Anthropogenic disturbances are increasing in arid lands, as are expectations to successfully minimize impacts to natural resources and reclaim sites to publicly acceptable levels. This research explores the effectiveness of reclamation practices on a 60 mile natural gas pipeline constructed in September of 2014 that spans from west of Tucson to the border of Mexico. First, a controlled field experiment was conducted to assess the effects of seeding, grazing, and trampling (vehicular, cattle, and human foot traffic) on the reclaimed pipeline Right-Of-Way (ROW). Vegetation establishment (native plant cover; undesirable plant cover; species richness; herbaceous biomass), soil movement, and plant functional group community development was compared among the treatments. Reclaimed ROW areas left to recover without seeding resulted in similar vegetation cover, species, and community composition as undisturbed desert areas, although the presence of undesirable species was greater. The combined impacts of grazing and trampling resulted in reduced vegetation establishment and increased soil erosion. Second, the impacts of the pipeline construction on ephemeral wash channels were analyzed in terms of channel morphology and riparian vegetation changes. Channel cross section dimensions were measured upstream of the ROW, downstream of the ROW, and within the ROW before and after the 2015 Monsoon season to evaluate impacts on channel morphology and erosion processes. High resolution aerial imagery taken before and after pipeline construction was used to evaluate changes in riparian vegetation cover. Reduced herbaceous vegetation cover downstream of the ROW was detected, which may have been the result of increased channel scour within the ROW and increased sediment deposition downstream of the ROW. This research improves our understanding of and may aid in selection of appropriate reclamation practices.

Agriculture for rural communities in semi-arid areas is a risky exercise. The adverse weather conditions (high evaporative demand and low rainfall) of these regions, coupled with comparatively limited mechanization and often soil of poor chemical and physical constitution make crop production difficult and seldom sustainable. To some this problem represents a conundrum to be solved, to others an inconvenience to be avoided. Reduction of agricultural risk in these communities can be addressed in numerous ways, but should always begin with a thorough investigation of the agricultural imperatives of the community targeted, with the recommended system then tailored specifically to meet these imperatives. Agroforestry (combining trees and crops in agricultural systems temporally or spatially simultaneously) has been recommended for, and often been very successful in, many rural communities in tropical Africa and Asia. Adoption in semi-arid Africa has been less widespread, and often less successful once implemented. Nevertheless, the risk reduction possibilities that agroforestry offers through crop complementarity and yield diversification warrant further investigation into the practice in these regions. These studies sought to quantify yield advantage or disadvantage of hedgerow intercropping or alleycropping systems (combining hedgerow Leucaena leucocephala with various annual alley crops of importance to rural South African communities) compared to pure stands, and to investigate the use and distribution of, and competition for, water and light in these systems. Although alley-cropped annuals seldom outperformed pure stand annual crops, the diversification of yield, enabled by combining trees and crops, compensated for lower yields of annual crops in dry seasons or when yield losses occurred through disease. Whether or not this compensation for yield loss would be to the ultimate benefit of the target community would depend on the relative value of the different products resulting from the intercropping system. Using modifications of the renowned Land Equivalent Ratio and energy contents of products of the system, attempts were made to quantify possible benefits of intercropping in terms valid for the community targeted. Studies of water and light distribution in these systems illuminated often-severe water shortages in alley rows close to hedgerows and showed little benefit in altering row orientation for improved light distribution. Water emerged, as expected, as the primary concern to possible adopters of these systems in semi-arid zones. Crop modeling with mechanistic, biophysically sound models should be considered as an extremely important tool in combining needs of communities with environmental constraints of the area targeted. / Dissertation (MSc(Agric) : Pasture Science)--University of Pretoria, 2008. / Plant Production and Soil Science / unrestricted

This thesis is concerned with the conditions of generating a livable Karoo landscape and the arts of living on a damaged Karoo veld. It takes place in a context where the anthropogenic influences on land degradation, desertification and biodiversity loss continues to haunt the Karoo in the present. The Karoo is a semi-arid region that spans the interior of South Africa. It is also region that has been subject to ongoing and widespread concern of the impact of overgrazing, threatening the livability of the Karoo landscape. This is a result of human/nonhuman relations that have been grounded in a colonial mastery of the land, whereby the advent of private property regimes, modernist technologies and capitalist extraction has allowed for the land to be cheapened, exhausted and severely degraded in a process of colonial dispossession. This research is a qualitative ethnography interacting with farmers and nonhumans on rangelands in the Great Karoo. This thesis shows how the earlier degradation of the Karoo has demanded farmersto pay attention to the relationalities between ecology and economy, since their economic/ecological survival depends entirely on the ongoing multispecies assemblages of which humans form a part. Infrastructures and technologies have become grounds for new ontological practices of regenerating the Karoo veld. Infrastructures (namely fencing) and sheep are used in ways that mimic the earlier migration of large herds of antelope. Here, the bodies of sheep are curated and moved in order to perform a particular ordering of a Karoo ‘nature’. This movement is believed to instigate multispecies liveliness. Sheep, who were once destroyers of the veld, are now enrolled in practices that are believed to bring back the ‘natural’ vegetation of the Karoo. The thesis problematises the ongoing Western ways of knowing that separate the world into binaries of ‘nature’/’culture’, ‘human’/’non-human’, ‘subject’/object’, ‘domestic’/‘wild’, ’economy’/‘ecology’, ‘life’/‘death’. Rather, it argues that a concern with ontological plurality is a process of paying attention to the mutual ecologies and multiple species that gather in human/nonhuman worlding projects on rangelands in the Karoo.

Density dependent flow occurs in areas where high-salinity groundwater interacts with low-salinity groundwater to create a brine-to-freshwater interface that defies common assumptions about groundwater movement. Yet the geologic and hydrologic factors that impact interface dynamics and migration remain poorly defined. With less than 20 mm•yr-1 of precipitation and with an extremely dense (i.e. 1.2 g•cm-3) naturally occurring brine, Chile’s Salar de Atacama (SdA) provides an excellent analog for exploring interface dynamics in other arid regions. Site-specific 2-D models of the interface in the southeastern region of SdA, with interpretations of the hydrostratigraphic framework, provide an analysis for density-driven response rates to climatic change. A separate parametric, equally probable series of distributions of hydraulic conductivity provides a means for expanding analysis to other similar arid salar (i.e. “salt flat”) environments. Comparing the modeled interface’s geometry and response to perturbations in the rates of lateral recharge in each hydrostratigraphic realization yields insight into the dynamics of interface migration to coupled climatic and geologic conditions. Changes in hydrologic conditions, informed by paleoclimatic interpretations and previously modeled climate predictions, are introduced to each hydrostratigraphic realization following the interface reaching an initial dynamic equilibrium, and the interface’s response is assessed subsequent to it reaching a new dynamic equilibrium. Metrics for model evaluation include migration rate, change in the interface’s areal extent, change in interface slope, and the response rate following the introduction to a perturbation in the aquifer’s hydrology. Model analyses suggest that evaporation rates strongly control the interface’s geometry and sensitivity despite climatic and geologic conditions; continuity of high-permeability pathways controls interface slope; increasing continuity also decreases interface stability in terms of time required to reach a new steady state. While these results have implications for interface dynamics in both salars specifically and arid climates in general, they also indicate the importance of considering hydrostatigraphic continuity for saline water intrusion in coastal regions. They also provide a compelling method for assessing interface dynamics in other climatic and geologic conditions.

Estimation of evaporation from open water is essential for hydrodynamics, manufacturing industries, irrigation, farming, environmental protection and many other purposes. It is also important for proper management of hydrological resources such as reservoirs, lakes and rivers. Recent methods are mostly data-driven methods, such as using Artificial Intelligence techniques. Adaptive Neuro Fuzzy Inference System (ANFIS) is one of them and has been widely adopted in many hydrological fields for its simplicity. The current research presents a comparative study on the impact of optimization techniques such as Firefly Algorithm (FFA), Genetic Algorithm (GA), Particle Swarm Optimizer (PSO) and Ant Colony Optimization (ACO) on obtained results. In addition, a practical method named Multi Gene-genetic Programming (MGGP) is employed to propose an equation for the estimation of the Evaporation. Six different measured weather variables are taken, which are maximum, minimum and average air temperature, sunshine hours, wind speed and relative humidity. Models are separately calibrated with total data set collected over an eight-year period of 2010-2017 at the specified station “Arizona” in the United States of America. Ten statistical indices are calculated to verify the results. All optimizers were observed and compared to check if the results are better than ANFIS or not. The objectives of the adoption of different optimizer techniques was to verify the accuracy of the prediction by ANFIS model. Comparisons showed that ANFIS and MGGP are slightly better than the other models. MGGP model is different from other models in a way that it provides a set of equations instead of showing numerical values; therefore, the computational time is high. PSO, FFA, ACO and GA are considered as optimizers in the main model. Though PSO provided very similar results to the ANFIS model and MGGP gives even better results than basic ANFIS model. ANFIS is easier in terms of model formation. ANFIS is simpler to build and easy to operate. Since the prediction was quite identical in all cases, the ANFIS model was suggested due to its simplicity.

Pearl millet is a staple food source for millions of African families living in semi-arid regions of the continent. Yet, despite its importance and ability to provide consistent yields, very little research and resources have been directed towards understanding mechanisms governing this crop’s resilience to biotic and abiotic stresses. The research outlined in this thesis therefore aimed to elucidate defence response mechanisms in pearl millet, a non-model cereal crop. This was accomplished through the construction and characterisation of a pearl millet defence response cDNA library, which was subsequently utilised in large scale gene expression studies to profile pearl millet’s response to the defence signalling compounds nitric oxide (NO), methyl jasmonate (MeJA) and salicylic acid (SA), and to the biotrophic rust fungus Puccinia substriata var. indica. A pearl millet cDNA library was constructed by treating pearl millet plants with the defence elicitors chitin and flagellin, and by wounding the plants. Suppression subtractive hybridisation (SSH) was employed to enrich the library for defence response transcripts. In order to characterise the cDNA libraries, a quantitative cDNA microarray-based screening method was developed that enabled identification of false positive transcripts, as well as clones that represented rare or abundant transcripts. Based on this screening method, a number of clones were selected for sequence analysis, and their identity ascertained through homology searches with previously sequenced genes. This revealed a number of genes known to play important roles during pathogen attack. The pearl millet SSH defence response library, consisting of 1920 cDNAs either up- or down regulated in defence response, was spotted onto a glass slide microarray and used in transcript profiling studies to examine pearl millet’s response to the defence signalling molecules NO, MeJA and SA. Whilst only 45 cDNAs responded significantly to NO treatment, 279 and 224 cDNAs responded to MeJA and SA sprays, respectively. Closer examination of MeJA and SA responsive genes revealed that many of the induced transcripts were common to both signalling pathways, demonstrating that a substantial network of regulatory interactions exists between the salicylate and jasmonate pathways, which were previously believed to act in an antagonistic manner. Pathology studies indicated that pretreatment of pearl millet with SA conferred resistance to a virulent isolate of P. substriata var. indica, whereas MeJA application did not significantly reduce subsequent infection levels. Transcript profiling of a susceptible pearl millet line in response to virulent rust infection revealed that genes common to both the jasmonate and salicylate pathways were induced, suggesting that the plant adopts elements from a number of defence signalling pathways in an attempt to ward off infection by the virulent rust fungus. However, in view of results obtained from pearl millet defence signalling molecule pretreatments, it is probably genes that are significantly induced in response to SA, but to a lesser extent by MeJA that actually confer resistance to an avirulent rust isolate. Treatment of pearl millet plants with an avirulent P. substriata strain and subsequent microarray analysis would answer this hypothesis by revealing whether an incompatible reaction elicits more elements of the salicylate defence response pathway. / Thesis (PhD (Botany))--University of Pretoria, 2009. / Plant Science / unrestricted

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

Irrigation with saline waters is an agricultural practicethat is becoming increasingly common as competition for freshwater increases. In this thesis the mechanisms behind salinityand drought stress has been studied using data from fieldexperiments in combination with a modelling tool, theCoupModel. Measurements from field experiments on salinity,boron toxicity and drought stressed tomatoes grown during twoclimatically different seasons in the Arava desert, Israel,showed a linear relationship between relative growth andevapotranspiration, for all treatments and seasons. Data fromthe spring was used to concurrently simulate growth andtranspiration, hence accounting for feedback mechanisms betweenthe plant and the environment. Salinity stress was modelled asan osmotic effect (reduction of water uptake at high soilsalinities, W approach) or a toxicity effect (direct reductionof photosynthesis with soil salinity, G approach). Goodagreement between simulated growth and transpiration wasachieved with both salinity stress approaches, with twoexceptions. When growth and transpiration were simulated withthe W approach at different salinity levels, transpiration wasunderestimated at high stress. The G approach resulted in anunderestimation of growth at high water stress under moderatesalinity. A direct decrease of photosynthesis leads to adecreasing water-use efficiency with salinity while water-useefficiency remains constant with salinity when the salinitystress is modelled as a reduction in water uptake. Measurementsshowed decreasing water-use efficiency for the salinitygradient, explaining why the W approach was not applicable. Itwas not possible to detect any considerable differences betweenthree different approaches for water uptake tested in thestudy. <b>Keywords:</b>Water-use efficiency; osmotic effect; iontoxicity; semi-arid. / NR 20140805

>Magister Scientiae - MSc / There have been increasing calls to monitor Groundwater-Dependent Ecosystems (GDEs) more effectively, since they are biodiversity hotspots that provide several ecosystem services. The accurate monitoring of GDEs is an indispensable under Sustainable Development Goal (SDG) 15, because it promotes the existence of phreatophytes. It is imperative to monitoring GDEs, since their ecological significance (e.g., as biodiversity hotspots) is not well understood in most environments they exist. For example, vegetation diversity in GDEs requires routine monitoring, to conserve their biodiversity status and to preserve the ecosystem services in these environments. Such monitoring requires robust measures and techniques, particularly in arid environments threatened by groundwater over–abstraction, landcover and climate change. Although in–situ methods are reliable, they are challenging to use in extensive transboundary groundwater resources such as the Khakea-Bray Transboundary Aquifer.

High structural diversity amongst plant species in the arid winter rainfall region of southern Africa is common to other arid regions of the world. Details of the range and combinations of structural attributes in species, and within plant communities, are not widely known for southern African arid ecosystems. Hence little is known of how plant-form distributions vary within and between arid ecosystems. and of the environmental factors that may be responsible for any variations found. Nor is much information available on how phenological behaviour relates to the structural attributes of plant species. This study examined structural attributes of perennial plant species on the Worcester Veld Reserve, southwestern Cape. in relation to their distribution and phenology. Species were grouped on the basis of above ground structural and anatomical criteria. The distribution of species and plant-forms was assessed through a phytosociological survey along an environmental gradient in the area, and their phenology determined through qualitative and quantitative monitoring of species phenophases over a two year period. The results show that species of the predefined structural groups i) Co-occur throughout the area. but relative abundances vary from site to site and in relation to topography. aspect and the presence of Mirna-like mounds; ii) Phenological patterns for the flora overall are strongly seasonal, but the timing and periods of phenophases differ between, but are relatively uniform within, the defined structural plant groups. Since phenological patterns are indicative of resource-use patterns. these results indicate that the different plant-forms have different functional responses to the conditions of limited water availability and summer drought. This conceivably facilitates the co-existence of species in this water-limited environment. Habitat variability. which can be related to land-form patterns. is also implicated as a factor facilitating the co-existence of a diversity of species and plant-forms. Structural functional relationships known for arid region plants help to explain the relative uniformity of behaviour within plantform groups. and aid in understanding the ecological significance of distribution patterns of plant-forms in the arid landscape. The conclusion is reached that because of the close coupling between photosynthesis and water-use. the water storage potential and photosynthetic organ type are plant attributes which can serve as useful criteria by which arid region species can be grouped into ecologically meaningful categories or functional guilds. The formulation of a practical and meaningful functional classification is necessary to facilitate the understanding of complex vegetation patterns and processes within arid ecosystems. and allow for meaningful inter-ecosystem comparisons.