Theses and Dissertations
This collection includes both ASU Theses and Dissertations, submitted by graduate students, and the Barrett, Honors College theses submitted by undergraduate students.
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Description
Flowering phenology offers a sensitive and reliable biological indicator of climate change because plants use climatic and other environmental cues to initiate flower production. Drylands are the largest terrestrial biome, but with unpredictable precipitation patterns and infertile soils, they are particularly vulnerable to climate change. There is a need to increase our comprehension of how dryland plants might respond and adapt to environmental changes. I conducted a meta-analysis on the flowering phenology of dryland plants and showed that some species responded to climate change through accelerated flowering, while others delayed their flowering dates. Dryland plants advanced their mean flowering dates by 2.12 days decade-1, 2.83 days °C-1 and 2.91 days mm-1, respectively, responding to time series, temperature, and precipitation. Flowering phenology responses varied across taxonomic and functional groups, with the grass family Poaceae (-3.91 days decade1) and bulb forming Amaryllidaceae (-0.82 days decade1) showing the highest and lowest time series responses respectively, while Brassicaceae was not responsive. Analysis from herbarium specimens collected across Namibian drylands, spanning 26 species and six families, revealed that plants in hyper-arid to arid regions have lower phenological sensitivity to temperature (-9 days °C-1) and greater phenological responsiveness to precipitation (-0.56 days mm-1) than those in arid to semi-arid regions (-17 days °C-1, -0.35 days mm-1). The flowering phenology of serotinous plants showed greater sensitivity to both temperature and precipitation than that of non-serotinous plants. I used rainout shelters to reduce rainfall in a field experiment and showed that drought treatment advanced the vegetative and reproductive phenology of Cleome gynandra, a highly nutritional and medicinal semi-wild vegetable species. The peak leaf length date, peak number of leaves date, and peak flowering date of Cleome gynandra advanced by six, 10 and seven days, respectively. Lastly, I simulated drought and flood in a greenhouse experiment and found that flooding conditions resulted in higher germination percentage of C. gynandra than drought. My study found that the vegetative, and flowering phenology of dryland plants is responsive to climate change, with differential responses across taxonomic and functional groups, and aridity zones, which could alter the structure and function of these systems.
ContributorsKangombe, Fransiska Ndiiteela (Author) / Throop, Heather (Thesis advisor) / Sala, Osvaldo (Committee member) / Vivoni, Enrique (Committee member) / Pigg, Kathleen (Committee member) / Hultine, Kevin (Committee member) / Kwembeya, Ezekeil (Committee member) / Arizona State University (Publisher)
Created2023
Description
Hydrological models in arid and semi-arid ecosystems can be subject to high uncertainties. Spatial variability in soil moisture and evapotranspiration, key components of the water cycle, can contribute to model uncertainty. In particular, an understudied source of spatial variation is the effect of plant-plant interactions on water fluxes. At patch scales (plant and associated soil), plant neighbors can either negatively or positively affect soil water availability via competition or hydraulic redistribution, respectively. The aboveground microclimate can also be altered via canopy shading effects by neighbors. Across longer timescales (years), plants may adjust their physiological (water-use) traits in response to the neighbor-altered microclimate, which subsequently affects transpiration rates. The influence of physiological adjustments and neighbor-altered microclimate on water fluxes was assessed around Larrea tridentata in the Sonoran Desert. Field measurements of Larrea’s stomatal behavior and vertical root distributions were used to examine the effects of neighbors on Larrea’s physiological controls on transpiration. A modeling based approach was implemented to explore the sensitivity of evapotranspiration and soil moisture to neighbor effects. Neighbors significantly altered both above- and belowground physiological controls on evapotranspiration. Compared to Larrea growing alone, neighbors increased Larrea’s annual transpiration by up to 75% and 30% at the patch and stand scales, respectively. Estimates of annual transpiration were highly sensitive to the presence/absence of competition for water, and on seasonal timescales, physiological adjustments significantly influenced transpiration estimates. Plant-plant interactions can be a significant source of spatial variation in ecohydrological models, and both physiological adjustments to neighbors and neighbor effects on microclimate affect small scale (patch to ecosystem) water fluxes.
ContributorsKropp, Heather (Author) / Ogle, Kiona (Thesis advisor) / Hultine, Kevin (Committee member) / Sala, Osvaldo (Committee member) / Vivoni, Enrique (Committee member) / Wojciechowski, Martin (Committee member) / Arizona State University (Publisher)
Created2015
Description
Sustainability requires developing the capacity to manage difficult tradeoffs to advance human livelihoods now and in the future. Decision-makers are recognizing the ecosystem services approach as a useful framework for evaluating tradeoffs associated with environmental change to advance decision-making towards holistic solutions. In this dissertation I conduct an ecosystem services assessment on the Yongding River Ecological Corridor in Beijing, China. I developed a `10-step approach' to evaluate multiple ecosystem services for public policy. I use the 10-step approach to evaluate five ecosystem services for management from the Yongding Corridor. The Beijing government created lakes and wetlands for five services (human benefits): (1) water storage (groundwater recharge), (2) local climate regulation (cooling), (3) water purification (water quality), (4) dust control (air quality), and (5) landscape aesthetics (leisure, recreation, and economic development).
The Yongding Corridor is meeting the final ecosystem service levels for landscape aesthetics, but the new ecosystems are falling short on meeting final ecosystem service levels for water storage, local climate regulation, water purification, and dust control. I used biophysical models (process-based and empirically-based), field data (biophysical and visitor surveys), and government datasets to create ecological production functions (i.e., regression models). I used the ecological production functions to evaluate how marginal changes in the ecosystems could impact final ecosystem service outcomes. I evaluate potential tradeoffs considering stakeholder needs to recommend synergistic actions for addressing priorities while reducing service shortfalls.
The Yongding Corridor is meeting the final ecosystem service levels for landscape aesthetics, but the new ecosystems are falling short on meeting final ecosystem service levels for water storage, local climate regulation, water purification, and dust control. I used biophysical models (process-based and empirically-based), field data (biophysical and visitor surveys), and government datasets to create ecological production functions (i.e., regression models). I used the ecological production functions to evaluate how marginal changes in the ecosystems could impact final ecosystem service outcomes. I evaluate potential tradeoffs considering stakeholder needs to recommend synergistic actions for addressing priorities while reducing service shortfalls.
ContributorsWong, Christina P (Author) / Kinzig, Ann P (Thesis advisor) / Lee, Kai N. (Committee member) / Muneepeerakul, Rachata (Committee member) / Ouyang, Zhiyun (Committee member) / Vivoni, Enrique (Committee member) / Arizona State University (Publisher)
Created2014