Dissertations / Theses: 'Semi-arid environments'

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Patrick, Cecil. "Reservoir tillage for semi-arid environments." Thesis, Cranfield University, 2005. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426071.

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Hutton, Christopher Joseph. "Modelling watershed processes in semi-arid environments." Thesis, University of Exeter, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.529295.

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Torofder, Golam. "Manipulating wheat yield in semi-arid environments." Thesis, University of Aberdeen, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394451.

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Findings from a number of recent glasshouse studies are reported and their relevance to wheat production practices in Bangladesh is discussed. It was found that application of large amounts of urea gave highest grain yield when the total amount of urea was added immediately after irrigation following germination. The same amount of urea applied before irrigation or in smaller doses throughout the growing season gave lower yield and resulted in higher post-harvest concentrations of soil nitrate. Reducing the total urea application to one quarter of the typical maximum reported value, did not cause a reduction in yield and this could be achieved with only one occasion of irrigation (as opposed to two) following germination. The findings confirm the recommended dosage of urea (typically 250 kg urea ha^-1) and indicate the importance of applying urea after irrigation to maximise yield and minimise post-harvest soil nitrate concentrations. Adding a nitrate fertiliser as opposed to the same amount of urea-N did not result in a significant yield increase. The results indicate that application of urea-N following irrigation results in a rapid availability of soil N for plant uptake. Where severe soil drying occurs in the upper rooting zone, grain field was drastically reduced. This occurred even where longer roots had access to non-limiting amounts of water and nutrients. It was found that roots in the drying soil produced the plant hormone abscisic acid (ABA) and that this had a likely causal significance in decreasing yield. ABA was also produced in plants with ammonium- as opposed to nitrate nutrition and this was also associated with reduced yield. It was concluded that breeding for deep rooting alone would be insufficient to attain high yield if the upper part of root system was exposed to severe soil water deficit. Breeding of deep rooting in combination with a decreased sensitivity of stomatal closure to ABA, is an attractive possibility for plant and yield improvement for semi-arid zones. In the interim, current measures of tillage and mulching that enhance the water content of the upper rooting zone should be encouraged. Such measures are likely to counter the potential ABA-induced inhibition of yield associated with partial root dehydration and incomplete nitrification of soil ammonium.

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Van, der Meer Frans-Bauke Willem. "Modelling tropical soil water regimes in semi-arid environments." Thesis, Loughborough University, 2000. https://dspace.lboro.ac.uk/2134/27070.

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Soil moisture available to crops is among the main constraints on crop production by smallholder farmers in semi-arid Zimbabwe. Other restrictions, such as limited use of fertilisers and herbicides, stem primarily from socio-economic rather than biophysical constraints. To improve smallholder farming, it is essential to promote soil and water conservation practices (SWC) that consider farmers' management constraints, such as limited availability of labour and Draught Animal Power (DAP).

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Mitchell, John Talmadge. "A Framework for Development in Rural Arid and Semi-Arid Environments in Africa: The Somalia Case." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/98224.

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This study proposes a framework and a process promoting creation of sustainable jobs and businesses in rural, arid and semi-arid agricultural conflict zones of Sub Saharan Africa, focusing on Somalia's societal stabilization and conflict mitigation. This task requires developing risk-reducing measures for infrastructure and service delivery in rural, post-conflict zones. Literature reviews identified two economic growth theories rooted in sustainability concepts for localized, pro-poor development. Ecological Economics Theory (EET) and Endogenous Growth Theory (EGT) are the philosophical bases establishing investment priorities. Additional research regarding Somali culture, key conflict factors, and potential business opportunities, provides an understanding of salient facts in Somalia's on-going, 27-years of war and potential culturally acceptable development pathways. Informal sources, Somali and non-Somali, were consulted to further identify and verify potential avenues for economic growth, sustainability, educational opportunities, allowing Somalia to emerge from the strife it has endured. Visits to Somalia and Somaliland confirmed that livestock, its products and related requirements, are key components for economic growth and job creation. Investigation, via pilot testing and case studies, was undertaken of technologies with potential to improve productive capacity and disrupt existing value chains. Initial framework elements were evaluated for job and business creation, through unstructured, semi-structured interviews, and questionnaire of Somali officials, and Somali and non-Somali conflict zone development practitioners. The pilot test used a small sample size and is a limitation of this work. Findings from the literature review, informal discussions, and the pilot test are synthesized into the framework presented in Chapter 5. The framework proposes development of an innovative, disruptive, and scalable business model that facilitates the simultaneous implementation of renewable energy production. It targets education for the livestock and agroforestry industry of Somalia, improving job and business opportunities. The model proposes modification of used shipping containers for the creation of modular elements, to satisfying infrastructural building components to initiate skills practice, job, and business growth.
Doctor of Philosophy
The wars and conflicts of various types in Africa have made the continent poorer and prevented development in many countries. One of the major, and seemingly intractable conflict locations, is Somalia located in the East Horn of Africa (EHA). This research provides an understanding of salient facts in Somalia's 27 years of war by examining culture and key conflict factors. The objective of this assessment is to identify potential culturally acceptable pathways that will lead to business opportunities and development as a means of conflict mitigation. The improvement of job opportunities for youth is viewed as a means to offset the current participation in the ongoing conflict. Somali and non-Somali sources were consulted to identify and verify avenues for economic growth, sustainability, and educational opportunities. Visits to Somalia and Somaliland confirmed that livestock, and related products, are key components for development and job creation. Technologies with potential to improve productive capacity and disrupt existing value chains were also evaluated. Findings from informal discussions and a pilot test of a proposed framework are presented. The framework identifies elements for development of an innovative, disruptive, and scalable business model that facilitates the implementation of renewable energy production. In addition, it targets education for the livestock and agroforestry industries, improving job and business opportunities.

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Meerkerk, André. "Rainfed orchards in semi-arid environments : retaining the water and the soil." Université catholique de Louvain, 2008. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-08282008-005955/.

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The spatial distribution and properties of rainfed orchards in semi-arid environments result from complex interactions between man and the physical and economical environment. This thesis investigates a number of these interactions in the context of the mechanisation of management practices since the 1950's. It is shown how the practice of clean sweeping (i.e. frequent shallow tillage) influences the orchard water balance and how the removal of traditional soil and water conservation structures affects the connectivity of overland flow to the river system. Although clean sweeping prevents transpiration and competition by weeds, it also constrains the root growth in the plough layer, so that the trees cannot access the water from small rain events. In addition, clean sweeping promotes accelerated soil erosion. It appears that the practice of clean sweeping limits the water availability in orchards on loamy soils with an annual rainfall in the order of 300 mm. It is demonstrated that the presence and properties of rainfed orchards are related to spatial patterns of soil characteristics and climate. The observed decline in conservation structures like terraces and check-dams leads to an increase in the connectivity of water and sediment to the river system. An alternative for these traditional techniques to retain the water and the soil is the application of cover crops. The advantage of cover crops is that they do not limit the field size. A drawback in dry areas is the competition for water and nutrients between the cover crop and the trees. Field evidence and water balance simulations suggest that cover crops are feasible in areas with an annual precipitation of 500 mm or more.

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Puttock, Alan Keith. "Vegetation change and water, sediment and carbon dynamics in semi-arid environments." Thesis, University of Exeter, 2013. http://hdl.handle.net/10871/13541.

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This study develops understanding of vegetation change and water, sediment and carbon dynamics in semi-arid environments. Objectives were addressed using an integrated ecohydrological and biogeochemical approach. Fieldwork, over two contrasting grass-woody transitions at the Sevilleta National Wildlife Refuge, New Mexico, USA; quantified vegetation structure, soil structure and the spatial distribution of soil carbon resources. Over both transitions; woody sites showed a lower percentage vegetation cover and a greater heterogeneity in vegetation pattern, soil properties and soil carbon. Soil organic carbon differed in both quantity and source across the sites; with levels higher under vegetation, particularly at the woody sites. Biogeochemical analysis revealed soil organic carbon to be predominantly sourced from grass at the grassland sites. In contrast, at the woody sites soil organic carbon under vegetation patches was predominantly sourced from woody vegetation, whilst inter-patch areas exhibited a strong grass signature. Investigation of function focussed on the hydrological response to intense rainfall events. Rainfall-runoff monitoring showed woody sites to exhibit greater; runoff coefficients, event discharge, eroded sediment and event carbon yields. In contrast to grass sites, biogeochemical analysis showed the loss of organic carbon from woody sites to exhibit a mixed source signal, reflecting the loss of carbon originating from both patch and interpatch areas. To examine the linkages between vegetation structure and hydrological function, a flow length metric was developed to quantify hydrological connectivity; with woody sites shown to have longer mean flow pathways. Furthermore, in addition to rainfall event characteristics, flow pathway lengths were shown to be a significant variable for explaining the variance within fluxes of water, sediment and carbon. Results demonstrating increased event fluxes of sediment and carbon from woody sites have important implications for the quality of semi-arid landscapes and other degrading ecosystems globally. It is thus necessary to translate the understanding of carbon dynamics developed within this study to the landscape scale, so changing fluvial carbon fluxes can be incorporated into carbon budgets, research frameworks and land management strategies at policy-relevant scales.

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Hamilton, Jeffrey Muir. "Arugula Crop Production in Arid and Semi-Arid Regions: Nutritional Value, Postharvest Quality, and Sustainability in Controlled Environments." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/195968.

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Plant responses to abiotic stress are neither singular nor linear. The research represented within this dissertation was intended to evaluate selected biochemical and physiological responses in two Arugulas (Images 1-5), to agronomic interventions designed to mitigate extreme environmental abiotic factors, characteristic of arid agricultural production regions. Plant stress responses were investigated under field conditions and within controlled environments (CE), during the course of a preliminary trial and three independent studies, all four directly related. The preliminary trial evaluated harvest and postharvest nutritional content (i.e., antioxidants) of two Arugulas, Eruca sativa (L.) Cav. ssp. sativa (P. Mill.) and Diplotaxis tenuifolia (L.) DC cv. Sylvetta; grown under field conditions in the semi-arid upper Sonoran Desert. In this trial, we defined baseline harvest and postharvest antioxidant values for the Arugulas, cultivated in a semi-arid environment. The initial study, conducted within a CE utilizing a water recycling system, evaluated changes in the nutritional value of three specialty leafy cruciferous vegetables: D. tenuifolia, E. sativa and Lepidium sativum; when subjected to increasing salinity levels in the nutrient solution. It was concluded that, when specific Crucifers are irrigated with moderately high levels of salinity, neither harvest nor postharvest nutritional values are compromised. The second study, investigated the response of a suite of plant physiological parameters (e.g., yield and photosynthetic rate) in the three Crucifers to salinity, within the CE. This research provided guideline salinity values where yields did not decline, and encourages growers to consider water resources compromised by salinity and nutrient solution recycling. During the third study, the influence of environmental conditions on the nutritional content in leafy vegetables, prevalent immediately before harvest, was investigated; by subjecting plants to reduced sunlight treatments and early irrigation termination. We observed that, modulating light intensity late in the season, and early irrigation termination strategies, modify the nutritional content of leafy vegetables; and potentially the subsequent postharvest shelf life. Collectively evaluated, this research suggests that simple agronomic interventions are valuable, yet practicable, tools that can enhance the nutritional content of specialty vegetables, in arid regions: be that intervention an imposed controlled-stress, utilizing nutrient recycling systems within a CE, or basic light-reduction and irrigation termination strategies within conventional fields systems.

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Bradley, Richard G. "Modelling the growth and water use of tropical cereals in semi-arid environments." Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319604.

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Skirvin, Susan. "Vegetation distributions in semi-arid environments: Spatial analysis for climate and landscape characterization." Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/280033.

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Spatially explicit knowledge of land cover is increasingly important for environmental modeling and decision support for land managers. Such knowledge is often provided over large regions by thematic maps produced from remotely sensed satellite data. Remote sensing of vegetation in semi-arid areas is complicated, however, by high levels of landscape spatial heterogeneity, resulting in large part from spatially varying soils, topography, and microclimates. Increased understanding of spatial distributions of vegetation and the factors affecting them will enhance our ability to inventory and monitor natural resources, and to model potential consequences of land management alternatives and larger issues such as global climate change. In addition, the uncertainty in spatial knowledge must be made spatially explicit in order to determine where more information is needed and where predictions maybe less reliable. Geostatistical kriging and multiple linear regression interpolation were used to map climate spatial distributions over the San Pedro River watershed, southeastern Arizona. Both methods used climate station location and elevation and climate data. Although mean interpolation errors were similar, kriging climate with elevation as external drift was preferred due to the patterns of spatial bias in regression errors. Interpolation results provided a step toward understanding climate influence on vegetation in this area. Accuracies of four land cover maps covering the upper San Pedro watershed, mapped from remotely sensed data, were determined using aerial photography, digital orthophoto quadrangles, and airborne video data reference data sets as alternatives to contemporaneous ground-collected data. Overall map accuracies were 67--75%; class accuracies varied more for smaller classes than for larger ones. Finally, the uncertainty of occurrence of the low-accuracy Mesquite Woodland class was mapped using simple indicator kriging with locally varying means and data derived from accuracy assessment information. Enhanced class discrimination in an independent validation data set confirmed the utility of this procedure. The results of these analyses can provide direct input for use in environmental modeling and can inform land management decision making, and the methods can be employed in other settings where spatial variability and uncertainty play large roles in the landscape.

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Ali, Sani Muhammad. "Measured and perceived conditions of indoor environmental qualities (IEQ) of university learning environments in semi-arid tropics." Thesis, University of Portsmouth, 2018. https://researchportal.port.ac.uk/portal/en/theses/measured-and-perceived-conditions-of-indoor-environmental-qualities-ieq-of-university-learning-environments-in-semiarid-tropics(b611ff99-e930-42bc-b254-36d29cf6de97).html.

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This study investigates the conditions and the levels of satisfaction with indoor environmental quality (IEQ) in naturally ventilated (NV) learning environments in Bayero University, Kano and compares the results to international comfort standards' thresholds. It examines the thermal and visual comfort, acoustic quality as well as the indoor air quality of six learning environments in the University consisting of four lecture theatres and two laboratories. Researches in IEQ have shown that good quality indoor environment enhances occupants' comfort, wellbeing, raises their productivity, and most importantly for this research, it raises students' performances, reduces absenteeism, and reduces stress and fatigue among teachers. IEQ researches are mostly being undertaken in the four most advanced continents that are situated in the temperate regions of the world, but not in sub-Saharan Africa. Using both measurement and survey methods, internal and external physical parameters (air and radiant temperatures, air velocity, relative humidity, background noise, sound pressure level, horizontal and vertical illumination level, carbon dioxide concentration and particulate matter) were evaluated. The assessments were undertaken three times covering ten months, August 2016 to May 2017, which coincided with the three distinct seasons (warm and wet; cool and dry & hot and dry) in Kano. PMV model, as always, failed to predict the thermal conditions of the learning environments. Similarly some of the measured and calculated IEQ parameters, have not met the thresholds specified by the adaptive components of ASHRAE-55, but were in agreement with EN 15251, the respondents expressed their acceptance of their learning environments, subjectively. This is not surprising as these standards were often based on experiments implemented in developed countries, where the severity of the climatic conditions and the culture are dissimilar to sub Saharan Africa. The outcome of the research is hoped to raise awareness of IEQ potentialities among the academia, building industry professionals, building owners, university managers and other education policy makers in the region.

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Maas, Sylvana, and n/a. "Population dynamics and control of feral goats in a semi-arid environment." University of Canberra. Resource, Environmental & Heritage Sciences, 1997. http://erl.canberra.edu.au./public/adt-AUC20060825.132138.

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The ability of feral herbivores to reduce the amount of food available to domestic livestock has rarely been quantified. This thesis seeks to examine the degree to which feral goats (Capra hircus) reduce the availability of pasture and shrub biomass for other herbivores. The interaction between feral goat populations and their food supply will be explored using a modelling approach. In addition to this it will also examine the cost of controlling goats and attempt to identify the cost efficient target densities for control operations. The implications of this information for management will be discussed. There are two ways an animal population can interact with its food supply, through: (1) intrinsic food shortages, and (2) extrinsic food shortages. Intrinsic food shortages occur when a negative feed-back loop exists between the animal population and their food supply. This means the animals affect the availability of their food and their food supply affects the dynamics of the animal population. Since the animals are affecting their own food supply it could be said that they will also affect the availability of that food to other herbivores if they consume the same species. Extrinsic food shortages occur when there is no feed-back from the animals to their food supply. Food availability is determined by extrinsic factors such as rainfall and is unaffected by the animal population. To determine how feral goats interact with their food supply several models will be examined, and these include: (1) single species models which use data from the animal population only. These have historically been used to identify density dependence which is commonly caused by the animal population being regulated through their food supply in the case of large herbivores, and (2) trophic models which incorporate data from at least two trophic levels in an ecosystem, in this case those being the animal population and the vegetation they are thought to consume. These models allow a more direct examination of the relationship between the feral goat population and their food supply. The various models were fitted to data collected on the field sites and the following results were obtained: (1) the dynamics of the feral goat populations could not be represented by single-species models. This was most probably due to the stochastic environment in which they lived causing the level of density dependence experienced by the goats to vary greatly masking its presence. (2) the rate of increase of the goat population could be predicted by the numerical response of rate of increase to pasture biomass. This demonstrated that food availability influenced the dynamics of the goat population. (3) goat density affected the availability of some species of shrub biomass. There was, however, no response seen in the availability of pasture species to changes in goat density. Since the study was conducted during a drought this is in agreement with other studies which indicated that goats will primarily browse during dry spells but switch to pasture species when conditions improve following rainfall. These results indicate that a negative feed-back loop does exist between feral goat populations and their food supply since the goats affected the availability of some shrub species and so they suffer intrinsic food shortages. This means goats have the ability to reduce the availability of food to other herbivores providing both are eating the same species. Cost-efficiency analysis showed that the cost of removing individual feral goats increases exponentially as density decreases because the search time per animal becomes greater. This relationship was used to construct a model that predicted the cost of achieving a target density. The model describing cost of control over density was also combined with a productivity model based on the numerical response of feral goats to pasture biomass to predict the cost of maintaining target densities under different environmental conditions. Using these models the most cost-efficient density identified was 11 goats/km2. From this study we can make the following conclusions: (1) feral goats have the ability to reduce the amount of shrub biomass available to other herbivores during dry conditions (2) their ability to influence the availability of pasture species remains unknown (3) given the cost of initial and ongoing control and the minimal benefits that result it would be difficult to justify controlling goats during a drought on the field sites.

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Alchin, Mark David. "A test of landscape function theory in the semi-arid shrublands of Western Australia." Thesis, Curtin University, 2011. http://hdl.handle.net/20.500.11937/1498.

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Australia’s rangelands encompass approximately 80% of the continent and generate significant wealth through a range of industries. The rangelands comprise four major ecosystem types, these are: grasslands, shrublands, woodlands and savanna. The ecological legacy of early pastoral development in most of Australia‟s semi-arid shrublands is largely one of degradation and desertification (Wilcox and McKinnon, 1974; Curry et al. 1994; McKeon et al. 2004; Mabbutt et al. 1963; Pringle and Tinley, 2001). Since the 1980‟s, there has been a slow and general shift by the pastoral industry towards sustainable stocking rates (Watson et al. 2007; Pringle and Tinley, 2001).To implement grazing systems that better align stocking rates with carrying capacity in the semi-arid shrublands, pastoralists require a much more advanced understanding of patch patterning and ecological processes at a paddock scale. This understanding of theory could improve the management decisions made by pastoralists and other land managers (e.g. mining environmental officers, carbon offset developers, conservation park rangers, Indigenous communities) and assist them in their immediate challenge of cost-effective rehabilitation of degraded areas. Landscape function theory was largely developed for this purpose.Landscape function theory was developed as a way to assess and interpret patch patterns and ecological processes that occur at a range of spatial scales (Ludwig et al. 1997). Landscape function theory is used to explain the concept of „functional heterogeneity‟ which is an information-rich phenomenon that has enabled the development of cross-scale metrics. Landscape function theory is based on four primary principles, these are: 1. Patchiness can be characterised by patch size, orientation, spacing and soil surface condition. 2. Natural landscapes have a characteristic spatial self-organisation, often expressed as patchiness. 3. Deviations from the „characteristics‟ or „natural‟ patchiness are seen as degrees of dysfunctionality and there is a long continuum from highly functional to highly dysfunctional patches. 4. Restoration or replacement of missing or ineffective processes in the landscape will improve soil surface conditions and soil habitat quality.Landscape function theory and the associated landscape function analysis (LFA) methodology have become an accepted standard for the ecological assessment of rangeland environments. However, there have been a limited number of studies in Australia that have thoroughly examined the four principles that underpin the landscape function theory. Further interrogation of the principles that underpin the theory has the potential to enhance its utility and validate its assumptions. Therefore, the aim of this thesis was to test the four principles of landscape function theory in a semi-arid shrubland environment.The overarching hypothesis of this thesis was that clear spatial patch patterns occur at a range of scales within the case study paddocks and these patterns determine the ecological functionality and resilience of the area. Specifically, I sought to find evidence of distinct patch-interpatch patterns and associations at a range of scales in the lower Murchison region of Western Australia (WA) and examined the impact that grazing and seasonal conditions can have on this natural patchiness. The study involved four components: 1. Empirical quantification of patch-scale heterogeneity and investigation into the existence of a gradient of functionality at a patch-scale. 2. Measurement of patch patterning at a paddock scale and an evaluation of sequences and associations of patch-interpatches in the context of their contribution to landscape functionality. 3. Investigation of the impact of grazing and seasonal conditions on perennial grass populations and the potential impacts of this on patch patterning and ecological processes. 4. Investigation of livestock grazing behaviour and its implications for patch patterning and ecological processes.Significant variation was detected (P<0.05) between the physical and chemical properties of 11 different patch-interpatch subclasses. Heterogeneity within individual patches was also significant (P<0.05) and the greatest variation occurred within ecologically stable, high-order patches. Higher-order patch-interpatch subclasses were highly functional and when compared to the lower-order patch-interpatch subclasses, the former had: higher soil respiration rates (>45%) (P<0.05), this indicates these subclasses are more biologically active; more than twice the number of perennial plant species within the patch (P<0.05); higher soil infiltration rates (>70% more rapid) (P<0.05), this indicates these subclasses can capture more rainfall and surface runoff when it occurs; and five times more carbon and nitrogen. A gradient of highly functional patches and highly dysfunctional interpatches was identified.Distinct patch patterning between different land-types was found. The granitic shrubland land-type had a much greater proportion of the lower-order resource-shedding interpatch subclass (>85% of the area) compared to the other land-types. In contrast, Acacia sandplains had a higher proportion of the ecologically functional patches compared to granitic shrublands. Depending on the land-type, it was concluded that a functional ecosystem will generally have balanced proportions of particular patch-interpatch subclasses as this is likely to lead to the efficient capture and cycling of water and nutrients. In contrast, a degraded ecosystem will have higher proportions of ecologically dysfunctional patch-interpatch subclasses. A number of significant spatial associations and repeating sequences of individual patch-interpatch subclasses were found to occur in the study area. In the case study paddocks, distance-from-water did not have any significant effect on the relative proportions of the different patch-interpatch subclasses.Native perennial grasses support perennial shrub patches in maintaining ecological stability and landscape processes in semi-arid shrublands. Perennial grasses were monitored over a 12 month period to determine whether summer rest from Merino sheep grazing had an impact on perennial grass populations. The change in the number of perennial grasses over the 12 month period was variable ranging from a 36.7% increase to mortality rates as high as 80.2%. There was evidence to suggest that the grasses in the exclosure treatments (i.e. no grazing) may have been conditioned by previous grazing events in such a way that made them highly susceptible to extended periods of moisture stress. Land-type, distance-from-water and stocking rate did not have a significant impact on the change in the number of perennial grasses over the 12 month period. Resting perennial grasses during the summer may be of benefit; however, given the high mortality rates in most of the paddocks, it was clear that seasonal conditions had a substantial overriding influence on the outcome.Five major factors influenced sheep grazing behaviour in the study paddock; these include: land-type, greenness cover, time of day, air temperature and distance-from-water. The GPS-collared sheep demonstrated a clear grazing preference for the higher value land-types (i.e. alluvial plains and hardpan washplains). The results also indicated that the sheep were selectively grazing areas with high greenness cover (as expressed by Normalised Difference Vegetation Index [NDVI]). The results highlight the importance of understanding the selective grazing characteristics of Merino sheep when designing paddock layouts and developing management plans. This is because repetitive, selective grazing of high-value land-types has the potential to modify the natural patch patterning and ecological processes.This study found empirical evidence which substantiates landscape function theory and concludes that it has significant application at a range of spatial scales in the semi-arid shrublands. The results explain why landscape function theory is the current standard for the assessment and interpretation of rangeland environments in Australia. Landscape function theory is the result of an evolutionary synthesis of earlier work, and it continues to be progressively refined as our knowledge of the complex patterns and ecological processes of the rangelands is improved.Based on the findings of this study, I consider that there are three areas of further inquiry which could assist land managers to practically apply landscape function theory and contribute towards the restoration of degraded Australian rangelands, these are: determination of the „functional‟ composition of patch-interpatches subclasses for a range of land-types in the Australian rangelands that could be used as benchmarks for land managers; further empirical quantification of the ecological processes that drive landscape function to assist in simulation modeling and the estimation of cost / benefit of rehabilitation efforts; and the potential role that grazing management can play in the restoration of dysfunctional patch-interpatch patterns and ecological processes in the semi-arid shrublands.

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Garg, Pradeep Kumar. "Development of a catchment scale erosion model for semi-arid environments and its implementation through remote sensing." Thesis, University of Bristol, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303765.

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Dickie, Jennifer Ann. "Relationships among the physical and chemical properties of soil, vegetation and land degradation in semi-arid environments." Thesis, University of Leicester, 2006. http://hdl.handle.net/2381/30410.

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This study examines the spatial patterns of soil parameters to test the hypothesis that shrub encroachment initiates a change in scale of soil heterogeneity, which consequently influences a landscape's biotic and abiotic interactions and thus the susceptibility of soil to erosion. Grassland, shrubland and badland sites were established in two semi-arid environments; the Karoo, South Africa and the Sevilleta National Wildlife Refuge, New Mexico, U.S. 108 soil samples from each of the eleven 60m x 60m plots were analysed for bulk density, shear strength, texture, aggregate stability, organic matter content, pH, conductivity and available sodium, calcium, magnesium, potassium and phosphorus content. Geostatistical analyses determined that, at a scale representative of the vegetation community, the grassland landscape appeared relatively homogeneous in its distribution of soil parameters. Shrublands, however, demonstrated an increase in heterogeneity of all soil parameters. Periodicity in the semi-variograms indicated that regular patterns across the landscape were evident for all parameters and thus likely to represent the differences between shrub and intershrub regions. Due to the complex plant-soil interactions, and the interactions amongst the soil parameters themselves, the cyclic patterns represent areas of high and low erodibility. More pronounced patterns were identified in the badlands. This indicates that, if the conditions are right, changes in plant-soil interactions caused by soil parameter redistribution in shrubland landscapes can exacerbate erosion leading to further degradation in the form of badlands. Comparisons between the two semi-arid regions suggest that although local variations in soil type and different species of vegetation will affect the intensity of the spatial response, the underlying patterns are similar at both locations and hence, potentially, at a global scale.

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Finnerty-Rae, Eileen Claire. "The Effects of Mesquite Tree Removal on Soil Microbial and Nutrient Cycling Processes in Semi-Arid Environments." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/195790.

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The expansion of mesquite (Prosopis velutina) in southeastern Arizona and attempts to control or remove mesquite have been well documented. However, removal of woody plants may affect the distribution and quantities of nutrient resources within soil including changes in carbon (C) and nitrogen (N) cycling and changes in the amounts of C and N sequestered in these soils. We hypothesized that mechanical mesquite removal would alter soil microclimate and nutrient inputs, leading to changes in soil C and N cycling and microbial communities and activities.This study was conducted at two separate semi-arid grassland sites south of Tucson, AZ during a three-year period. There were six study plots at each site, three plots from which mature mesquite trees had been mechanically removed and three plots where mature mesquite trees were left intact. We measured the soil temperature and moisture, C and N pools, N2O and CO2 fluxes, N mineralization rate, and microbial resistance and resilience to determine if short term changes in any of these parameters were taking place.No significant differences in N mineralization rate or microbial resistance or resilience were found between the soils under intact mesquite and from plots where mesquite had been mechanically removed. Soil temperature was not statistically analyzed because temperature was taken in only one plot per treatment and without within-treatment replicates, t-tests could not be performed. Statistically significant differences in soil moisture, total soil C and N, microbial biomass C and N, heterotrophic plate counts, and CO2 and N2O fluxes were found between treatments on different dates throughout the experiment. Despite this finding of some significant differences between treatments for some parameters measured, no recognizable pattern of changes was observed during this study. Over the course of the experiment, the data did not support our overall hypothesis, that short term changes in microclimate following mesquite removal would alter soil C and N cycling and microbial communities and activities.

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Dixon, Shannon A. "A Stochastic Model for Water-Vegetation Systems and the Effect of Decreasing Precipitation on Semi-Arid Environments." DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/5995.

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Current climate change trends are affecting the magnitude and recurrence of extreme weather events. In particular, several semi-arid regions around the planet are confronting more intense and prolonged lack of precipitation, slowly transforming these regions into deserts. In this thesis we present a stochastic (meso-scale) model for vegetation-precipitation interactions for semi-arid landscapes. Extensive simulations with the model suggest that persistence in current trends of precipitation decline in semi-arid landscapes may expedite desertification processes by up to several decades.

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Alqaisi, Othman [Verfasser]. "Nutritional, ecological, and economic evaluation of dairy farming systems and feeding strategies in semi-arid environments / Othman Alqaisi." Kiel : Universitätsbibliothek Kiel, 2013. http://d-nb.info/1036406253/34.

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Hosseini, Mohammad Khajeh. "The response of soybean seeds to the stresses of semi-arid environments during germination and early seedling growth." Thesis, University of Aberdeen, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324912.

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Reduced water availability and salinity are two major environmental factors influencing crop establishment in semi-arid environments. Therefore the effect of reduced water availability using polyethylene glycol (PEG) 4000 solutions and of salinity (NaCl) on the germination of six soybean cultivars was examined. Cultivars differed in their response to reduced water availability and salinity and in their ability to recover from the stresses. A large increase in germination during a recovery period at 0 MPa following water stress suggested that PEG was not toxic whilst the failure of seeds to recover from high salinity revealed the toxic effects of NaCl. At the same water potential, germination in saline conditions was higher than that in PEG and the rate of water uptake by individual seeds was more rapid in NaCl solutions than in PEG. The most plausible explanation for the greater water uptake and germination in NaCl is that seeds accumulated salts which lowered their osmotic potential. The effects of NaCl on seedling growth were much greater when experiments were conducted in a hydroponic system compared with a paper towel method. However, analysis of the solutions soaking the paper towels revealed that 4.25 mMolal Ca2⁺ was available to the seeds in this system in saline conditions. This may have reduced Na⁺ uptake or provided a protective effect against Na⁺ toxicity. Germination (40%) was possible at a tissue Na⁺ concentration in the embryonic axis of 9.3mg g-1 FW whilst seedling growth was completely inhibited at a tissue Na⁺ concentration of 6.1 mg g^-1FW. Germination at higher tissue Na⁺ concentrations was associated with higher K⁺+Ca2⁺ concentrations, suggesting that these ions may protect the seeds in the pregermination phase against salinity. A reduction in seed vigour due to ageing resulted in reduced germination under saline conditions compared to the germination of unaged seeds, but there was no significant interaction between salinity and seed ageing. However, unaged seeds showed a greater increase in germination after transfer to 0 MPa than did the aged seeds. Since both the site of ageing and the toxic effect of NaCl is the cell membrane, there may be additive effects of NaCl toxicity on cell membrane in aged seeds.

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Smith, Mark William. "Overland flow resistance & flood generation in semi-arid environments : explaining the restrained draining of the rain in Spain." Thesis, Durham University, 2009. http://etheses.dur.ac.uk/2919/.

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Resistance equations developed for pipe flows and open channel flows cannot be applied to model overland flows uncritically. The formulation of these equations employs several assumptions that are specific to the conditions in which they were developed and cannot be universally applied. The hydraulic behaviour of overland flow is distinct from that of pipe and channel flows and can be characterised by a high degree of variability both over space and over time as roughness elements are progressively inundated with increasing depth. A novel methodology of measuring overland flows in the field at a high- resolution permits examination of the interaction between flow variables and surface roughness. Reconstructing the water surface from elevation data and flow extent provides an estimation of the distribution of flow depths and offers a complementary perspective to more conventional approaches. Overland flows are observed to be highly variable both across and between hillslopes. The distribution of flow depths can be modelled using a two-parameter gamma distribution; both parameters show distinct variations with distance downslope and represent the progressive inundation of roughness elements with increasing depth. The flow interacts with soil surface form where it is capable of eroding its bed and the observed slope- independence of rill velocity can be explained by a feedback between flow state (as characterised by the Froude number) and surface roughness. While the existence of this interaction is affected by soil-type, the soil is observed to have little influence on the relationship between surface roughness and overland flow. Resistance is found to be spatially variable; some of this variability could be explained by the classification of areas of similar microtopogiaphy as identified in the field. This classification can be approximated by a thresholded index-based classification and provides a tool for up-scaling to the hillslope scale. Relating roughness to resistance is not straightforward. Complex natural soil surfaces vary in innumerable ways. Traditional roughness measures fall short of providing an adequate description of the complex soil surfaces observed in the field. A variety of alternative measures are developed, each of which captures a different attribute of surface form. These measures are tested to examine their influence on overland flow resistance and a suite of roughness-resistance models is developed which includes the effect of hillslope position to different degrees. Modelled flow resistance can be separated into a constant term and a depth-dependent term and can be easily incorporated into models of hillslope hydrology. This resistance is observed to decline where a hydrological connection, once established, is then maintained. Examination of the concept of hydrological connectivity in a semi-arid context suggests that the interaction between runoff generation and transfer determines not just flood peaks but also total flow amount. It is suggested that flow resistance and hence runoff transfer should be afforded the same detailed consideration as infiltration parameters, i.e. a spatially distributed and variable value (as a function of depth) that can be organised into discrete units akin to those developed for runoff generation. The parameterisation of both infiltration and resistance in this way provides a crucial interaction through the redistribution of soil moisture and runoff over hillslope surfaces. Through this mechanism, the observed complex and nonlinear runoff response to storm events may be explained as these attributes interact with rainfall characteristics and flow network development. Further understanding of this interaction could have practical implications for catchment management and affect the prioritisation of land management decisions.

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Stürz, Sabine [Verfasser], and Folkard [Akademischer Betreuer] Asch. "Effects of Water Management on Microclimate and Yield Physiology in Irrigated Rice in Semi-arid Environments / Sabine Stürz. Betreuer: Folkard Asch." Hohenheim : Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim, 2014. http://d-nb.info/1055990267/34.

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Jebreen, Hassan [Verfasser], Stefan [Gutachter] Wohnlich, and Frank [Gutachter] Wisotzky. "Karst water management in semi-arid environments: Central West Bank, Palestine / Hassan Jebreen ; Gutachter: Stefan Wohnlich, Frank Wisotzky ; Fakultät für Geowissenschaften." Bochum : Ruhr-Universität Bochum, 2019. http://d-nb.info/1182682316/34.

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Nadal, Sala Daniel. "Living on the edge: modeling climate change impacts on sub-humid forests growing in semi-arid environments = Vivint al límit: modelant els impactes del canvi climàtic sobre els boscos semi-humits creixent en entorns semi-àrids." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/668301.

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Semi-arid environments are zones where annual precipitation is less than a half of annual potential evapotranspiration, yet water availability is high enough to allow tree growth. Climate change is expected to have a major impact on forests growing at those regions. Rising atmospheric [CO2] (Ca) is expected to increase forest productivity. However, this fertilizing effect may be partially offset by an increase in water stress, either by reductions in water availability or by increases in atmospheric evaporative demand. Additionally, species-specific responses to climate change may further promote invasive tree species expansion. GOTILWA+ process-based model was used to project the performance of sub-humid forests growing in semi-arid conditions under climate change. However, a carpenter is just as good as the least sharpened of his tools. So, firstly it was developed and tested the RheaG Weather Generator Algorithm, a first-order Markov transition matrix-based WGA, in order to assure the ability to generate statistically robust meteorological time-series. Then, Bayesian inverse modeling was applied in order to calibrate GOTILWA+ model from “in situ” observations from two different forest stands, both occupied by water-demanding tree species growing surrounded by semi-arid conditions. Firstly, combined effects of increased vapor pressure deficit (D), increased Ca and decreased water availability in an S.W. Australian Eucalyptus salinga Sm. plantation were evaluated. Increasing Ca up to 700 ppm alone was projected to increase E. saligna productivity up to a 33%, and forest carbon stock up to a ~60%. However, combined reductions in water availability and D increases offset part of this fertilizing effect, down to 13% and 35%, respectively. Furthermore, limitations on forest productivity due to D increases were projected to occur in a magnitude similar than productivity reductions due to reduced soil water availability. Afterwards, in a N.E. Iberian Mediterranean riparian forest where black locust (Robinia pseudoacacia L.) is outcompeting three autochthonous deciduous tree species, sap flow observations were used to calibrate GOTILWA+ model for black locust and European Ash tree (Fraxinus excelsior L.). Field observations suggested that black locust success was explained by its facultative phreatophytic behavior, as well as an increased water use efficiency in stem growth, when compared with co-occurring autochthonous tree species. GOTILWA+ projections, including regionalized climate change scenarios, suggested that under global warming black locust productivity and growth would be further enhanced than its native counterpart, the European ash. The reasons are an increase on daily productivity as Ca increases, and an enlargement of its vegetative period as temperature rises. As conclusions, the invasive black locust growth performance is expected to be favored by global warming in Mediterranean riparian forests. On the other hand, E. saligna responses to climate change will strongly depend on the balance between the beneficial effects of increasing Ca and physiological limitations due to water stress increase. At stand level, results highlight the importance of accounting for the water available for the trees at the whole soil column, and not only at the superficial soil layers, a challenging issue that is often not resolved in simulation models. Moreover, results also highlight that properly accounting for vapor pressure deficit changes is of a major importance when projecting forest responses to climate change, as it will strongly determine stand changes in productivity and water use efficiency. This thesis also highlights the importance of training simulation models from field observations, not only to describe ecophysiological processes, but also to obtain the most likely set of parameters providing "in situ" observations.

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Schmidt, Sebastian [Verfasser], Martin [Akademischer Betreuer] Sauter, and Heinz [Akademischer Betreuer] Hötzl. "Hydrogeological characterisation of karst aquifers in semi-arid environments at the catchment scale – Example of the Western Lower Jordan Valley / Sebastian Schmidt. Gutachter: Martin Sauter ; Heinz Hötzl. Betreuer: Martin Sauter." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2014. http://d-nb.info/1059004526/34.

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Ching, Suzanne Sadler. "Acoustic Emission and Environmental Monitoring of Two Natural Granite Boulders| Semi-Arid vs. Temperate Environment." Thesis, The University of North Carolina at Charlotte, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10814489.

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The role of insolation as an instigator for crack initiation in rock is still a continuously perplexing topic. An immense amount of data has been collected on the influence of insolation on cracking—however, ongoing questions arise regarding the role this process plays in physical weathering. A study conducted by Dr. Martha Cary Eppes (2016) focused on the role of insolation in the initiation of cracking on a granite boulder in a temperate climate (North Carolina, USA), where 11 months of continuously recorded acoustic emissions (AE) data were used as a proxy for cracking. When these data were compared with simultaneously collected climate and rock surface data, it was found that insolation is a preliminary and contributing factor of crack initiation. However, this comprehensive data set was only representative of one climate zone—therefore, it was necessary to evaluate this relationship in other climates to support these conclusions. The following is a comparative study involving a similar granite boulder placed for an unprecedented three-year period in a semi-arid climate (New Mexico, USA). Utilizing the instrumentation of the Eppes 2016 study, acoustic emission sensors, strain gages, thermocouples, moisture sensors, and a site-located scientific weather station were deployed and monitored. During the 3-year study, 303,912 AE events (avg. 101,304 per year) occurred over a total 14,853 individual minutes over 713 days. A total 212,856 events occurred between 12:58 p.m. and 9:04 p.m. accounting for 70% of the overall deployment period. Comparable to the results of the Eppes 2016 study, high-event days (≥ 50 events) accounted for 98% of total events. Both boulders experienced the majority of events in the northern hemisphere and eastern position of the rock and no trends were indicated concerning the timing of events with precipitation. The results of this study 1) support the hypotheses that diurnal insolation contributes to the initiation and continuation of physical rock weathering and cracking whether alone or combined with temperature variations, and 2) suggest that this is characteristic of variable global locations, climates, and rock types.

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Giacomelli, Gene, and Kathryn Hahne. "Evaporative Cooling in Semi-Arid Climates." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2008. http://hdl.handle.net/10150/146294.

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2 pp.
In the semi-arid climate of southern AZ, evaporative cooling systems are commonly used and very effective for cooling homes (swamp coolers), outdoor areas (misters), and for greenhouses used for commercial and horticultural plant production (pad-and-fan, high-pressure-fog). The purpose of this brochure is to educate users about strategies they can employ to save water and improve the performance of evaporative cooling systems. Principles of operation, a list of advantages and disadvantages, and a comparison of common systems is also included, to help users decide the best system for them.

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Sen, Omer Lutfi, and Omer Lutfi Sen. "Atmospheric Exchanges of Riparian Vegetation in a Semi-Arid Environment." Thesis, The University of Arizona, 1996. http://hdl.handle.net/10150/626826.

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The relationship between photosynthesis and transpiration from riparian vegetation in a semi-arid region is the primary focus of interest in this study. An eddy covariance system was used to measure fluxes of energy, momentum, and carbon over an extended period which included a monsoon season and a subsequent prolonged dry period. The photosynthetic portion of the measured CO2 flux was obtained by subtracting the mean value of nighttime CO2 flux (respiration) from the daytime CO2 flux, and the resulting photosynthesis estimates were then compared with transpiration and other variables. Because the data revealed a somewhat complex relationship between photosynthesis and transpiration on both an hourly and a daily basis, a further analysis was made involving both the calculation of the canopy conductance and a 'stand alone' version of the Simple Biosphere (SiB2) Model. The results showed the assumed relationship between canopy photosynthesis and canopy conductance used in SiB2 is inconsistent with observations, however Monteith's suggestion that the ratio of the CO2 concentration inside leaves to that outside leaves is approximately constant, which leads to a linear relationship between canopy conductance and photosynthesis, is consistent with observations.

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Abraham, Jennifer. "Stormwater Monitoring and Resident Behavior in a Semi-Arid Region." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/637.

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The combined effect of land-use alterations and introduced diffuse anthropogenic pollutants to the earth's surface in suburban/urban zones often sparks a decrease in stormwater quality in the area, and contributes to nonpoint source pollution in receiving waters. The ponds at the Utah Botanical Center (UBC) located in Kaysville, UT, regularly experience algal blooms, which in turn cause low dissolved oxygen levels in the waters, indicating high concentrations of inflowing pollutants. The goal of this thesis paper was to describe the findings from the water quality monitoring implemented at both the inlet and outlet of the UBC ponds in order to assess pollutant loading to the ponds. A survey was mailed to the homeowners in the drainage area with the intention of gaining a baseline understanding of residents' perceptions of stormwater issues, and their lawn care practices that might influence stormwater quality. Results from the weekly monitoring found that the TN, TP and TSS levels were all below respective medians reported for urban areas around the United States. Baseflow separation calculations revealed that 47% of inflow was due to precipitation falling onto the watershed and therefore 53% of inflow was a product of non-stormflow. With only 47% of the inflow coming from local runoff, potential effectiveness of educational efforts was considered minimal. Survey results reported that 86% of respondents had never received educational materials regarding stormwater. Second, fertilizer is used by 92.3% of respondents and in most cases, homeowners perform more than one application per year. Of the respondents, 98.1% of them believed that individual residents had an impact (positive or negative) on the quality of water resources in the area. No significant association was found between the education component of the survey and whether participants undertook certain stormwater-related behaviors.

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Yaraghi, N. (Navid). "Assessing the impacts of artificial groundwater recharge structures on river flow regime in arid and semi-arid regions." Master's thesis, University of Oulu, 2017. http://urn.fi/URN:NBN:fi:oulu-201709062799.

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In dry and semi-dry climate, Artificial Groundwater Recharge Structures are used for flood control and managed aquifer recharge. These damps basin runoff response decrease the maximum flows and increase the runoff duration through wet seasons. In this study, a framework to quantify the role of AGWRS in headwater tributaries on the total water balance of major basin and alteration of flow pattern in the main river has been presented. The study contains four main subroutines: rainfall-runoff model, reservoir flood routing, river analysis system and seepage analysis. The flood hydrographs with different return periods are estimated based on the climatic data and the characteristics of headwater basin. River flow analysis below the structure is carried out for two unsteady flow scenarios, first with the hydrographs of the natural system (as pre-impact: quick flood with significant peak flow) and second the altered flow hydrographs due to detention process in the reservoir (as post-impact: damped flood lower peak with longer duration time). Two sets of dynamic water surface along the river (from the location of detention structure (x=0) to the confluence point with the main river (x=L) are developed based on two hydrologic conditions as results of river analysis system. The results of framework define the impact of flood detention structure by comparing the timing, magnitude, and variability of flow. The Kamal Abad artificial groundwater recharge in Mahrlou Lake basin in Southern Iran was selected as case study to demonstrate the application of the created framework. Through the probability analysis, the return period for hydrological drought has been compared to the pre-impact and post-impact condition. The results clearly showed how embankments influence floods in tributaries and in some cases the flow reduced significantly and disappear in tributaries.

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Radulovic, Daniel John. "Biogeochemical investigation of the Mt. Gunson minesite and surrounding semi-arid environment /." Title page, contents and abstract only, 2002. http://web4.library.adelaide.edu.au/theses/09SB/09sbr132.pdf.

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Ng, Gene-Hua Crystal. "Probabilistic estimation and prediction of groundwater recharge in a semi-arid environment." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/46788.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 153-161).
Quantifying and characterizing groundwater recharge are critical for water resources management. Unfortunately, low recharge rates are difficult to resolve in dry environments, where groundwater is often most important. Motivated by such concerns, this thesis presents a new probabilistic approach for analyzing diffuse recharge in semiarid environments and demonstrates it for the Southern High Plains (SHP) in Texas. Diffuse recharge in semi-arid and arid regions is likely to be episodic, which could have important implications for groundwater. Our approach makes it possible to assess how episodic recharge can occur and to investigate the control mechanisms behind it. Of the common recharge analysis methods, numerical modeling is best suited for considering control mechanisms and is the only option for predicting future recharge. However, it is overly sensitive to model errors in dry environments. Natural chloride tracer measurements provide more robust indicators of low flux rates, yet traditional chloride-based estimation methods only produce recharge at coarse time scales that mask most control mechanisms. We present a data assimilation approach based on importance sampling that combines modeling and data-based estimation methods in a consistent probabilistic manner. Our estimates of historical recharge time series indicate that at the SHP data sites, deep percolation (potential recharge) is indeed highly episodic and shows significant interannual variability. Conditions that allow major percolation events are high intensity rains, moist antecedent soil conditions, and below-maximum root density. El Niño events can contribute to interannual variability of percolation by bringing wetter winters, which produce modest percolation events and provide wet antecedent conditions that trigger spring episodic recharge.
(cont.) Our data assimilation approach also generates conditional parameter distributions, which are used to examine sensitivity of recharge to potential climate changes. A range of global circulation model predictions are considered, including wetter and drier futures. Relative changes in recharge are generally more pronounced than relative changes in rainfall, demonstrating high susceptibility to climate change impacts. The temporal distribution of rainfall changes is critical for recharge. Our results suggest that increased total precipitation or higher rain intensity during key months could make strong percolation peaks more common.
by Gene-Hua Crystal Ng.
Ph.D.

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Toledo, Cristian EpifÃnio de. "Hydrological connectivity in semi-arid environment: case study of the OrÃs reservoir." Universidade Federal do CearÃ, 2013. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=11002.

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CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior
Para tentar auxiliar na resoluÃÃo do problema da seca, as decisÃes polÃticas priorizaram a construÃÃo de reservatÃrios, produzindo âredes de alta densidade de reservatÃriosâ na regiÃo Nordeste Brasileira. Via de regra, a construÃÃo de um reservatÃrio interrompe o fluxo natural do rio, interferindo, assim, na dinÃmica de Ãgua a jusante. Objetivou com esse trabalho estudar os processos envolvidos na conectividade hidrolÃgica, bem como a interferÃncia da rede de mÃltiplos reservatÃrios na conectividade hidrolÃgica de uma grande bacia semiÃrida. O estudo de caso Ã a bacia hidrogrÃfica do aÃude OrÃs â BHAO (24.211 km2), situada no SemiÃrido do CearÃ. A pesquisa foi iniciada com o levantamento da topologia da rede densa de reservatÃrio da BHAO, realizada utilizando tÃcnicas de sensoriamento remoto (SR), ferramentas de geoprocessamento (SIG) e imagem de satÃlite no fim do perÃodo chuvoso de 2011. A anÃlise da conectividade hidrolÃgica foi realizada usando o modelo âReservoir Network Modelâ (ResNetM), que simulou os processos hidrolÃgicos e considerou a conectividade hidrolÃgica entre os reservatÃrios, conforme os critÃrios estabelecidos nesta pesquisa. Na busca de se identificar os principais elementos naturais e antrÃpicos da bacia que afetam a conectividade hidrolÃgica, foi realizada uma anÃlise de sensibilidades (IS) de alguns parÃmetros de entrada do modelo, o que possibilitou avaliar o impacto da rede de reservatÃrios sobre o volume armazenado no aÃude OrÃs. O levantamento da rede de reservatÃrios com SR e ferramentas automÃticas de SIG demonstrou duas falhas: a interpretaÃÃo de sombras como reservatÃrios e a mÃ identificaÃÃo da superfÃcie da Ãgua real devido Ã presenÃa de macrÃfitas nos reservatÃrios. Desse modo, foram gerados automaticamente 6.002 polÃgonos, dos quais, apÃs ajuste manual, confirmaram-se, como reservatÃrios, apenas 4.717 polÃgonos (79%). A pesquisa constatou que, na Ãltima dÃcada, ocorreu um aumento de 17,5% no nÃmero de reservatÃrio da BHAO e que, nas regiÃes com embasamento cristalino, a densidade de reservatÃrios Ã 80% maior do que nas regiÃes sobre geologia sedimentar. A anÃlise de sensibilidade indicou que o nÃmero de reservatÃrio da rede foi a variÃvel Ã qual o sistema apresentou maior sensibilidade (IS = 1,07), considerando-se a conectividade hidrolÃgica. Contrariamente, a variaÃÃo da evaporaÃÃo (IS = 0,19) e da perda em trÃnsito (IS= 0,01) nÃo induziu a mudanÃas significativas da conectividade hidrolÃgica da BHAO. O volume armazenado no aÃude OrÃs nÃo sofreu mudanÃas significativas (IS = 0,21) ao se modificar a topologia da rede de reservatÃrio. Por exemplo, ao se simular a retirada dos pequenos e mÃdios reservatÃrios da rede (4.664, ou 98,9% dos reservatÃrios), o aÃude OrÃs indicou um acrÃscimo de apenas 14% em seu volume mÃdio armazenado. Com base nas observaÃÃes, concluiu-se que ocorreu uma reduÃÃo na taxa de incremento anual de reservatÃrios na BHAO nos Ãltimos 10 anos, o que marca o inÃcio da fase de estabilizaÃÃo da referida rede. Entre os elementos naturais avaliados, o coeficiente de escoamento superficial (natural) foi o que demonstrou maior significÃncia para a conectividade hidrolÃgica. Sua importÃncia deve-se ao fato de, no sistema natural da BHAO, raramente se observa escoamento de base significativo. Dos elementos antrÃpicos analisados, a rede densa de reservatÃrios, obteve a maior importÃncia para a conectividade hidrolÃgica. O motivo para esse comportamento Ã que os reservatÃrios promovem a laminaÃÃo da onda de cheia, aumentando o nÃmero de dias com vazÃo fluvial e, consequentemente, maior frequÃncia da conectividade hidrolÃgica. AlÃm disso, novos reservatÃrios diminuem o comprimento dos trechos a serem ligados, atenuando as perdas em trÃnsito e facilitando a ocorrÃncia da conectividade hidrolÃgica. A variaÃÃo da rede de reservatÃrio comprovou que, ao diminuir o nÃmero de reservatÃrio da rede, ocorre uma reduÃÃo na conectividade hidrolÃgica da BHAO, porÃm, nÃo altera significativamente a vazÃo afluente ao aÃude OrÃs, o exutÃrio da bacia deste trabalho. A rede densa de reservatÃrios provou que, no inÃcio do perÃodo chuvoso, atua como barreira Ã vazÃo fluvial, causando a quebra da conectividade hidrolÃgica. Com o passar do tempo e com a continuidade da precipitaÃÃo, os milhares de reservatÃrios favorecem a conectividade hidrolÃgica por meio da laminaÃÃo da onda de cheia.
Attempting to solve the drought problem, political decisions prioritized the construction of reservoirs, what eventually resulted in the construction of a "high density network of reservoirs" in the Brazilian Northeast. Usually, a reservoir interrupts the natural river flow, thus interfering in the water dynamics downstream. This work was aimed at studying the processes involved in the hydrological connectivity as well as the interference of multiple reservoirs in the hydrologic network connectivity of a large semiarid basin. The case study is the catchment area of the OrÃs - BHAO (24,211 km2 ) reservoir, located in Semiarid CearÃ. The research began with a survey of the BHAO dense reservoir network topology, conducted using remote sensing (RS), GIS tools (GIS) and satellite image at the end of the 2011 rainy season. The hydrological connectivity analysis was performed using the 'Reservoir Network Model' (ResNetM), which simulated hydrologic processes and considered the hydrological connectivity between the reservoirs, according to the criteria established in this research model. While seeking to identify the key natural and anthropogenic factors affecting the hydrological connectivity of the basin, an analysis of input sensitivity (IS) of some input parameters of the model was performed, this allowed us to evaluate the reservoir network impact on the stored volume on the OrÃs reservoir. The survey of the network of reservoirs with SR and automatic GIS tools showed two shortcomings: the misinterpretation of shadows as reservoirs and the misidentification of the actual water surface due to the macrophyte presence in reservoirs. Thus, of the 6,002 automatically generated polygons, only 4717 polygons (79%) were confirmed as reservoirs, after manual adjustment. The survey found that in the last decade, there was a 17.5% increase in the number of BHAO reservoirs and that, in regions with crystalline geology, the density of reservoirs is 80% higher than in regions of sedimentary geology. The sensitivity analysis indicated that the number of reservoirs in the network was the variable to which the system showed higher sensitivity (SI = 1.07), considering the hydrological connectivity. In contrast, the evaporation variation (SI = 0.19) and loss in transit (SI = 0.01) did not induce significant changes on BHAO hydrological connectivity. Also, the volume stored in the OrÃs reservoir showed no significant changes (SI = 0.21) when the reservoir network topology was modified. For example, when the removal of small and medium network reservoirs (4,664, or 98.9% of the reservoirs) was simulated, the OrÃs reservoir indicated an increase of only 14% in its average volume stored. Based on observations, it was concluded that there was a reduction in the rate of annual BHAO reservoir increment in the past 10 years, marking the beginning of the stabilization phase of the said network. Among the evaluated natural elements, it was the (natural) runoff coefficient which was demonstrated to have the most significance for the hydrological connectivity. Its importance is due to the fact that in the BHAO natural system, underground flow is infrequent. Of the human elements analyzed, the dense reservoir network, obtained the highest importance for hydrological connectivity. The reason for this is that the reservoirs promote the lamination of the flood wave, increasing the number of days with river flow and, consequently, increase the frequency of hydrological connectivity. In addition, new reservoirs decrease the length of the passages to be connected, reducing losses in transit and promoting hydrological connectivity. The variation of the reservoir network demonstrated that decreasing the number of network reservoirs, a decrease in BHAO hydrological connectivity occurs, not changing, however, significantly the inflow to the OrÃs reservoir, the convergence focus of the network. A dense reservoir network showed that, at the beginning of the rainy season, it acts as a barrier to river flow, breaking hydrological connectivity. Over time and with continued rainfall, the thousands of reservoirs promote hydrological connectivity by lamination of the flood wave.

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Lohmann, Dirk. "Sustainable management of semi-arid African savannas under environmental and political change." Phd thesis, Universität Potsdam, 2012. http://opus.kobv.de/ubp/volltexte/2013/6506/.

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Drylands cover about 40% of the earth’s land surface and provide the basis for the livelihoods of 38% of the global human population. Worldwide, these ecosystems are prone to heavy degradation. Increasing levels of dryland degradation result a strong decline of ecosystem services. In addition, in highly variable semi-arid environments changing future environmental conditions will potentially have severe consequences for productivity and ecosystem dynamics. Hence, global efforts have to be made to understand the particular causes and consequences of dryland degradation and to promote sustainable management options for semi-arid and arid ecosystems in a changing world. Here I particularly address the problem of semi-arid savanna degradation, which mostly occurs in form of woody plant encroachment. At this, I aim at finding viable sustainable management strategies and improving the general understanding of semi-arid savanna vegetation dynamics under conditions of extensive livestock production. Moreover, the influence of external forces, i.e. environmental change and land reform, on the use of savanna vegetation and on the ecosystem response to this land use is assessed. Based on this I identify conditions and strategies that facilitate a sustainable use of semi-arid savanna rangelands in a changing world. I extended an eco-hydrological model to simulate rangeland vegetation dynamics for a typical semi-arid savanna in eastern Namibia. In particular, I identified the response of semi-arid savanna vegetation to different land use strategies (including fire management) also with regard to different predicted precipitation, temperature and CO2 regimes. Not only environmental but also economic and political constraints like e.g. land reform programmes are shaping rangeland management strategies. Hence, I aimed at understanding the effects of the ongoing process of land reform in southern Africa on land use and the semi-arid savanna vegetation. Therefore, I developed and implemented an agent-based ecological-economic modelling tool for interactive role plays with land users. This tool was applied in an interdisciplinary empirical study to identify general patterns of management decisions and the between-farm cooperation of land reform beneficiaries in eastern Namibia. The eco-hydrological simulations revealed that the future dynamics of semi-arid savanna vegetation strongly depend on the respective climate change scenario. In particular, I found that the capacity of the system to sustain domestic livestock production will strongly depend on changes in the amount and temporal distribution of precipitation. In addition, my simulations revealed that shrub encroachment will become less likely under future climatic conditions although positive effects of CO2 on woody plant growth and transpiration have been considered. While earlier studies predicted a further increase in shrub encroachment due to increased levels of atmospheric CO2, my contrary finding is based on the negative impacts of temperature increase on the drought sensitive seedling germination and establishment of woody plant species. Further simulation experiments revealed that prescribed fires are an efficient tool for semi-arid rangeland management, since they suppress woody plant seedling establishment. The strategies tested have increased the long term productivity of the savanna in terms of livestock production and decreased the risk for shrub encroachment (i.e. savanna degradation). This finding refutes the views promoted by existing studies, which state that fires are of minor importance for the vegetation dynamics of semi-arid and arid savannas. Again, the difference in predictions is related to the bottleneck at the seedling establishment stage of woody plants, which has not been sufficiently considered in earlier studies. The ecological-economic role plays with Namibian land reform beneficiaries showed that the farmers made their decisions with regard to herd size adjustments according to economic but not according to environmental variables. Hence, they do not manage opportunistically by tracking grass biomass availability but rather apply conservative management strategies with low stocking rates. This implies that under the given circumstances the management of these farmers will not per se cause (or further worsen) the problem of savanna degradation and shrub encroachment due to overgrazing. However, as my results indicate that this management strategy is rather based on high financial pressure, it is not an indicator for successful rangeland management. Rather, farmers struggle hard to make any positive revenue from their farming business and the success of the Namibian land reform is currently disputable. The role-plays also revealed that cooperation between farmers is difficult even though obligatory due to the often small farm sizes. I thus propose that cooperation needs to be facilitated to improve the success of land reform beneficiaries.
Semiaride (halbtrockene) Savannen bedecken große Teile der Erdoberfläche und sichern die Lebensgrundlage von vielen Millionen Menschen. Die häufigste Form der Landnutzung in diesen Trockengebieten ist die Produktion von Vieh in extensiver Weidelandbewirtschaftung. In Folge klimatischer Veränderungen und als Konsequenz aus der teils intensiven Beweidung dieser Trockengebiete kommt es häufig zur Degradierung derselben in Form einer Zunahme von ‚unerwünschter‘ holziger Vegetation auf Kosten von futterverwertbaren Gräsern. Dieser als Verbuschung bezeichnete Prozess hat schwere negative Auswirkungen auf die betroffenen Ökosysteme und ist die Ursache für einen zunehmenden Rückgang der ökonomischen Leistungsfähigkeit der betroffenen Betriebe. In meiner Dissertation befasse ich mich mit den Auswirkungen von Klimawandel und politischen Veränderungen auf die Savannenvegetation im südlichen Afrika und auf die Möglichkeiten für die Nutzung dieser Ökosysteme in Form von Viehwirtschaft. Hierbei möchte ich sowohl das allgemeine Verständnis der ökologischen Zusammenhänge verbessern, als auch Strategien für die nachhaltige Nutzung der Savannen identifizieren und bewerten. Da nicht nur ökologische, sondern auch ökonomische und politische Einflussfaktoren, wie zum Beispiel die umfangreichen Landumverteilungen im Rahmen der Bodenreform im südlichen Afrika auf die tatsächliche Landnutzung wirken, habe ich im Rahmen der Dissertation zudem untersucht, nach welchen Umwelt und Kapitalvariablen sich die Farmer, welche Ihr Land im Rahmen der Bodenreform zugeteilt bekommen haben, bei Ihren Entscheidungen richten. Methodisch verwende ich verschiedene Simulationsmodelle, welche zur Untersuchung der langfristigen Veränderungen von verschiedensten Szenarien (Klimawandel, Landnutzung) geeignet sind. Hierbei habe ich teilweise bestehende Modelle angepasst, aber auch ein neues Modell, welches zur Befragung von Farmern in Namibia verwendet wurde, entwickelt. Meine Dissertation führt im Wesentlichen zu vier Erkenntnissen: Erstens, zeigen meine Ergebnisse, welche große Bedeutung die spezifischen ökologischen Eigenschaften der Bäume und Sträucher in semiariden Savannen für die Vorhersage der Entwicklung dieser Systeme unter Klimawandel hat. Hierbei zeigte sich, dass insbesondere die Sensitivität der Keimlinge gegenüber Trockenheit und Feuer eine entscheidende Rolle spielt. Daraus folgt die zweite wesentliche Erkenntnis: Feuer eignet sich in herausragender Weise, um halbtrockene Savannen vor der Verbuschung zu bewahren. Drittens haben die Rollenspiele mit Farmern in Namibia gezeigt, dass deren Entscheidungen im Wesentlichen von finanziellen Schwierigkeiten und nicht von Umwelteinflüssen getrieben werden. Dennoch zeigten meine Ergebnisse, dass diese Farmer mit Ihrem derzeitigen Verhalten wahrscheinlich nicht zur weiteren Degradierung der Savannenvegetation beitragen. Die vierte, und mit am bedeutendste Erkenntnis aus meiner Arbeit ist, dass konservative Beweidungsstrategien mit geringen und konstanten Viehdichten notwendig sind um semiaride Savannen dauerhaft in ökologisch und ökonomisch nachhaltiger Weise zu Nutzen.

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34

Murdoch, Fiona University of Ballarat. "Restoration ecology in the semi-arid woodlands of north-west Victoria." University of Ballarat, 2005. http://archimedes.ballarat.edu.au:8080/vital/access/HandleResolver/1959.17/12794.

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Arid areas are often overgrazed and dysfunctional with poor recruitment of desirable species, diminished control over resources and altered soil properties. Restoration ecology re-establishes these valued processes. State-and-transition models summarise knowledge of vegetation dynamics and tools for restoration, and encourage the incorporation of new information. The model developed here for semi-arid woodlands of north-west Victoria highlighted the unknown cause of observed, natural recruitment and the need for a technique, other than direct seeding and handplanting, for enhancing the recruitment of desirable species. I pursued these knowledge gaps for two dominant, woodland trees: Allocasuarina luehmannii and Casuarina pauper. Natural recruitment of juvenile C. pauper was found to be limited and primarily from root suckers. Extensive recruitment of A. luehmannii was shown to be mostly seedlings established following substantial reductions in grazing pressure since 1996. Seedlings were associated with areas devoid of ground flora near a female tree. The importance of competition between seedlings and ground flora, spatial variation in soil moisture and individual variation in the quantity of seed produced deserves further investigation to enhance future restoration success. Root suckers of both C. pauper and A. luehmannii can be artificially initiated, albeit in low numbers and this was found to be a feasible, new tool for restoration. Suckers are preceded by the growth of callus tissue on exposed or damaged, living, shallow roots. Both male and female trees can produce suckers and spring treatments may be more successful. Genetic fingerprinting of mature A. luehmannii and C. pauper trees in six populations did not identify any clonal individuals indicating that recruitment in the past has been from seedlings. Despite this, the high level of gene flow suggests that the impact of introducing small numbers of root suckers into existing populations is unlikely to impact negatively on the population genetics of these species.
Doctor of Philosophy

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Murdoch, Fiona. "Restoration ecology in the semi-arid woodlands of north-west Victoria." University of Ballarat, 2005. http://archimedes.ballarat.edu.au:8080/vital/access/HandleResolver/1959.17/14630.

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Arid areas are often overgrazed and dysfunctional with poor recruitment of desirable species, diminished control over resources and altered soil properties. Restoration ecology re-establishes these valued processes. State-and-transition models summarise knowledge of vegetation dynamics and tools for restoration, and encourage the incorporation of new information. The model developed here for semi-arid woodlands of north-west Victoria highlighted the unknown cause of observed, natural recruitment and the need for a technique, other than direct seeding and handplanting, for enhancing the recruitment of desirable species. I pursued these knowledge gaps for two dominant, woodland trees: Allocasuarina luehmannii and Casuarina pauper. Natural recruitment of juvenile C. pauper was found to be limited and primarily from root suckers. Extensive recruitment of A. luehmannii was shown to be mostly seedlings established following substantial reductions in grazing pressure since 1996. Seedlings were associated with areas devoid of ground flora near a female tree. The importance of competition between seedlings and ground flora, spatial variation in soil moisture and individual variation in the quantity of seed produced deserves further investigation to enhance future restoration success. Root suckers of both C. pauper and A. luehmannii can be artificially initiated, albeit in low numbers and this was found to be a feasible, new tool for restoration. Suckers are preceded by the growth of callus tissue on exposed or damaged, living, shallow roots. Both male and female trees can produce suckers and spring treatments may be more successful. Genetic fingerprinting of mature A. luehmannii and C. pauper trees in six populations did not identify any clonal individuals indicating that recruitment in the past has been from seedlings. Despite this, the high level of gene flow suggests that the impact of introducing small numbers of root suckers into existing populations is unlikely to impact negatively on the population genetics of these species.
Doctor of Philosophy

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36

Scoging, Helen Mary. "A theoretical and empirical investigation of soil erosion in a semi-arid environment." Thesis, London School of Economics and Political Science (University of London), 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308942.

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This thesis is concerned with soil erosion from hillslopes in semi-arid Spain. It approaches the problem f rom three related angles which are reflected in its structure: Part 1: The literature is evaluated to determine the current conceptual understanding of the processes of soil erosion, and the organisation of those concepts and evidence from field and laboratory studies into predictive models of the major processes of erosion - rainfall dynamics, rainsplash, infiltration and runoff generation, runoff routing and wash erosion mechanics. Part 2: A field study of the major factors of erosion and their results is conducted over two field seasons for four experimental hilislope sites in southern Spain, and provides detailed information on the spatial and temporal patterns of erosion and their controls. Four main contextual variables are analysed - topography, vegetation cover, surface sediments (soil and coarse fraction) and micro-topographic roughness. The results from four process experiments are presented - infiltration from ponded and simulated rainfall experiments; runoff generation and soil loss from fifty microplot rainfall simulations; natural storm runoff and erosion losses from sub-site plots situated at the midpoint and base of each site; and seasonal and annual patterns of ground surface change derived from soil pin data. Part 3: Concern is with the development of selected erosion process simulation models. These include - the stochastic generation of a temporally nested rainfall series (yield, intensity, duration of wet and dry periods) for the annual/seasonal distribution of daily rainfall, and, subject to threshold criteria, the hourly pattern of storms within a day; an infiltration-runoff generation model based on a modified Green and Ampt (1911) infiltration equation, which predicts time to runoff, volume of pre-saturation soil storage, and runoff volumes. The latter are routed across plots according to an algorithm which determines potential flow lines in three dimensional space. A finite difference kinematic flow model using the Manning flow equation is developed and calibrated from microplot data; finally an erosion model developed from the prototype of Meyer and Wischmeier (1969) predicts spatial and temporal variability of erosion from hillslopes. Major changes to the original model include three-dimensional space and contour curvature, dynamic modelling of flow generation and routing, and physically based detachment and transport mechanics of overland flow. The thesis is divided into two volumes - Volume I comprises the text arranged into three parts. Volume II, for ease of reference, presents supporting and background material, which may be read in parallel with Volume I, and includes Appendices of raw data, results of data analysis, computer programs and simulation results; a list of symbols by chapter; a set of photographic plates, and a full bibliography.

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Cory, Toussaint Dawn. "Thermoregulation in three southern African bat species inhabiting a hot, semi-arid environment." Diss., University of Pretoria, 2012. http://hdl.handle.net/2263/24646.

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Bats inhabiting arid, subtropical environments face diverse challenges related to energy and water balance. First, they may have to conserve water and energy during cool, dry winters when water is scarce and insect availability reduced. Second, during hot summers when air temperature may routinely exceed body temperature, bats may need to avoid both hyperthermia and dehydration. A common response to the energetically challenging winter period in temperate, subtropical and tropical species is heterothermy (i.e. torpor and hibernation). Despite evidence suggesting that heterothermy is of major significance in the energy balance of tropical and subtropical bats, its occurrence in southern African species especially those in semi-arid subtropical regions have received relatively little attention. Moreover, the physiological and thermoregulatory responses of bats to high air temperatures (Ta) are relatively poorly known. The goal of my project was to investigate various seasonal physiological challenges imposed on bats in an arid, sub-tropical climate. I investigated the occurrence of winter heterothermy in Nycteris thebaica (Nycteridae) in the Limpopo Valley. Skin temperatures (Tskin) were measured using temperature-sensitive transmitters, and roost temperatures (Troost) were recorded using miniature temperature loggers. N. thebaica used multiple roosting sites, including a hollow baobab tree (Adansonia digitata) and several caves, and exhibited only moderate heterothermy. Tskin was maintained around normothermic levels, with differences of 3-9°C (7.5±1.7°C) between overall maximum and minimum Tbs. A minimum Tskin of 28.4°C occurred at Troost = 23.8°C, and patterns of thermoregulation did not appear to be influenced by prevailing weather conditions. Roost temperatures did not decrease below 10°C, and averaged 21.2±2.8°C and 23.3±2.9°C respectively. The lack of pronounced heterothermy in N. thebaica is surprising, particularly in view of the daily torpor cycles observed in many insectivorous bat species. I also investigated the physiological responses of three sympatric bat species during summer using an open-flow respirometry system to measure resting metabolic rates (RMR) and evaporative water loss (EWL) over a range of Tas ~ 10-42°C, with body temperatures (Tb) simultaneously recorded via temperature-sensitive passive integrated transponder (PIT) tags. Basal metabolic rates for Nycteris thebaica and Taphozous mauritianus were 8.9±2.7mW.g-1 and 6.6±2.2mW.g-1 respectively, falling within the 95% prediction intervals for bat BMR, whereas the value for Sauromys petrophilus (3.4±0.6mW.g-1) fell below the lower 95% prediction interval. Maximum EWL for N. thebaica, T. mauritianus and S. petrophilus were 18.6±2.1mg.g-1.h-1 (Ta=39.4°C), 14.7±3.1mg.g-1.h-1 (Ta=41.9°C) and 23.7±7.4mg.g-1.h-1 (Ta=41.7°C) respectively. Maximum individual Tbs recorded were 46.5°C in N. thebaica (Ta=39.3°C), 44.9°C in T. mauritianus (Ta=41.8°C) and 46.5°C in S. petrophilus (Ta=41.7°C). Overall, I found that N. thebaica was the least heat tolerant species, with T. mauritianus and S. petrophilus being more heat tolerant. In the face of climate change, heat tolerance together with specific thermal properties of a given roost may play a major role in the ability of a species to persist in a hot, arid environment.
Dissertation (MSc)--University of Pretoria, 2012.
Zoology and Entomology
unrestricted

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Bahteamy, Ayman Eliewa Elsayed Abdelhamid [Verfasser]. "Spaceborne SAR Remote Sensing for Monitoring of Vegetation Dynamics in Arid and Semi-arid Environment / Ayman Eliewa Elsayed Abdelhamid Bahteamy." Bonn : Universitäts- und Landesbibliothek Bonn, 2020. http://d-nb.info/1208937448/34.

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39

Stone, Rosemary Jane. "Radar remote sensing of a semi-arid environment : a case study in central Tunisia." Thesis, Durham University, 1988. http://etheses.dur.ac.uk/6632/.

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This work examines the potential of spaceborne microwave remote sensing for the discrimination and analysis of morphological and surface cover-features in semi-arid Tunisia. The study area in central Tunisia comprises a region of overlap between two satellite radar passes: namely Seasat and SIR-A. This allows the influence of two different radar depression angles, look directions and resolutions upon image appearance to be determined. Botn these systems operated at a wavelength of 23cm and hence the characteristic responses of semi-arid surfaces at this wavelength are assessed. This is achieved through visual and digital image interpretation and discriminant analysis of image data. As SIR-A data is available only in optical format, the image had to be digitised before digital image processing could be undertaken. Several radiometric and geometric pre-processing procedures have to be accomplished. Despite the time-lag and calibration difficulties involved, the dominant ground controls on radar backscatter are identified through statistical analysis of information collected in the field. Surface relief, feature geometry and surface roughness are the most important parameters for both systems. The difference in depression angle causes relief information to dominate the Seasat image, while roughness information dominates the SIR-A image. The availability of Landsat Thematic Mapper data for part of the SIR-A swath west of the coastal study area provides a valuable opportunity to assess the complementary nature of data from the visible, infra-red and microwave parts of the electromagnetic spectrum. This is examined through digital and statistical analysis of image data. In the mountain environments, slope angle and aspect are found to be the dominant parameters influencing SIR-A backscatter through their effect on local radar incidence angle. The special quality of radar is its sensitivity to relief and roughness information. This is exploited in a number of applied studies that assess the contributions of radar to environmental management in semi-arid areas. Finally, recommendations are made for future research in the light of the multi-parameter radar systems due to be launched in the 1990s.

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40

Aralova, Dildora, Kristina Toderich, Ben Jarihani, Dilshod Gafurov, Liliya Gismatulina, Babatunde A. Osunmadewa, and Abualgasim Majdaldin Rahamtallah. "Environmental resilience of rangeland ecosystems: Assessment drought indices and vegetation trends on arid and semi-arid zones of Central Asia." SPIE, 2016. https://tud.qucosa.de/id/qucosa%3A35118.

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The Central Asian (CA) rangelands is a part of the arid and semi-arid ecological zones and spatial extent of drylands in CA (Tajikistan, Kazakhstan, Uzbekistan, Kyrgyzstan, and Turkmenistan) is vast. Projections averaged across a suite of climate models, as measured between 1950-2012 by Standardised Precipitation-Evapotranspiration Index (SPEI) estimated a progressively increasing drought risks across rangelands (Turkmenistan, Tajikistan and Uzbekistan) especially during late summer and autumn periods, another index: Potential Evapotranspiration (PET) indicated drought anomalies for Turkmenistan and partly in Uzbekistan (between 1950-2000). On this study, we have combined a several datasets of drought indices ( SPIE, PET, temperature_ToC and precipitation_P) for better estimation of resilience/non-resilience of the ecosystems after warming the temperature in the following five countries, meanwhile, warming of climate causing of increasing rating of degradations and extension of desertification in the lowland and foothill zones of the landscape and consequently surrounding experienced of a raising balance of evapotranspiration (ET0). The study concluded, increasing drought anomalies which is closely related with raising (ET0) in the lowland and foothill zones of CA indicated on decreasing of NDVI indices with occurred sandy and loamy soils it will resulting a loss of vegetation diversity (endangered species) and raising of wind speeds in lowlands of CA, but on regional level especially towards agricultural intensification (without rotation) it indicated no changes of greenness index. It was investigated to better interpret how vegetation feedback modifies the sensitivity of drought indices associated with raising tendency of air temperature and changes of cold and hot year seasons length in the territory of CA.

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41

Sivandran, Gajan. "The role of rooting strategies on the eco-hydrology of semi-arid regions." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/70762.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 193-205).
Arid regions are characterized by high variability in the arrival of rainfall, and species found in these areas have adapted mechanisms to ensure the capture of this scarce resource. In particular, the rooting strategies employed by vegetation can be critical to their survival. However, land surface models currently prescribe rooting profiles as a function of only the plant functional type of interest with no consideration for the soil texture or rainfall regime of the region being modeled. Additionally, these models do not incorporate the ability of vegetation to dynamically alter their rooting strategies in response to transient changes in environmental forcings or competition from other plant species, and therefore tend to underestimate the resilience of these ecosystems. To address the simplicity of the current representation of roots in land surface models, a new dynamic rooting scheme was incorporated into the framework of the distributed ecohydrologic model tRIBS+VEGGIE. The new scheme optimizes the allocation of carbon to the root zone to reduce the perceived stress of the vegetation, so that root profiles evolve based upon local climate and soil conditions. The strength of this scheme lies in its ability to optimize the rooting profile in a computationally-efficient manner, without requiring additional parameterization by the model user. The ability of the new scheme to capture the complex dynamics of natural systems was evaluated by comparisons to hourly-timescale energy flux, soil moisture and vegetation growth observations from the Walnut Gulch Experimental Watershed, Arizona. Very good agreement was found between the model and observations, providing confidence that the improved model is able to capture the multidirectional interactions between climate, soil and vegetation at this site. The power of the new scheme was demonstrated through simulation of observed forms of within-hillslope vegetation patterning and the model's ability to represent competition-colonization dynamics between different plant functional types under non-equilibrium conditions.
by Gajan Sivandran.
Ph.D.

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Ivanov, Valeri Yuryevich 1974. "Effects of dynamic vegetation and topography on hydrological processes in semi-arid areas." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/34613.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006.
Includes bibliographical references (p. 425-453).
Ecosystems of dry climates represent a particularly interesting object for ecohydrological studies, as water is generally considered to be the key limiting resource. This work focuses on vegetation-water-energy dynamics occurring in the complex terrain of a semi-arid area characteristic of central New Mexico. The study constructs a dynamic model of coupled interactions, [tRIBS+VEGGIE], that considers essential water and energy processes over the river basin and links them to the basic plant life regulatory processes. After model calibration, a set of numerical experiments is carried out for two small-scale synthetic domains that exhibit characteristic hillslope curvatures. A weather generator is used to create the long-term series of meteorological forcing. The linkages between terrain attributes and patterns of C4 grass productivity and water balance components are examined for three generic soil types: sand, loam, and clay. It is argued that in conditions of negligible moisture exchange, site aspect and slope are the key determinants of both the hydrologic behavior and the degree of "favorability" to vegetation.
(cont.) As shown, certain topographic locations are more favorable to vegetation development, as compared to a flat horizontal surface not affected by lateral effects such as radiative shading or water transfer. These locations are associated with sites of northerly aspect with surface slopes within a narrow range of magnitudes. Contributions from both the rainfall and radiation forcings are discussed to explain the existence of these niches. The sensitivity of results is investigated relative to modifications in the meteorological forcing and the dominant mechanism of lateral water transfer. The analysis unequivocally demonstrates the critical role of soil texture type in regulating the spatio-temporal aspects of coupling between vegetation-hydrology processes. Two additional controlling topographic features are suggested, corresponding to the local and global terrain convergence levels. Furthermore, it is argued that grass productivity and water fluxes of a site can be characterized as a function combining local and global terrain properties.
by Valeriy Yuryevich Ivanov.
Ph.D.

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Harrington, Rhidian. "The effects of artificial watering points on the distribution and abundance of avifauna in an arid and semi-arid mallee environment." Connect to this title online, 2002. http://repository.unimelb.edu.au/10187/2874.

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The role of artificial watering points in the avifaunal dynamics of the semi-arid mallee woodlands of southeast Australia was examined. Species richness and abundance were monitored throughout the year at different distances from water to determine how birds were distributed around water points and how this changed in relation to environmental factors such as climate. Vegetation attributes were also measured to determine which factors explained patterns in the avifauna with distance from water, and also to allow a description of the vegetation in relation to the water points. Water points were monitored throughout the year to determine which species were utilising them, under which environmental circumstances and for what purposes. Knowledge of the water utilisation behaviour of individual bird species allowed some explanation of their distribution patterns, as well as an ability to predict the likely effects of water point closure on those bird species. The closure of two water points during the study allowed an assessment of the immediate effects of water point closure on avifauna (For complete abstract open document)

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Snyder, Keirith Ann. "Environmental and physiological controls on water source use by semi-arid riparian tree species." Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/279782.

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A general paradigm in semi-arid and arid systems is that woody plants with dimorphic root systems will exhibit preferential use of deeper soil water because it represents a more stable source of water than short duration pulses of shallow soil moisture derived from summer rainfall. However, whether this holds across all woody species and whether use of deeper soil water interacts with use of shallow soil water is not determined for many species in different ecosystems. Understanding the amount of water plants derive from groundwater and shallow soil water is critically important to accurate calculations of local and regional water balance. The focus of this research was to determine if dominant woody species in semi-arid riparian ecosystems used shallow soil water and how depth to groundwater and defoliation might affect root proliferation and water uptake. This research found that the functional grouping "phreatophytes" encompasses a variety of responses to environmental variation. Stable isotopic analyses determined that Prosopis velutina Woot. (Velvet mesquite) and Populus fremontii Wats. (Fremont cottonwood) used shallow soil water derived from summer rainfall, and the proportion of shallow soil water was higher at sites with greater depth to groundwater. In contrast Salix gooddingii Ball (Goodding willow) did not use shallow soil water at any location regardless of depth to groundwater. Field experiments using defoliation treatments, to limit carbon assimilation and reduce plant photosynthate pools, confirmed that Prosopis velutina exhibited flexible response in water uptake patterns in response to defoliation. Defoliation, which presumably reduced available photosynthate, increased the reliance of this species on shallow soil water; contrary to predictions that woody species should maintain extensive deep root systems to buffer themselves from seasonal drought. Greenhouse experiments with Populus fremontii and Prosopis velutina also indicated changes in belowground biomass of fine roots, which were associated with changes in water-source use for Populus fremontii, but not for Prosopis velutina. These results imply that in terms of predicting plant response to changes in future climates, or modeling fluxes of water from the soil to the atmosphere that are largely controlled by plant transpiration, intra- and interspecific variability will need to be considered.

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Hogue, Terri S. "A multi-criteria evaluation of land-surface models and application to semi-arid regions." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/289890.

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Soil-Vegetation-Atmosphere-Transfer Schemes (SVATS) are used in global climate studies to simulate and help understand the complex interactions between the climate and the biosphere. There currently exists a multitude of SVATS of varying complexity differing in terms of the modeled physics and the manner and sophistication with which the processes are represented. This analysis uses systems-based multi-criteria techniques to investigate the performance and sensitivity of various SVATS and their parameters. Results indicate that, once complexity reaches a certain level, incorporating more physics does not necessarily result in improved simulations or reduced errors and that several parameters in the models are insensitive regardless of the input data (i.e., vegetation type). To better understand SVATS performance in semi-arid regions, and to evaluate the various impacts of data on the parameter estimation problem, an intensive calibration and validation study is undertaken. Findings show that calibrated parameters result in improved performance over default, proxy site parameters result in similar performance for many time periods, and there is a need to include wet periods with elevated latent heat to capture the variability of climatic conditions such as the monsoon and El Nino winters. Last, a preliminarily investigation of the performance of the BATS2 model is undertaken to evaluate the capabilities to simulate carbon (along with energy and water) fluxes in semi-arid regions. Results show poor performance for carbon flux simulations and that improvements are needed to better represent C4 vegetation for semi-acid regions. Future research will be directed toward integrated modeling (carbon, energy, and water) in semi-arid regions.

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Ladbrook, Megan. "Spatial and temporal patterns (1973-2012) of bushfire in an arid to semi-arid region of Western Australia." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2015. https://ro.ecu.edu.au/theses/1660.

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Aim and background The aim of this study was to reconstruct fire regimes/history of an extensive arid to semi-arid region of Western Australia for the last 40 years by studying temporal and spatial fire scar patterns using remote sensing in a Geographic Information System environment. Methods A fire history database was constructed, for the years 1973-2012 of an area of Western Australia between the Murchison and Minilya Rivers, of all bushfires greater than 1 ha that were visible from Landsat satellite imagery ranging from 30 – 60m ground resolution. The data was analysed to characterise a general bushfire regime for the region which included: mean and median size of fire scars; range and mean count of bushfire numbers; and the effect that land-systems, vegetation types/structures, land tenure and climate had on the bushfire regime. The 82 land-systems were grouped into 4 main land types and the 141 vegetation types were grouped into 7 vegetation groups and 7 vegetation structural groups. The percentages of areas burnt were calculated and a correlation coefficient was calculated between total area and total area burnt for each variable within the study area. Land tenure was divided into 3 types and two discrete areas in the northern study area were compared to determine if land tenure had an impact on fire regimes. To assess the effect climate had on the bushfire extent I calculated their correlation to both cumulative rainfall and mean maximum temperature. A generalised linear model was used to determine which climatic variables impacted on the bushfire regime. Results A total of 23.8% of the total study area burnt during the study period. The individual fire scars ranged from4000 km2. The frequency of fires ranged from 10-40+ years across the different vegetation types. The land type that burnt the most extensively in both the southern and northern study areas was Sandplains/coastal (southern — 16.6%; northern — 57%). The land type that burnt the least extensively in the southern study area was Alluvial/plains with eucalypts/claypans group (2.3%), and in the northern study area it was the Hills/mesas group (~1%). The Heathland vegetation (54%) burnt the most extensively in the southern study area and Hummock grassland (68%) in the northern. The northern study area had a greater variety of vegetation groups that burnt than the southern area (northern — 37; southern — 22). The Acacia Shrubland vegetation group contained the greatest number of fire fronts that stopped shortly after burning into this group. Only Shrub and Mallee structural groups burned in the southern study area (grass, tree, samphire shrub, chenopod shrub and bare did not burn); all structural groups except Mallee burnt in the northern study area. Two regions in the northern study area with structurally similar vegetation showed some differences in fire frequency when grazing activity by feral goats was restricted vs. unrestricted, though there was insufficient data for statistically relevant findings. The variables retained in the generalised linear models of fire extent were; rain in the previous two years to year of fire (positive relationship) and rain in the previous three years to fire (negative relationship) for the northern study area, and number of annual days over 35°C (positive relationship), rain in the year of fire (negative relationship) and rain in the three years prior to fire (positive relationship) in the southern study area. Conclusions Bushfire size distribution and frequency are comparable to other regimes in similar climates; however on average they tended to be larger. Infrequent, extensive (>4000 km2) bushfires can skew the statistics since the area burnt contributes to mean values to a greater degree as the individual fires get larger. Such large fires are strongly linked to 2 year antecedent above average rainfall episodes, especially in the northern study area and particularly when pluvial periods are followed by droughts and above-average temperatures. The extent of a bushfire is partially dependent on vegetation type and structure, and land-system. More research needs to be undertaken to see how much of an influence (if any) grazing practices leads to difference in bushfire regimes. Predicted future changes in climate may lead to more frequent and higher intensity bushfires in the study area. This research furthers the understanding of bushfire regimes in arid Western Australia. It also contributes to expanding current knowledge of bushfires in an arid Acacia shrubland ecosystem and it should improve predictions and management of bushfires in these extensive regions of Australia.

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Keswick, Tobias. "Ecology and morphology of the Kalahari tent tortoise, Psammobates oculifer, in a semi-arid environment." Thesis, University of the Western Cape, 2012. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_6549_1355385737.

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Southern Africa harbours one-third of the world&rsquo
s Testudinid species, many of which inhabit arid or semi-arid areas, but ecological information on these species is scant. I studied the habitat, morphology and ecology of Kalahari tent tortoises over 13 months in semi-arid Savanna at Benfontein farm, Northern Cape Province, South Africa. In order to allow continuous monitoring of individuals, I attached radiotransmitters to males and females, split equally between two habitats, sites E (east) and W (west), with apparent differences in vegetation structure. Results of the study were based on data obtained from 27 telemetered tortoises and 161 individuals encountered opportunistically. Female Kalahari tent tortoises were larger than males and the sex ratio did not differ from 1:1. Based on person-hours to capture tortoises, the population appeared to have a low density, with more time required to capture a juvenile (35 hours) than an adult (10-11 hours). The frequency distribution of body size ranges was indicative of recruitment. Relative age, based on annuli counts, suggested that males were younger than females, perhaps because males as the smaller sex are more predation-prone than females. Linear relationships between annuli counts and shell volume indicated that, after reaching sexual maturity, female body size increased faster in volume than did male body size, possibly because a larger volume may enhance female reproductive success. Body condition differed between sites, sexes and among seasons. The hot and dry summer may account for low summer body condition, whereas vegetation differences and size effects, respectively, may account for the low body condition of tortoises in site W and in males. Site E was sandy with grasses, particularly Schmidtia pappophoroides, being the prevalent growth form. This habitat resembled a Savanna vegetation type Schmidtia pappophoroides &ndash
Acacia erioloba described for a neighbouring reserve. Site W was stonier, dominated by shrubs, and was reminiscent of Northern Upper Karoo vegetation (NKu3). Neither site resembled Kimberley Thornveld (SVk4), the designated vegetation type of the area. Differences in substrate and grazing intensity may have contributed to site vegetation differences. Rainfall had an important influence on seasonal vegetation. Short grass abundance correlated with rainfall and annual plants sprouted after spring rain. Refuge use changed according to season and sex. Males selected denser refuges than females did, perhaps because males were smaller and more vulnerable to predation and solar heat. Tortoises selected sparse, short grass as refuges in cool months, probably to maximise basking whilst remaining in protective cover. During hot periods, mammal burrows were preferred to vegetation as refugia. The smaller males spent more time in cover than females, which may be related to predator avoidance or thermoregulation.
Females spent more time basking than males, perhaps due to their larger size and to facilitate reproductive processes. Tortoises did not brumate, but through a combination of basking, and orientation relative to the sun in their refuges, managed to attain body temperatures that allowed small bouts of activity. Body temperature for active tortoises was similar among seasons, and was higher for more specialised active behaviours, such as feeding and socialising, than for walking. Increased activity by males in spring could relate to mating behaviour while females were more active in autumn, when they foraged more than males, perhaps due to the high cost of seasonal reproductive requirements. Males displaced further per day than did females, but home range estimates did not differ between sexes. Annual home range estimates varied substantially among individuals: 0.7&ndash
306 ha for minimum convex polygons and 0.7&ndash
181 ha for 95% fixed kernel estimates. The ability to
cover large areas would assist tortoises in finding resources, e.g., food, in an area where resource distribution may be patchy. Differences among seasonal home ranges and movements probably reflect seasonal climatic change
activity areas shrinking when temperatures were extreme. In order to assess the effects of a semi-arid environment on the morphology of P. oculifer, I compared its morphology to that of its &lsquo
cool-adapted&rsquo
sister taxon Psammobates geometricus, using live and museum specimens. Both P. oculifer and P. geometricus are sexually dimorphic and differences between the two species could indicate environmental or sexual selection effects, or a combination of the two. The shorter bridge length, which allowed more leg space, and wider front feet in P. oculifer cohorts probably represent traits for manoeuvring in a sandy habitat, while wider heads in P. oculifer possibly relate to interspecific differences in diet. The flatter shell in female P. oculifer, relative to P. geometricus, may represent a trade-off between space for reproductive structures, e.g., eggs, and the need to fit into small refuges, e.g., mammal burrows. Male P. oculifer had wider shells, more space around their hind legs, and wider hind feet than P. geometricus males had, all characteristics which may assist males to fight and mate in a sandy environment.

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Rahman, Mohammed Magfurar. "MAPPING SURFACE SOIL MOISTURE AND ROUGHNESS BY RADAR REMOTE SENSING IN THE SEMI-ARID ENVIRONMENT." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1193%5F1%5Fm.pdf&type=application/pdf.

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49

Chen, Heyin. "Simulating the hydrologic impacts of land cover and climate changes under a semi-arid environment." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1384426212.

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50

Bunnell, Michael Cameron. "Water Use of Four Commonly Planted Landscape Tree Species in a Semi-Arid Suburban Environment." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/6146.

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Native plant communities and agricultural land are commonly converted to urban areas as cities across the Western United States continue to grow and expand. This expansion is typically accompanied by afforestation where a common goal among communities is to maximize shade tree composition. Planted forests in these regions are commonly composed of introduced tree species native to mesic environments and their ability to persist is dependent on consistent irrigation inputs. Many potential ecosystem services may be derived from planting trees in urban and suburban areas; however, there are also costs associated with extensive afforestation, and shade tree cover may have significant implications on municipal water budgets. In this study I evaluate variation in daily and seasonal water use of regionally common suburban landscape tree species in the Heber Valley (Wasatch County, Utah). I had two primary objectives: (1) to identify and understand the differences in transpiration between landscape tree species in a suburban setting and (2) to assess the sensitivity of sap flux and transpiration to variation in vapor pressure deficit, wind speed, and incoming shortwave radiation. I used Granier's thermal dissipation method to measure the temperature difference (ΔT) between two sap flux probes. The empirical equation developed by Granier was used to convert ΔT into sap flux density (Jo) measurements, which were then scaled to whole-tree transpiration. There were consistent and substantial differences in sap flux between tree species. I found that Picea pungens under irrigated growing conditions, on average, had Jo rates that were 32% greater and whole tree water use (ET) rates that were 550% greater than all other species studied. The findings of Jo may be partially explained by xylem architecture and physiological control over stomatal aperture. However, the rate of water flux in the outermost portion of sapwood does not necessarily determine the magnitude of whole tree transpiration. Rather, ET in this study was largely explained by the combined effects of irrigation, tree size, and sapwood to heartwood ratio.

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