Matching Items (28)
Description
The Prosopis genus of trees, also known as mesquites, are uniquely equipped to allow for an agroforestry regime in which crops can be grown beneath the canopy of the tree. Mesquites have the ability to redistribute water moisture in such a way that allows plants under the canopy to use water that has been brought up by the roots of mesquite trees. This means that there is a potential for food crops to be grown under the trees without using additional irrigation measures. This could be used where access to water is limited or for a sustainability-minded farmer who is trying to reduce water inputs in an arid environment. Mesquite trees produce a variety of products, including lumber and bean pods that can be ground down into an edible flour. Both products demand a high price in the marketplace and are produced in addition to the crops that can potentially be grown beneath the mesquite tree. In order to determine whether or not it is possible to grow crops under mesquite trees, I reviewed a wide range of literature regarding hydraulic redistribution, mesquite trees in general, and what plants might be best suited for growing beneath a mesquite. The list of plants was narrowed down to four crops that seemed most likely to survive in shaded, low water conditions in a hot environment. There has not been any research done on crops growing beneath mesquite trees, so the next step for research would be to experiment with each of the crops to determine how well each species can adapt to the specified conditions.
ContributorsMesser, Luke Winston (Author) / Eakin, Hallie (Thesis director) / Hall, Sharon (Committee member) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
“Extremophile” is used to describe life that has adapted to extreme conditions and the conditions they live in are often used to understand the limits of life. In locations with low precipitation and high solar radiation, photosynthetic cyanobacteria can colonize the underside of quartz fragments, forming ‘hypoliths.’ The quartz provides protection against wind, reduces solar radiation, and slows the rate of evaporation following infrequent rain or fog events. In most desert systems, vascular plants are the main primary producers. However, hypoliths might play a key role in carbon fixation in hyperarid deserts that are mostly devoid of vegetation. I investigated hypolith distribution and carbon fixation at six sites along a rainfall and fog gradient in the central Namib Desert in Namibia. I used line point intersect transects to assess ground cover (bare soil, colonized quartz fragment, non-colonized quartz fragment, non-quartz rock, grass, or lichen) at each site. Additionally, at each site I selected 12 hypoliths and measured cyanobacteria colonization on quartz and measured CO2 flux of hypoliths at five of the six sites.
Ground cover was fairly similar among sites, with bare ground > non-colonized quartz fragments > colonized quartz fragments > non-quartz rocks. Grass was present only at the site with the highest mean annual precipitation (MAP) where it accounted for 1% of ground cover. Lichens were present only at the lowest MAP site, where they accounted for 30% of ground cover. The proportion of quartz fragments colonized generally increased with MAP, from 5.9% of soil covered by colonized hypoliths at the most costal (lowest MAP) site, to 18.7% at the most inland (highest MAP) site. There was CO2 uptake from most hypoliths measured, with net carbon uptake rates ranging from 0.3 to 6.4 μmol m-2 s-1 on well hydrated hypoliths. These carbon flux values are similar to previous work in the Mojave Desert. Our results suggest that hypoliths might play a key role in the fixation of organic carbon in hyperarid ecosystems where quartz fragments are abundant, with MAP constraining hypolith abundance. A better understanding of these extremophiles and the niche they fill could give an understanding of how microbial life might exist in extraterrestrial environments similar to hyperarid deserts.
Ground cover was fairly similar among sites, with bare ground > non-colonized quartz fragments > colonized quartz fragments > non-quartz rocks. Grass was present only at the site with the highest mean annual precipitation (MAP) where it accounted for 1% of ground cover. Lichens were present only at the lowest MAP site, where they accounted for 30% of ground cover. The proportion of quartz fragments colonized generally increased with MAP, from 5.9% of soil covered by colonized hypoliths at the most costal (lowest MAP) site, to 18.7% at the most inland (highest MAP) site. There was CO2 uptake from most hypoliths measured, with net carbon uptake rates ranging from 0.3 to 6.4 μmol m-2 s-1 on well hydrated hypoliths. These carbon flux values are similar to previous work in the Mojave Desert. Our results suggest that hypoliths might play a key role in the fixation of organic carbon in hyperarid ecosystems where quartz fragments are abundant, with MAP constraining hypolith abundance. A better understanding of these extremophiles and the niche they fill could give an understanding of how microbial life might exist in extraterrestrial environments similar to hyperarid deserts.
ContributorsMonus, Brittney Daniel (Author) / Throop, Heather (Thesis director) / Hall, Sharon (Committee member) / Cadillo-Quiroz, Hinsby (Committee member) / School of Life Sciences (Contributor) / School of Earth and Space Exploration (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
The mainstream American environmental movement has a reputation for being ethnically homogenous (i.e., white), especially within the field of conservation. Low minority involvement has been noted and discussed in the conservation literature and within environmental organizations, but these discussions aren't always informed by the explicit social justice concerns critical to understanding the complex intersection of environmental and social issues. Communities of color have expressed concern for environmental and conservation issues, but often frame those issues in a different way than is common in mainstream conservation science, a framing that we can appreciate through a deeper analysis of the values and goals of the environmental justice (EJ) movement. A more thorough inclusion of EJ principles could be an effective method to increase ethnic diversity in the field of conservation, particularly within higher education conservation programs like the Conservation Biology and Ecology (CBE) concentration at Arizona State University. This thesis frames the broader challenge of diversity in conservation, the history and current state of the conservation movement, and the history of the environmental justice movement via a literature review. I then evaluate the university's CBE program on the basis of its diversity through an analysis of demographic data on undergraduate ethnicity from the School of Life Sciences. I conclude with a series of recommendations for enhancing the diversity of ASU's CBE program moving forward.
ContributorsLiska, Kelly Margaret (Author) / Minteer, Ben (Thesis director) / Richter, Jennifer (Committee member) / Hall, Sharon (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
Jaguar population decline is largely attributed to habitat loss and retaliatory hunting. Maintaining a viable prey base in the wild can help to mitigate this issue and decrease human-wildlife conflicts. This study aims to assess the presence of prey species in jaguar habitat in order to inform conservation efforts to maintain and improve the health and relative abundance of the wildlife community. We analyzed nearly 40,000 photographs from 85 camera traps to assess the presence of prey species at sites where jaguars are known to occur. Jaguar-prey site overlap was calculated based on the percent of jaguar sites where each prey species was present. Medium-sized mammal prey species (e.g. Central American agouti) were present across the majority (up to 87%) of sites, while large mammal prey species were present in 16%-42% of sites, varying by species. These results suggest that conservation management of jaguars would benefit from improved monitoring and maintenance of a stable prey community.
ContributorsLewis-Quan, Kaidence (Author) / Schipper, Jan (Thesis director) / Hall, Sharon (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor) / School of Geographical Sciences and Urban Planning (Contributor)
Created2023-05
Description
The climate conversation is growing more important and necessary than ever. The media has a way of promoting a "doom and gloom" sentiment over conservation efforts and what the public has the power to do in terms of making a change. Now due to the effects of COVID-19 on the population's attention spans and memories, there is a need for a way to communicate climate science effectively and to encourage those who feel discouraged by climate change to find their inner power. The answer lies in photography. Making science accessible and intriguing through the art of photography is what can get people more interested and empowered to fight against climate change and alter their attitudes towards environmentalism. This thesis explains psychological research and the reasons why people feel helpless in terms of our global future. In then dives into human subjects research conducted on ASU's campus and how the survey results argue in favor of the paper's hypothesis. Additionally, ways to get involved and reasons why we need to remain hopeful are discussed.
ContributorsGorlick, Vanessa (Author) / Hall, Sharon (Thesis director) / Makings, Elizabeth (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor) / The Sidney Poitier New American Film School (Contributor) / Dean, W.P. Carey School of Business (Contributor)
Created2023-05
Description
Vector control plays an important role in the prevention and control of mosquito-borne diseases (MBDs). As there are no (prophylactic) drugs and/or vaccines available for many arboviral diseases (such as zika, chikungunya, Saint Louis encephalitis, Ross River virus), the frontline approach to prevent or reduce disease morbidity and mortality is through the reduction of the mosquito vector population size and/or reducing vector-human contact using insecticides. Frontline tools in malaria (an MBD caused by a parasite) control and elimination have been drugs (targeting the malaria parasite) and insecticides (targeting the vectors) through indoor residual spraying (IRS) (spraying the internal walls and sometimes the roofs of dwellings with residual insecticides to kill adult mosquito vectors), and long-lasting insecticidal nets (LLINs), while arboviral vectors are frequently targeted using outdoor fogging and space spraying (indoor or outdoor spraying of insecticides to kill adult mosquito vectors). Integrative and novel vector control efforts are urgently needed since the aforementioned tools may not be as effective against those mosquito species that are resistant to insecticides and/or have a different (or changed) behavior allowing them to avoid existing tools. In Chapters 2 and 3, I investigate mosquito vector surveillance in Arizona by (i) discussing the species composition and public health implications of the State’s mosquito fauna, and (ii) comparing the effectiveness of 4 different carbon dioxide (CO2) sources in attracting different mosquito species on the Arizona State University Tempe Campus. In Chapters 4 and 5, I investigate a novel vector control tool by (i) completing a literature review on using electric fields (EFs) to control insects, and (ii) presenting novel data on using Insulated Conductor Wires (ICWs) to generate EFs that prevent host-seeking female Aedes aegypti from entering spaces. In Chapter 6, I discuss the non-target effects of chemical malaria control on other arthropods, including other biological and mechanical infectious disease vectors. Overall, this dissertation highlights the important role that the development of novel surveillance and vector control tools could play in improved mosquito control, which ultimately will reduce disease morbidity and mortality.
ContributorsJobe, Ndey Bassin (Author) / Paaijmans, Krijn (Thesis advisor) / Cease, Arianne (Committee member) / Hall, Sharon (Committee member) / Huijben, Silvie (Committee member) / Arizona State University (Publisher)
Created2024
Description
Aboveground net primary production (ANPP) is an important ecosystem process that, in drylands, is most frequently limited by water availability. Water availability for plants is in part controlled by the water holding capacity of soils. Available water holding capacity (AWHC) of soils is strongly influenced by soil texture and depth. This study drew upon localized rain gauge data and four data-sets of cover-line and biomass data to estimate ANPP and to determine annual precipitation (PPT). I measured soil depth to caliche and texture by layer of 112 plots across the four landscape units for which estimation of ANPP were available. A pedotransfer function was used to estimate AWHC from soil depth increments to depth of caliche measurements and texture analysis. These data were analyzed using simple and multivariate regression to test the effect of annual precipitation and available water holding capacity on aboveground net primary production. Soil texture remained constant among all plots (sandy loam) and depth to caliche varied from 15.16 cm to 189 cm. AWHC and the interaction term (PPT*AWHC) were insignificant (p=0.142, p=0.838) and annual PPT accounted for 18.4% of the variation in ANPP. The y-intercept was significantly different for ANPP ~ annual PPT when considering AWHC values either above or below 3 cm. Shrub ANPP was insensitive to precipitation regardless of AWHC (R2=-0.012, R2=0.014). Results from this study indicate that a model incorporating annual PPT and AWHC may not serve as a good predictor for ANPP at a site level where there is little variation in soil texture.
ContributorsWagner, Svenja K (Author) / Sala, Osvaldo E. (Thesis advisor) / Cease, Arianne (Committee member) / Hall, Sharon (Committee member) / Peters, Debra (Committee member) / Arizona State University (Publisher)
Created2019
Description
Rangelands are an extensive land cover type that cover about 40% of earth’s ice-free surface, expanding into many biomes. Moreover, managing rangelands is crucial for long-term sustainability of the vital ecosystem services they provide including carbon (C) storage via soil organic carbon (SOC) and animal agriculture. Arid rangelands are particularly susceptible to dramatic shifts in vegetation cover, physical and chemical soil properties, and erosion due to grazing pressure. Many studies have documented these effects, but studies focusing on grazing impacts on soil properties, namely SOC, are less common. Furthermore, studies testing effects of different levels of grazing intensities on SOC pools and distribution yield mixed results with little alignment. The primary objective of this thesis was to have a better understanding of the role of grazing intensity on arid rangeland soil C storage. I conducted research in long established pastures in Jornada Experimental Range (JER). I established a 1500m transect in three pastures originating at water points and analyzed vegetation cover and SOC on points along these transects to see the effect of grazing on C storage on a grazing gradient. I used the line-point intercept method to measure and categorize vegetation into grass, bare, and shrub. Since soil adjacent to each of these three cover types will likely contain differing SOC content, I then used this vegetation cover data to calculate the contribution of each cover type to SOC. I found shrub cover and total vegetation cover to decrease, while grass and bare cover increased with decreasing proximity to the water source. I found areal (g/m2) and percent (go SOC to be highest in the first 200m of the transects when accounting for the contribution of the three vegetation cover types. I concluded that SOC is being redistributed toward the water source via foraging and defecation and foraging, due to a negative trend of both total vegetation cover and percent SOC (g/g). With the decreasing trends of vegetation cover and SOC further from pasture water sources, my thesis research contributes to the understanding of storage and distribution of SOC stocks in arid rangelands.
ContributorsBoydston, Aaron (Author) / Sala, Osvaldo (Thesis advisor) / Throop, Heather (Committee member) / Hall, Sharon (Committee member) / Arizona State University (Publisher)
Created2018
Description
It’s no secret that wetlands have dramatically declined in the arid and semiarid American West, yet the small number of wetlands that persist provide vital ecosystem services. Ciénega is a term that refers to a freshwater arid-land wetland. Today, even in areas where ciénegas are prominent they occupy less than 0.1% of the landscape. This investigation assesses the distribution of vascular plant species within and among ciénegas and address linkages between environmental factors and wetland plant communities. Specifically, I ask: 1) What is the range of variability among ciénegas, with respect to wetland area, soil organic matter, plant species richness, and species composition? 2) How is plant species richness influenced locally by soil moisture, soil salinity, and canopy cover, and regionally by elevation, flow gradient (percent slope), and temporally by season? And 3) Within ciénegas, how do soil moisture, soil salinity, and canopy cover influence plant species community composition? To answer these questions I measured environmental variables and quantified vegetation at six cienegas within the Santa Cruz Watershed in southern Arizona over one spring and two post-monsoon periods. Ciénegas are highly variable with respect to wetland area, soil organic matter, plant species richness, and species composition. Therefore, it is important to conserve the ciénega landscape as opposed to conserving a single ciénega. Plant species richness is influenced negatively by soil moisture, positively by soil salinity, elevation, and flow gradient (percent slope), and is greater during the post-monsoon season. Despite concerns about woody plant encroachment reducing biodiversity, my investigation suggests canopy cover has no significant influence on ciénega species richness. Plant species community composition is structured by water availability at all ciénegas, which is consistent with the key role water availability plays in arid and semiarid regions. Effects of canopy and salinity structuring community composition are site specific. My investigation has laid the groundwork for ciénega conservation by providing baseline information of the ecology of these unique and threatened systems. The high variability of ciénega wetlands and the rare species they harbor combined with the numerous threats against them and their isolated occurrences makes these vanishing communities high priority for conservation.
ContributorsWolkis, Dustin (Author) / Stromberg, Juliet C. (Thesis advisor) / Hall, Sharon (Committee member) / Salywon, Andrew (Committee member) / Makings, Elizabeth (Committee member) / Arizona State University (Publisher)
Created2016
Description
Cities can be sources of nitrate to downstream ecosystems resulting in eutrophication, harmful algal blooms, and hypoxia that can have negative impacts on economies and human health. One potential solution to this problem is to increase nitrate removal in cities by providing locations where denitrification¬— a microbial process in which nitrate is reduced to N2 gas permanently removing nitrate from systems— can occur. Accidental urban wetlands– wetlands that results from human activities, but are not designed or managed for any specific outcome¬– are one such feature in the urban landscape that could help mitigate nitrate pollution through denitrification.
The overarching question of this dissertation is: how do hydrology, soil conditions, and plant patches affect patterns of denitrification in accidental urban wetlands? To answer this question, I took a three-pronged approach using a combination of field and greenhouse studies. First, I examined drivers of broad patterns of denitrification in accidental urban wetlands. Second, I used a field study to test if plant traits influence denitrification indirectly by modifying soil resources. Finally, I examined how species richness and interactions between species influence nitrate retention and patterns of denitrification using both a field study and greenhouse experiment.
Hydroperiod of accidental urban wetlands mediated patterns of denitrification in response to monsoon floods and plant patches. Specifically, ephemeral wetlands had patterns of denitrification that were largely unexplained by monsoon floods or plant patches, which are common drivers of patterns of denitrification in non-urban wetlands. Several plant traits including belowground biomass, above- and belowground tissue chemistry and rooting depth influenced denitrification indirectly by changing soil organic matter or soil nitrate. However, several other plant traits also had significant direct relationships with denitrification, (i.e. not through the hypothesized indirect relationships through soil organic matter or soil nitrate). This means these plant traits were affecting another aspect of soil conditions not included in the analysis, highlighting the need to improve our understanding of how plant traits influence denitrification. Finally, increasing species richness did not increase nitrate retention or denitrification, but rather individual species had the greatest effects on nitrate retention and denitrification.
The overarching question of this dissertation is: how do hydrology, soil conditions, and plant patches affect patterns of denitrification in accidental urban wetlands? To answer this question, I took a three-pronged approach using a combination of field and greenhouse studies. First, I examined drivers of broad patterns of denitrification in accidental urban wetlands. Second, I used a field study to test if plant traits influence denitrification indirectly by modifying soil resources. Finally, I examined how species richness and interactions between species influence nitrate retention and patterns of denitrification using both a field study and greenhouse experiment.
Hydroperiod of accidental urban wetlands mediated patterns of denitrification in response to monsoon floods and plant patches. Specifically, ephemeral wetlands had patterns of denitrification that were largely unexplained by monsoon floods or plant patches, which are common drivers of patterns of denitrification in non-urban wetlands. Several plant traits including belowground biomass, above- and belowground tissue chemistry and rooting depth influenced denitrification indirectly by changing soil organic matter or soil nitrate. However, several other plant traits also had significant direct relationships with denitrification, (i.e. not through the hypothesized indirect relationships through soil organic matter or soil nitrate). This means these plant traits were affecting another aspect of soil conditions not included in the analysis, highlighting the need to improve our understanding of how plant traits influence denitrification. Finally, increasing species richness did not increase nitrate retention or denitrification, but rather individual species had the greatest effects on nitrate retention and denitrification.
ContributorsSuchy, Amanda Klara (Author) / Childers, Daniel L. (Thesis advisor) / Stromberg, Juliet C. (Thesis advisor) / Grimm, Nancy (Committee member) / Hall, Sharon (Committee member) / Sabo, John (Committee member) / Arizona State University (Publisher)
Created2016