021-02-05)
    Pollinator refuges such as wildflower strips are planted on farms with the goals of mitigating wild pollinator declines and promoting crop pollination services. It is unclear, however, whether or how these goals are impacted by managed honey bee (Apis mellifera L.) hives on farms. We examined how wildflower strips and honey bee hives and/or their interaction influence wild bee communities and the fruit count of two pollinator-dependent crops across 21 farms in the Mid-Atlantic U.S. Although wild bee species richness increased with bloom density within wildflower strips, populations did not differ significantly between farms with and without them whereas fruit counts in both crops increased on farms with wildflower strips during one of 2 years. By contrast, wild bee abundance decreased by 48%, species richness by 20%, and strawberry fruit count by 18% across all farm with honey bee hives regardless of wildflower strip presence, and winter squash fruit count was consistently lower on farms with wildflower strips with hives as well. This work demonstrates that honey bee hives could detrimentally affect fruit count and wild bee populations on farms, and that benefits conferred by wildflower strips might not offset these negative impacts. Keeping honey bee hives on farms with wildflower strips could reduce conservation and pollination services.
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    Improving Pest Management and Pollination with Farmscaping
    O'Rourke, Megan E.; Philips, Chris; Kuhar, Thomas P. (Virginia Cooperative Extension, 2019-08-30)
    Provides information about ways to naturally control agricultural and garden pests while increasing pollinators by including various species of flowers.
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    An Integrated Pest Management Program Outperforms Conventional Practices for Tomato (Solanum lycopersicum) in Cambodia
    Porras, Mitzy F.; Malacrino, Antonino; An, Chanratha; Seng, Kim Hian; Socheath, Ong; Norton, George; Miller, Sally; Rosa, Cristina; Rajotte, Edwin G.; O'Rourke, Megan E. (American Phytopathological Society, 2022-04)
    For several years, pest management in tomato production in Cambodia has generally focused on the use of synthetic pesticides. We compared conventional pest management (farmers' traditional practices) with an integrated pest management (IPM) program on 12 farms in the northwestern part of Cambodia. The IPM program combined cultural, biological, and chemical practices. We found that IPM practices reduced aphid damage by 46%, and diseases such as Fusarium wilt and damping-off were substantially reduced. Our results indicate that the IPM package increased tomato yield and income by an average of 23 and 34%, respectively, compared with conventional practices during both dry and rainy seasons.
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    Living Soil for a Sustainable Future: Cover Crop Effects on Soil Health and Productivity
    Taggart, Samantha P. (Virginia Tech, 2017-08-24)
    Agricultural land management practices impact the physical, chemical, and biological characteristics of soil, including the structure of the community of microorganisms present in the soil. The community of soil microorganisms, in turn, directly influences processes such as nutrient cycling and water infiltration and retention, which shape the long-term fertility and productivity of an agricultural landscape. The purpose of this study was to examine the effects of cover cropping on the soil biological and chemical features that contribute to soil fertility. The study looked at two summer cover crops – cowpea (Vigna unguiculata) and sorghum-sundangrass (Sorghum xdrummondii) in comparison with no-cover control – and their effects on soil respiration, soil organic matter and nitrogen availability, and lettuce production. Using soil samples taken from the in-field experiment, a parallel laboratory aerobic incubation study was conducted to examine the effects of the cover crop treatments on the transformation of nitrogen over five weeks. Both cover crops significantly increased soil organic matter, total organic carbon, and extractable potassium and magnesium by over 17% compared to the no-cover crop control. Cowpea significantly increased extractable soil nitrate and respiration rate compared to the no-cover control. Cowpea also resulted in the largest lettuce crop production as measured by both fresh weight and leaf area, but not different from the no-cover control. Sorghum-sudangrass decreased extractable soil nitrate concentration as well as lettuce fresh weight and leaf area compared to the control and cowpea. In conclusion, the study found that sorghum-sudangrass and cowpeas both increased soil organic matter, but only cowpea increased extractable inorganic N and lettuce production for sandy loam soils in the Mid-Atlantic and should be considered for these vegetable cropping systems.
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    Mapping High Tunnels in the Local Food Systems
    Foust-Meyer, Nathaniel; O'Rourke, Megan E. (2014)
    High tunnels (HTs) represent a quietly growing, local level response to globalization of the food system. As semi-permanent greenhouses, HTs bring practical on-farm solutions to biophysical growing constraints; they extend the growing season and buffer delicate crops from extreme weather events. In 2009, the Natural Resource Conservation Service (NRCS) began subsidizing the construction of HTs with the documented goals of increasing environmental stewardship and the added benefit of promoting local foods. However, many questions remain about the impacts of HTs. Where are they located? Who is benefiting from the NRCS HT program? Do HTs benefit rural or urban communities more? Are the benefits and access to HT produce equitably distributed between rural and urban consumers? This poster will illustrate the impacts of the NRCS HT program and high tunnels in general on farmers, consumers, and the local food movement. The poster will present information about where these high tunnels are in relation to metropolitan areas, food deserts, and the food insecure. Insights provided by GIS analysis about where HTs are located will lead to better projections into where they should be, in order to bring healthy food to more people, while conserving the environment.
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    Modeling Whole Farm Systems to Enhance Beginning Small Farmer Success in Southwest Virginia
    Sorensen, Emily Allyson (Virginia Tech, 2016-08-19)
    The number of very small farms (<10 acres) is increasing and beginning farmers (in practice for <10 years) are more likely to run them. Very small farms are typically complex systems in which the farmer manages both production of a diverse array of crops and marketing of crops directly to consumers and their failure rate in early years is high. This work seeks to increase the likelihood of success for beginning farmers by understanding these complex systems better. We collected qualitative and quantitative data from interviews with three successful beginning farm operations in Southwest Virginia covering practical and philosophical aspects of farm production, sales and management. We mapped social, environmental and economic aspects of farming systems and studied how farmers use resources (Community Capitals) and management to enhance their system's success, developing a broader definition of success that encompasses what farmers gain from farming beyond profitability. Using these maps, we created a system dynamics model of a small farm system in STELLA including unique components such as customer attraction and retention. Through model development, we learned that these successful farmers began their operations with experience and financial resources, and employed their skills, resourcefulness and cultural and social capital to charge prices for their products that could sustain their operations financially. Using our model, current and aspiring farmers, service providers, and small farm advocates will be able to simulate real or hypothetical farm systems to better understand what establishing a successful small farm might require and how to confront potential challenges.