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1
James, Jeremy Joseph. "Plant growth and physiological responses to soil resource heterogeneity in desert ecosystems /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.
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Walters, Ashley Daniell. "Using multiple lines of evidence to uncover hidden biodiversity in desert spring ecosystems." Miami University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=miami1533045376808751.
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Jacobson, Peter James. "An ephemeral perspective of fluvial ecosystems: Viewing ephemeral rivers in the context of current lotic ecology." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30582.
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Hydrologic and material dynamics of ephemeral rivers were investigated in the Namib Desert to assess how hydrologic regimes shape the physical habitat template of these river ecosystems. An analysis of long-term hydrologic records revealed that the variation in mean annual runoff and peak discharge were nearly four times higher than the global average, rendering the rivers among the most variable fluvial systems yet described. Further, a pronounced downstream hydrologic decay characterized all of the rivers. The high spatio-temporal variability in flow was reflected in patterns of material transport. Retention of woody debris increased downstream, in contrast to patterns typically reported from more mesic systems, largely attributable to hydrologic decay. Woody debris piles were the principal retentive obstacles and played an important role in channel dynamics. They were also key microhabitats for various organisms, forming "hotspots" of heterotrophic activity analogous to patterns reported from perennial streams. Large amounts of fine particulate and dissolved organic matter (FPOM and DOM) deposited in the lower reaches of the rivers serve to fuel this heterotrophic biota. As a result of the hydrologic decay, sediment concentration (both organic and inorganic) increased downstream and the lower reaches of these rivers acted as sinks for material exported from their catchments. FPOM and DOM concentrations were among the highest reported for any aquatic system, and, contrary to patterns reported from more mesic systems, FPOM dominated the total organic load transported in these rivers. Inorganic solute concentration also increased downstream, resulting in a downstream increase in soluble salt content in floodplain soils. Soils within the river's lower reaches served as effective long-term integrators of hydrologic variability. The mean extent of floods entering the lower river was defined by an alluviation zone, evident from the convexity exhibited in the lower section of the rivers' longitudinal profiles. A downstream increase in the proportion of silt within floodplain soils is associated with increased sediment deposition. Silt deposition had a positive influence on moisture availability, plant rooting, and habitat suitability for various organisms, including fungi and invertebrates. In addition, a strong positive correlation was observed between silt, organic matter, and macronutrients. Thus, the hydrologic control of transport and deposition patterns has important implications for the structure and function of ephemeral river ecosystems. Finally, an examination of the influence of elephants upon riverine vegetation highlighted the importance of these systems as isolated resource patches interspersed in an arid and hostile landscape. Further, it illustrated that flooding was a key ecological process and that hydrologic alterations would affect the fluvial ecosystem as well as the regional landscape they drain.Ph. D.
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Lee, Rebecca Irene. "Dendrochronological Methods to Examine Plant Competition with Changing Fire Regimes in Desert and Forest Ecosystems." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8708.
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Human activities are changing wildfire regimes globally through ignition, spread of invasive species, fire suppression, and climate change. Because of this, ecosystems are experiencing novel fire regimes that may alter plant growth and patterns of succession. Annual growth rings are one metric that can track changes in tree and shrub growth patterns over time in response to changing fire frequency. In Chapter 1 we explored the effects of fire on resprouting native shrubs in the Mojave Desert. Fires are becoming increasingly frequent due to the spread of highly flammable invasive grasses in the region. We monitored growth and fruit production of Larrea tridentata D.C. (creosote bush) on burned and unburned transects from three independent 2005 wildfires. Even though creosote has a high fire mortality rate, we found that resprouting creosote produced 4.7 times the amount of fruit and had stems that grew nearly twice as fast compared to creosote in unburned areas. Our data suggest that creosote can resprout after fire and thrives in its growth rates and reproduction in post-fire environments. In Chapter 2 we used annual Basal Area Increment to investigate how fire suppression has altered facilitation and competition interactions through stages of succession in mixed aspen-conifer forests. We found that aspen had lower growth rates in mixed aspen-conifer stands compared to aspen dominant stands. We also found that aspen growing with an associated fir tree due to facilitation had increasingly lower growth rates over time than those growing independently. Fir trees in mixed stands were facilitated over time by associated aspen trees while fir trees growing in association and independently in aspen stands showed no statistical difference from each other but grew better than independent fir trees in mixed stands. Our data suggest that restoring a more frequent fire regime will balance competitive interactions between aspen and conifer in subalpine forests.
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Buras, Allan [Verfasser]. "Assessing the carbon sequestration potential of Populus euphratica and Haloxylon spec. in Central Asian Desert ecosystems / Allan Buras." Greifswald : Universitätsbibliothek Greifswald, 2013. http://d-nb.info/1044301376/34.
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Neilson, Julia Worsley. "Bacterial Diversity of the Atacama Desert, Chile: The Challenges of Characterizing the Community Dynamics of Extreme Oligotrophic Ecosystems." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/242364.
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This dissertation examines the bacterial diversity of hyperarid and arid regions of the Atacama Desert, Chile, as a first step towards understanding the global biogeochemical significance of arid-land microbial communities. The specific objectives were to characterize bacterial diversity and infer the possible metabolic potential of these bacterial communities, and to evaluate the influence of moisture exposure on community structure. In addition, the strengths and limitations of available tools for probing microbial diversity and activity in terrestrial ecosystems were characterized for their application to extreme oligotrophic communities. Preliminary PCR-DGGE analysis of a west-east elevational transect from the Pacific Ocean near Antofagasta to the western slopes of the central Andes indicated that bacterial communities along this transect belonged to two distinct community types: 1) hyperarid (700 - 2000 m) and 2) arid (2500 - 4500 m) communities that included both vegetated and unvegetated regions. Subsequent diversity analysis of these two regions revealed novel but distinct communities in both regions. A greater diversity was observed in the unvegetated arid regions than in the unvegetated hyperarid areas. The unvegetated arid sites were characterized by a bacterial community harboring a combination of radiotolerant and halotolerant heterotrophs as wells as diverse phylotypes closely related to chemolithoautotrophs. These rare phylotypes may be uniquely adapted to arid ecosystems. Molecular tools evaluated for community diversity analysis included PCR-DGGE, Sanger-clone and 454-pyrosequencing analysis of 16S rRNA gene libraries, and the use of reverse transcriptase quantitative PCR (RT-qPCR) for quantifying the impact of environmental variables on the metabolic activity of a specific organism. These techniques were evaluated using the ecosystems of the Atacama Desert as well as model ecosystems designed to address specific questions. Molecular tools are invaluable to the study of microbial ecology because they facilitate the study of fastidious organisms that are difficult or impossible to culture, but the analysis presented in this dissertation demonstrates that each of these methods has limitations and biases which must be acknowledged to avoid inaccurate conclusions from skewed results. The most complete picture of the taxonomic and functional profile of a microbial community is obtained by employing a combination of molecular techniques.
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Bahr, Jason R. "Exploring Post-Fire Recovery of Biocrusts and Desert Ecosystem Services." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4285.
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Biocrusts and the ecosystem services they provide are becoming more susceptible to fire as exotic annual grass invasions facilitate the spread of desert wildfires. Further, precipitation patterns across the western United States are predicted to change over the next century, and have the potential to dramatically influence fire regimes and the recovery of burned biocrusts. Despite these changes to desert fire and precipitation cycles, our understanding of post-fire biocrust recovery is limited, especially regarding the first two years after fire. To investigate biocrust recovery, we created burn manipulations (i.e., unburned and burned) and tracked crust form and function over two years in one cold and one hot desert ecosystem (UT, USA). We evaluated the entire bacterial community, but focused on Cyanobacteria species that confer soil stability and N fixation capabilities to biocrusts. Specifically, we quantified shifts in biocrust bacterial community composition using target metagenomics of 16S rDNA; monitored biocrust moss and lichen cover; measured N fixation potential; and assessed soil infiltration rates and soil stability. We found little evidence that biocrust form or function recovered from fire within two years. Based on pyrosequencing results, fire altered biocrust community composition in interspace and shrub biocrusts. Cyanobacteria species were almost completely eliminated by fire, constituting 9-21% of unburned plots and less than 0.01% of burned interspace and shrub biocrust communities. Based on cover estimates, no lichen or moss species survived the fire or recovered within two years. N fixation potentials decreased by at least six-fold in burned interspace biocrusts, representing a reduction in soil N inputs into already N-limited desert soils. Soil infiltration rates also drastically declined in burned biocrusts and remained depressed, but only remained depressed for one year. To investigate the interactions between biocrust recovery, fire, and precipitation, we nested precipitation treatments manipulating the amount of monthly rainfall (i.e., ambient, plus 30% and minus 30%) within burn treatments during the second year. Soil NH4+ was the only parameter to be affected by precipitation, and exhibited a positive relationship with precipitation magnitude at the end of one year. Our results demonstrate that fire is a strong destabilizer of the bacterial components of biocrust communities and that the ecosystem services provided by crusts recover at different rates, with N dynamics recovering more slowly than soil ecohydrology.
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Dlamini, Titus. "Fertile island effects in a succulent desert ecosystem in northern Namaqualand." Bachelor's thesis, University of Cape Town, 1996. http://hdl.handle.net/11427/26687.
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Sunderman, Stephanie O. "Fire patterns and post-fire vegetation response in a Mojave Desert spring ecosystem." abstract and full text PDF (UNR users only), 2009. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1472982.
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Sharp, Christopher John. "Cultural Ecosystem Services as a Framework for Evaluating Wilderness Values in Public Land Settings." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/301660.
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The Wilderness Act of 1964 states the purpose of the National Wilderness Preservation System is "to secure for the American people of present and future generations the benefits of an enduring resource of wilderness." But, how to accomplish this mandate is a complex task. The application of the Ecosystem Services model is ideal for facilitating the complex duel goals of securing benefits and preserving wilderness resources. Ecosystem Services directly addresses benefits derived from a landscape, even if the specifics of the benefits change over time. This dissertation employs Ecosystem Services as a framework to provide a more complete understanding of wilderness values. In three separate studies conducted in wilderness areas in Southern Arizona, (Assessing Border-Related Human Impacts at Organ Pipe Cactus National Monument, Linking Visitor Flows and Patterns of Use with General Management Planning in Saguaro National Park and Monitoring and Estimating Visitor Use at the Madrona Ranger Station and Surrounding Landscape) elements of Cultural Ecosystem Services (CES) are illuminated.I found that the more holistic epistemology of Ecosystem Services allowed for the inclusion of better scientific data in the management process. The inclusion of quantitative, repeatable, defensible studies of user behavior in wildlands allows for dynamic management options that are rooted in real conditions (mutable, undesirable or unique). Specifically Cultural Ecosystem Services address the value and significance of the unique landscape of wilderness. Previous models for wildland management sought specific metrics of carrying capacity to limit use and control impact. Ecosystem Services combines diverse scientific fields to provide real understanding of the landscape. The addition of ES to manager's decision processes allows for better understanding of real conditions.
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Browning, Dawn M. "Woody Plant Dynamics in a Sonoran Desert Ecosystem across Scales: Remote Sensing and Field Perspectives." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/195333.
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Historic land uses impose discernable legacy effects that may influence ecosystem function, a concern of particular importance in actively managed landscapes. In recent history (ca. 150 years) tree and shrub abundance has increased at the expense of native grasses in savannas and grasslands. The magnitude and patterns of change are spatially heterogeneous, highlighting the need for analytical approaches spanning multiple spatial scales, from individual plants to patches to landscapes. The overarching goal of this dissertation was to explore long-term dynamics associated with woody plant encroachment with aerial photography and field studies to examine cover, density, soils and land use history at the Santa Rita Experimental Range.The first study characterized patterns in woody cover change on contrasting soils over 60 years using aerial photography. Woody patch dynamics revealed encroachment and stabilization phases in woody plant proliferation. Soil properties reflected the rate at which uplands reached a dynamic equilibrium, but not the endpoint (ca. 35% cover). Fluctuations around dynamic equilibrium reflected net change in patch growth and acquiescence combined with colonization and mortality. Efforts to characterize changes in land cover will require patch-based assessments beyond coarse estimates of percent cover.The second study capitalized on historic field measurements of shrub canopies to validate estimates of shrub cover derived from the earliest aerial photography, quantified detection limitations of 1936 aerial photographs for mapping shrub cover, assessed species-specific contributions to percent cover, and translated detection limitations to proportions of velvet mesquite (Prosopis velutina var Woot.) biomass missed with 1930s aerial photography.The third study was a field-based approach investigating how livestock grazing influenced mesquite cover, density, biomass, and stand structure over 74 years. The study supplemented traditional statistical analysis of grazing effects with methods quantifying spatial autocorrelation structure of mesquite density by grazing treatment. The outcome re-affirmed the supposition that mesquite cover may be dynamically stable at ca 30%, and revealed that livestock grazing slowed the shrub encroachment process from 1932 to 2006, counter to expectation. Results indicate that shrub growth trajectories persist long-term. Overall, this work affirms the importance of land use legacies and long-term perspectives in rangeland shrub dynamics.
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Shepard, Christopher. "Soil Modulation of Ecosystem Response to Climate Forcing and Change Across the US Desert Southwest." Thesis, The University of Arizona, 2014. http://hdl.handle.net/10150/323416.
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The dryland ecosystems of the US Desert Southwest (SW) are dependent on soil moisture for aboveground productivity; the generation of soil moisture in the SW is dependent on both soil physical properties and climate forcing. This study is one of the first regional point-scale analyses that explores the role of soil physical properties in modulating aboveground vegetation dynamics in response to climate forcing in the SW. Soil texture accounted for significant differences in average aboveground primary productivity across the SW. However, soil texture could not account for differences in inter-annual aboveground productivity variation across the SW. Subsurface soil texture was tightly coupled with precipitation seasonality in accounting for differences in long-term average seasonal aboveground productivity in the Mojave and Sonoran Deserts. The results of this study indicate that the subsurface is a significant factor in modulating aboveground primary productivity, and needs to be included in future modeling exercises of dryland ecosystem response to climate forcing and change.
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Merkley, Steven S. "An Invasive Species Reduces Aquatic Insect Flux to Terrestrial Food Webs." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2806.
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Although it is well documented how introduced species can negatively affect native species, we only poorly understand how they may alter ecosystem functions. We investigated how an invasive fish affected the flux of aquatic insects to terrestrial food webs using mesocosms in a desert spring ecosystem. We compared aquatic insect emergence between alternative community states with monocultures and polycultures of two native species of fish, least chub (Iotichthys phlegethontis) and Utah chub (Gila atraria) plus, introduced western mosquitofish (Gambusia affinis). We tested three hypotheses: (1) aquatic insect biomass will be greater than terrestrial insect biomass and thus, constitute a vital source of energy for terrestrial consumers (2) invasive mosquitofish will negatively impact the biomass of emerging aquatic insects, and (3) terrestrial consumers will negatively respond to decreased emerging aquatic insect biomass. Aquatic insects represented 79% of the flying insect community, and treatments with mosquitofish significantly reduced emergent aquatic insect biomass by 60% relative to the control without mosquitofish. Behavioral traits of invasive species are important, because mosquitofish most heavily affected insects that emerged during the day. Also, spiders that build horizontal webs were negatively correlated with decreasing aquatic insect biomass. Invasive mosquitofish can achieve very dense populations because of their high intrinsic rate of population increase, which can significantly disrupt the flow of energy between aquatic and terrestrial ecosystems, thereby reducing the energy available for terrestrial consumers.
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Rizk, Samuel, and Johanna Wickström. "Desertopia." Thesis, KTH, Arkitektur, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-122855.
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Today over 80 million Egyptians and the majority of the country’s agricultural land are squeezed into an area the size of Stockholm county. This doesn’t have to be the case since Egypt also has an area about twice the size of Sweden covered by unutilized desert land. We have investigated how Egypt could use the endless resources of the sun and the sea water to colonize its own desert and give its citizens a chance to build a better future. Desertopia covers eight different scales, from the global (1:15 000 000) to the building construction (1:25) and uses architecture and urban design to deal with the issues of climate change, desertification, poverty and unemployment. Desertopia combines traditional vernacular building techniques with the latest climate technology to create a structure that can be used by common Egyptians to take charge of their own future.Idag är över 80 miljoner egyptier och majoriteten av landets jordbruksmark ihopklämda på en yta motsvarande Stockholms län. Det skulle dock inte behöva vara så eftersom Egyptens landyta är dubbelt så stor som hela Sverige. En yta som dock är täckt av öken. Vi har undersökt hur Egypten skulle kunna använda de ändlösa resurserna solen och havsvattnet för att kolonisera sin egen öken och ge sina invånare chansen att bygga sig en bättre framtid. Desertopia täcker åtta olika skalor, från den globala (1:15 000 000) till den enskilda byggnadens konstruktion (1:25) och använder arkitektur och stadsbyggnad för att hantera klimatförändringen, ökenspridningen, fattigdomen och arbetslösheten. Desertopia kombinerar ökenklimatets traditionella byggnadstekniker med den senaste klimatteknologin för att skapa en struktur som kan användas av vanliga egyptier för att ta makten över sin egen framtid.
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"Desert Playa Wetlands: Ecological Controls of their Functioning and Responses to Climate Change." Doctoral diss., 2016. http://hdl.handle.net/2286/R.I.40695.
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abstract: The Basin and Range province of southwestern USA are composed of different grassland and shrubland ecosystems. Particularly understudied ecosystems in this region are playas, which are ephemerally-flooded wetlands located in topographic low areas of hydrologically-closed dryland catchments. There is not much known about the ecological functioning of playas and the role of playas within desert basins. Even less is known about how global change drivers may affect playas in the future. The main objective of this thesis was to better understand the ecological functioning and the impact of climate change on desert playa wetlands. I collected new data, used existing long-term data, and used simulation modelling techniques to address this objective. I compared playa soils to upland soils and found that playas were hotspots of soil organic carbon and nutrient storage within a desert basin. I also used existing data to analyze the response of above-ground net primary productivity (ANPP) to annual precipitation in playas and upland ecosystems. I found that playa ANPP responded in a non-linear concave-down relationship with annual precipitation amount. Playa ANPP peaked in moderately wet years and declined in very wet years, which was most likely due to flooding; whereas, upland ANPP increased linearly with precipitation. I measured soil organic carbon and nitrogen concentrations in a representative subset of playas and measured the biophysical characteristics of the upland catchments associated with each playa. I found that both catchment geomorphology and vegetation cover were correlated to differences in soil organic carbon and nitrogen among playas. These results showed the importance external soil-inputs delivered via surface runon to playas. Finally, I empirically measured groundwater recharge beneath playas and combined these empirical data with modelling data to forecast how playa groundwater recharge may change in the future. I concluded that playas contribute to groundwater recharge in desert aquifers, playa runon is a strong predictor of playa groundwater recharge, and climate change will have a net-positive impact on groundwater recharge beneath playas. Overall, my thesis research increased the understanding of the role of desert playas on the functioning of dryland ecosystems.Dissertation/Thesis
Doctoral Dissertation Biology 2016
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"Soil Moisture Availability and Energetic Controls on Belowground Network Complexity and Function in Arid Ecosystems." Doctoral diss., 2014. http://hdl.handle.net/2286/R.I.24934.
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abstract: The explicit role of soil organisms in shaping soil health, rates of pedogenesis, and resistance to erosion has only just recently begun to be explored in the last century. However, much of the research regarding soil biota and soil processes is centered on maintaining soil fertility (e.g., plant nutrient availability) and soil structure in mesic- and agro- ecosystems. Despite the empirical and theoretical strides made in soil ecology over the last few decades, questions regarding ecosystem function and soil processes remain, especially for arid areas. Arid areas have unique ecosystem biogeochemistry, decomposition processes, and soil microbial responses to moisture inputs that deviate from predictions derived using data generated in more mesic systems. For example, current paradigm predicts that soil microbes will respond positively to increasing moisture inputs in a water-limited environment, yet data collected in arid regions are not congruent with this hypothesis. The influence of abiotic factors on litter decomposition rates (e.g., photodegradation), litter quality and availability, soil moisture pulse size, and resulting feedbacks on detrital food web structure must be explicitly considered for advancing our understanding of arid land ecology. However, empirical data coupling arid belowground food webs and ecosystem processes are lacking. My dissertation explores the resource controls (soil organic matter and soil moisture) on food web network structure, size, and presence/absence of expected belowground trophic groups across a variety of sites in Arizona.Dissertation/Thesis
Ph.D. Biology 2014
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"Direct and indirect ecological consequences of human activities in urban and native ecosystems." Doctoral diss., 2014. http://hdl.handle.net/2286/R.I.25911.
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abstract: Though cities occupy only a small percentage of Earth's terrestrial surface, humans concentrated in urban areas impact ecosystems at local, regional and global scales. I examined the direct and indirect ecological outcomes of human activities on both managed landscapes and protected native ecosystems in and around cities. First, I used highly managed residential yards, which compose nearly half of the heterogeneous urban land area, as a model system to examine the ecological effects of people's management choices and the social drivers of those decisions. I found that a complex set of individual and institutional social characteristics drives people's decisions, which in turn affect ecological structure and function across scales from yards to cities. This work demonstrates the link between individuals' decision-making and ecosystem service provisioning in highly managed urban ecosystems.
Second, I examined the distribution of urban-generated air pollutants and their complex ecological outcomes in protected native ecosystems. Atmospheric carbon dioxide (CO2), reactive nitrogen (N), and ozone (O3) are elevated near human activities and act as both resources and stressors to primary producers, but little is known about their co-occurring distribution or combined impacts on ecosystems. I investigated the urban "ecological airshed," including the spatial and temporal extent of N deposition, as well as CO2 and O3 concentrations in native preserves in Phoenix, Arizona and the outlying Sonoran Desert. I found elevated concentrations of ecologically relevant pollutants co-occur in both urban and remote native lands at levels that are likely to affect ecosystem structure and function. Finally, I tested the combined effects of CO2, N, and O3 on the dominant native and non-native herbaceous desert species in a multi-factor dose-response greenhouse experiment. Under current and predicted future air quality conditions, the non-native species (Dissertation/Thesis
Doctoral Dissertation Plant Biology 2014
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Prater, Margaret Rose. "Ecosystem consequences of post-fire invasive species in the Great Basin Desert /." 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3223695.
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Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3556. Adviser: Evan DeLucia. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.
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"Ecosystem Spatial Heterogeneity: Formation, Consequences, and Feedbacks." Doctoral diss., 2015. http://hdl.handle.net/2286/R.I.35960.
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abstract: An understanding of the formation of spatial heterogeneity is important because spatial heterogeneity leads to functional consequences at the ecosystem scale; however, such an understanding is still limited. Particularly, research simultaneously considering both external variables and internal feedbacks (self-organization) is rare, partly because these two drivers are addressed under different methodological frameworks. In this dissertation, I show the prevalence of internal feedbacks and their interaction with heterogeneity in the preexisting template to form spatial pattern. I use a variety of techniques to account for both the top-down template effect and bottom-up self-organization. Spatial patterns of nutrients in stream surface water are influenced by the self-organized patch configuration originating from the internal feedbacks between nutrient concentration, biological patchiness, and the geomorphic template. Clumps of in-stream macrophyte are shaped by the spatial gradient of water permanence and local self-organization. Additionally, significant biological interactions among plant species also influence macrophyte distribution. The relative contributions of these drivers change in time, responding to the larger external environments or internal processes of ecosystem development. Hydrologic regime alters the effect of geomorphic template and self-organization on in-stream macrophyte distribution. The relative importance of niche vs. neutral processes in shaping biodiversity pattern is a function of hydrology: neutral processes are more important in either very high or very low discharge periods. For the spatial pattern of nutrients, as the ecosystem moves toward late succession and nitrogen becomes more limiting, the effect of self-organization intensifies. Changes in relative importance of different drivers directly affect ecosystem macroscopic properties, such as ecosystem resilience. Stronger internal feedbacks in average to wetter years are shown to increase ecosystem resistance to elevated external stress, and make the backward shifts (vegetation loss) much more gradual. But it causes increases in ecosystem hysteresis effect. Finally, I address the question whether functional consequences of spatial heterogeneity feed back to influence the processes from which spatial heterogeneity emerged through a conceptual review. Such feedbacks are not likely. Self-organized spatial patterning is a result of regular biological processes of organisms. Individual organisms do not benefit from such order. It is order for free, and for nothing.Dissertation/Thesis
Doctoral Dissertation Biology 2015
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Robin, L. "The rise of ecological consciousness in Victoria: the Little Desert dispute, its context and consequences." 1993. http://repository.unimelb.edu.au/10187/3524.
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The central event in this thesis is the Little Desert dispute, a 1969 controversy about whether land in western Victoria should be developed for agriculture or retained as natural bushland. The Little Desert dispute has lived on in the minds of protagonists and later environmentalists as a cultural icon and a ‘win’ for conservation. This pivotal event provides a framework within which the politics of nature conservation, ecology and land management can be examined. The thesis explores the role of ‘public science’ – science in government, bureaucracy and the community – in this context, as well as tracing the history of the science of ecology in post-war Australia.The second focus of this thesis is ‘the rise of ecological consciousness’ – the rise of the political relevance of the natural world and emerging concerns about the place of people in nature. This is a multifaceted concept, and includes ‘ecological’ in both its scientific and philosophical guises. ‘Consciousness’ is studied I the individual, collective and political senses.
The Little Desert dispute occurred just as ecological consciousness was beginning to rise in Australia and throughout the western world. The resolution of the dispute through the establishment of the Conservation Council of Victoria and the Land Conservation Council, in 1969 and 1970 respectively, was played out against a backdrop of changing environmental values and systems. The dispute had antecedents in diverse utilitarian, scientific, aesthetic and romantic conservation traditions. It was these values that motivated the leading protagonists, who were conservationists but not environmentalists. However, many environmentalists today look back on the Little Desert dispute as the beginning of the new ‘ecologically conscious’ era. The contribution of earlier conservationists to the environmental movement is often overlooked in environmentalist literature. Through examining closely the role of science and scientists in land management, this thesis explores some of the continuities as well as the discontinuities of the ‘environmental revolution’ in Australia.
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"Sources and Decomposition of Dissolved Organic Matter in Desert Streams." Master's thesis, 2018. http://hdl.handle.net/2286/R.I.51657.
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abstract: Dissolved organic matter (DOM) is an important part of aquatic foodwebs because it contains carbon, nitrogen, and other elements required by heterotrophic organisms. It has many sources that determine its molecular composition, nutrient content, and biological lability and in turn, influence whether it is retained and processed in the stream reach or exported downstream. I examined the composition of DOM from vascular wetland plants, filamentous algae, and riparian tree leaf litter in Sonoran Desert streams and its decomposition by stream microbes. I used a combination of field observations, in-situ experiments, and a manipulative laboratory incubation to test (1) how dominant primary producers influence DOM chemical composition and ecosystem metabolism at the reach scale and (2) how DOM composition and nitrogen (N) content control microbial decomposition and stream uptake of DOM. I found that differences in streamwater DOM composition between two distinct reaches of Sycamore Creek did not affect in-situ stream respiration and gross primary production rates. Stream sediment microbial respiration rates did not differ significantly when incubated in the laboratory with DOM from wetland plants, algae, and leaf litter, thus all sources were similarly labile. However, whole-stream uptake of DOM increased from leaf to algal to wetland plant leachate. Desert streams have the potential to process DOM from leaf, wetland, and algal sources, though algal and wetland DOM, due to their more labile composition, can be more readily retained and mineralized.Dissertation/Thesis
Masters Thesis Biology 2018
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"Understanding Introduced Megafauna in the Anthropocene: Wild Burros as Ecosystem Engineers in the Sonoran Desert." Master's thesis, 2017. http://hdl.handle.net/2286/R.I.43984.
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abstract: Megafauna species worldwide have undergone dramatic declines since the end of the Pleistocene, twelve thousand years ago. In response, there have been numerous calls to increase conservation attention to these ecologically important species. However, introduced megafauna continue to be treated as pests. This thesis evaluates the extent of this conservation paradox in relation to changing megafauna diversity from the Pleistocene to the Anthropocene and finds that introductions have provided refuge for a substantial number threatened and endangered megafaunal species and has restored generic diversity levels per continent to levels closer to the Pleistocene than the Holocene. Furthermore, this thesis describes a previously unstudied behavior of wild burros (Equus asinus), an introduced megafauna whose pre-domestic ancestors are Critically Endangered. Wild burros dig wells to access groundwater and in doing so substantially increase water availability on several scales, create sites that are visited by numerous species and are comparable to natural water sources in terms of species richness, and provide germination nurseries for important riparian pioneer plant species. My results suggest that relaxing concepts of nativity in an age of extinction will provide new understandings of ecological function and can help focus attention on broader conservation goals.Dissertation/Thesis
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Appendix F
Masters Thesis Biology 2017
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"Personality in the City: Relationship Between Animal Behavioral Traits And Urbanization in a Fragile, Human-impacted Desert Ecosystem." Doctoral diss., 2018. http://hdl.handle.net/2286/R.I.51787.
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abstract: Human-inhabited or -disturbed areas pose many unique challenges for wildlife, including increased human exposure, novel challenges, such as finding food or nesting sites in novel structures, anthropogenic noises, and novel predators. Animals inhabiting these environments must adapt to such changes by learning to exploit new resources and avoid danger. To my knowledge no study has comprehensively assessed behavioral reactions of urban and rural populations to numerous novel environmental stimuli. I tested behavioral responses of urban, suburban, and rural house finches (Haemorhous mexicanus) to novel stimuli (e.g. objects, noises, food), to presentation of a native predator model (Accipiter striatus) and a human, and to two problem-solving challenges (escaping confinement and food-finding). Although I found few population-level differences in behavioral responses to novel objects, environment, and food, I found compelling differences in how finches from different sites responded to novel noise. When played a novel sound (whale call or ship horn), urban and suburban house finches approached their food source more quickly and spent more time on it than rural birds, and urban and suburban birds were more active during the whale-noise presentation. In addition, while there were no differences in response to the native predator, rural birds showed higher levels of stress behaviors when presented with a human. When I replicated this study in juveniles, I found that exposure to humans during development more accurately predicted behavioral differences than capture site. Finally, I found that urban birds were better at solving an escape problem, whereas rural birds were better at solving a food-finding challenge. These results indicate that not all anthropogenic changes affect animal populations equally and that determining the aversive natural-history conditions and challenges of taxa may help urban ecologists better understand the direction and degree to which animals respond to human-induced rapid environmental alterations.Dissertation/Thesis
Doctoral Dissertation Biology 2018
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Dror, Libby. "Hydro-Solar Fields." Thesis, 2010. http://hdl.handle.net/10012/5515.
Full textAbstract:
In the current context of escalating climate catastrophes paralleled with depleting energy resources, degrading fresh water supplies and diminishing agricultural lands, there is an increasing preoccupation with the prospects of a fast approaching ecological global crisis. Arid regions, which under normal circumstances are places of acute extremes, are afflicted by these trends more profoundly. Dryland ecosystems are places where survival hangs on a most fragile equilibrium, therefore any anomaly or scarcity can be detrimental to their viability. Alternatively, due to their unique ecosystem properties, not available in other more moderate environments, deserts can represent places of immeasurable potential for a prosperous subsistence.
The Negev desert accounts for two thirds of the land area of Israel and is employed as a case study for this exploration. The thesis investigates the following four narratives:
FERTILE VISIONS dissects the ethos of blooming the desert and the inherent contradictions of realized utopias.
EPHEMERAL FLOWS constructs a broad framework of the Negev’s ecosystem, while mapping the operating forces and their affect on the system’s stability.
VITAL SIGNS curates a catalogue of strategies, systems and technologies in the fields of water management, solar energy and controlled environments. Their juxtaposition starts to suggest plausible hybrids.
Finally, EFFECTIVE TERRAINS defines design strategies for new models of desert living, based on integrated infrastructural systems. It envisions a prototype for a community planned through the synthetic interweaving of the existing desert ecosystem with water, energy and agricultural production.
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"Deep Percolation in Arid Piedmont Watersheds and Its Sensitivity to Ecosystem Change." Doctoral diss., 2017. http://hdl.handle.net/2286/R.I.48444.
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abstract: Population growth within drylands is occurring faster than growth in any other ecologic zone, putting pressure on already stressed water resources. Because the availability of surface water supplies in drylands tends to be highly variable, many of these populations rely on groundwater. A critical process contributing to groundwater recharge is the interaction between ephemeral channels and groundwater aquifers. Generally, it has been found that ephemeral channels contribute to groundwater recharge when streamflow infiltrates into the sandy bottoms of channels. This process has traditionally been studied in channels that drain large areas (10s to 100s km2). In this dissertation, I study the interactions between surface water and groundwater via ephemeral channels in a first-order watershed located on an arid piedmont slope within the Jornada Experimental Range (JER) in the Chihuahuan Desert. To achieve this, I utilize a combination of high-resolution observations and computer simulations using a modified hydrologic model to quantify groundwater recharge and shed light on the geomorphic and ecologic processes that affect the rate of recharge. Observational results indicate that runoff generated within the piedmont slope contributes significantly to deep percolation. During the short-term (6 yr) study period, we estimated 385 mm of total percolation, 62 mm/year, or a ratio of percolation to rainfall of 0.25. Based on the instrument network, we identified that percolation occurs inside channel areas when these receive overland sheetflow from hillslopes. By utilizing a modified version of the hydrologic model, TIN-based Real-time Integrated Basin Simulator (tRIBS), that was calibrated and validated using the observational dataset, I quantified the effects of changing watershed properties on groundwater recharge. Distributed model simulations quantify how deep percolation is produced during the streamflow generation process, and indicate that it plays a significant role in moderating the production of streamflow. Sensitivity analyses reveal that hillslope properties control the amount of rainfall necessary to initiate percolation while channel properties control the partitioning of hillslope runoff into streamflow and deep percolation. Synthetic vegetation experiments show that woody plant encroachment leads to increases in both deep percolation and streamflow. Further woody plant encroachment may result in the unexpected enhancement of dryland aquifer sustainability.Dissertation/Thesis
Doctoral Dissertation Geological Sciences 2017
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"Fertility of frost boils and the effect of diapirism on plant nitrogen uptake in a polar desert ecosystem of the Canadian High Arctic." Thesis, 2016. http://hdl.handle.net/10388/ETD-2016-02-2431.
Full textAbstract:
Polar desert environments are limiting in plant available nutrients, mainly nitrogen (N) and phosphorus (P) that severely limit plant growth and establishment. Cryogenic activity regularly patterns the ground into a patchwork of frost boils – sorted circles that are associated with an increase in moisture, fertility and plant cover. Within some frost boils, the accumulation of ice-rich soil at the permafrost table can cause an upward flow of soil organic carbon (SOC) enriched permafrost material into the active layer. These diapiric intrusions are predicted to fuel microbial activity and enrich the horizon in N and P; however, the enrichment of the diapir horizon and accessibility by plants has yet to be studied. The aim of this research was to characterize the N distribution within diapir horizons located in frost boils and the effect of these intrusions on vascular plant N uptake in a polar desert ecosystem of the Canadian High Arctic. Natural abundance and enriched isotope 15N techniques were used to trace the flow of N through the soil-plant system. Surface and diapir horizons contained the highest total C and total N content within frost boils. Natural abundance δ15N analysis indicated that uptake by Salix arctica plants located on frost boils in the absence of a diapir horizon were sourcing N from the surface. However, when diapir nutrients became available, S. arctica plants began sourcing N from the diapir horizon and underlying low SOC sources in the soil, while reducing uptake from the surface. The altered foraging strategy of S. arctica in response to diapir horizon formation was further indicated by significant uptake of atom%15N nutrients that were injected directly into diapir horizons. These findings suggest diapir horizons are enriched in N and accessible by plants roots as an important nutrient source that is instrumental in their survival within frost boils of a polar desert ecosystem in the high arctic.
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GREGORY, FIONA MARIANNE. "BIOPHYSICAL REMOTE SENSING AND TERRESTRIAL CO2 EXCHANGE AT CAPE BOUNTY, MELVILLE ISLAND." Thesis, 2011. http://hdl.handle.net/1974/6953.
Full textAbstract:
Cape Bounty, Melville Island is a partially vegetated High Arctic landscape with three main plant communities: polar semi-desert (47% of the study area), mesic tundra (31%) , and wet sedge meadows (7%). The objective of this research was to relate biophysical measurements of soil, vegetation, and CO2 exchange rates in each vegetation type to high resolution satellite data from IKONOS-2, extending plot level measurements to a landscape scale. Field data was collected through six weeks of the 2008 growing season. Two IKONOS images were acquired, one on July 4th and the other on August 2nd. Two products were generated from the satellite data: a land-cover classification and the Normalized Difference Vegetation Index (NDVI).
The three vegetation types were found to have distinct soil and vegetation characteristics. Only the wet sedge meadows were a net sink for CO2; soil respiration tended to exceed photosynthesis in the sparsely vegetated mesic tundra and polar semi-desert. Scaling up the plot measurements by vegetation type area suggested that Cape Bounty was a small net carbon source (0.34 ± 0.47 g C m-2 day-1) in the summer of 2008.
NDVI was strongly correlated with percent vegetation cover, vegetation volume, soil moisture, and moderately with soil nitrogen, biomass, and leaf area index (LAI). Photosynthesis and respiration of CO2 both positively correlated with NDVI, most strongly when averaged over the season. NDVI increased over time in every vegetation type, but this change was not reflected in any significant measured changes in vegetation or CO2 flux rates.
A simple spatial model was developed to estimate Net Ecosystem Exchange (NEE) at every pixel on the satellite images based on NDVI, temperature and incoming solar radiation. It was found that the rate of photosynthesis per unit NDVI was higher early in the growing season. The model estimated a mean flux to the atmosphere of 0.21 g C m-2 day-1 at the time of image acquisition on July 4th, and -0.07 g C m-2 day-1 (a net C sink) on August 2nd. The greatest uncertainty in the relationship between NDVI and CO2 flux was associated with the polar semi-desert class.Thesis (Master, Geography) -- Queen's University, 2011-12-28 23:27:34.824