Browsing by Author "Reid, John Leighton"

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    Evaluating native warm-season grass and wildflower mixtures for beef cattle production in the Mid-Atlantic
    Kubesch, Jonathan Omar Cole (Virginia Tech, 2023-12-20)
    Tall fescue grasslands are the dominant form of grasslands in the North American transition zone, however, warm-season forages provide necessary forage for livestock in the summer. Pollinators require steady forage availability in the same fashion as cattle. Native warm-season grasses (NWSG) and wildflowers (WF) could be incorporated into tall fescue (TF) grasslands to improve pollinator resources within agricultural landscapes without sacrificing livestock production. This balance of ecosystem services can be considered bee-friendly beef. Previous establishment experiments suggests that bee-friendly beef is a possibility, although establishment and persistence of NWSG-WF stands warrants additional research. Three small plot experiments were conducted to evaluate different planting methods designed to optimize establishment of NWSG-WF stands. Additionally, a grazing study examined whether NWSG-WF pasture enhancement could improve animal performance in TF grazing systems. The small plot experiments experienced extreme weed competition in the establishment year, although plots with higher NWSG content had fewer weeds over time. Floral production was comparable across treatment, which suggests lower WF seeding rates can generate comparable pollinator resources. Major findings from these experiments suggested that spatial or temporal separation of NWSGWF was unnecessary to generate successful establishment, varying the ratio of NWSG-WF in seed mixtures produced similar establishment outcomes, and that adding companion crops to NWSG-WF mixtures did not improve establishment success appreciably. In the grazing experiment, animal performance was improved in the biodiverse grazing systems when heifers 3 had access to the NWSG. Biodiverse and shaded grazing systems modified animal behavior and reduced body temperature relative to control grazing systems, although only biodiverse grazing systems improved animal performance. Native WF species failed to establish within the biodiverse grazing system, but white clover provided all subsequent floral production. Establishing WF in pastures is challenging and warrants additional study on more effective weed control strategies and systems to ensure establishment success. Selecting WF for agronomic performance or breeding such plant material will be necessary to improve emergence and establishment dynamics. Ideally trait data can identify the optimal WF species for specific grazing systems. Biodiverse NWSG-WF can be highly effective at improving summer weight gain in beef cattle. Future studies should focus on finding a more optimal balance of NWSG, WF, and TF that can benefit beef cattle production, pollinator services, and ecosystem services regarding soil and water quality, as well as pasture resiliency to dynamic conditions.
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    Germination niche of an emergent invasive grass, Arthraxon hispidus
    Beall, Michael Christian (Virginia Tech, 2022-07-01)
    Joint-head grass (Arthraxon hispidus) is a widespread nonindigenous plant species in the eastern United States. It is observed forming large monodominant patches that impact native and managed grassland systems. With such little understanding of its foundational biology or ecological impacts, leaving land managers desperate for effective control measures to manage A. hispidus invasion. We conducted a series of complementary experiments on six populations of A. hispidus to better understand how environmental factors affect seed germination. Germination is a critical life stage that allows a species to disperse. Freshly harvested seeds germinated effectively within 14 days of imbibition in the dark at 23°C, exhibiting little to no dormancy or influence by light. A pH range of 5 - 10 resulted in ≥ 80% germination, suggesting that pH will not limit colonization in other portions of the United States. Arthaxon hispidus was tolerant to abiotic stressors such as salinity and osmotic potential. The concentration required to limit germination to 50% (LD50) in the populations tested surpassed soil salinity found in the contiguous United States and some tidal systems (Frederick, MD = 354; Lincoln, MO = 354; Williamsburg, VA = 298 mM NaCl). While drought adversely affects A. hispidus germination, the LD50 occurred in moderate to more severe osmotic potentials (Frederick, MD = -0.67; Lincoln, MO = -0.37; Williamsburg, VA = -0.25 MPa) making A. hispidus expansion more likely in wetter years and regions. Constant temperature treatments resulted in germination percentages across a range of temperatures (8 - 37°C), and A. hispidus is well distributed in several major temperature regimes found in the United States. Finally, emergence greatly decreased with burial depth. Emergence occurred at ≥ 43% at 1 - 2 cm, decreasing to 5% at 6 cm, and 0% at 8-cm depths. With adequate soil moisture, a broad range of germination temperatures, and a decreased emergence rate with depth, we believe A. hispidus is unlikely to develop a seed bank. These initial studies on A. hispidus' germination posit a broad range of environmental tolerances; although, it may be limited by other life stages.
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    Global change effects on ant-mediated seed dispersal
    Burt, Melissa Ann (Virginia Tech, 2024-05-20)
    Seed dispersal mutualisms, including seed dispersal by ants, are critical to the assembly of communities and the function of ecosystems. However, the consequences of human-caused global change factors, such as habitat fragmentation and climate change, for the future of these mutualisms are not fully understood. My dissertation consists of five chapters that investigated the effects of habitat fragmentation and climate change on ants and their seed dispersal mutualisms. Chapter 1 is an introduction that provides background information on habitat fragmentation and anthropogenic climate change and their impacts on biodiversity. In Chapter 1, I also introduce my study system of ant-mediated seed dispersal mutualisms, myrmecochory. My next two chapters (Chapters 2 and 3) explored the effects of reconnecting fragmented habitat patches with corridors in restored longleaf pine savanna systems in South Carolina. We used a landscape scale experiment to investigate how reducing isolation affects the assembly of ant communities over time (Chapter 2) and seed dispersal of the myrmecochorous forb, Piriqueta cistoides (Chapter 3). For Chapter 2, we found evidence that both habitat connectivity and edge effects underly the effects of corridors on ant communities over time. We found that connected patches accumulated ant species faster than isolated patches over time suggesting that corridors function by facilitating colonization. We also found evidence that edge effects play a role with greater ant functional group diversity in patches with higher edge than patches with lower edge amounts. For Chapter 3, we also found evidence of corridor and edge effects with ants dispersing seeds of P. cistoides longer distances in patches connected via corridors than isolated patches, but only in the center of patches. In Chapter 4, we investigated the effects of predicted climate change scenarios for seed dispersal mutualisms in eastern deciduous forests. For this chapter, we conducted a mesocosm experiment in which we crossed temperature with altered precipitation magnitude and frequency. Our mesocosms contained a common spring ephemeral wildflower, Sanguinaria canadensis, and whole colonies of their mutualist seed disperser, Aphaenogaster rudis. This design allowed us to collect high-resolution data on how ants interacted with seeds under different climate change scenarios that incorporated warming temperatures and altered precipitation. We found that warming effects depended on the precipitation treatment with negative effects of warming on the collection of seeds by ants under historical precipitation regimes and positive effects of warming under simulated precipitation conditions altered under predicted climate change. Finally, Chapter 5 describes my general conclusions from this body of work. Taken together, the research making up my dissertation provides valuable insights into how changing environmental conditions under habitat fragmentation and climate change may alter ant seed dispersal mutualisms. Importantly, we often found that the impacts of global change were context dependent and that our experiments were important tools in disentangling that context dependency. Further, this work demonstrates the value of understanding the basic ecology of the interactions among organisms. Understanding the natural history of organisms across changing environmental conditions will benefit the ways in which we conserve and restore ecosystems in a fragmented and warmer world.
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    Honey Bee Colony Resource Acquisition, Population Growth, and Pollen Foraging in Diversified Native Grass-Wildflower Grazing System
    Larcom, Raven Miranda (Virginia Tech, 2023-09-01)
    Compounding evidence suggests a current or impending sixth mass extinction event and pollinator crisis. While several factors contribute to pollinator declines, the most notable driver is habitat loss and degradation. Agricultural grasslands provide crucial habitat for wild and domesticated fauna, regulate water and nutrient cycles, store carbon, and maintain soil stabilization. However, conventional tall fescue pastures, which dominate the southeastern United States, limit pollinator habitat, reduce ecosystem services, and diminish cattle productivity if infected with toxic endophytes. Establishing wildflowers (WFs) and native warm season grasses (NWSGs) into tall fescue pastures has the potential to boost both pollinator ecosystem services and cattle productivity. This study monitored the differences in honey bee colony health, productivity, and pollen foraging behavior between diversified and conventional grazing pastures in south west Virginia. Chapter 1 sought to evaluate the health and productivity of hives within NWSGW+ diversified and conventional grazing systems. Chapter 2 sought to 1) determine whether honey bees used sown wildflower species in diversified pastures as significant sources of pollen, 2) compare species composition and nutritive value of pollen collected from hives within diversified and conventional pasture systems, and 3) evaluate temporal trends in pollen collection. Floral surveys revealed diversified pastures had almost 4x greater mean bloom density than conventional pastures, with over half of all blooms recorded in diversified pastures belonging to unsown species. Results from this study suggest that colonies in diversified pasture systems may have a slight advantage in population resource acquisition, population growth, and winter survival following the first year of establishment, though further research is needed. Pollen DNA metabarcoding revealed that honey bees in both diversified and conventional pasture systems have similar diets, and that sown species were foraged upon primarily in the fall. Samples collected from diversified pasture systems yielded greater pollen weight, species richness, and protein content. In conjunction with previous research, these results indicate that diversified pastures could ultimately provide a more complex nutritional support system for pollinators in grazing agroecosystems. However, individual pasture renovation may not be large enough to yield statistically significant differences in honey bee colony success.
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    Native Forb Establishment in Tall Fescue-dominated Cattle Pastures
    Bellangue, David Nsame (Virginia Tech, 2023-02-20)
    Temperate grasslands and the services they provide are threatened with severe degradation from human-driven land use changes. Among the worst affected services is pollinator support with grassland degradation contributing to the global decline in insect abundance due to habitat loss and a lack of floral resources. This has prompted conservation organizations to support pollinator conservation on working landscapes by increasing floral resources, but gaps remain in the consistent establishment of native forbs in intensively managed agricultural areas. We evaluated factors that influence native forb establishment during seed-based enrichment planting of tall fescue-dominated cattle pastures in two separate experiments: one testing a range of site preparation treatments with different seasons of sowing and comparing their effects on tall fescue suppression and seeded native plant establishment and the other investigating the effects of seed rate and pre-seeding cold stratification on native forb establishment on separate plots. For the site preparation experiment, we observed a mean target plant density of 0.12 target plants per m2 (SD = 0.247) The greatest target plant stem density (P < 0.0001) and species richness (P < 0.001) was in plots treated with a 2% glyphosate solution and sown with native seeds in early summer with the next five best treatments composed solely of fall sown replicates. For the seed and stratification experiment, we observed a mean target plant density of 88 target plants per m2 (SD = 73.9). Higher seeding resulted in greater target plant abundance in plots (P < 0.0001) with a seed rate of 56 kg/ha-1 resulting in almost three times as many target plants compared to 2.24 kg/ha-1. Pre-seeding stratification resulted in an increase in target plant abundance (P < 0.01). Target species richness was consistent between treatment levels. Results suggest that native forb establishment can be enhance by eliminating pasture grasses prior to seeding and the use of high seeding rates sown in the fall or using stratified seed.
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    Site Preparation and Planting Strategies to Improve Native Forb Establishment in Pasturelands
    Bellangue, David; Barney, Jacob; Flessner, Michael; Kubesch, Jonathan; O’Rourke, Megan; Tracy, Benjamin; Reid, John Leighton (MDPI, 2024-11-14)
    Increasing the diversity of native forbs in pasturelands can benefit insect pollinator populations, which have been declining widely. Establishing native forbs into existing pasturelands can be challenging, however, and information about effective planting strategies in these systems is lacking. In this study, we evaluated several planting strategies to improve native forb establishment. Two field experiments were conducted in Virginia, USA in 2021 and 2022. Experiment 1 evaluated how six herbicide treatments and tillage affected establishment success when forbs were planted in summer or fall. Experiment 2 investigated how different seeding rates from 2.2 to 56 kg/ha and pre-seeding cold stratification affected forb establishment. In experiment 1, treatments using Roundup/glyphosate and tillage resulted in the most forb establishment. Planting in summer improved establishment with Roundup/glyphosate application. In experiment 2, native forb plant establishment was positively associated with seeding rate (p < 0.001), with a rate of 56 kg/ha resulting in almost 3x more forbs compared to the lowest seeding rate. Cold stratification also increased target plant establishment (p < 0.01), but these effects were inconsistent among species. Our results suggest that effective native forb establishment can be achieved through intensive site preparation with Roundup/glyphosate or tillage to suppress vegetation and planting at rates no higher than 11 kg/ha.