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1
Reed, James. "Pragmatic Encroachment, Evidentialism, and Epistemic Rationality." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1470454095.
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Fritz, James Christopher. "Knowledge and the Many Norms on Action." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu156268632958823.
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Buono, Jared. "Assessing the Ecohydrologic Consequences of Woody Plant Encroachment." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/195347.
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This three part study attempted to enhance our understanding of vegetation change and its potential effects on ecohydrology in drylands. The first study developed a method to measure the velocity of shallow overland flow. Under rainfall simulation, dye tracers were applied to runoff and photographed to calculate mean surface velocity. Results showed this approach was a significant improvement explaining 13% more of the variation in mean velocity compared to traditional methods. Results from the first study were used to compare hydraulic parameters on shrub- and grass-dominated plots in the second study. Previous research has suggested microtopography in shrublands acts to concentrate flow, leading to increased runoff velocity compared to grasslands. However, present findings showed that flow velocities were similar on many grass and shrub plots; only plots with ground cover > 90% exhibited significantly lower flow velocities, and some shrub-dominated plots had lower flow velocities than grass-dominated plots implying that horizontal water flux is reduced under certain states of woody plant encroachment. In terms of ground cover characteristics, velocity increased rapidly with increases in the fraction of bare soil, up to a value of ~20% bare soil. Above ~20% bare soil, basal gap became a dominant factor suggesting a possible threshold where spatial metrics related to the distance between plants become important indicator of shallow flow velocity. The third study tested an approach to quantify woody plant canopy metrics over large areas. Radar has been used to map biomass in forests but few studies have examined open canopy ecosystems. Field measurements of shrublands were compared to satellite images to identify the relationship between radar signal and height and cover of woody vegetation. Results indicated that radar signal increased positively with shrub height or shrub volume explaining 74% and 90% of the variation, respectively. The effect of surface roughness and sub-canopy species on radar signal appears reduced when images are collected at large incidence angles.
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Souza, Felipe de Sá Palis e. "Efeito de uma espécie de planta invasora na diversidade de aves em áreas úmidas." Universidade Federal de Mato Grosso, 2014. http://ri.ufmt.br/handle/1/661.
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A diversidade biológica pode ser representada pela abundância e riqueza de espécies, e pela mudança na composição de espécies entre locais e gradientes ambientais. Essa mudança pode estar associada a alguns fatores, como as condições e recursos ofertados pelo ambiente. Vários fatores determinam os padrões de distribuição de espécies em escala regional e local. Em áreas úmidas, como o Pantanal, as dinâmicas de inundação e seca, juntamente com os diferentes tipos de hábitats, afetam a distribuição de aves. Além disso, algumas espécies vegetais também podem se beneficiar com a dinâmica de inundações, como o cambará (Vochysia divergens Pohl), conhecida pela grande capacidade de invadir ambientes campestres e nele se expandir e por formar ambientes com estrato arbóreo monodominantes, chamados cambarazais. Esse adensamento da vegetação, comum em várias regiões, é chamado de encroachment, sendo responsável pela conversão de campos e savanas (áreas abertas) em vegetação arbustiva ou arbórea. Nesse estudo foi avaliado o efeito de cambarazais sobre a estrutura de assembleias de aves e como esse hábitat contribui na manutenção da diversidade regional desse grupo. O trabalho foi realizado na região do Pirizal, localizada na sub-região do Pantanal de Poconé - MT. Os dados foram coletados na grade de pesquisas do Pirizal, que é composta por 30 parcelas com diferentes fitofisionomias abertas e florestadas: cambarazal, landizal, cordilheiras, campos de murundus e pastagem exótica. Para a amostragem da avifauna foram utilizados dois métodos, redes de neblina e censos por pontos. Para análise de dados fizemos regressões lineares simples entre riqueza, abundância ou composição de aves (representada por uma dimensão de NMDS) em função das variáveis ambientais (primeiro eixo da PCA, composta pela densidade de cambarás, riqueza vegetal e duração do alagamento). Para avaliar se os padrões encontrados se deviam ao grau de proximidade entre as parcelas, foi realizado um teste de Mantel Parcial, com a distância biológica em função da distância ambiental e da distância geográfica. Para o segundo objetivo foi realizado uma Permanova para verificar se existe diferença na composição de aves entre os tipos de vegetação. Além disso, simulamos como acréscimos graduais de manchas de cambarazais afetam a diversidade de aves na paisagem. Foram registradas 183 espécies de aves nos cambarazais distribuídas em 45 famílias. O resultado da primeira regressão mostrou que a riqueza de espécies aumentou em função do eixo ambiental, principalmente em locais com maiores densidades de cambarás e que permaneceram mais tempo alagados. Em outras palavras, o encroachment teve reflexos positivos na riqueza de aves. A composição também foi afetada pelas variáveis ambientais e o resultado do teste de Mantel Parcial mostrou que não houve efeito da distância geográfica sobre a composição de espécies de aves. Os resultados da Permanova e da simulação mostraram que a composição foi diferente entre as fitofisionomias e que os cambarazais contribuem muito para a diversidade regional de aves. A mudança nas características do hábitat ocorre mesmo em escalas pequenas e é determinante para a distribuição das espécies. Hábitats com estruturas diferentes têm maiores chances de apresentar comunidades também diferentes, o que de fato contribui para o aumento da diversidade regional. A contribuição dos cambarazais não é somente em termos de aumento da diversidade; representa também um ambiente adicional e importante para várias espécies da região. Assim, o processo de encroachment do cambará, para essa região estudada, é um fenômeno importante para a diversidade de aves.
The biological diversity can be represented by the abundance and species richness and by the change in the composition between places and environmental gradients. This change can be associated with the conditions and resources offered by the environment. Several factors determine the patterns of species distribution at local and regional level. In Wetlands, the dynamics of flood and drought, together with the different types of hábitats, affect bird´s distribution. In addition, some plant species can also benefit with the dynamic of floods, as the cambara (Vochysia divergens Pohl), known by the great ability of invasion and expansion and by forming monodominant environments with arboreal stratum considered, called cambarazais. This overgrowth, common in several regions, is called encroachment, being responsible for the conversion of fields and savannas in shrub vegetation. In this study it was evaluated the effect of cambarazais on the structure of bird assemblies and how this hábitat contributes in maintaining regional diversity of this group. The work was carried out in the region of the Pirizal, located in the sub-region of the Pantanal of Poconé. The data were collected in grid research of Pirizal, which features 30 plots with different environments: “cambarazal”, “landizal”, “cordilheiras”, “campos de murundus” and exotic fields. For the bird sampling were used two methods, mist nets and census by points. The environmental variables used were the density of cambaras, richness and plant composition and the duration of flooding on the plots. For data analysis we have made simple linear regressions between richness, abundance or composition of birds (represented by one dimension of NMDS) and environmental variables (first axis of the PCA, composed by density of cambaras, plant species richness and flooding duration). To assess whether the patterns found were due to degree of proximity between the plots, it was carried out a Partial Mantel test, with the biological distance in function of environmental and geographic distance. For the second objective, was performed a Permanova to check if there is any difference in bird composition among the different environments. In addition, we simulate as gradual increases of patches of cambarazais affect the bird diversity in landscape. We recorded 183 species of birds in cambarazais distributed in 45 families. The result of the first regression showed that the species richness increased with the change in environmental variables, especially in places with higher densities of cambaras which were more time flooded. In other words, the encroachment has had positive impacts on bird richness. The composition was also affected by environmental variables. The result of Partial Mantel test showed that there was no effect of geographic distance on the bird species composition. The results of the Permanova and simulation showed that the composition was different between different environments and that the cambarazais contribute very much to the bird diversity. The change in the characteristics of the hábitat occurs even in small scales and is determinant for the species distribution. Hábitats with different structures have higher chances of presenting different communities also, what actually contributes to the increasing of regional diversity. The contribution of cambarazais is not only in terms of increasing diversity; it also represents an additional and important environment for several species in the region. Thus, the process of encroachment of cambara, for this studied region, is an important phenomenon for the bird diversity.
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Hogan, Matthew Brooks Clement Thangadurai Prabhakar. "Understanding the flow and mixing dynamics of saline water discharged into coastal freshwater aquifers." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Fall/Theses/HOGAN_MATTHEW_43.pdf.
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Thompson, Joseph. "Mechanisms of Native Shrub Encroachment on a Virginia Barrier Island." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4297.
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Species composition, temperature, soil nutrients, and leaf area index (LAI) were recorded across three encroaching Morella cerifera thicket edges and three free- standing shrubs on Hog Island, Virginia to characterize the effect of shrub thickets on the plant community and microclimate. Electron transport rate (ETR) was taken on shrub leaves to determine if microclimate benefits M. cerifera physiology. Species richness was lowest inside shrub thickets. Soil water content and LAI were higher in shrub thickets compared to grassland. Soil organic matter, N, and C were higher inside shrub thickets. Summer and fall maximum temperatures were more moderate in shrub thickets and at free-standing shrubs. Fall and winter minimum temperatures were higher inside shrub thickets. ETR was higher at the free-standing shrubs compared to the thicket edge. Morella cerifera impacts microclimate characteristics and species composition immediately upon encroachment. Improved shrub physiology was neither supported nor rejected by the research presented here.
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Ivehammar, Pernilla. "How to deal with the encroachment costs in road investment CBA." Doctoral thesis, Linköping : Ekonomiska institutionen, Linköpings universitet, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-7718.
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Ivehammar, Pernilla. "How to deal with the encroachment costs in road investment CBA /." Linköping : Ekonomiska Inst., Linköpings Univ, 2007. http://www.gbv.de/dms/zbw/52762540X.pdf.
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Weller, Austin W. "Pyramids and the City: Urban Encroachment on Chinese Heritage in Xi'an." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1367925417.
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Gray, Emma Fiona. "Some consequences of woody plant encroachment in a mesic South African savanna." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/10563.
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This study investigates the diversity present in the patch mosaic of vegetation, and also investigates how woody plant encroachment is affecting ecosystem services in Hluhluwe Game Reserve, with a focus on biodiversity, carbon storage and recreation and tourism.
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Westbrook, Matthew R. "Local scale forest encroachment into alpine habitat: past patterns and future predictions." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1396530374.
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Foster, Erich L. "A robust solution to Henry's problem." abstract and full text PDF (free order & download UNR users only), 2006. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1433003.
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Shaw, Adrienne Kara. "Conservation and ecological restoration of Rocky Mountain subalpine meadows: vegetation responses to tree encroachment." Thesis, University of Victoria, 2009. http://hdl.handle.net/1828/1396.
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Over the past century tree encroachment has occurred in North American subalpine meadows. Causes of tree establishment have been related to climate influences and exclusion of fire, but very few studies have looked at the consequence of tree encroachment on meadow vegetation. Within the southern Canadian Rocky Mountains, Waterton Lakes National Park and Castle Special Management Area,
14 meadows were randomly selected at wet and dry sites. Nonmetric multidimensional scaling showed that species composition changed during the transition of open meadow to forest for both wet and dry habitats. There were no significant differences in these two management areas in terms of conifer encroachment and the effects on meadow species. Results of this study show that conifer encroachment has increased over the last century with the consequences of loss in meadow species through a decrease in abundance, richness and diversity. Wet sites were significantly more sensitive to conifer encroachment than dry sites. The greatest
inhibitory effects of trees on meadow vegetation within the ecotone occurred when trees were 54-72 years old for wet sites and 77-112 years old for dry sites. Ecological restoration of these meadows is important for ongoing habitat conservation, maintaining species and landscape diversity and ecosystem resilience.
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Fathoni, Tachrir. "Managing conflict in national parks : the case of encroachment in Kerinci Seblat, Indonesia." Thesis, University of Edinburgh, 1998. http://hdl.handle.net/1842/27997.
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Kerinci Seblat National Park (KSNP) is the largest national park in Indonesia. It surrounds Kerinci District, the biggest enclave inside any comparable national park in the world. For these reasons, the people-park problems are potentially the most complex among all parks in Indonesia. The greatest threat to the integrity of KSNP comes from encroachment which is largely aimed at the cultivation of cinnamon trees. Traditional approaches to park management and enforcement activities to exclude local people from the park have been unable to solve this problem. This study attempts to fill gaps in our knowledge of people-park interactions in KSNP and aimed to incorporate encroachment problems in the park's management plan. The objectives of this study were: (1) to examine characterisation of encroachment systems, people's attitudes towards the Park and encroachment; (2) to measure the degree of people pressure on the park and analyse impacts of encroachment on soil properties; (3) to model historical land use dynamics in an attempt to predict future encroachment; and (4) to provide alternative management options for the Park using a multi-criteria decision making (MCDM) model, and define the trade-offs that will exist between economic, environmental and social variables associated with alternative options. These results demonstrate that shortage of land and people's perception of cinnamon are significant factors influencing encroachment activities in KSNP. Land use dynamics in the District are strongly influenced by the twin processes of encroachment and forest degradation. The most critical zone for encroachment in the District is the area in the elevation between 500-1500 m with slope less than 40 percent. Due to human encroachment, the Park is now under serious population pressure. Therefore, four scenarios of land allocation for buffer and traditional use zones were produced to lessen the pressure. A model was developed for identifying the area most likely to be encroached in the future. These results were utilised in order to develop eleven alternative management options for resolving conflict between encroachment and sustainable park management.
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Al-Qasimi, S. M. "Arab ?piracy? and the East India Company encroachment in the Gulf 1797-1820." Thesis, University of Exeter, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353800.
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Alford, Aaron L. "Eastern redcedar encroachment in southern Great Plains grasslands : wildlife consequences and management implications /." Available to subscribers only, 2009. http://proquest.umi.com/pqdweb?did=1878976501&sid=5&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Thesis (Ph. D.)--Southern Illinois University Carbondale, 2009."Department of Zoology." Keywords: Grasslands, Juniperus virginiana, Small mammals, Tree removal, Woody encroachment. Includes bibliographical references (p. 94-110). Also available online.
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Alford, Aaron Larrs. "Eastern Redcedar Encroachment In Southern Great Plains Grasslands: Wildlife Consequences And Management Implications." OpenSIUC, 2009. https://opensiuc.lib.siu.edu/dissertations/55.
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Anthropogenic change in the Great Plains of North America within the past two centuries has facilitated extensive woody encroachment by eastern redcedar (Juniperus virginiana, hereafter redcedar). Conversion of grassland to redcedar woodland occurs rapidly as a result of the interaction between changing disturbance and land use patterns. In addition, redcedar encroachment causes compositional shifts in grassland floral and faunal assemblages, and may alter abiotic factors such that grassland restoration efforts are limited. The objectives of this study were to: 1) track vegetation and faunal assemblages in grasslands along a gradient of redcedar encroachment, 2) assess the capacity for experimental tree removal to promote re-colonization of grasslands by associated flora and fauna, and 3) examine the influence of scale on spatial relationships between small-mammal abundance and redcedar cover. During the first phase of my study, I examined herbaceous vegetation, woody vegetation, and small-mammal assemblages at grassland sites along a redcedar encroachment gradient in north-central Oklahoma. I noted hump-shaped trends in the capture rate, species diversity, and species evenness of small mammals along the redcedar encroachment gradient. In addition, higher levels of encroachment were associated with compositional shifts from grassland- to woodland-associated small mammals. Characteristics of the small-mammal assemblage along the gradient corresponded to increases in redcedar cover and the frequency of episodic management events within the past two decades. Experimental redcedar removal during the second phase of my study generally increased vegetation and faunal diversity in 2 years following treatment, and treatment sites having the highest pre-treatment levels of redcedar cover exhibited the greatest responses to tree removal. The results of my study suggested that within the time frame I examined, redcedar encroachment had altered the biotic characteristics of this system, but did not facilitate abiotic shifts capable of constraining rapid grassland recovery. Tree removal also appeared to modulate the effects of consecutive drought and flood years on small-mammal diversity during post-treatment. During the third phase of my study, I examined the strength of association between differences in percent redcedar cover and spatial abundance patterns of 4 common small-mammal species. I examined small-mammal abundance at three relatively small spatial scales (38, 154, and 616 m2) to determine how redcedar-mammal associations were stronger with increases in spatial scale. In addition, I determined whether the influence of spatial scale on redcedar-mammal associations varied along a gradient of redcedar encroachment. The strength of redcedar-mammal associations increased with spatial scale, but was strongest at sites having the lowest levels of encroachment. These results corresponded to variation in the spatial distribution of redcedar cover and compositional differences in the small-mammal species assemblage along the encroachment gradient. Studies examining the effects of woody encroachment will extend our understanding of successional processes and ensure that appropriate management is implemented in the conservation of these imperiled grassland ecosystems.
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Gesualdi, Maxine. "Extending Organizational Role Theory to Understand Shared Resources and Role Encroachment in Organizations." Diss., Temple University Libraries, 2017. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/459103.
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Media & CommunicationPh.D.
This dissertation follows in the tradition of role theory and organizational scholarship by examining how one role can be taken over by another, which can be referred to as encroachment. Previous organizational role research has not explored fully encroachment and its effects. Therefore, this study investigated factors that lead to role encroachment, especially the sharing of internal resources, and how individuals cope with the effects of encroachment. To conduct the study, focus groups of marketing and public relations departments were analyzed to explain how roles are enacted within their practical context. The goals of this dissertation were to (a) investigate how shared resources affect role boundaries and role enactment that can lead to encroachment, (b) explain the concept of encroachment and how it affects role enactment, and (c) investigate the conflict between public relations and marketing that can lead to encroachment in the age of social media. The study found themes related to: (a) definitions of encroachment, (b) factors facilitating encroachment, (c) factors affecting the intensity of encroachment, (d) shared resources and their effects on encroachment, (e) implications of encroachment to the individual, department, and organization, and (f) ways people deal with encroachment. First, encroachment was defined in three ways: the overtaking of tasks, or receiving unwanted strategic guidance, or interference of organizational processes. Second, the study found that role ambiguity and the communication of and adherence to cultural norms invite or prevent encroachment. Third, role ambiguity and organizational culture were found to be the dominant factors that affect the intensity of encroachment. Fourth, the study found that tangible macro resources, like organizational culture and structure, and practical resources, such as information and skill sets, facilitate encroachment. Fifth, findings indicated that implications of encroachment include stress, frustration, and confusion at the individual level; an us versus them mentality and role conflict at the departmental level; and broken relationships with external partners, lack of organizational nimbleness, and wasted time and money at the organizational level. Lastly, the study found that people deal with encroachment by providing and receiving emotional and informational social support, and by accumulating and spending social capital through relationship building within the organization. Theoretical implications of this research indicate that role conflict, role ambiguity, and boundary spanning role theory relate to encroachment. In addition, previous theory focused on external resource use by organizations can be expanded to evaluate the internal use of resources. Theory from interpersonal communication, such as social exchange theory, social support, and social capital, relate to how people facing encroachment cope with their roles being infringed upon. Practical implications of this dissertation include recommendations for organizations including increased communication of role boundaries and evaluations of restrictive cultural norms. The findings from this study provide an understanding of encroachment and indicate directions for further development of theory about encroachment and role enactment.
Temple University--Theses
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Ralitsoele, Teboho. "Analysing the road reserve encroachment in Maseru Lesotho using remote sensing and image analysis." Master's thesis, Faculty of Engineering and the Built Environment, 2021. http://hdl.handle.net/11427/33912.
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The increasing rate of urbanization and the problem of road reserve encroachment mean that there is no space for road expansion and sometimes for maintenance and road furniture, these and other problems have exposed the problem of road reserve encroachment. The main aim of this study was to investigate methods of finding the road reserve encroachment in Maseru Lesotho using aerial photos. The study used single image analysis and multiple image analysis methods. In single image analysis, the study used three methods of image classifications to find objects that are in the road reserve. Under classification, the study used both supervised and unsupervised image classifications. For supervised classification, the study used the direct image classification method where the aim was to look for every object found in the road reserve. For the indirect approach, the study looked for the ground to find objects in the road reserve. For unsupervised image classification, the study assumed that small clusters are encroachment. In multiple images analysis, the study used the 2015 and 2017 images to determine permanent objects found to have encroached road reserves. Here the assumption was that encroachment does not change over time, which means that unchanged objects during the change detection have encroached on the road reserve. The confusion matrix was used to tell the best performing method and the results show that the indirect method, both in Qoaling and Maqalika performed best. All the methods showed that there was an encroachment on a road reserve, and found that permanent objects were; houses, shops, and shopping centers. The study recommended the use of images with higher resolution and more bands, also that images be taken frequently.
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Metz-Estrella, Tania M. "Issues and Responses to Urban Encroachment at the Edge of Western Protected Public Lands." Thesis, The University of Arizona, 2007. http://hdl.handle.net/10150/190384.
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Ryan, Paige Brell. "EFFECTS OF OVARIECTOMY AND ANATOMICAL LOCATION ON OSTEONAL ENCROACHMENT IN ADULT CORTICAL OVINE BONE." DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/932.
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The purpose of this study is to further quantify adult ovine ovariectomized bone for new remodeling characteristics to obtain a better understanding of how remodeling is occurring and the effectiveness of this animal model for the study of postmenopausal osteoporosis. Postmenopausal osteoporosis is a major health concern and animal models to test new treatment options are needed. The ovine model is a good option because the ewes undergo Haversian remodeling, are a large sized animal, and have a similar hormone profile to humans. Ewes, however, do not undergo a natural menopause, so an ovariectomy surgery was conducted in the sheep to simulate the decreased levels in estrogen. Columbia-Rambouillet sheep were used in this study: some that have been ovariectomized as a model for postmenopausal osteoporosis and some that underwent a sham surgery to serve as a control. The sheep were sacrificed 12 months post operatively in the month of August, so the seasonal effects of remodeling were accounted for. The left radius was then processed into microradiographs of 6 regional cortical beams, where the cranial (tensile side) and caudal (compressive side) anatomical sections were analyzed in this study to determine regional differences in remodeling. Previous students’ theses have analyzed the similar samples for basic bone remodeling histology measurements, resulting in some significant seasonal, anatomical, and treatment differences. However, most of the results showed no particular increase in the amount of remodeled area for the ovariectomized sheep compared to the sham sheep, even though an ovariectomy is believed to cause a burst of remodeling in bone due to the decreased levels in estrogen.
In this study, a new repeatable method was developed that further examines secondary bone by quantifying the extent to which secondary osteons encroach on previously-existing secondary osteons. Encroached and unencroached secondary osteons were quantified using two different methods: a point count method that measured the percentage of the area the encroached and unencroached secondary osteons inhabited and an osteon count method that measured the number of encroached and unencroached secondary osteons per area. These raw measurements were calculated into 18 parameters and 2-way repeated measures ANOVAs were run to determine the effects of surgery and anatomical region on each of the bone remodeling parameters. The results found significant effects from estrogen deletion which were different depending on if the bone region was predominately in compression or tension. The ovariectomy surgery caused an increase in remodeling, which was mostly confined on the compressive side to areas that have been previously remodeled, but on the tensile side, bone remodeling expanded into areas that used to be primary bone. The new secondary osteons, as a result of the ovariectomy surgery, were larger than in the control animals. There however, was not an increase in porosity from the ovariectomy surgery, which is one of the main characteristics of osteoporosis. The model could be further studied to determine what sheep are doing that prevents them from losing bone and that knowledge could be greatly beneficial for human treatment plans of postmenopausal osteoporosis.
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Bagaria, Morató Guillem. "Time lags in plant community assembly after forest encroachment into Mediterranean grasslands: drivers and mechanisms." Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/295705.
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La pèrdua, fragmentació i transformació dels hàbitats representen una gran amenaça per a la biodiversitat en els ecosistemes terrestres d'arreu del món, desencadenant tant extincions com colonitzacions amb un resultat incert en la composició i la riquesa d'espècies. Els retards de diverses dècades, coneguts com a deute d'extinció i crèdit de colonització, són habituals després dels canvis en els usos del sòl. No obstant, hi ha una manca d'estudis que abordin l'ensamblatge de comunitats tenint en compte tant el deute d'extinció pels especialistes de l'hàbitat previ com el crèdit de colonització pels especialistes del nou hàbitat. L'objectiu d'aquesta tesi és, per tant, abordar les causes i els mecanismes dels efectes diferits del canvi en l'hàbitat i el paisatge sobre les comunitats vegetals en prats calcaris semi-naturals en ambients mediterranis des d'una aproximació inclusiva, tenint en compte tant els canvis en la riquesa com en la composició d'espècies i els seus retards potencials. El deute d'extinció i el crèdit de colonització han estat quantificats després de diverses dècades de canvis en l'hàbitat, i les seves causes han estat investigades (Capítol 1). Amb l'objectiu de desentrellar els processos que hi ha darrere els canvis de la comunitat, s'han investigat els patrons i causes de les extincions i colonitzacions d'espècies que ja s'han donat, a través dels dos components de la β-diversitat: recanvi d'espècies i diferències de riquesa (Capítol 2). D'altra banda, el paper dels atributs de les plantes com a mediadors de l'extinció d'espècies de l'hàbitat previ (Capítol 3), i els mecanismes poblacionals i individuals del retard en l'extinció d'un dels especialistes de prat més freqüents (Aphyllanthes monspeliensis; Capítol 4) han estat abordats després del canvi en l'hàbitat. Els estudis s'han dut a terme a les muntanyes del sud de Catalunya (nord-est de la Península Ibèrica), on la forestalització s'ha donat com a conseqüència de la reducció en la pastura durant la segona meitat del segle XX. Tot i que han passat més de 50 anys des de l'inici d'aquest procés de forestalització dels prats, s'ha detectat un important deute d'extinció per als especialistes de prat i crèdit de colonització per als especialistes de bosc. El deute d'extinció també ha estat confirmat per l'especialista de prat A. monspeliensis, ja que la seva abundància depèn de la connectivitat passada però no de l'actual. A més a més, un efecte rescat des dels prats circumdants i un lent decaïment vegetatiu i reproductiu després del deteriorament de l'hàbitat han estat identificats com a mecanismes que afavoreixen el deute d'extinció. El crèdit de colonització de les plantes de bosc, al seu torn, probablement es manté per una limitació de la dispersió. Tot i que la riquesa ha canviat poc després de la forestalització, sí que s'ha donat un elevat recanvi d'espècies per al conjunt de la comunitat, fruit d'extincions i colonitzacions idiosincràtiques dels especialistes de prat i de bosc, respectivament. No obstant, mentre la fragmentació de l'hàbitat ha afectat negativament alguns especialistes de prat, no s'ha trobat un paper important dels atributs de les plantes en la mediació de les extincions per a aquest grup. S'espera que la pèrdua generalitzada d'espècies de prat i el guany generalitzat d'espècies de bosc, que resulten del pagament del deute d'extinció i el crèdit de colonització, continuïn a l'àrea d'estudi fins i tot en el cas que no avancés el procés de forestalització.Habitat loss, fragmentation and transformation are major threats for biodiversity in terrestrial ecosystems worldwide, driving both species extinctions and colonisations with an uncertain outcome on species composition and richness. Time lags of several decades, known as extinction debt and colonisation credit, often occur after land-use change events. Nevertheless, there is a lack of studies addressing community assembly taking into account both extinction debt for habitat specialists of the former habitat and colonisation credit for habitat specialists of the new habitat. The aim of this thesis is, therefore, to address the drivers and mechanisms of time-lagged effects of habitat and landscape change on plant communities in semi-natural Mediterranean calcareous grasslands from a comprehensive approach, taking both changes in species richness and composition and their potential time lags into account. Extinction debt and colonisation credit are quantified after several decades of habitat change, and their drivers are investigated (Chapter 1). In order to disentangle the processes behind community change, the patterns and drivers of species extinctions and colonisations that already occurred are investigated through the two components of β-diversity: species replacement and richness differences (Chapter 2). Moreover, the role of plant traits in mediating extinctions of species of the former habitat (Chapter 3), and the population and individual-level mechanisms of extinction delay for one of the most frequent grassland specialists (Aphyllanthes monspeliensis; Chapter 4) are assessed after habitat change. The studies were conducted in the southern mountains of Catalonia (northeastern Iberian Peninsula), where forest encroachment occurred following grazing reduction during the second half of the 20th century. Although more than 50 years elapsed since the beginning of forest encroachment into these grasslands, both an important extinction debt for grassland specialists and colonisation credit for forest specialists are detected. Extinction debt was also confirmed for the grassland specialist A. monspeliensis, since its abundance depends on historical but not current connectivity. In addition, a rescue effect from surrounding grasslands and a slow vegetative and reproductive decay after habitat deterioration were identified as mechanisms enhancing extinction debt. Colonisation credit of forest plants, in turn, was probably maintained by dispersal limitation. Although species richness changed little after forest encroachment, high species replacement for the whole community occurred, resulting from idiosyncratic grassland specialists' extinctions and forest specialists' colonisations. However, while habitat fragmentation negatively affected some grassland specialists, no clear role of plant traits was found in mediating extinctions of this group. A generalised loss of grassland species and gain of forest species, resulting from the payment of extinction debt and colonisation credit, is expected to continue in the studied area even if no further forest encroachment occurs.
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Skowno, Andrew Luke. "Woody plant encroachment in arid and mesic South African savanna-grasslands: same picture, different story?" Thesis, Rhodes University, 2018. http://hdl.handle.net/10962/62603.
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Woody plant encroachment in South Africa’s savanna-grasslands has been considered a rangeland management problem since the early 1900s. This phenomenon, which has been observed globally, is particularly important in Africa given the extent of tropical grassy biomes on the continent and their importance for rural livelihoods. In this study, local and regional scale approaches were used to investigate woody cover change in South Africa across the important savanna-grassland rainfall threshold of 650 mm mean annual precipitation (MAP). The aim was to test this threshold using remote sensing and demographic surveys in order to better understand the patterns, mechanisms and drivers of encroachment. Rates of encroachment and population demographics of Vachelia karroo were compared at arid and mesic savanna sites in the Eastern Cape, using time-series analysis of historical aerial photographs in conjunction with field surveys. Changes in the extent of woodland vs. grassland were then quantified at a national scale (1990-2013) by combining optical and synthetic aperture radar remote sensing data. This produced the first map of woodland- grassland shifts for South Africa and provided the basis for a spatially explicit investigation of the key drivers of change. The local studies revealed higher rates of encroachment at mesic sites than at arid sites, with a correlation between drought and rate of encroachment at the arid site. Vachelia karroo seedlings and stunted saplings were more prevalent at mesic sites than at arid sites and the growth form of adult trees differed significantly between sites. The national remote sensing investigation showed that woodland replaced grassland in over 5% of South Africa’s savanna- grasslands between 1990 and 2014, at rates consistent with other global and regional studies. Spatially explicit models showed a pattern of incremental expansion of woodland along a ‘tree front’ and complex relationships between woodland increase and fire, rainfall, terrain ruggedness and temperature. Overall, the local and regional scale findings of this work highlight the importance of the savanna rainfall threshold (~650 mm MAP) and the presence / absence of fire in understanding savanna dynamics and woody cover change in the context of global drivers such as elevated atmospheric CO2.
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Lecomte, Xavier Jean François. "Effects of grazing exclusion and shrub encroachment on the ecosystem ecology of evergreen oak woodland." Doctoral thesis, ISA, 2018. http://hdl.handle.net/10400.5/15334.
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Doutoramento em Engenharia Florestal e dos Recursos Naturais - Instituto Superior de AgronomiaShrub encroachment, an increase in density and cover of shrub plant communities, is affecting biodiversity and functioning of ecosystems around the world. Through feeding and trampling ungulates affect the structure and species composition of plant communities, including shrublands, and are key drivers in shrub encroachment processes. This thesis, conducted within a long-term browsing exclosure experiment, investigates the effects of ungulates (red deer Cervus elaphus and fallow deer Dama dama) on the encroachment of C. ladanifer, a dominant Mediterranean shrub, into a mixed cork (Quercus suber) and holm (Quercus rotundifolia) evergreen oak woodland in Southern Portugal. Five paired fenced (ungulate-excluded) and unfenced (ungulate-allowed) plots of 25 m x 25 m were established in the study area in July 2001. Fenced plots had a 2.20 m height fence to exclude deer occurring in the site. Data on C. ladanifer reproduction structures (buds, fruits and flowers), soil seed bank, population density and biomass, were collected in fenced and open plots in 2007, 2013 and 2015. Ungulates consumed buds, flowers and fruits and decreased the soil seed bank of C. ladanifer. Plant reproductive costs (loss of fruits) were higher than potential benefits (seed dissemination) and the population density and biomass of C. ladanifer, decreased in the open plots by the end of the experiment. Ungulates decreased above-ground carbon (C) storage but also the amount of fine fuel loads reducing fire hazard and the probability of crown fires, and consequent adult oak mortality, in open plots. Therefore ungulate may potential benefit long-term ecosystem C storage. A drought year during data monitoring allowed quantifying jointly effects of ungulate browsing and drought on C. ladanifer mortality which increased in open plots. Changes in live:dead plant biomass affected fire hazard. Results show that ungulate ecology needs to be considered when investigating shrub encroachment processes
N/A
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Rajala, Kiandra F. "Ecosystem Transformation Across a Changing Social Landscape: Landowner Perceptions and Responses to Woody Plant Encroachment." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/86724.
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The conversion of grasslands to woodlands is an ecosystem transformation that threatens grassland biodiversity, the provision of important ecosystem services, and the sustainability of rural livelihoods. A global phenomenon, woody plant encroachment (WPE) has been particularly problematic in the Southern Great Plains of the United States where the actions of private landowners are integral to sustaining grasslands. Increased diversity in landowners’ motivations for owning land have shifted the social landscape of rural areas necessitating a better understanding of landowners’ perspectives about WPE and their subsequent management actions. Towards this purpose, I employed a mail survey to private landowners in the Edwards Plateau of Texas, Central Great Plains of Oklahoma, and Flint Hills of Kansas to investigate landowner perceptions and management responses to WPE. First, I assessed landowners’ acceptance of WPE as a function of how they relate to their land (i.e., sense of place), their beliefs about the positive and negative consequences of woody plants, and their perceived threat of grassland conversion. Then, I examined the drivers of landowners’ goal intentions to manage woody plants and their current use of five adaptive management practices that prevent WPE. My results demonstrate that landowners vary in their sensitivity to WPE based on how they feel connected to their land. This was true even though most landowners had low acceptance thresholds for WPE, believed it led to numerous negative outcomes, and perceived it as increasingly threatening at greater levels of encroachment. Most landowners wanted to control or remove woody plants and were actively engaged in management practices to do so. These findings address uncertainties about landowners’ acceptance of WPE and grassland conservation actions and provide broad implications for how people perceive and respond to ecosystem transformation.Master of Science
Around the world, grasslands are converting to tree and shrub woodlands at an unprecedented rate. This transformation profoundly reduces habitat available for grassland plants and animals and diminishes many ecosystem services that people and rural communities rely on. This loss of grasslands has been especially far-reaching throughout the Southern Great Plains of the United States. Because most of this region is privately owned, the management actions of landowners play a crucial role in preventing or allowing this conversion to continue. Recent shifts in land ownership motivations expanding beyond traditional agricultural production have created increased uncertainty about how private landowners view and react to this change. To investigate how landowners perceive and respond to this woody plant encroachment (WPE) phenomenon, I conducted a mail survey of landowners in the Edwards Plateau of Texas, the Central Great Plains of Oklahoma, and the Flint Hills of Kansas. Using sense of place, landowners’ beliefs about the potential positive and negative consequences of woody plants, and their perceptions of how threatening grassland conversion is, I assessed the thresholds at which landowners’ do or do not accept WPE. Then, I examined how acceptance of WPE relates to landowners’ management goals and current use of management practices to control or reduce woody plants. I found that most landowners believed that woody plants had many negative consequences and perceived increasing levels of threat at greater levels of encroachment. This related to low levels of acceptance for woody plants in grasslands. However, landowners’ threat perceptions and acceptance of WPE varied based on their sense of place. Finally, most landowners wanted to control or remove woody plants and were actively engaged in management practices to do so. My results provide critical information regarding how current landowners’ view and respond to grassland conversion and offer broad implications for how people perceive and respond to large-scale environmental change.
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Vick, Jaclyn. "WOODY ENCROACHMENT MECHANISMS OF A SYMBIOTIC N-FIXING SHRUB: ECOPHYSIOLOGY, FACILITATION, AND RESOURCE USE EFFICIENCY." VCU Scholars Compass, 2011. http://scholarscompass.vcu.edu/etd/2599.
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Causes and consequences of woody encroachment into grass dominated systems have been widely studied, however functional mechanisms which promote encroachment are largely unknown. Many expansive woody species are shrubs with rhizobial or actinorhizal N-fixing symbiotic associations. Morella cerifera L. (Myricaceae) is an actinorhizal N-fixing shrub which rapidly expands into grasslands on the barrier islands off the coast of Virginia, USA. The objective of this research was to determine physiological drivers of woody encroachment resulting in increased woody cover of M. cerifera on Southeastern, US barrier islands. Variations in physiology and resource use efficiencies (RUE) of M. cerifera and co-occurring shrubs were determined, and edaphic characteristics beneath shrub thicket canopies and in open areas were quantified as indications of resource availability. Analysis of dune vegetation and soils showed severe freshwater limitation and reduced plant height of dune forbs suggesting dunes represent an upper elevational boundary for M. cerifera distribution. Soil N availability was higher beneath shrubs compared to open areas, and both physiology and isotope effects showed facilitation of the non-fixing shrub, Baccharis halimifolia, by M. cerifera which may lead to increased rates of woody encroachment as B. halimifolia colonizes expanding thicket edges. Morella cerifera and other N-fixers had higher %refixation within stems which resulted in higher carbon use efficiency (CUE) and water use efficiency of N-fixing shrubs compared to non-fixers. Results of an N-fertilization experiment suggest B. halimifolia has higher dependence on and demand for soil nutrients compared to M. cerifera. Morella cerifera showed no signs of resource deficiency or reduced physiological capacity even at 0 ppm total Nsoil. Morella cerifera transitioned from utilizing solely fixation derived N to soil N as N concentrations increased providing another mechanism leading to increased CUE and, indirectly, overall RUE. In summary greater RUE, lower resource demand, and greater resource availability for M. cerifera compared to co-occurring shrubs may result from symbiotic root associations with bacteria and fungi. While expansion of M. cerifera thickets is limited to lower elevational interdunal depressions, expansion may continue and result in increased rates of woody encroachment through facilitation of co-occurring shrubs.
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Shiflett, Sheri. "PHYSIOLOGICAL MECHANISMS OF SHRUB ENCROACHMENT: LINKING ENHANCED HYDRAULIC CAPACITY TO EFFICIENT LIGHT CAPTURE AND PROCESSING." VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/3208.
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Woody plant expansion has been documented for decades in many different ecosystems, often due to anthropogenic disturbances to the environment and yielding vast changes in ecosystem functioning. While causes and consequences of woody expansion have been well documented, few studies have investigated functional traits of woody species that promote rapid expansion in range. My objective was to determine if hydraulic efficiency confers enhanced photosynthetic efficiency so that functional traits representing light and water use may be possible mechanisms facilitating woody encroachment into grasslands and forest understories. I quantified leaf-level light environment, photosynthetic activity, and hydraulic characteristics of three sympatric broadleaf evergreens of varying leaf life span (Ilex opaca, Kalmia latifolia, and Myrica cerifera) in a deciduous forest understory to understand seasonal intra- and interspecific ranges of broadleaf evergreen physiology. Additionally, I investigated the effects of age on physiological efficiency of M. cerifera across a chronosequence (i.e., space for time substitution) of shrub thicket development in order to understand possible age-related physiological mechanisms facilitating shrub expansion. Lastly, I determined functional traits and resulting physiology that contribute to rapid expansion and thicket formation of an invasive, deciduous, N-fixing shrub, Elaeagnus umbellata, and a native, evergreen, N-fixing shrub M. cerifera. When compared to co-occurring evergreen species, electron transport rate (ETR) of M. cerifera was nearly double that of I. opaca or K. latifolia in summer. Photosynthetic capacity was positively related to hydraulic capacity among understory evergreens. Furthermore, photosynthetic and hydraulic efficiency of M. cerifera remained consistent despite considerable differences in thicket age and development. Both similar and contrasting functional traits of E. umbellata and M. cerifera allowed for enhanced light capture and water movement, and reductions in subcanopy light penetration. Enhanced hydraulic and photosynthetic efficiency relative to co-occurring species contributes to rapid range expansion and thicket formation by promoting enhanced productivity and limiting successful colonization of other species. My results indicate that there may be suites of functional traits linked to expansive success and thicket-formation, yet differences in functional traits between native and invasive species represent alternative strategies leading to rapid growth and thicketization.
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Brantley, Steven. "CONSEQUENCES OF SHRUB ENCROACHMENT: LINKING CHANGES IN CANOPY STRUCTURE TO SHIFTS IN THE RESOURCE ENVIRONMENT." VCU Scholars Compass, 2009. http://scholarscompass.vcu.edu/etd/1686.
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Shrub expansion in herbaceous ecosystems is emerging as an important ecological response to global change, especially in mesic systems where increases in canopy biomass are greatest. Two consequences of woody encroachment are increases in belowground resources, such as carbon and nitrogen, and reductions in above-ground resources such as light, which affect diversity, community trajectory, and ecosystem function. My objective was to determine how expansion of the nitrogen-fixing shrub Morella cerifera affected the resource environment across a chronosequence of shrub expansion on a Virginia barrier island. I quantified changes in carbon (C) and nitrogen (N) cycling, canopy structure and understory light associated with M. cerifera expansion. Litterfall in shrub thickets exceeded litterfall for other woody communities in the same region, and due to high N concentration, resulted in a return of as much as 169 kg N ha-1 yr-1 to the soil, 70% of which was from symbiotic N fixation. Litter and soil C and N pools were 3-10 times higher in shrub thickets than in adjacent grasslands. Understory light in shrub thickets decreased to as low as 0.5% of above-canopy light. Sunflecks in shrub thickets were shorter, smaller and less intense than sunflecks in forest understories. However, relative to other shrub species such as Elaeagnus umbellata, M. cerifera was less efficient at intercepting light. Although M. cerifera had the highest leaf area index (LAI) of five shrub species studied, M. cerifera was relatively inefficient at light attenuation due to low levels of branching, steep leaf angles and a relatively shallow canopy. The shift from grassland to shrub thicket on barrier islands, and in other mesic systems, results in a significant change in canopy structure that alters understory resource availability and greatly alters ecosystem function and trajectory.
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Swanger, William Rodgers Shelly. "Revisiting fund-raising encroachment of public relations in light of the theory of donor relations." Diss., Columbia, Mo. : University of Missouri--Columbia, 2008. http://hdl.handle.net/10355/5795.
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The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on October 5, 2009). Thesis advisor: Dr. Shelly Rodgers, Includes bibliographical references.
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Goswami, Rohit Raj Clement Prabhakar Thangadurai. "Experimental and numerical analysis of variable-density flow and transport scenarios." Auburn, Ala, 2008. http://hdl.handle.net/10415/1430.
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Bybee, Jordan Ann. "Understory Vegetation Response to Mechanical Mastication of Piñon and Juniper Woodlands." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3817.
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Piñon and juniper encroachment and infilling can alter ecosystem processes and decrease resilience and resistance in sagebrush grasslands. Land managers employ a variety of techniques to eliminate these trees and mitigate their negative effects. Mechanical mastication or shredding is an increasingly popular method of removing these trees in Utah. It is a versatile treatment that can reduce canopy fuels, increase infiltration, and reduced sediment loss. We compared vegetation cover for annual and perennial vegetation functional groups on shredded and adjacent unshredded areas across a range of sites. Our approach was to categorize sites by ecological site type (encroachment or tree) and subplots by treatment (untreated, shredded, and shredded-seeded) and initial tree cover. Mixed model analysis of covariance and the Tukey-Kramer test were used to determine significant differences among ecological site type and treatment combinations for each 5% increment of untreated or initial tree cover. Shrub cover was unaffected by treatment and decreased with increasing tree cover. In general, perennial herbaceous understory cover increased after shredding to equal or exceed initial encroachment and infilling levels. This held true for both ecological site types and treatments, even at high pretreatment tree cover percentages. Cheatgrass also increased in cover after tree shredding although this trend was dampened in the seeded treatments indicating some suppression of cheatgrass by seeding. Shredding when there is high cover of perennial herbaceous plants and shrubs or seeding in conjunction with shredding where initial tree cover exceeds 35-40% will help discourage dominance by weeds.
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Temmers, Zsa-Zsa. "Building encroachments and compulsory transfer of ownership." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5326.
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Thesis (LLD (Private Law))--University of Stellenbosch, 2010.Bibliography
ENGLISH ABSTRACT: South African courts seem to be adopting a new approach to the problem of building encroachments. For pragmatic and policy reasons courts are now inclined to exercise its discretion in favour of leaving building encroachments in place, against compensation, despite the common law right to demand removal. It has been widely accepted that courts indeed have the discretion to award damages instead of removal of the building encroachment. However, the circumstances involved and the consequences of these orders are uncertain and hence these orders result in confusion. It is unclear how this discretion is exercised. Furthermore, it is uncertain whether this discretion includes the power to order transfer of the encroached-upon land to the encroacher. There are doctrinal and constitutional implications that may be triggered by these court orders that leave building encroachments in place. The doctrinal issues centre on what happens when an encroachment is not removed and nothing is said about the rights of the respective parties after the order is made. Possible solutions are investigated to provide a doctrinally sound outcome in encroachment disputes. It is clear that the encroacher is allowed to continue occupying the portion of property on which the encroachment is erected. It seems as though a use right is indirectly created when the encroachment remains in place. The constitutional difficulty lies in the fact that the court orders may result in infringements that conflict with section 25 of the Constitution. The focus is specifically to determine whether these orders result in the compulsory loss of property or property rights. With reference to Germany, the Netherlands and Australia, a comparative perspective is provided in order to support the doctrinal and policy arguments. The comparative law provides a source of guidelines for what may work effectively and informs the ultimate suggestion of this project, namely the need for legislation to regulate building encroachments in South Africa. The legislation envisaged would have to prescribe with at least some sort of certainty how and in which circumstances the discretion should be exercised. It should also provide clarity with regard to the right that is created when the encroachment is not removed and how the compensation that is awarded in exchange for removal, should be determined. The unnecessary confusion and uncertainty that result from court orders made in the context of building encroachments may be cleared up by legislation.
AFRIKAANSE OPSOMMING: Suid Afrikaanse howe begin al hoe meer om ‘n nuwe benadering te volg ten opsigte van oorskrydende bouwerke. Dit lyk asof howe meer geneig is om hul diskresie uit te oefen ten gunste daarvan om die oorskryding vir pragmatiese en beleidsredes teen vergoeding in stand te hou, ten spyte van die gemeenregtelike reg om verwydering te eis. Daar word algemeen aanvaar dat howe wel die diskresie het om in die konteks van oorskrydende bouwerke skadevergoeding toe te ken in plaas van verwydering. Die omstandighede betrokke by en die nagevolge van hierdie beslissings is egter onseker en daarom lei dit tot verwarring. Dit is nie altyd duidelik hoe hierdie diskresie uitgeoefen word nie. Daarbenewens is daar ook onsekerheid oor of die diskresie die bevoegdheid insluit om oordrag van die grond waarop die oorsrkryding staan, te gelas. Die beslissings kan ook doktrinêre en grondwetlike implikasies hê. In terme van die doktrinêre probleem is daar vrae oor wat gebeur as die oorskryding nie verwyder word nie en niks word gesê oor die regte van beide partye in die dispuut nie. Oplossings word ondersoek om die beste moontlike doktrinêre verduideliking te probeer vasstel. Die eienaar van die oorskrydende bouwerk mag voortgaan om die grond waarop die oorskryding staan te okkupeer. Dit lyk asof ‘n gebruiksreg indirek geskep word ten gunste van die oorskryder wanneer die oorskryding nie verwyder word nie. ‘n Grondwetlike probleem mag veroorsaak word deur die moontlike oortreding van artikel 25 van die Grondwet. Die beslissings mag lei tot die gedwonge verlies van grond of regte, wat aan die vereistes van artikel 25 moet voldoen. ‘n Vergelykende perspektief met verwysing na Duitsland, Nederland en Australië word verskaf om die doktrinêre en beleidsargumente te ondersteun. Die vergelykende reg bied ‘n bron van riglyne vir wat effektief kan werk en het dus die wetgewing wat in hierdie proefskrif voorgestel word geïnspireer. Die wetgewing wat beoog word sal moet voorskryf hoe en onder watter omstanghede die diskresie uitgeoefen moet word. Dit moet ook sekerheid gee ten opsigte van die reg wat geskep word as die oorskryding nie verwyder word nie en hoe die skadevergoeding bepaal moet word. Die onnodige verwaring en onsekerheid wat veroorsaak word deur hierdie hofbeslissings kan opgeklaar word deur die promulgering van wetgewing om oorskrydende bouwerke te reguleer.
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Afinowicz, Jason David. "Evaluation of shrub encroachment and brush control on water availability in the Upper Guadalupe River watershed." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/210.
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Wooded plant encroachment has dramatically changed the composition of rangelands in the arid and semiarid rangelands of the southwestern United States and may have significantly affected hydrologic and biogeochemical process in these environments. In particular, suspicions that encroaching species waste an undue amount of water through evapotranspiration (ET) has prompted much discussion concerning the possibility of using brush control to enhance water supplies in Texas. This study focuses on two broad goals for evaluating the effects of wooded growth in rangelands. The first of these is the assessment of wooded cover with the use of remotely sensed imagery. A methodology for delineating differing land cover classes, including different levels of brush cover, is described, applied, and validated for the Upper Guadalupe River watershed, Texas. This portion of the research resulted in an 81.81% success rate for correctly matching land cover varieties and showed that 88.8% of the watershed was covered with various amounts of woody plant growth. The second portion of this study incorporated the previously developed land cover product along with a number of other highly detailed data sources to model the North Fork of the Upper Guadalupe River watershed using the Soil and Water Assessment Tool (SWAT). The role of topography, brush cover, and soil slope, which are hypothesized to contribute to successful implementation of brush removal for water yield, were tested in a scientifically conscious and practical experiment to determine their influence upon water availability at a watershed scale. The effects of brush removal were found to be comparable to the quantities documented in field experiments, but less than the levels presented in previous modeling studies. Brush density was found to be the most important factor in determining locations for successful brush removal in regards to reducing ET. Slope was also found to have significant effect in increasing lateral flow while shallow soil had lesser effects on hydrology than other criteria. Large quantities of deep recharge simulated by the model raise questions concerning measurement of ET in the Edwards Plateau region and the extent of deep water recharge to the Trinity Aquifer.
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Kelemen, Julia C. "Effects of tree encroachment on the water balance of a Scottish raised mire : a lysimeter study." Thesis, University of Dundee, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320593.
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Kraaij, Tineke. "Effects of rain, nitrogen, fire and grazing on bush encroachment in semi-arid savanna, South Africa." Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/52817.
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Thesis (MScFor)--Stellenbosch University, 2002.ENGLISH ABSTRACT: Increases in woody plant density ('bush encroachment') reduce livestock production and biodiversity. By convention, soil moisture, soil nutrients, fire and herbivory are regarded as the principal factors governing the tree-grass ratio of savannas. An experiment with a completely-crossed design was employed to investigate woody seedling (Acacia me/lifera) recruitment near Kimberley, Northern Cape, South Africa, after fire and under conditions of maximum-recorded rainfall, nitrogen addition and grazing. The field experiment was repeated as a garden experiment to determine if the two experiments yield comparable results. Tree germination in the field was extremely low, probably due to below-average natural rainfall in plots that only received natural rain, and insufficient watering frequency in irrigated plots. As a result of low germination, none of the treatments (rain/nitrogen/fire/grazing) had a significant effect on tree recruitment in the field experiment. The duration of the experiment (2000/2001 growing season) was insufficient for the treatments to affect grass composition, although the high rainfall treatment and grazing exclusion significantly improved grass cover and height. The garden experiment showed that frequent watering, no nitrogen addition and grass clipping significantly enhanced tree germination and survival (termed 'recruitment'). There were also significant interactions among rain, nitrogen and grazing in their effects on tree recruitment. The effects of rain on tree recruitment were more pronounced under nitrogen supplementation and vice versa. Similarly, high rain and high nitrogen enhanced the effect of grazing on tree recruitment. It is inferred that above-average rainfall years with frequent rainfall events are required for mass tree recruitment. Tree seedlings can further benefit from space and resources which are made available through grass defoliation. Conversely, nitrogen enrichment improves the competitive ability of the fast-growing grasses relatively more than that of the N2-fixing tree component, thereby suppressing tree recruitment. In contrast to conventional wisdom that grazing alone causes encroachment, it is suggested that there are complex interactions between the abovementioned factors and 'triggering' events such as unusually high rainfall. Contrary to many claims that equilibrium models are inappropriate for explaining savanna dynamics, it was shown that consumer-resource theory has explanatory power for bush-grass dynamics of the savanna studied. The state-space approach that was used facilitated the understanding of savanna dynamics and enabled predictions about the system's response to perturbations. The applicability of consumer-resource theory to semi-arid nutrient-poor savannas confirmed the importance of resource competition in structuring natural systems.
AFRIKAANSE OPSOMMING: Toenames in die digtheid van houtagtige plante ('bosverdigting') verlaag veeproduksie en biodiversiteit. Volgens konvensie word grondvog, grondvoedingstowwe, vuur en beweiding beskou as die belangrikste faktore wat die boom-gras verhouding van savannas bepaal. 'n Volledig-gekruisde ("completely crossed") eksperiment is ontwerp om boomsaad-ontkieming (Acacia mellifera) naby Kimberley, Noord-Kaap, Suid- Afrika, te bestudeer na 'n brand en onder toestande van maksimum-aangetekende reënval, stikstof toevoeging en beweiding. Die veldeskperiment is herhaal as 'n tuineksperiment om vas te stel hoe resultate van die twee eksperimente vergelyk. Boomsaad-ontkieming was uiters laag in die veld, waarskynlik weens ondergemiddelde reënval in persele wat slegs natuurlike reënvalontvang het, en 'n te lae benattingsfrekwensie in die besproeide persele. As gevolg van lae ontkieming in die veldeksperiment, het geen behandeling (reënval/stikstof/brand/beweiding) boomsaad-ontkieming beduidend geaffekteer nie. Die duur van die eksperiment (2000/2001-groeiseisoen) was te kort vir die behandelings om grassamestelling te beïnvloed, alhoewel besproeiing en geen beweiding die grasbedekking en -hoogte betekenisvol verhoog het. Die tuineksperiment het getoon dat boomsaadontkieming en vroeë oorlewing (genoem 'vestiging') betekenisvol verhoog is deur gereëlde benatting, geen stikstof toevoeging en die sny van gras. Daar was ook beduidende interaksies tussen reën, stikstof en beweiding in hul invloed op boomvestiging. Die reënbehandeling het 'n groter uitwerking op boomvestiging gehad onder stikstoftoevoeging en vice versa. Hoë reënval en stikstoftoevoeging het ook die invloed van beweiding op boomvestiging versterk. Die afleiding is dat bogemiddelde reënvaljare met gereëlde reënbuie 'n vereiste is vir grootskaalse boomvestiging. Boomsaailinge kan verder voordeel trek uit die spasie en hulpbronne wat beskikbaar raak wanneer gras ontblaar word. Daarteenoor verhoog stikstofverryking die mededingendheid van die vinniggroeiende grasse meer as dié van die N2-bindende boomkomponent, met die gevolg dat boomvestiging onderdruk word. In kontras met die konvensionele veronderstelling dat beweiding opsigself bosverdigting veroorsaak, word voorgestel dat ingewikkelde interaksies plaasvind tussen die bogenoemde faktore en ander 'sneller-gebeurtenisse', soos buitengewoon hoë reënval. In teenstelling met baie aansprake dat ekwilibrium modelle ontoepaslik is om savanna-dinamika te verklaar, is getoon dat die verbruikers-hulpbron teorie ("consumer-resource theory") oor verklaringsvermoë beskik vir boom-gras dinamika van die savanna wat bestudeer is. Die staat-spasie ("state-space") benadering gebruik, het begrip van savanna-dinamika bevorder en voorspellings moontlik gemaak aangaande die sisteem se reaksie op versteurings. Die toepaslikheid van verbruikers-hulpbron teorie vir semi-ariede, nutriënt-arm savannas bevestig dat kompetisie vir hulpbronne 'n sentrale rol speel in die strukturering van ekologiese sisteme.
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Killian, Paul D. "Mechanisms driving woody encroachment in the tallgrass prairie: an analysis of fire behavior and physiological integration." Thesis, Kansas State University, 2012. http://hdl.handle.net/2097/14197.
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Master of ScienceDepartment of Biology
John M. Briggs
Woody encroachment has altered the vegetative structure of grasslands worldwide and represents a potentially irreversible shift in grassland dynamics and biodiversity. Clonal woody species appear to be one of the greatest contributors to the shift from graminoid to woody dominance in the tallgrass prairie. Part of the high success rate of clonal species may be attributed to an ability to circumvent recruitment filters through the integration of environmental heterogeneity and acropetal translocation of resources from mother to daughter ramets. The clonal shrub Cornus drummondii persists in a tension zone of the graminoid-dominated tallgrass prairie, where the dominance structure is primarily maintained through the direct and indirect effects of fire. The competitive displacement of native herbaceous vegetation associated with the establishment and expansion of C. drummondii causes a major alteration in the fuel dynamics responsible for the propagation and sustainment of fire, potentially contributing to biofeedback mechanisms that facilitate shrub expansion. The goal of this research was to quantify fire behavior parameters (temperature, intensity, rate of spread, and heat flux) in relation to C. drummondii invasions and to test physiological integration as a mechanism driving encroachment, using manipulation experiments at the Konza Prairie Biological Station. We observed a significant decrease in fireline intensity associated with the encroachment of C. drummondii, which was amplified by the effects of stem density and shrub island area. This alteration in fire behavior also led to reduced heat flux at stems within shrub islands, reducing the likelihood of tissue necrosis and top-kill. With additional fuel, temperatures and fire intensities were higher, similar to open grasslands. In severing rhizomes, and effectively severing the integration of clonal ramets, we observed a higher risk of mortality of daughter ramets. These rhizome severed ramets were more water stressed, had lower photosynthetic rates, and lower woody and foliar biomass production. These results indicate that C. drummondii significantly alters fire behavior, releasing ramets from the fire trap of successive top-killing, while the integration of intraclonal ramets allows daughter ramets to survive mid-summer drought and increases the likelihood of successful establishment and further clonal reproduction.
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Gxasheka, Masibonge. "Euryops floribundus encroachment in Eastern Cape communal rangelands: indigenous and scientific understanding of effects on range." Thesis, University of Fort Hare, 2013. http://hdl.handle.net/10353/d1016203.
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The study was conducted in Eastern Cape Province to 1) investigate local people’s knowledge and perceptions on Euryops floribundus and 2) landscape distribution and effect of Euryops floribundus on herbaceous vegetation and soil. A total of 90 households who own livestock were randomly selected from the three communal areas, namely; Tsengiwe, Upper Mnxe and Manzimdaka for household surveys and group discussions. For landscape study, a total of about 5 ha of land were selected at Upper Mnxe communal area. Selection criteria included the presence of E. floribundus and different landscape gradients. A total of four 50mx50 plots were marked along the landscape gradients: Bottom, Middle, and Upper Slope and upland positions. To study the effect of E. floribundus invasion on the herbaceous vegetation and soil, a total of 4 ha communal land was selected in an accessible area which had a largely flat terrain. The area was selected to have adjacent sites with no invasion (< 5% shrub cover), light (5-15% shrub cover), moderate (>15-35) and heavy invasions (>35% shrub cover) of E. floribundus. The average household size in the study area was 6.8± 0.7. All people in the three communal areas unanimously ranked sheep as the most important species for their livelihood, but the ranking of cattle and goat varied among the communal areas. All elder groups agreed that Europs floribundus decreases both the quantity and quality of herbaceous forage as well as livestock production. Moreover, invaded patches create more bare areas which are responsible for the loss of top fertile soils and the formation of rills and gullies. The result showed that the total density of E. floribundus significantly increased from the topland (2301 plants ha-1) moving to the bottomland (4888 plants ha-1). Canopy cover was significantly lowest in the topland (17.9%), but the remaining gradients had similar cover. Grass dry matter yield was higher in the bottomlands and sloppy gradients than the toplands. Soil organic carbon was significantly higher (P<0.05) in the flat than the sloppy terrain. Soils from higher elevations (toplands and upper sloppy) had significantly higher N than the lower elevations (bottomlands and Middle sloppy). The lowest dry matter was observed at low invasion and non-invaded sites. Soil chemical properties were generally different from all density levels. In conclusion, E. floribundus encroachment was found to be major cause of decline in the peoples’ livelihood because as this reduces the vegetation diversity and livestock production, both of which are the major of their livelihoods.
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Cutulle, Matthew Anthony. "Turfgrass species composition, resistance mechanisms, and management strategy impacts on brown patch incidence and weed encroachment." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/39297.
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Tall fescue (Festuca arundinacea Schreb.) has great utility as a low maintenance turfgrass in the northern and transition zone regions of the United States. However, it is difficult to successfully maintain tall fescue of high quality over consecutive summers because of its susceptibility to the fungal pathogen Rhizoctonia solani, which causes the disease brown patch. Not only is brown patch aesthetically unpleasing in a stand of tall fescue but it can also thin out the turf and allow for the encroachment of undesirable weedy species. Cultivar selection, cultural practices, mixing turf species and timing of pesticide applications all can impact the epidemiology of brown patch in tall fescue. Research was conducted in tall fescue to quantify chitinase activity in different cultivars, elucidate the impact of mowing height and nitrogen fertility on brown patch and bermudagrass (Cynodon dactylon L.) encroachment, to evaluate seeding mixtures of tall fescue with hybrid bluegrass (Poa pratensis x Poa arachnifera) on diseases and weeds as well as measuring the impact of the herbicide bispyribac-sodium on brown patch. Chitinase activity was greater in the tall fescue cultivar that was less susceptible to brown patch. In the mowing-fertility studies, cutting tall fescue at 10 cm generally reduced brown patch and bermudagrass encroachment compared to 6 cm. Mixing hybrid bluegrass with tall fescue reduced disease and weed species infestations compared to tall fescue alone. Applying bispyribac-sodium earlier in April resulted in less brown patch and better weed control compared to application in May. Based on this research brown patch severity and subsequent weed species infestations can be reduced by selecting a tall fescue cultivar with a high basal level of chitinase, mowing it at 10 cm and mixing it with a hybrid bluegrass cultivar.Ph. D.
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Devine, Aisling Patricia. "The effects of fire on the characteristics of woody vegetation and encroachment in an African savanna." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/18538.
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African savannas have experienced considerable woody encroachment over the last century, presenting an increasing problem from both ecological and socioeconomic viewpoints. Despite decades of work by savanna ecologists, the reasons for woody encroachment remain unclear. A major barrier to understanding the causes is the difficulty of disentangling the effects of broader-scale environmental changes, such as climate change and associated increases in atmospheric CO2, from localised effects such as fire. In this thesis I examine the effects of sixty years of experimental burning on the characteristics of woody vegetation in two climatically distinct African savannas, a wet and a dry savanna, to examine how long-term burning interacts with other potential drivers of woody encroachment. I examine tree abundance, woody cover, tree structure, diversity and community composition under four different fire regimes: annual, biennial, triennial and fire exclusion. Differences between sites and plots subject to different burning regimes are compared along with changes in these differences through time. Additionally, variation in the densities of Acacia, Combretum, Terminalia and Dichrostachys species were examined to establish how dominant species, particularly those responsible for encroachment, are affected by fire. Overall, I found that the effects of fire depend on savanna type. Fire lowered tree abundance and woody cover much more in the wet savanna than in the dry savanna. However, the maximal height of trees was much more constrained by increased fire frequency in the dry savanna than in the wet savanna. Woody encroachment occurred across both savanna types during the sixty year time period, but was much more rapid at the wet savanna. Additionally, encroaching species of Dichrostachys cinerea and Terminalia sericea in the wet savanna were shown to be more difficult to manage using fire. Overall as fire regimes were kept constant over the last sixty years, yet woody encroachment occurred across all fire treatments, it is most likely that an external driver is responsible. Rainfall change in both areas was minimal over the duration of the study, thus increased atmospheric CO2 would appear to be the most likely cause of woody encroachment. However, the magnitude and characteristics of woody encroachment are strongly mediated by fire and rainfall. Wet savannas would appear to be much more vulnerable to woody encroachment and existing management strategies are likely to become increasingly ineffective at keeping woody cover below potential maximum levels. Overall this thesis demonstrates that the effects of fire on woody vegetation in savannas vary depending on regional differences in rainfall and that processes of woody encroachment differ depending on savanna type.
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Aye, Aye Saw. "Deforestation and Local Livelihood Strategy: A Case of Encroachment into the Wunbaik Reserved Mangrove Forest, Myanmar." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225673.
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Rau, Benjamin M. "Assessing carbon and nitrogen in a central Nevada pinyon woodland with tree encroachment and prescribed fire." abstract and full text PDF (UNR users only), 2009. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3355563.
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Calandrelli, John D. "Prediction of Suburban Encroachment on the Ethan Allen Firing Range and Camp Johnson, Chittenden County, Vermont." DigitalCommons@USU, 1999. https://digitalcommons.usu.edu/etd/6568.
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Suburban encroachment is a growing concern for many National Guard training installations. The Ethan Allen. Firing Range and Camp Johnson, Vermont, are either experiencing or are completely enclosed by urban encroachment. The objective of this study was to analyze the trends of suburban growth within Chittenden County, Vermont, to evaluate growth and explore future training site viability of the Ethan Allen Firing Range and Camp Johnson.
This study focused on historical data, recent real estate transactions, population projections, and county plans for growth. Using historical and contemporary data, I developed a predictive model of suburban encroachment on Camp Johnson and the Ethan Allen firing Range facilities by residential and commercial development. This model may assist land managers make decisions and illustrate the viability of these installations as National Guard training sites. This model may also be applied to other installations with similar concerns.
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Wepener, Jean-Pierre. "The control of Stoebe vulgaris encroachment in the Hartbeesfontein area of the North West Province / J.P. Wepener." Thesis, North-West University, 2007. http://hdl.handle.net/10394/2044.
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Sun, Wei. "Velvet mesquite (Prosopis velutina) encroachment and ecosystem CO₂ exchange in semiarid grassland insights from stable isotope measurements /." Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1960208391&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Riley, Alyssa J. "Effects of riparian woody vegetation encroachment on prairie stream structure and function with emphasis on whole-stream metabolism." Diss., Kansas State University, 2011. http://hdl.handle.net/2097/8545.
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Doctor of PhilosophyDepartment of Biology
Walter K. Dodds
Much of the North American tallgrass prairie ecosystem has been converted to cropland or urbanized. One threat to the remaining prairie ecosystems, and the streams within, is woody vegetation encroachment. Stream productivity, measured as metabolism, is a fundamental process comprised of gross primary production (GPP) and (CR) community respiration. Understanding GPP and CR is important because these processes are vital to ecosystem function and can be impacted by a change in canopy cover. First, I investigated improvements in existing methods for estimating whole-stream metabolism as estimated from diel patterns of oxygen (O2). I compared measured and modeled O2 and aeration (a physical parameter required for measurement of metabolism) rates to determine if direct measurement of aeration is necessary and the importance of temperature correction of metabolism. Modeling was moderately successful in determining aeration rates, and temperature correction of GPP and CR substantially improved model fits. Second, effects of woody vegetation encroachment on prairie stream function were investigated. Stream metabolism was measured for four years in duplicate reaches with varying canopy cover (closed canopy, naturally open canopy, and vegetation removal reaches). The removal reaches had closed canopy for the first two years and open canopy for the last two years. Canopy cover increased CR rates and had minimal effects on GPP. Third, the same experiment was used to determine the effects of woody vegetation encroachment on prairie stream ecosystem structure and food web interactions. Chlorophyll a and filamentous algal biomass were greater in naturally open and vegetation removal reaches, although the effects were stronger on filamentous algal biomass. As canopy cover decreased, the filamentous algal biomass to chlorophyll ratio increased, indicating a shift in algal community structure. Stable isotope analysis indicated some shift in pathways of nitrogen and carbon flux into the food web related to degree of canopy cover, but overlap in the signature of food sources made distinct food sources difficult to identify. The data indicate that riparian encroachment can influence ecosystem structure and function in prairie streams and restoration to remove woody riparian cover may restore some ecosystem features of naturally open canopy streams.
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Barron-Gafford, Greg Alan. "TEMPERATURE AND PRECIPITATION CONTROLS OVER SOIL, LEAF AND ECOSYSTEM LEVEL CO2 FLUX ALONG A WOODY PLANT ENCROACHMENT GRADIENT." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/193976.
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Woody plant encroachment (WPE) into historic grasslands not only alters ecosystem structure but also yields a mosaic of vegetative growth-forms that differ in their inherent physiological capacities and physical attributes. C₃ plants tend to have a relatively broad range of temperature function but at the expensive of a lower optimum rate of photosynthesis. In contrast, C₄ grasses have a greater capacity for maximum uptake but across a relatively narrow range of temperatures. In considering which of these functional groups will outcompete the other within these regions undergoing WPE, one must account not only for these leaf physiological traits, but also the growth form induced differences in rooting depth, and therefore, potential access to deeper subsurface water. Laid upon these competitive interactions is an ever-changing environment, which for the semiarid southwestern US is predicted to become progressively warmer and characterized by highly variable precipitation with longer interstorm periods. In addition to aboveground changes in CO₂ assimilation, WPE influences soil nutrient, water, and carbon cycling. The objectives of this dissertation were to quantify: (1) the influence that temperature and available soil moisture have on regulating soil respiratory efflux within the microhabitats that results from WPE to estimate the influence this vegetative change will have on ecosystem CO₂ efflux; (2) the sensitivity of CO₂ uptake within grassland and woodland ecosystems to temperature and precipitation input in an effort to characterize how WPE might influence regional carbon and water balance; and (3) the role access to stable groundwater has in regulating the temperature sensitivity of ecosystems and their component fluxes. Major findings and contributions of this research include illustrating seasonal patterns of soil respiration within the microhabitats that result from WPE, such that an analysis of the relative contributions of these different components could be made. We found that soil respiration was not only consistently greater under mesquites, but that the relative contributions of these microhabitats varied significantly throughout the year, the duration of soil respiration after each rain was habitat-specific, and that the relationship between soil respiration and temperature followed a hysteretic pattern rather than a linear function (Appendix A). We found that a woodland ecosystem demonstrated a lower temperature sensitivity than a grassland across all seasonal periods of varying soil moisture availability, and that by maintaining physiological function across a wider range of temperatures throughout periods of limited precipitation, C₃ mesquites were acquiring large amounts of carbon while C₄ grasses were limited to functioning within a narrower range of temperatures (Appendix B). Finally, we found that having a connectivity to stable groundwater decoupled leaf and ecosystem scale temperature sensitivities relative to comparable sites lacking such access. Access to groundwater not only resulted in the temperature sensitivity of a riparian shrubland being nearly half that of the upland site throughout all seasonal periods, but also actual rates of net ecosystem productivity and leaf level rates of photosynthesis being dramatically enhanced (Appendix C).
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Wasiolka, Bernd. "The impact of overgrazing on reptile diversity and population dynamics of Pedioplanis l. lineoocellata in the southern Kalahari." Phd thesis, Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1661/.
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Die Vegetationskomposition und –struktur, beispielsweise die unterschiedliche Architektur von Bäumen, Sträuchern, Gräsern und Kräutern, bietet ein großes Spektrum an Habitaten und Nischen, die wiederum eine hohe Tierdiversität in den Savannensystemen des südlichen Afrikas ermöglichen. Dieses Ökosystem wurde jedoch über Jahrzehnte weltweit durch intensive anthropogene Landnutzung (z.B. Viehwirtschaft) nachhaltig verändert. Dabei wurden die Zusammensetzung, Diversität und Struktur der Vegetation stark verändert. Überweidung in Savannensystemen führt zu einer Degradation des Habitates einhergehend mit dem Verlust von perennierenden Gräsern und krautiger Vegetation. Dies führt zu einem Anstieg an vegetationsfreien Bodenflächen. Beides, sowohl der Verlust an perennierenden Gräsern und krautiger Vegetation sowie der Anstieg an vegetationsfreien Flächen führt zu verbesserten Etablierungsbedingungen für Sträucher (z.B. Rhigozum trichotomum, Acacia mellifera) und auf lange Sicht zu stark verbuschten Flächen. Die Tierdiversität in Savannen ist hiervon entscheidend beeinflusst. Mit sinkender struktureller Diversität verringert sich auch die Tierdiversität.
Während der Einfluss von Überweidung auf die Vegetation relativ gut untersucht ist sind Informationen über den Einfluss von Überweidung auf die Tierdiversität, speziell für Reptilien, eher spärlich vorhanden. Zusätzlich ist sehr wenig bekannt zum Einfluss auf die Populationsdynamik (z.B. Verhaltensanpassungen, Raumnutzung, Überlebensrate, Sterberate) einzelner Reptilienarten.
Ziel meiner Doktorarbeit ist es den Einfluss von Überweidung durch kommerzielle Farmnutzung auf die Reptiliengemeinschaft und auf verschiedene Aspekte der Populationsdynamik der Echse Pedioplanis lineoocellata lineoocellata zu untersuchen. Hinsichtlich bestimmter Naturschutzmaßnahmen ist es einerseits wichtig zu verstehen welchen Auswirkungen Überweidung auf die gesamte Reptiliengemeinschaft hat. Und zum anderen wie entscheidende Faktoren der Populationsdynamik beeinflusst werden. Beides führt zu einem besseren Verständnis der Reaktion von Reptilien auf Habitatdegradation zu erlangen.
Die Ergebnisse meiner Doktorarbeit zeigen eindeutig einen negativen Einfluss der Überweidung und der daraus resultierende Habitatdegradation auf (1) die gesamte Reptiliengemeinschaft und (2) auf einzelne Aspekte der Populationsdynamik von P. lineoocellata.
Im Teil 1 wird die signifikante Reduzierung der Reptiliendiversität und Abundanz in degradierten Habitaten beschrieben. Im zweiten Teil wird gezeigt, dass P. lineoocellata das Verhalten an die verschlechterten Lebensbedingungen anpassen kann. Die Art bewegt sich sowohl häufiger als auch über einen längeren Zeitraum und legt dabei größere Distanzen zurück. Zusätzlich vergrößerte die Art ihr Revier (home range) (Teil 3). Im abschließenden Teil wird der negative Einfluss von Überweidung auf die Populationsdynamik von P. lineoocellata beschrieben: In degradierten Habitaten nimmt die Populationsgröße von adulten und juvenilen Echsen ab, die Überlebens- und Geburtenrate sinken, währen zusätzlich das Prädationsrisiko ansteigt. Verantwortlich hierfür ist zum einen die ebenfalls reduzierte Nahrungsverfügbarkeit (Arthropoden) auf degradierten Flächen. Dies hat zur Folge, dass die Populationsgröße abnimmt und die Fitness der Individuen verringert wird, welches sich durch eine Reduzierung der Überlebens- und Geburtenrate bemerkbar macht. Und zum anderen ist es die Reduzierung der Vegetationsbedeckung und der Rückgang an perennierenden Gräsern welche sich negativ auswirken. Als Konsequenz hiervon gehen Nischen und Mikrohabitate verloren und die Möglichkeiten der Reptilien zur Thermoregulation sind verringert. Des Weiteren hat dieser Verlust an perennierender Grasbedeckung auch ein erhöhtes Prädationsrisikos zur Folge. Zusammenfassend lässt sich sagen, dass nicht nur Bäume und Sträucher, wie in anderen Studien gezeigt, eine bedeutende Rolle für die Diversität spielen, sondern auch das perennierende Gras eine wichtige Rolle für die Faunendiversität spielt. Weiterhin zeigte sich, dass Habitatdegradation nicht nur die Population als gesamtes beeinflusst, sondern auch das Verhalten und Populationsparameter einzelner Arten. Des Weiteren ist es Reptilien möglich durch Verhaltensflexibilität auf verschlechterte Umweltbedingen zu reagieren.In semi-arid savannah ecosystems, the vegetation structure and composition, i.e. the architecture of trees, shrubs, grass tussocks and herbaceous plants, offer a great variety of habitats and niches to sustain animal diversity. In the last decades intensive human land use practises like livestock farming have altered the vegetation in savannah ecosystems worldwide. Extensive grazing leads to a reduction of the perennial and herbaceous vegetation cover, which results in an increased availability of bare soil. Both, the missing competition with perennial grasses and the increase of bare soils favour shrub on open ground and lead to area-wide shrub encroachment. As a consequence of the altered vegetation structure and composition, the structural diversity declines. It has been shown that with decreasing structural diversity animal diversity decline across a variety of taxa. Knowledge on the effects of overgrazing on reptiles, which are an important part of the ecosystem, are missing. Furthermore, the impact of habitat degradation on factors of a species population dynamic and life history, e.g., birth rate, survival rate, predation risk, space requirements or behavioural adaptations are poorly known. Therefore, I investigated the impact of overgrazing on the reptile community in the southern Kalahari. Secondly I analysed population dynamics and the behaviour of the Spotted Sand Lizard, Pedioplanis l. lineoocellata. All four chapters clearly demonstrate that habitat degradation caused by overgrazing had a severe negative impact upon (i) the reptile community as a whole and (ii) on population parameters of Pedioplanis l. lineoocellata. Chapter one showed a significant decline of regional reptile diversity and abundance in degraded habitats. In chapter two I demonstrated that P. lineoocellata moves more frequently, spends more time moving and covers larger distances in degraded than in non-degraded habitats. In addition, home range size of the lizard species increases in degraded habitats as shown by chapter three. Finally, chapter four showed the negative impacts of overgrazing on several population parameters of P. lineoocellata. Absolute population size of adult and juvenile lizards, survival rate and birth rate are significantly lower in degraded habitats. Furthermore, the predation risk was greatly increased in degraded habitats. A combination of a variety of aspects can explain the negative impact of habitat degradation on reptiles. First, reduced prey availability negatively affects survival rate, the birth rate and overall abundance. Second, the loss of perennial plant cover leads to a loss of niches and to a reduction of opportunities to thermoregulate. Furthermore, a loss of cover and is associated with increased predation risk. A major finding of my thesis is that the lizard P. lineoocellata can alter its foraging strategy. Species that are able to adapt and change behaviour, such as P. lineoocellata can effectively buffer against changes in their environment. Furthermore, perennial grass cover can be seen as a crucial ecological component of the vegetation in the semi-arid savannah system of the southern Kalahari. If perennial grass cover is reduced to a certain degree reptile diversity will decline and most other aspects of reptile life history will be negatively influenced. Savannah systems are characterised by a mixture of trees, shrubs and perennial grasses. These three vegetation components determine the composition and structure of the vegetation and accordingly influence the faunal diversity. Trees are viewed as keystone structures and focal points of animal activity for a variety of species. Trees supply animals with shelter, shade and food and act as safe sites, nesting sites, observation posts and foraging sites. Recent research demonstrates a positive influence of shrub patches on animal diversity. Moreover, it would seem that intermediate shrub cover can also sustain viable populations in savannah landscapes as has been demonstrated for small carnivores and rodent species. The influence of perennial grasses on faunal diversity did not receive the same attention as the influence of trees and shrubs. In my thesis I didn’t explicitly measure the direct effects of perennial grasses but my results strongly imply that it has an important role. If the perennial grass cover is significantly depleted my results suggest it will negatively influence reptile diversity and abundance and on several populations parameters of P. lineoocellata. Perennial grass cover is associated with the highest prey abundance, reptile diversity and reptile abundance. It provides reptiles both a refuge from predators and opportunities to optimise thermoregulation. The relevance of each of the three vegetation structural elements is different for each taxa and species. In conclusion, I can all three major vegetation structures in the savannah system are important for faunal diversity.
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Snyder, Matthew Thomas. "Geochemical Trends Associated with the seawater-freshwater mixing zone in a Surficial Costal Aquifer, Sapelo Island, GA." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/26017.
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Langman, Jeff B. "A multi-tracer study of saltwater origin, cross-formational flow, and the geochemical evolution of groundwater in the southern High Plains Aquifer along the western caprock escarpment, east-central New Mexico." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2008. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Ryan, Mikel R. "AN INTRODUCTION TO SPECTRUM REALLOCATION LEGISLATION." International Foundation for Telemetering, 1999. http://hdl.handle.net/10150/608743.
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International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, NevadaIn the past four years Congress has passed legislation mandating the reallocation of 255 MHz of radio frequency bands from Federal to non-Federal or “MIXED USE.” Several of the frequency bands supporting telemetering functions were affected, and more legislation of this nature is forecasted.