College of Agriculture & Natural Resources
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item MOSQUITOES AND VEGETATION ACROSS SOCIOECONOMIC GRADIENTS(2024) Rothman, Sarah; Leisnham, Paul T; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The biomass and composition of local vegetation is a key resource for juvenile mosquitoes, affecting a suite of life history traits including survival, development rate, and body size. In cities across the United States, both plant and mosquito communities vary with socioeconomics. Vegetation is typically more abundant and biodiverse in high-income neighborhoods, whereas mosquitoes are often more numerous and more likely to vector diseases in low-income neighborhoods. While prior work has examined the effects of plant resources on mosquitoes, my dissertation evaluates how these communities interact across a socioeconomically diverse urban landscape. Chapter 1 is a scoping review of current knowledge of the individual relationships between mosquitoes, plants, and socioeconomics in cities. In Chapter 2, I describe fine-scale vegetation surveys on socioeconomically diverse residential properties in Baltimore, MD and Washington, D.C. that revealed less canopy cover, more vines, and more non-native plant species on lower-income blocks. In Chapter 3, I used leaves from the most frequently observed canopy species on low- and high-income blocks, and species common to both, as detrital resource bases in competition trials between two dominant urban mosquitoes, Aedes albopictus and Culex pipiens. Population performance for both species was greater when reared with characteristically low-income than characteristically high-income detritus, suggesting that socioeconomically diverse plant communities are an important factor in shaping urban mosquito communities. Overall, population performances were greatest when mosquitoes were reared in the regionally representative detritus, and I used this detritus base in Chapter 4 to evaluate the effects of varying temperatures. Aedes albopictus population performance was optimized at higher mean temperatures characteristic of low-income blocks, while C. pipiens performance was best at lower mean temperatures characteristic of high-income blocks. Population performance was often lower, however, when temperatures fluctuated around a high or low mean than when the temperature was stable, suggesting that laboratory studies may need to mimic field conditions to obtain applicable results. My research provides a deeper understanding of the mechanisms behind previously observed relationships, and may help guide management and policy strategies to address environmental injustices and public health threats.Item THE EFFECTS OF HISTORICAL AND CURRENT LAND USE ON THE HABITAT USE AND COMMUNITIES OF URBAN WILDLIFE IN THE WASHINGTON, D.C. METROPOLITAN AREA(2024) Collins, Merri Kathleen; Gallo, Travis; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding past legacies of urban land use is important to identify ecological processes and inform best management practices for wildlife-friendly cities in the future. My first dissertation chapter is an overview of my personal research philosophy and how it relates to this dissertation. The second chapter is a systematic literature review that addresses the state of global urban wildlife research. Urban wildlife research is predominantly conducted in North America, Europe, and Australia by academic researchers, and less so in the Global South. The third chapter explores how a gregarious species, the Eastern wild turkey (Meleagris gallopavo silvestris) once extant from the Washinton, D.C. landscape, is making a comeback. Wild turkey had a higher probability of occupying sites further from roads and at lower elevations. The fourth and concluding chapter looks at historic neighborhood valuation in Washington, D.C. to identify any legacy effects of racist and discriminatory urban planning on mammal communities. While I did not find any relationship, I did find similar mammal communities across the city regardless of neighborhood categorization and I derive management implications from this information.Item INVASIVE LIANA HEDERA HELIX (ENGLISH IVY) IMPACTS ON ECOLOGICAL CHARACTERISTICS AND NUTRIENT CYCLING IN BALTIMORE FOREST PATCHES(2023) Shdaimah, Elad; Pavao-Zuckerman, Mitchell A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The effects of invasive plants on forest ecology and nutrient cycling are highly variable and poorly understood. Many studies have found that species and location make each plant invasion unique. Thus, studying invasive plants on the species and local level is necessary to understand how they impact ecosystems and how to manage them. Ninety-four percent of forest patches in Baltimore contain invasive plants. Hedera helix is one of the most prominent. My study explores how different characteristics and intensities of H. helix invasion impact ecology and nutrient cycling in Baltimore forest patches. I analyzed canopy structure, litter properties, soil properties, and steps of C and N cycling in forest patch plots. I compared findings across the invasion characteristics: presence, canopy invasion intensity, and ground cover presence. My study revealed that invasion characteristics and location strongly influence the impact of H. helix on Baltimore forest patch plots. The presence of ground cover appeared to be dictated by soil hydrology, which varied by location. Invaded plots with ground cover had significantly altered soil properties, increased soil respiration rates (2.86 times greater than control plots, p = 0.047), and may have increased decomposition rates. These differences in C cycling metrics appear to be driven by altered soil temperature, structure, and chemistry (i.e., 1.62 times more TN than control plots, p = 0.022). Canopy invasions may have caused tree loss and altered canopy structure, which indicate potentially negative consequences for forest patch ecology in the future. pH may have been higher in the presence of H. helix (1.17 times higher pH than control plots, p = 0.090). Several ecological characteristics and nutrient cycling variables may have also been more variable in the presence of H. helix. No significant differences were detected in N cycling due to invasion. These findings can help Baltimore forest patch managers to assess problematic H. helix invasions and allocate resources to control it when necessary. They also lay out further groundwork for plant invasion research, demonstrating the necessity of species-specific, location-specific studies.Item LEVERAGING FINE-SCALE GEOSPATIAL DATA TO ADVANCE BIODIVERSITY SENSITIVE URBAN PLANNING, WILDLIFE MANAGEMENT, AND GREEN CORRIDOR DESIGN: APPLICATION TO THE DISTRICT OF COLUMBIA(2023) Spivy, Annette Leah; Mullinax, Jennifer; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Typically, urban wildlife communities are made up of generalist species that are adept at utilizing human resources. However, many wildlife species struggle in the face of extensive urbanization and would benefit from increased conservation of urban green space, increased urban landscape connectivity, and proactive wildlife population management strategies. Unfortunately, maintaining and/or increasing the availability of quality habitat for biodiversity conservation in urban areas can be challenging as these conservation efforts are often influenced by the decreasing availability of critical resources and the challenges in allocating those resources among competing socioeconomic and environmental needs. Therefore, to improve the management and conservation of urban wildlife, accurate measurements of potential trade-offs between the environmental, economic, and social goals and management actions of a city’s sustainable development plan are needed. Until now, much of the effort in wildlife habitat modeling and biodiversity mapping has been across large geographic areas or broad spatial scales. Those efforts have provided valuable insights into overall biodiversity patterns, identifying key hotspots, and understanding large-scale ecological processes. However, in urban environments, the dynamics of wildlife, habitat availability, and ecosystem services operate differently than in natural or rural landscapes. As urbanization continues to expand, there is a growing need to focus on fine-scale factors to address specific conservation challenges in urban systems. This research seeks to address some of these challenges and demonstrates how new and traditional species-relevant geospatial datasets can be leveraged in urban planning and design to drive local-scale conservation decisions that put biodiversity in the forefront. This work links long-term, multi-taxon, wildlife survey data and high-resolution land use and land cover datasets (1m) to determine where high-quality, well-connected habitats exist, or could most easily be justified and acquired, within the District of Columbia. This work also evaluates the spatial patterns of ecosystem service provisions across the urban landscape to identify “win-win” areas for conservation or restoration that will benefit both biodiversity and human wellbeing. Finally, the work evaluates a local translocation effort of the vulnerable eastern box turtle (Terrapene carolina carolina) to inform mitigation strategies when a sudden loss of habitat in an urban environment is inevitable. This research is particularly relevant to wildlife managers and urban planners in highly urbanized areas, where large parcels of land with suitable habitat are minimal and municipal environmental departments are often under-resourced. Local policymakers interested in incentivizing conservation efforts to meet state or national goals can use this information for strategic urban conservation initiatives.Item TO WHAT EXTENT DO MODE OF REPRODUCTION, LEVELS OF GENOTYPIC DIVERSITY, AND CONNECTIVITY IN Vallisneria americana MICHX. CONFER RESILIENCE TO A CHANGING CLIMATE?(2023) Perkins, Carrie; Neel, Maile C.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The macrophyte Vallisneria americana Michx. (Hydrocharitaceae) is a foundational submersed aquatic vegetation (SAV) species that provides valuable ecosystem services, such as nutrition for waterfowl and shelter for fish. When healthy, V. americana can absorb excess nutrients from the water and stabilize sediments, but many of its meadows, which span freshwater to oligohaline environments in eastern North America, have been declining since European settlers cleared the land. Declines only intensified in the 1950s due to chronic environmental stressors and major storm events. To determine the extent to which remaining populations can adapt through natural selection or acclimate to novel environmental conditions, I combined observational field data, greenhouse experiments, and spatial modeling to quantify V. americana reproduction at local to regional scales, evaluate evidence of local adaptation and acclimation to environmental stress, and assess the extent to which high levels of connectivity in a V. americana-dominated landscape can absorb environmental stress.I quantified reproduction at 15 sites in the Chesapeake Bay and 14 sites in the Hudson River, with sites in each geographic region spanning the portion of the salinity gradient in which V. americana grows (0-12 ppt). Numbers of inflorescences, sex ratios, and distances among male and female inflorescences varied greatly across latitude and along salinity gradients. Hudson V. americana had fewer inflorescences across two sampling seasons than Chesapeake Bay V. americana but delayed phenology, skewed sex ratios, and large distances among males and females relative to the Chesapeake Bay were more pronounced in 2018. In 2018, warmer spring and summer water temperatures in the Chesapeake coincided with our findings of higher flowering, fruiting, and potential for pollination at the three Chesapeake sites that served as means of comparison to the Hudson. By contrast, in 2020 Hudson plants were larger and produced more inflorescences in July than Chesapeake plants produced in June, indicating that the regional difference in phenology may be smaller than our hypothesis of approximately 23 days, although it is difficult to estimate how much smaller. We attribute this result to sites in the Hudson – mainly those in the tidal-fresh zone of the river – being highly responsive to unusually warm 2020 spring water temperatures. But not all sites experienced this warmth. The tidal-saline zone of the Hudson and the non-tidal zone of the Chesapeake had the fewest flowers and fruits of either region, likely due to the synergistic effects of cold temperatures and high salinity and turbidity in the former and fast currents in the latter inhibiting growth and reproduction. Through greenhouse experiments evaluating growth and reproduction of Chesapeake and Hudson V. americana grown in different salinity conditions, we found evidence of one-way local adaptation in plants sourced from brackish waters of both the Chesapeake and Hudson. In the first experiment (parental-generation), brackish-source plants demonstrated phenotypic buffering, a stress-induced version of phenotypic plasticity. When exposed to three salinity treatments (0 ppt, 6 ppt, and 12 ppt) applied after plants had sprouted, brackish-source plants buffered the effects of salt stress via increased vegetative growth in the form of many ramets and turions at the cost of small stature. By contrast, plants sourced from fresh waters of both regions grew tall in fresh water, but photosynthetic leaf material declined from the time of salt application (June) to the end of the experiment (September). The most severe salinity treatment, 18 ppt, was lethal to most individuals regardless of source habitat. Unfortunately, neither phenotypic buffering nor phenotypic plasticity sensu stricto was carried over via transgenerational plasticity (TGP), when turions were exposed to 12 ppt immediately upon planting (offspring generation). This early-development salt exposure proved lethal for some individuals and sublethal (had a negative effect on growth but did not result in mortality) for others, with turions either failing to sprout or growing a single shoot that was minuscule in stature. Parental-generation salt exposure only exacerbated these offspring effects, producing a non-adaptive TGP effect, resulting in even lower chance of sprouting, higher chance of mortality, and smaller stature. Evidence of local adaptation and acclimation to salinity only when exposure begins later in development suggests that populations have potential for resilience to saltwater intrusion (movement of saline water into fresh water) only if salinities do not remain elevated during the time of early plant development (spring/early summer) and across multiple seasons. In the event of prolonged salinity stress, much habitat (~10,000 hectares) that is currently mesohaline (5-12 ppt) but within the range of tolerance for V. americana will become unsuitable. In our spatial model of SAV persistence in the V. americana-dominated Upper Chesapeake Bay, high connectivity and high probability of SAV presence were found not only in the freshwater head of the Bay, but also in mesohaline (5-12 ppt) and oligohaline (0.5-5 ppt) waters near Middle River. Persistence of predominantly freshwater aquatic macrophytes in Middle River suggests that either 1) plants are locally adapted to brackish waters or 2) existing connectivity buffers the stress of low-quality habitat. Excess nitrogen, an anthropogenic environmental stressor that remains at high levels in Baltimore Harbor and other tributaries, was correlated with a decreased probability of SAV presence in the southern portion of our study area. As expected, low nitrogen, low salinity, and high landscape connectivity at the head of the Bay coincided with the highest predicted probabilities of SAV presence, particularly in the core of the one of the largest SAV beds in the entire Chesapeake Bay, the Susquehanna Flats.Item Quantifying the impacts of climate-smart farming practices for improved management and long-term carbon storage(2023) Boniface, Helen S; Tully, Katherine L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Within agricultural production there is tension between feeding a rapidly growing population and conserving the finite resources at the foundation of our agroecosystems. Fortunately, in recent decades there has been a growing focus on farming practices that promote long-term soil health, land productivity, and resilience to climate change. The term ‘conservation agriculture’ encompasses practices that 1) promote minimum soil disturbance, 2) maintain permanent soil cover, and 3) diversify plant species. This research evaluated several conservation agriculture practices for their ability to deliver desired agroecosystem services across the Northeastern US. In the first study, a cover crop mixture field experiment was implemented in seven states to evaluate how climatic, edaphic, and management conditions affected the performance of cover crop bicultures that included species with varying functional traits. Seeding rate recommendations for mixtures are typically developed at the regional level, thus cover crop performance is highly variable due to site-level conditions and competition among species. Our results indicated that expected spring growing degree days and baseline soil fertility (i.e., inorganic N) are the most significant variables to consider when designing site-specific cover crop mixtures. The second study assessed the effects of long-term management on soil organic carbon (SOC) dynamics in mid-Atlantic grain cropping systems. At the time of sampling, five unique systems (two conventional, three organic) had been continuously managed for 25 years, representing a range of tillage and fertility practices and rotational complexities. Results showed SOC loss in all systems over time regardless of management, likely because of high baseline SOC stocks from long-term perennial forage production prior to research plot establishment. However, cropping systems that best maintained SOC over time included management with minimal soil disturbance, frequent manure inputs, and/or greater rotational diversity through perennial cropping or cover cropping. Both studies increase our understanding of the ability of specific conservation practices to support agroecosystem biodiversity, long term soil health, and potential carbon sequestration.Item Social-Ecological Processes and Dynamics of Urban Forests as Green Stormwater Infrastructure in Maryland, USA(2023) Ponte, Sarah; Pavao-Zuckerman, Mitchell A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Urban trees are part of social-ecological systems shaped by the interactions between human components (e.g., communities, management practices, and sociodemographic characteristics) and ecological components (e.g., trees, microclimate, and soil). This dissertation investigated the social-ecological factors that shape urban trees and forest outcomes. Urban trees can reduce stormwater runoff, mitigate flood risk, increase infiltration and water storage capacity in the soil, reduce nutrient loading, and improve water quality in developed areas. This dissertation begins by quantifying the influence of management context (single vs. clustered vs. closed canopy trees) on the transpiration of red maple (Acer rubrum L.), sweetgum (L. styraciflua L), and tulip poplar (L. tulipifera L.) trees as well as the relationship between tree transpiration and environmental drivers (vapor pressure deficit and soil moisture) in Baltimore and Montgomery County, MD. Results showed significantly lower transpiration rates in closed-canopy trees when compared to solitary trees. No significant differences were observed between transpiration rates across tree species in the closed canopy site during the growing seasons of 2018 and 2019. However, species differences in sap flux density were observed at the 24-h time-scale with tulip poplar trees being the most sensitive to drought. In addition to the ecological characteristics of urban forests, it is necessary to take into consideration the human factors and the resulting outcomes (e.g., tree canopy cover and green stormwater infrastructure distribution) for a better understanding of such complex social-ecological systems. Using regression models, spatial patterns and relationships between biophysical, social, and built components were explored at the neighborhood scale in Baltimore, MD. Results showed that the presence of voluntary green stormwater infrastructure (GSI) was positively associated with stewardship activity related to GSI. Median household income and race were significantly associated with the presence of regulatory GSI, and percent impervious cover was a significant predictor for the presence of voluntary GSI. The findings from this dissertation can aid the development and refining of stormwater crediting programs as urban trees can be more accurately incorporated into planning efforts. This dissertation also provides insights on how environmental stewardship and socio-demographics relate to landscape characteristics and informs future research directions regarding social-ecological systems.Item NATIVE PLANTING IN TIDAL WETLANDS FOR PHRAGMITES AUSTRALIS MANAGEMENT: FIELD AND MESOCOSM EXPERIMENTS(2022) Jacobson, Sylvia Rebecca; Baldwin, Andrew H.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Efforts have been made in U.S. wetlands to eradicate the invasive grass Phragmites australis. But eradication of Phragmites does not always lead to the return of native plants. This research investigated native vegetation recolonization across 12 tidal wetland study sites in the Chesapeake Bay watershed and tested the potential of planting perennial native wetland species to accelerate site recovery following Phragmites removal. Our study found that site salinity was a dominant driver of plant recolonization rate: low salinity sites (0.5-3 ppt) had, on average, 4.3x greater aboveground biomass and 2.5x higher vegetation cover than brackish sites (5-9 ppt) two or more growing seasons after Phragmites removal. The composition of returning plant species also differed by salinity, with a higher abundance of annuals and fewer graminoids at low-salinity sites. Site hydrology also influenced native plant recolonization—more frequently flooded sites had lower aboveground biomass of native vegetation two or more years following Phragmites removal. Experimental planting had variable results, with high die-off at several sites, but showed potential to accelerate vegetation recovery at brackish sites in the first years after Phragmites removal—plots with transplants at brackish sites had 17.5x, 2.4x, and 1.5x higher plant cover than unplanted plots in years one, two, and three, respectively, after planting. All sites had some amount of native vegetation recovery within three to four years following Phragmites removal, suggesting that native planting may not be necessary for many tidal wetland sites. Sites with especially high salinities and flooding frequencies may benefit the most from plantings, as larger plants may be able to survive in conditions that are not favorable for seedling emergence. In a mesocosm experiment, we planted six different clonal wetland species in a sand-vermiculite mixture at three different elevations in a tidal creek on the Rhode River in Maryland, USA. We found that peak plant biomass in the sandy substrate occurred at lower elevations and higher flooding frequencies than is typical in marsh environments and than was observed in other mesocosm experiments with organic soils. In well-drained, sandy substrates, wetland plants may benefit from more frequent tidal pulses, likely due to increased water supply and nutrient flux. This has implications for wetland-restoration practitioners using dredged sand to create or elevate tidal wetlands, as wetland species may grow at different elevations and flooding frequencies in these conditions than in a typical tidal marsh with organic soils.Item Investigating the hyperdiversity of fungal endophytes in wild Rubiaceae tropical plants and coffee plantations.(2022) Castillo Gonzalez, Humberto; Yarwood, Stephanie A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fungal endophytes are an essential component of a plant’s microbiome, their effect spreads to fitness, disease dynamics, stress tolerance, water acquisition and nutrient uptake. Plant ecosystems, from natural forest to plantations bear the indelible signature of its presence. The current investigation was designed to understand the diversity of endophytes in the Rubiaceae family, in plants associated to natural and managed ecosystems. The effect of location, leaf developmental stage, tissue type, host genotype, and anthropogenic interference was evaluated through amplicon sequencing. Costa Rica served as base for the sample collection. Leaves and sapwood from a variety of tropical plant species were collected in old-growth natural forests and foliar tissue from domesticated coffee plants were sampled in two plantations under different management. Fungal diversity was assessed by metabarcoding using the ITS2 nrDNA region fITS7 – ITS4, and library sequencing was completed by Ion Torrent. We identified a hyperdiversity of endophytes inhabiting these plants and were able to isolate a total of 659 fungi from coffee leaves. This investigation provides relevant information about overall community composition, the ecological drivers of community assemblage and the characteristics of the fungal endophytic communities, including potential interactions among the identified taxa. Endophytes may harness the potential to transform agriculture and conservation science, however we currently lack the knowledge to engineer microbial communities through breeding or management. It is essential to continue the efforts on understanding community functions and dynamics, and how host, endophyte interactions, and other ecological and human- related mechanisms influence their diversity in both forest species and agronomically important crops.Item ORGANIC MATTER SOIL AMENDMENTS, ANOXIC SOIL BIOGEOCHEMISTRY AND WETLAND RESTORATION(2021) Scott, Brian; Yarwood, Stephanie; Baldwin, Andrew H.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Organic Matter (OM) amendments are often used in wetland restoration – a practice required in Maryland and other states. This work summarizes a literature review and lab and field experiments to evaluate the consequences of OM amendment use. The literature review showed that although OM use is widely accepted, the evidence that they are effective is weak, and there can be negative effects. Transplanted topsoil is much more effective than allochthonous OM (e.g., manure). OM amendments were largely ineffective in a field study conducted on a mitigation wetland in Caroline County, MD, and negative consequences were possible, although composting the OM relieved negative effects. One example of ineffectiveness: OM is not needed to develop anaerobic conditions in saturated soil. While in some cases OM seems to be a benefit, as in aboveground biomass production, this is usually accompanied by a loss of diversity and it selects for undesired and invasive species. One of the negative consequences OM is the increased production of methane, a greenhouse gas, which became the focus of this work. Two lab microcosm studies and a field study revealed that rewetting dried soils (as in after mitigation wetland construction) immediately releases small amounts of methane, and methane sharply increases after about 7 weeks. Using OM affects methane production in two ways. First, overall methane production usually increases. Second, the time frame before there is a sharp increase in methane production is shorter, from ~7 weeks to as little as 1 or 2 weeks. These effects are somewhat reduced with composted OM. Using a Stable Isotope Probing microcosm study, the work also helped to identify the archaeal and bacterial taxa that are responsible for the sudden increase in methane. Methanosarcina is likely the primary taxa responsible for methane generation. Understanding the conditions that result in methane emanating from wetlands could lead to practices that reduce its release into the atmosphere, where it contributes to global warming. Methane is a more potent greenhouse gas than carbon dioxide, but is short lived, so controlling methane emissions can have a more immediate effect on climate change.