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Giardina, Mariah. "Challenges and Strategies for Spring Ecosystem Restoration in the Arid Southwest." Arizona-Nevada Academy of Science, 2011. http://hdl.handle.net/10150/296987.
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Whittington-Jones, Gareth Morgan. "The role of aardvarks (Orycteropus afer) as ecosystem engineers in arid and semi-arid landscapes of South Africa." Thesis, Rhodes University, 2007. http://hdl.handle.net/10962/d1005445.
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Arid and semi arid environments are characterised by extreme fluctuations in temperature and low rainfall which present significant challenges to the animals inhabiting these areas. Mammals, such as aardvarks (Orycteropus afer, Pallas 1766), excavate burrows in order to avoid predators and climatic extremes and are termed “ecosystem engineers” as they physically modify their environment and in doing so create new habitats and alter the availability of resources to other species. In this study I assessed the microhabitat conditions (maximum and minimum temperature, relative humidity and seed abundance) of aardvark burrows in relation to paired control sites. In addition, I evaluated the use of aardvark burrows by other vertebrate and invertebrate species and investigated the impact of aardvark burrow mounds on landscape scale floristic diversity. Maximum temperatures were significantly lower (p < 0.05) and minimum temperatures and midday humidity were significantly higher (p < 0.05) inside the burrows at the three study sites, Kwandwe Private Game Reserve (Kwandwe), Mountain Zebra National Park (MZNP) and Tswalu Kalahari Reserve (Tswalu). There were no significant differences between the concentration of seeds, the average numbers of unique individual small mammals, trap success or small mammal species richness recorded inside the burrows compared to outside (p > 0.05). At all three sites, small mammal species diversity was higher in the burrows but this result was also not significant (p > 0.05 for all). Trap success and the number of individuals captured was higher at Tswalu than the other two sites (p < 0.05 for both). The different methods used in this study revealed a total of 25 mammal, seven bird, one amphibian and six reptile species utilising aardvark burrows. There were significant differences in insect community assemblages between the burrows and open control areas at Kwandwe and Tswalu (p < 0.05 for both) but not at MZNP (p > 0.05). The parasitic guild was more prominent inside the burrows than outside but their abundance was not as high as anticipated, possibly due to the placement of traps closer to the burrow entrances than the sleeping chambers. The complex structure of the burrows prevented the placement of traps in close proximity to the sleeping chambers. As expected, the amount of bare earth was significantly higher on active and recently abandoned burrow mounds compared to the old burrow mounds and reference plots at all three sites (p < 0.05 for all), with the exception of the active burrows at Tswalu. Overall, the different plot types were characterised by significantly different plant communities during all the seasons at MZNP, during three of the seasons at Kwandwe and only during winter at Tswalu. The total species richness recorded on the reference plots was higher than on the burrow mounds at all three sites. However, species diversity on the reference plots was not significantly higher than the burrows at any of the sites (p > 0.05 for all sites). Although the results were not significant, the overall species diversity at a site level was greater than the reference patches at Kwandwe and Tswalu (p > 0.05 for both). Aardvarks fulfil the criteria of a significant ecosystem engineer and their presence in arid and semi-arid environments is likely to be critical to the survival of other individual organisms and species, particularly when alternative burrowing animals are either absent or restricted in their activities. Thus, aardvark populations should be considered a conservation priority in arid and semi-arid ecosystems.
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Snyder, Keirith A. 1967. "Patterns of plant species diversity and composition in a semi-arid riparian ecosystem." Thesis, The University of Arizona, 1995. http://hdl.handle.net/10150/278513.
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Understanding plant community structure is fundamental to successful restoration and conservation of riparian ecosystems. High plant species diversity is often cited as an important characteristic of riparian areas. Graphical summaries, principal components analysis, and analysis of variance were used on species composition and abundance data to determine community patterns in riparian areas and surrounding uplands. Woody plant composition varied with relative elevation above the primary channel, but herbaceous composition appeared unaffected by proximity to the riparian area. Alpha diversity indices, richness, Shannon's H', and Simpson's D, were not always higher within the riparian area. Alpha diversity of woody plants demonstrated no consistent pattern, however vertical structural diversity was highest near the stream. Herbaceous plants showed increased diversity in floodplain sites and decreased diversity in hillslopes sites, suggesting that topographical profile influenced diversity. Herbaceous richness was better predicted from overstory characteristics than herbaceous biomass and environmental variables.
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Maphangwa, Khumbudzo Walter. "Lichen thermal sensitivities, moisture interception and elemental accumulation in an arid South African ecosystem." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_7139_1307950118.
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Elevated temperatures accompanying climate warming are expected to have adverse effects on sensitive lichen species. This premise was examined by measuring the sensitivity of different lichen species to elevated temperatures in the laboratory and in the field. Laboratory studies involved the exposure of nine hydrated lichen species (Xanthoparmelia austro-africana, X. hyporhytida, Xanthoparmelia sp., Xanthomaculina hottentotta, Teloschistes capensis, Ramalina sp., Flavopuntelia caperata, Lasallia papulosa, Parmotrema austrosinensis) collected from sites of different aridity and mean annual temperature for 2 hourly intervals to temperatures ranging from 24º
C to 48º
C in a forced daft oven and measuring their respiration rates and maximum quantum yield of PSII. Field studies involved simultaneous hourly measurements of ground surface air temperatures and Lichen effective quantum yield of PSII of hydrated lichen species populations under ambient and artificially modified environmental conditions.
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James, Alexandra Iona Biological Earth & Environmental Sciences Faculty of Science UNSW. "Development of resource-rich patches by soil-disturbing animals in arid environments." Awarded by:University of New South Wales. Biological, Earth & Environmental Sciences, 2009. http://handle.unsw.edu.au/1959.4/44353.
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In arid landscapes limited resources are concentrated into fertile patches that allow greater productivity than would otherwise be expected. Fertile patches are created and maintained by processes that modify soil topography and interrupt the flow of resources across the landscape. These processes may be abiotic or biotic in origin. Species that modify, maintain or create habitat have been termed ecosystem engineers. One group of soil disturbing ecosystem engineers creates fertile patches by modifying soil microtopography through foraging for food and creating habitat. This thesis examines the effects of soil foraging animals on resource concentration in arid environments and how effects are moderated by species and landscape. Chapter 1 provides an overview of the importance of fertile patches in arid systems and describes previous research on the effects of ecosystem engineers in arid environments. Chapter 2 examines how fertile patch creation by a well-studied arid zone engineer, the ant, varies between ant species and landforms, demonstrating that while we can generalise about the effects of ant nests on water flow and nutrient levels, differences in soil type, nest density and ant species across sites are likely to moderate these effects. Chapters 3, 4 and 5 compare the engineering effects of reintroduced native species, the Greater bilby (Macrotis lagotis) and Burrowing bettong (Bettongia lesueur) with the Sand goanna (Varanus gouldii) and the invasive European rabbit (Oryctolagus cuniculus) across three Australian landforms, revealing differences between reintroduced and invasive engineers at the both patch and landscape scales. At the landscape scale, differences in pit densities and resource concentration in foraging pits between landforms suggest that fertile patch development is not uniform. Chapter 6 examines whether the structure of the pit or the presence of litter per se explains observed increases in plant germination in foraging pits, and compares temperature and soil moisture conditions in bilby and bettong pits to the soil surface. Chapter 7 is a review that builds upon previous chapters, published and unpublished literature of the potential for reintroductions of ecosystem engineers to restore ecosystem function in degraded environments. Chapter 8 summarises the research presented in this thesis and its implications, and suggests directions for future work.
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Petersen, Leif Michael. "Granivores as ecosystem regulators of woody plant increasers in semi-arid Savannas of the Lowveld, South Africa." Thesis, University of the Western Cape, 2006. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_8725_1210750329.
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In recent years, a global trend of increasing woody vegetation densities in semi-arid savanna habitats has been recorded, commonly described in South Africa as 'bush encroachment'. The shrubs and trees that do this (Increasers) have wrought significant economic and ecological impacts upon carrying capacities of large areas of savannas. This occurs, as suitable grazing areas are incrementally engulfed in shrubs and trees establishing new equilibria, from open savannas (essentially grasslands with scattered trees) into closed woodlands (treelands with scattered grasses). This thesis demonstrated a link between grass biomass, small mammal abundance and diversity, and their potential increaser seed/seedling predatory activities in the semi-arid Lowveld Savannas of South Africa.
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Aralova, Dildora, Kristina Toderich, Ben Jarihani, Dilshod Gafurov, Liliya Gismatulina, Babatunde A. Osunmadewa, and Abualgasim Majdaldin Rahamtallah. "Environmental resilience of rangeland ecosystems: Assessment drought indices and vegetation trends on arid and semi-arid zones of Central Asia." SPIE, 2016. https://tud.qucosa.de/id/qucosa%3A35118.
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The Central Asian (CA) rangelands is a part of the arid and semi-arid ecological zones and spatial extent of drylands in CA (Tajikistan, Kazakhstan, Uzbekistan, Kyrgyzstan, and Turkmenistan) is vast. Projections averaged across a suite of climate models, as measured between 1950-2012 by Standardised Precipitation-Evapotranspiration Index (SPEI) estimated a progressively increasing drought risks across rangelands (Turkmenistan, Tajikistan and Uzbekistan) especially during late summer and autumn periods, another index: Potential Evapotranspiration (PET) indicated drought anomalies for Turkmenistan and partly in Uzbekistan (between 1950-2000). On this study, we have combined a several datasets of drought indices ( SPIE, PET, temperature_ToC and precipitation_P) for better estimation of resilience/non-resilience of the ecosystems after warming the temperature in the following five countries, meanwhile, warming of climate causing of increasing rating of degradations and extension of desertification in the lowland and foothill zones of the landscape and consequently surrounding experienced of a raising balance of evapotranspiration (ET0). The study concluded, increasing drought anomalies which is closely related with raising (ET0) in the lowland and foothill zones of CA indicated on decreasing of NDVI indices with occurred sandy and loamy soils it will resulting a loss of vegetation diversity (endangered species) and raising of wind speeds in lowlands of CA, but on regional level especially towards agricultural intensification (without rotation) it indicated no changes of greenness index. It was investigated to better interpret how vegetation feedback modifies the sensitivity of drought indices associated with raising tendency of air temperature and changes of cold and hot year seasons length in the territory of CA.
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John, Ranjeet. "The Effects of Land cover/Land Use Change on Ecosystem Functions in Semi-arid Inner Mongolia." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1294335117.
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White, II David Allen. "Vegetation Controls on the Dynamics and Quality of Soil Organic Carbon in an Arid, Hyperthermic Ecosystem." Thesis, The University of Arizona, 2008. http://hdl.handle.net/10150/193315.
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Arid lands comprise vast regions of terrestrial land, highlighting the importance of understanding their role in the global carbon cycle. The objective of this study was to determine the effect of Prosopis velutina (mesquite), Larrea tridentata (creosote) and a combination of Bouteloua barbata, Bouteloua aristidoides, Aristida adscensionis, and some Cynodon dactylon (mixed grass) vegetation types on soil organic carbon (SOC) dynamics and quality in an arid, hyperthermic ecosystem of southern Arizona. This was accomplished by quantifying vegetation type control over: (i) local scale SOC stocks; (ii) soil aggregate stability; (iii) SOC turnover and microbial community composition; (iv) the distribution of SOC in physically defined fractions; and (v) the thermal nature and composition of SOC. The results from this study demonstrated significant variation in SOC dynamics and quality between vegetation with potential feedbacks to SOC sequestration of atmospheric CO₂.
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Waswa, Peter Fuchaka. "Abiophysical analysis of erosion damage in a semi-arid agro-ecosystem in Kenya : towards sustainable land management /." Bonn : Inst. für Städtebau, Bodenordnung und Kulturtechnik, Lehrstuhl für Landwirtschaftlichen Wasserbau und Kulturtechnik, 2000. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=009329302&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Seidel, Richard Alan. "Conservation Biology of the Gammarus pecos Species Complex: Ecological Patterns across Aquatic Habitats in an Arid Ecosystem." Miami University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=miami1251472290.
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Mitchell, Patrick John. "From conduits to communities : plant water use strategies and evapotranspiration in a semi-arid ecosystem in south-western Australia." University of Western Australia. School of Plant Biology, 2009. http://theses.library.uwa.edu.au/adt-WU2010.0034.
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[Truncated abstract] Understanding the ecohydrological dynamics of native vegetation can provide a benchmark for future efforts to restore landscape hydrology and allow predictions of potential landscape responses to climate uncertainty and associated changes in vegetation cover. The key drivers of evapotranspiration (Et) involved in maintaining a hydrological balance that minimises deep drainage in semi-arid ecosystems operate at a range of scales, and in this thesis I assessed the water relations of functionally and taxonomically diverse plant communities in south-western Australia from the leaf-level to ecosystem scale. For three key communities; heath shrubland, mallee (small multistemmed eucalypt) -heath, and open eucalypt woodland, populating a typical catenary sequence of soil types along a slope, I addressed the following questions: 1) What are the predominant water use strategies of wheatbelt native plant communities and what underlying trade-offs determine the distribution of plant water use strategies along the topographical gradient? 2) What are the roles of soil water and hydraulic limitation in controlling the spatial and temporal dynamics of transpiration in different functional types? 3) What is the magnitude and partitioning of total Et in the woodland community and what processes determine Et fluxes on a seasonal and annual basis? 4) What are the seasonal differences in Et among contrasting community-types and how do these patterns relate to canopy attributes and transpiration capacity along the topographical gradient? A key philosophical step in working with species-rich communities was to develop the concept of 'hydraulic functional types' (HFTs) to identify groupings of species using associations of physiological and morphological traits that define their hydrological functioning. .... However, as shallow soils dried during spring and summer, Et fluxes were significantly lower at the heath site (0.35 versus 0.66 mm day-1 for the woodland in February), demonstrating that the seasonality of Et fluxes differentiates communityscale contributions to regional water balance. Land-surface exchange of water over native vegetation is by no means uniform, but varies according to the spatial and temporal availability of water along topographical gradients. In general, shallow soils present fewer opportunities for water use partitioning and favour drought hardiness and a transpiration response that tracks recent rainfall patterns, whereas deeper soils promote greater differentiation in water use strategy and support canopies responsive to atmospheric demand. This thesis provides a unique description of ecosystem water balance in a global biodiversity hotspot by viewing complex vegetation mosaics in terms of their relevant hydrological units. This information is fundamental to sustainable agroforestry and revegetation efforts and our ability to gauge possible changes in vegetation structure and function under a changing climate.
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Simelane, Qandelihle G. S. N. "Temporal and Spatial Impacts of Termites on Local Soil and Vegetation Dynamics in a Semi Arid Savanna Ecosystem." Thesis, University of Newcastle Upon Tyne, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515051.
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Otieno, Dennis O. "Coordinated tree responses to drought vulnerability and sustainable production ; hypotheses on arid ecosystem adjustments to limitations in water resources /." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973199881.
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Grohmann, Constanze [Verfasser], and K. E. [Akademischer Betreuer] Linsenmair. "Termite mediated heterogeneity of soil and vegetation patternsin a semi‐arid savanna ecosystem in Namibia / Constanze Grohmann. Betreuer: K. E. Linsenmair." Würzburg : Universität Würzburg, 2011. http://d-nb.info/1102808806/34.
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Chambers, Samuel Norton. "Corridors and Elk Migration: A Comparative Analysis of Landscape Connectivity Models and GPS Data in the Greater Yellowstone Ecosystem." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/577193.
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Landscape connectivity models aim to map the links or corridors that wildlife would or do use between patches of habitat. Migratory species such as elk traverse between such patches which serve as seasonal ranges. The goal of this study was to compare and contrast the suitability of several landscape connectivity models for describing and predicting migration in a long-distance migrant. We measured the suitability of connectivity models for covering and predicting the migratory movements of elk in the Greater Yellowstone Ecosystem. GPS point data was converted to sequential networks for multiple populations of elk. GPS data was also used to delineate the summer and winter ranges of each population. The kernel density of routes in the networks was measured for comparison to connectivity models. The ranges served as the patches to be connected by such models. A resistance surface was produced using reclassified landcover data for mapping habitat suitability and linear road data for human presence or obstruction to movement. Landscape connectivity was measured for eleven migratory elk populations using three distinct models. The first measured connectivity using circuit theory; the second, agent based modeling; the third, least cost corridors. The model results were compared to the migratory network density by measuring correlation. This was followed by a new method of measuring the influence of autocorrelation between the models and networks. Some of the models were then altered to test for suspected influences. This study shows that least cost corridors and circuit theory can are limited in their ability to predict the migratory movements between summer and winter ranges but only so much. They lack the ability to predict exploratory movements that do not link conspicuous ranges to each other. They also lack the ability to account for all avoidance behaviors in the landscape. Our results suggest that connectivity models need improvement by accounting for exploration outside of prime habitat. It also suggests connectivity models are not adequate predictors of migratory movements and not suited to conservation planning of migratory networks. This supports Sawyer's (et al. 2009) ungulate conservation planning of considering connectivity but basing priority on migratory landscape usage. It is assumed that fragmentation or loss in connectivity impedes seasonal migration, cutting off wildlife from resources (Rudnick et al. 2012). This study shows that migratory elk are actually using less than prime and supposedly fragmented habitat in migration and that there is more than connectivity at play.
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GonÃalves, Ana Maria. "Study of the ecosystem of the ciliary forest of the brooks Cipà and Carrapateiras: Tauà - Ce." Universidade Federal do CearÃ, 2003. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=1631.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorAs sub-bacias dos riachos Cipà e Carrapateira estÃo inseridas nos Distritos de Barra Nova e Carrapateira, os quais fazem parte do MunicÃpio de Tauà â CE. Estas sub-bacias estÃo em uma das Ãreas mais degradadas do MunicÃpio de TauÃ, segundo estudos do Projeto WAVES. O MunicÃpio de Tauà possui 1.906,3 km de Ãreas degradadas suscetÃveis a desertificaÃÃo, o que representa 44,3% da Ãrea municipal, sendo caracterizada, segundo os Ãndices estabelecidos pela ONU, como Ãrea semi-Ãrida com alto Ãndice crÃtico (0,4), que reflete a fragilidade das terras secas. Configura-se com as seguintes limitaÃÃes geoecolÃgicas naturais: predominÃncia de rochas do embasamento cristalino, temperatura mÃdia em torno de 25ÂC a 28ÂC, propiciando intensa evapotranspiraÃÃo e, conseqÃentemente, Ãndices negativos no balanÃo hÃdrico anual; solos rasos e pedregosos; cobertura vegetal ciliar degradada em face da secular atividade agroextrativista, favorecendo o assoreamento do leito, alargamento das margens, o que acarreta riscos no potencial hÃdrico e pedolÃgico da regiÃo. A aÃÃo conjunta do clima, das condiÃÃes geolÃgicas e dos solos rasos da regiÃo produz um ecossistema frÃgil, que se reflete na vegetaÃÃo da regiÃo, onde a formaÃÃo caducifÃlia, com fisionomia arbÃreo-arbustiva, à incapaz de oferecer proteÃÃo aos solos contra os efeitos erosivos, conforme observado na Ãrea de estudo. Em virtude de a vegetaÃÃo ciliar encontrar-se seriamente ameaÃada pelo uso inadequado do solo, existe a necessidade de estudos especializados, como: composiÃÃo florÃstica e estrutura da comunidade, para verificar a condiÃÃo da comunidade vegetal no seu estado atual, com vistas ao seu aproveitamento racional e sustentabilidade, ante a situaÃÃo de desequilÃbrio em que esta se encontra. Vale ressaltar que a proteÃÃo da mata ciliar à de extrema importÃncia para a boa condiÃÃo dos recursos hÃdricos. A importÃncia da preservaÃÃo ou restauraÃÃo das florestas ao longo dos rios e ao redor de lagos e reservatÃrios fundamenta-se no amplo espectro de benefÃcios que este tipo de vegetaÃÃo traz ao ecossistema, exercendo funÃÃo protetora sobre os recursos naturais biÃticos e abiÃticos. Deste modo, a pesquisa preconizou os seguintes objetivos fundamentais: a) analisar o ecossistema mata ciliar dos riachos Cipà e Carrapateiras, de forma a obter indicadores de degradaÃÃo ambiental, verificando-se atravÃs dos efeitos das atividades agropecuÃrias e o extrativismo vegetal, sobre as condiÃÃes das comunidades potenciais dessa vegetaÃÃo, associando-as aos demais componentes ambientais e; b) fazer levantamento fitossociolÃgico da mata ciliar, fornecendo subsÃdios para um banco de dados que conduza ao uso sustentÃvel da terra para evitar ou deter o processo de degradaÃÃo, propiciando uma melhor qualidade de vida para a populaÃÃo local. Os estudos fitossociolÃgicos apontaram diferenciaÃÃes bastante significativas entre as duas Ãreas amostrais, onde a mata do riacho Cipà se apresentou mais conservada com exemplares de mata ciliar, enquanto que a mata do riacho Carrapateiras se encontra totalmente descaracterizada em funÃÃo da forte aÃÃo antrÃpica.
The sub-basins of the Cipà and Carrapateira belong to the districts of Barra Nova and Santo AntÃnio, which are part of Tauà Town in Cearà State, Brazil. These sub-basins are situated in one of the most degraded areas in Tauà Town, according to studies of the WAVES Project. Tauà Town has 1,906.3 km of degraded areas susceptible to desertification, what represents 44.3% of the municipal area, being characterized, according to the indexes established by the United Nations Organization, as a semi-arid area with a high critical index (0.4), what expresses the fragility of the dry lands. It has the following natural geo-ecological limitations: predominance of rocks having a crystalline base, average temperature around 25ÂC to 28ÂC, enabling a high evaporation rate and, as a result, negative values in the annual water balance; shallow and stony soils; a degraded ciliary plant cover due to the secular agro-extractivist activity, favoring sediment deposition in the riverâs bed and the river marginsâ widening, what endangers the water and pedological potential of the region. The combined action of the weather, of the geological conditions and the shallow soils of the region produces a fragile ecosystem, which reflects on the vegetation in the area, in which the caducifolia formation, with an arboreous and shrubby physiognomy, is unable to offer protection to the soils against the erosive effects, as observed in the study area. Because the ciliary vegetation is seriously threatened by the inadequate soil use, there is a need of detailed studies, such as: floristic composition and structure of the community, to check the plant community's condition in its current state in order to enable its rational use and sustainability in view of the unbalance in which it is. It is worth pointing out that the protection of the ciliary forest is of utmost importance for the good condition of water resources. It is important to preserve and restore the forests along the rivers and around lakes and reservoirs because that vegetation brings lots of benefits to the ecosystem, having the function of protecting the biotic and abiotic natural resources. This way, the research had the following main objectives: a) to analyze the ecosystem of the ciliary forest of the brooks Cipà and Carrapateiras, in order to obtain indicators of environmental degradation by checking the effects of agricultural activities and of the vegetable extractivism on the conditions of the potential communities of that vegetation conditions, combining those activities with other environmental factors, and; b) to make a phytosociological survey of the ciliary forest, supplying information to a database that leads to the sustainable land use to avoid or stop the degradation process, enabling a better life quality for the local population. The phytosociological studies showed significant differences between the two sample areas, in which the forest of the brook Cipà was more conserved with specimen of the ciliary forest, while the forest of the brook Carrapateiras totally is completely uncharacterized because of the high anthropic action.
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Ndhlovu, Thabisisani. "Impact of Prosopis (mesquite) invasion and clearing on ecosystem structure, function and agricultural productivity in semi-arid Nama Karoo rangeland, South Africa." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6751.
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Thesis (MScConEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: I evaluated the impact of Prosopis invasion and clearing on ecological structure, function and agricultural productivity in heavily grazed Nama Karoo rangeland on two sheep farms near the town of Beaufort West in the Western Cape Province of South Africa. My aims were to (1) determine the effects of invasion and clearing on rangeland vegetation composition, diversity (alien and indigenous species richness) and structure (alien and indigenous species cover), soil vegetation cover (plant canopy and basal cover) and agricultural productivity (grazing capacity), (2) describe the vegetation processes that underlay the invasion and clearing impacts and (3) evaluate the success of clearing in facilitating unaided restoration of ecological structure, function and agricultural productivity in formerly invaded rangeland. I hypothesised that invasion would significantly change rangeland vegetation composition and structure, leading to greater alien species richness and cover and lower indigenous species richness and cover while clearing would lead to lower alien species diversity and cover and greater indigenous species richness and cover. In addition I hypothesized that invasion would reduce rangeland plant canopy and basal cover and grazing capacity while clearing would substantially increase them. Finally I predicted that vegetation composition, alien and indigenous species cover and richness, plant canopy and basal cover and grazing capacity would revert to pre-invasion status and levels within four to six years of clearing. My results suggest that in heavily grazed Nama Karoo rangeland Prosopis invasion (~15 percent canopy cover) and clearing can significantly change rangeland vegetation composition, with invasion leading to greater alien species cover and lower indigenous species richness, while clearing leads to lower alien species richness and cover and greater indigenous species richness and cover. However invasion seems to have no effect on alien species richness and overall indigenous species cover. Clearing appears to facilitate the spontaneous restoration of alien species cover and indigenous species richness within four to six years but not species composition, alien species richness and indigenous species cover. In addition my results also indicate that Prosopis invasion can lower rangeland plant canopy and basal cover and grazing capacity while clearing, even under heavy grazing, can substantially raise them. Clearing however does not seem to facilitate the restoration of rangeland plant canopy and basal cover and grazing capacity to pre-invasion levels within four to six years after clearing.
AFRIKAANSE OPSOMMING: Ek het die impak van Prosopis indringing en verwydering van indringers op ekologiese struktuur, funksie en landbou produktiwiteit in ‘n swaar beweide Nama Karoo gebied op twee skaapplase naby Beaufort-Wes in die Wes-Kaap provinsie van Suid-Afrika geëvalueer. My doelwitte was om (1) te bepaal wat die gevolge van die indringing en verwydering van indringers op die natuurlike plantegroei samestelling, diversiteit (uitheemse en inheemse spesiesrykheid) en struktuur (uitheemse en inheemse spesies bedekking) sal wees, sowel as die effek op plantegroei bedekking (kroon en basalebedekking) en landbou produktiwiteit (weidingkapasiteit), (2) die plantegroei prosesse te beskryf wat onderliggend deur die impakte van indringing en verwydering van indringers veroorsaak word, en (3) die sukses van die verwydering van indringers te evalueer deur die fasilitering van blote restorasie van ekologiese struktuur en funksie en landbou produktiwiteit in voorheen ingedringde gebiede. My hipotese is dat indringing ‘n aansienlike verandering in natuurlike plantegroeisamestelling en struktuur sal veroorsaak, wat sal lei tot groter uitheemse spesiesrykheid en bedekking met minder inheemse spesiesrykheid en bedekking, terwyl die verwydering van indringers sou lei tot minder uitheemse spesie diversiteit en bedekking met 'n groter inheemse spesiesrykheid en bedekking. Verder vermoed ek dat indringing die natuurlike kroon- en basalebedekking en weidingkapasiteit sal verminder, terwyl die verwydering van indringers dit aansienlik sal verhoog. Ten slotte voorspel ek dat plantegroei samestelling, uitheemse en inheemse spesiesbedekking en -rykheid, kroon- en basalebedekking en weidingkapasiteit sou terugkeer na voor-indringing status en vlakke binne vier tot ses jaar na die verwydering van indringers. My resultate daarop dat die indringing van Prosopis (~ 15 persent kroonbedekking) en die verwydering van indringers in swaar beweide Nama Karoo gebiede ‘n aansienlike verandering in die gebied se natuurlike plantegroei samestelling toon, waar indringing gelei het tot groter uitheemse spesiesbedekking en minder inheemse spesiesrykheid, terwyl die verwydering van indringers lei tot minder uitheemse spesiesrykheid en groter inheemse spesiesrykheid en - bedekking. Dit lyk egter of indringing geen effek op uitheemse spesiesrykheid en algehele inheemse spesiesbedekking het nie. Die verwydering van indringers blyk om die spontane herstel van indringerbedekking en inheemse spesiesrykheid binne vier tot ses jaar te fasiliteer, maar nie spesiesamestelling, uitheemse spesiesrykheid of inheemse spesiesbedekking nie. Benewens dui my resultate ook aan dat Prosopis indringing die natuurlike kroon- en basalebedekking sowel as weidingskapasiteit verlaag, terwyl die verwydering van indringers, selfs onder swaar beweiding, die bedekking aansienlik kan verhoog. Verwydering van indringers lyk egter nie asof dit die herstel van die gebied se natuurlike kroon- en basalebedekking en weidingkapasiteit na voor-indringing vlakke toe kan fasiliteer binne vier tot ses jaar na die verwydering van indringers nie.
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De, Abreu Petra. "The short-term effect of rehabilitation on ecosystem services in the semi-arid succulent Karoo lowlands and the Little Karoo, South Africa." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/10422.
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This study has shown that using active rehabilitation in combination with improved management strategies (e.g. rest from grazing) may induce recovery of certain ecosystem services within practically relevant time scales. However, these benefits might not be tangible for landowners or society as of yet, due to the small-scale nature of the rehabilitation application along with the relatively high, short-term associated costs. To alleviate financial constraints on farmers and in order to socially and financially enhance local communities, the focus for now should be on sourcing funds from government and private sectors for rehabilitation implementation.
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DINIZ, Jurema Diniz. "Teores de glomalina e subst?ncias h?micas em diferentes est?gios sucessionais de floresta seca." Universidade Federal Rural do Rio de Janeiro, 2011. https://tede.ufrrj.br/jspui/handle/jspui/1201.
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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES
This study contributes to understanding the relationship between tropical dry forests regeneration and arbuscular mycorrhizal fungi activity. The specific objective of this study is to extract and quantify glomalin, glomerospores and humic substances in different sucessional stages of a dry forest. The main objective is to study the activity of AMFs in different stages of a dry forest and to colabore to the projects: ?Functional links between aboveground changes and belowground activity with land use in the Americas: Soil biodiversity and food security? e ?Human, Ecological and Biophysical Dimensions of Tropical Dry Forest?. Total Glomalin (TG) and carbon levels were higher in inicial and late stage of dry forest, indicating the carbon storage contribution to glomalin in soil. In addition, the higher number of glomerospores in this sucessional stage shows the more activity of AMF and its potential to regeneration of disturbed dry forests. The different chemical and physical properties of soil in intermediate stage possibly contributed to low glomalin and carbon levels. The higher levels of humic substances in this stage possibly contribute to the lower activity of AMF and can be explained by the higher diversity of plants in this area. It is important to study the influence of physical and chemical properties, humic substances and plant diversity in AMF activity, in different sucessional stages of dry forests.
Este trabalho contribui para o entendimento da rela??o da regenera??o de florestas tropicais secas, com a atividade dos fungos micorr?zicos arbusculares (FMAs). Tem como objetivos espec?ficos: a extra??o e a quantifica??o de glomalina, de glomerosporos e de subst?ncias h?micas em diferentes sucess?es de floresta seca. O objetivo ? avaliar a atividade dos FMAs em diferentes est?gios sucessionais de floresta seca, acrescentando e colaborando assim para o desenvolvimento dos projetos: ?Functional links between aboveground changes and belowground activity with land use in the Americas: Soil biodiversity and food security? e ?Human, Ecological and Biophysical Dimensions of Tropical Dry Forest?. Os teores de glomalina total e de carbono org?nico foram maiores na ?rea de sucess?o inicial e tardia de floresta seca, indicando maior influ?ncia do estoque de carbono na glomalina do solo. O maior n?mero de esporos e glomalina, na ?rea de sucess?o inicial, mostrou a maior atividade dos fungos micorr?zicos arbusculares em ?rea perturbada que est? se regenerando, sugerindo a contribui??o dos FMAs para essa recupera??o do ecossistema de florestas secas. As propriedades f?sicas e qu?micas diferentes do solo na ?rea de sucess?o intermedi?ria provavelmente contribu?ram para a baixa concentra??o de glomalina e carbono. Os maiores teores de ?cidos h?micos e f?lvicos no solo de sucess?o intermedi?ria podem ter contribu?do tamb?m para a baixa atividade dos FMAs e podem ser devidos ? maior diversidade de esp?cies vegetais nesta ?rea. ? importante desenvolver estudos que comparem as propriedades qu?micas e f?sicas do solo com a atividade desses microorganismos simbiontes em diferentes sucess?es vegetais; que analisem a influ?ncia das subst?ncias h?micas na atividade dos FMAs em campo; e da influ?ncia da diversidade de esp?cies vegetais na atividade dos FMAs.
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Schiborra, Anne Kathrin [Verfasser]. "Short-term effects of defoliation on herbage productivity and herbage quality in a semi-arid grassland ecosystem of Inner Mongolia, P.R. China / Anne Kathrin Schiborra." Kiel : Universitätsbibliothek Kiel, 2010. http://d-nb.info/1019951974/34.
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Maurice, Kenji. "Structuration des communautés et des réseaux microbiens des sols et des plantes dans un écosystème aride." Electronic Thesis or Diss., Université de Montpellier (2022-....), 2024. http://www.theses.fr/2024UMONG006.
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La diversité, la composition et les assemblages du microbiome du sol et des plantes sont conditionnés en partie par l’environnement et les interactions biotiques. L’oasis d’AlUla, située dans le désert d’Arabie Saoudite, est caractérisé par de fortes contraintes abiotiques, liées à un pH hyper alcalin et à la faible disponibilité en eau et en nutriments. L’activité et la croissance des organismes est donc soumise à cette disponibilité ponctuelle et spatialement hétérogène des ressources. En résulte une répartition spatiale discontinue des végétaux, les îlots de fertilité, qui influencent la composition du sol et des communautés microbiennes. Les plantes sont également associées dans des relations symbiotiques à des microorganismes, qui vont influencer leur santé, leur résistance à la sècheresse, améliorer l’acquisition des ressources minérales et en eau, et sont particulièrement critiques dans ces milieux à fortes contraintes. Enfin, ces écosystèmes, déjà fragilisés par le changement climatique, sont également soumis à des pressions agricoles importantes qui conduisent à une dégradation des sols et de leur biodiversité associée. La biodiversité des écosystèmes chauds et arides est aujourd’hui peu connue, particulièrement concernant l’Arabie Saoudite, un pays aux frontières longtemps restées fermées.Le but de cette thèse est de caractériser le microbiome bactérien et fongique du sol et des plantes, en lien avec son environnement, et sa réponse à différents usages des terres par le biais de séquençage d’amplicons. Afin de dépasser le cadre analytique de l’étude de la diversité et de la composition des communautés, j’ai cherché à utiliser les métriques des réseaux de co-occurrence et explorer de nouvelles méthodologies pour leur étude. Dans un premier chapitre, l’influence mutuelle des plantes, du sol et des microorganismes dans un micro-environnement, les îlots de fertilité, est caractérisée. Puis, une campagne d’échantillonnage sur le terrain au cours de deux saisons m'a permis de réaliser une analyse extensive du microbiome des plantes par l’approche des réseaux de co-occurrence. En se focalisant sur les relations intra- et inter-royaumes microbiens des taxons symbiotiques, il y est démontré la redondance de l’assortativité des champignons mycorhiziens, et de l’intégration des bactéries fixatrices d’azote dans le microbiome étendu des plantes. La réponse du microbiome à un événement simulé de précipitation sur le terrain a également permis de caractériser la réponse taxonomique du microbiome à la disponibilité en eau dans le sol. Dans un troisième chapitre, la réponse du microbiome face à des contingences historiques de nature anthropique ou naturelle, décrit comment des cycles de dessiccation et d’inondation affectent les communautés microbiennes contemporaines. Par l’étude de la stabilité de leur interaction, il y est montré comment l’activité agricole passé impacte de manière durable la structure du microbiome. Enfin, la quantification des processus d’assemblage des communautés a permis de déterminer l’effet de perturbations anciennes sur les processus de sélection bactérienne et fongique.Collectivement, les résultats de cette thèse permettent d’améliorer la compréhension de l’assemblage et de la structure du microbiote du sol et des plantes dans un écosystème désertique encore peu connu. De plus, les analyses de cooccurrence se sont révélées un outil précieux dans la formulation de nouvelles hypothèses fondamentales sur le rôle fondateur des symbioses, et de la réponse du microbiote aux perturbations. La poursuite de l’étude de la stucture complexe des réseaux, complémentée par l’étude des fonctions microbiennes et d’approches réductionnistes pour lier les relations de covariance aux processus écologiques promet de prochaines avancées majeures en écologie microbienneThe diversity, composition and assemblages of the soil and plant microbiome are partly determined by the environment and biotic interactions. The AlUla oasis, located in the Saudi Arabian desert, is characterized by strong abiotic constraints, linked to a hyper-alkaline pH and low availability of water and nutrients. The activity and growth of organisms is therefore subject to this punctual and spatially heterogeneous availability of resources. This leads to a spatially discontinuous distribution of plants, known as islands of fertility, which influence soil composition and microbial communities. Plants also form symbiotic relationships with microorganisms, which influence their health, resistance to drought and the acquisition of mineral and water resources, and are particularly critical in this ecosystem. Finally, these ecosystems, already weakened by climate change, are also subject to significant agricultural pressures, leading to soil degradation and associated biodiversity loss. Little is known at present about the biodiversity of hot, arid ecosystems, particularly in Saudi Arabia, a country whose borders have long remained closed.The goal of this thesis is to characterize the bacterial and fungal microbiome of soil and plants in relation to its environment, and its response to different land uses through amplicon sequencing. In order to extend the analytical framework of the study of community diversity and composition, I have sought to use co-occurrence network metrics and explore new methodologies for their study. In a first chapter, the mutual influence of plants, soil and microorganisms in a micro-environment, the fertility islands, is characterized. Then, a field sampling campaign over two seasons enabled me to carry out an extensive analysis of the plant microbiome using the co-occurrence network approach. Focusing on the intra- and inter-kingdom relationships of symbiotic taxa, this work demonstrated the redundant assortativity of mycorrhizal fungi, and the integration of nitrogen-fixing bacteria into the extended plant microbiome. The microbiome's response to a simulated precipitation event in the field was also used to characterize the microbiome's taxonomic response to water availability in the soil. In the third chapter, the microbiome's response to historical contingencies of an anthropogenic or natural nature, describes how cycles of desiccation and flooding affect contemporary microbial communities. By studying the stability of their interactions, it shows how past agricultural activities has had a lasting impact on the structure of the microbiome. Finally, the quantification of community assembly processes has made it possible to determine the effect of past disturbances on bacterial and fungal selection processes.Collectively, the results of this thesis improve our understanding of the assembly and structure of soil and plant microbiota in a little-known desert ecosystem. In addition, co-occurrence analyses have proven to be a valuable tool in the formulation of new fundamental hypotheses on the founding role of symbioses, and the response of the microbiota to disturbance. Continued study of the complex structure of networks, complemented by the exploration of microbial functions and reductionist approaches to be able to couple covariance relationships to ecological processes, promises major advances in microbial ecology in the future
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Fox, John Tyler. "Spatiotemporal Patterns and Drivers of Surface Water Quality and Landscape Change in a Semi-Arid, Southern African Savanna." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/81462.
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The savannas of southern Africa are a highly variable and globally-important biome supporting rapidly-expanding human populations, along with one of the greatest concentrations of wildlife on the continent. Savannas occupy a fifth of the earth's land surface, yet despite their ecological and economic significance, understanding of the complex couplings and feedbacks that drive spatiotemporal patterns of change are lacking. In Chapter 1 of my dissertation, I discuss some of the different theoretical frameworks used to understand complex and dynamic changes in savanna structure and composition. In Chapter 2, I evaluate spatial drivers of water quality declines in the Chobe River using spatiotemporal and geostatistical modeling of time series data collected along a transect spanning a mosaic of protected, urban, and developing urban land use. Chapter 3 explores the complex couplings and feedbacks that drive spatiotemporal patterns of land cover (LC) change across the Chobe District, with a particular focus on climate, fire, herbivory, and anthropogenic disturbance. In Chapter 4, I evaluated the utility of Distance sampling methods to: 1) derive seasonal fecal loading estimates in national park and unprotected land; 2) provide a simple, standardized method to estimate riparian fecal loading for use in distributed hydrological water quality models; 3) answer questions about complex drivers and patterns of water quality variability in a semi-arid southern African river system. Together, these findings have important implications to land use planning and water conservation in southern Africa's dryland savanna ecosystems.Ph. D.
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Grimm-Seyfarth, Annegret [Verfasser], Florian [Akademischer Betreuer] Jeltsch, and Klaus [Akademischer Betreuer] Henle. "Effects of climate change on a reptile community in arid Australia : exploring mechanisms and processes in a hot, dry, and mysterious ecosystem / Annegret Grimm-Seyfarth ; Florian Jeltsch, Klaus Henle." Potsdam : Universität Potsdam, 2017. http://d-nb.info/1218403748/34.
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Wellens, Jane. "Monitoring and modelling rangeland vegetation in Tunisia using satellite and meteorological data." Thesis, University of Reading, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359492.
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Lee, Enhua School of Biological Earth & Environmental Science UNSW. "The ecological effects of sealed roads in arid ecosystems." Awarded by:University of New South Wales. School of Biological, Earth and Environmental Science, 2006. http://handle.unsw.edu.au/1959.4/26265.
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The effects of roads on landscapes and wildlife and their ecological processes are substantial and represent a major anthropogenic disruption to the natural environment. Current understanding of the impacts of roads for their strategic management is hampered by a lack of information on 1) the influence of the ecosystems on road effects, 2) the effects of roads on higher-order ecosystem responses (populations and communities), and 3) the overall impacts of roads on ecosystems and their wildlife (on both abiotic and biotic ecosystem components). This study used the Silver City Highway in arid New South Wales, Australia, as a model for a typical road in an arid ecosystem to investigate the ecological effects of arid-zone roads and their management. The study examined the spatial variation of soil, vegetation, kangaroo and small mammal variables in relation to the road, explored the factors contributing to these respective spatial variations, investigated the effects of arid-zone road management on vegetation, assessed the fragmentation effect of the arid-zone road on small mammals, and determined the patterns, causes and effects of kangaroo-vehicle collisions. The study revealed that the arid-zone road influenced most of the variables measured, skewed the population demographics of two kangaroo species, and altered the community composition of small mammals, with two small mammal species listed as threatened in NSW and of national significance (Sminthopsis macroura and Leggadina forresti) negatively impacted by the road. Increases in the amount of water along the road edge drove many of the subsequent effects of the arid-zone road as arid-zone flora and fauna are adapted to exploiting limited and patchily distributed resources. However, current arid-zone road management also influenced vegetation quality, microclimates around the road influenced kangaroo densities and small mammal communities, and kangaroo flight behaviour and temporal variations in traffic volume affected roadkill frequency. Together, these results suggest that roads have a high overall ecological impact in arid ecosystems. Conservation managers need to first rank the impacts of arid-zone roads in order of their conservation importance and need for mitigation, and from there, devise relevant informed management frameworks to target these impacts.
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Potts, Daniel Lawrence. "Rainfall Variability and Carbon Cycling in Semi-Arid Ecosystems." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1338%5F1%5Fm.pdf&type=application/pdf.
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Lee, Enhua. "The ecological effects of sealed roads in arid ecosystems." Connect to this title online, 2006. http://www.library.unsw.edu.au/~thesis/adt-NUN/public/adt-NUN20070315.091920/.
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Sanchez, Cohen Ignacio. "Evaluating strip farming systems for arid ecosystems: A stochastic approach." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186696.
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The objectives of this study were: (a) to delineate a methodology for determining the feasibility of a water harvesting system for an arid ecosystem, (b) to develop a simulation model for the water balance of a water harvesting strip farming system, and (c) to perform a sensitivity analysis of the simulation model. The discussion focuses on the feasibility as constrained by risk. A computer program was developed for the computations. The results indicate that light textured soils cannot be used for this type of farming system since their hydrodynamic characteristics do not allow runoff from light rains (i.e. the threshold value is high). Medium textured soils require a minimum of 50% of initial soil water content and a CCAR of 2:1. Heavy soils require a minimum of 20% of initial soil water content and a CCAR greater than 5:1. As a general rule, the system is more efficient, in terms of water use efficiency (eᵤ), as the conditions become dryer. In this way, for CCAR ranging from 0 to 5 eᵤ is around 95% for all three textures. Beyond that point, as the CCAR increases eᵤ decreases being more efficient light soils and less efficient heavy soils. The shapes of the curves of profit, reflect the impact of weather conditions on the response of output to varying CCAR. Lack of rainfall prior to and during the growing season results in poor outputs. The risk (probability of loss) will depend on both the farmers own criteria and the economical situation. Thus, these criteria can be divided into two broad categories: risk-taking (those farmers who pursue a high level of investment relative to the probability of failure), and risk-adverse (those farmers with low level of investment relative to the probability of failure). Curves of minimum risk-maximum net benefit (minimax) were developed as a guide for decision making processes. According to the minimax curves, for medium soils, the minimum risk maximum net benefit is achieved with CCAR 2:1 and initial soil water content of 100%. This implies a risk of 0.2 and net benefit of $510.00. For heavy textured soils, the minimum risk maximum net benefit is achieved with CCAR 10:1 and initial soil water content of 100% with a risk of 0.55 and net benefit of $580.00. The sensitivity analysis indicate that the model is sensitive to: (1) initial soil water content, (2) soil depth and (3) soil texture in terms of reduction on yield (actual/potential yield).
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Abubeker, Hassen. "Characterization and evaluation of Indigofera species as potential forage and cover crops for semi-arid and arid ecosystems." Pretoria : [s.n.], 2006. http://upetd.up.ac.za/thesis/available/etd-03292006-171339.
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Zachmann, Luke J. "Drivers of Plant Population Dynamics in Three Arid to Subhumid Ecosystems." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/544.
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Understanding the relative importance of density-dependent and density-independent factors in driving population dynamics is one of the oldest challenges in ecology, and may play a critical role in predicting the effects of climate change on populations. We used long-term observational data to describe patterns in plant population regulation for 57 forb and grass species from three different ecosystems (arid desert grassland, semiarid sagebrush steppe, and subhumid mixed-grass prairie). Using a hierarchical partitioning approach, we (i) quantified the relative influence of conspecific density, heterospecific composition, and climate on temporal variation in population growth rates, and (ii) asked how the relative importance of these drivers depends on site aridity, species growth form and life expectancy, and abundance and spatial patterns. The data from one of the sites in this analysis are presented in one of the chapters of this thesis. We found that density-dependence had the strongest effect on species. Climate often had a significant effect, but its strength depended on growth form. Community composition rarely explained significant variation in growth rates. The relative importance of density, composition, and climate did not vary among sites, but was related to species' life histories: compared to forbs, grasses were more sensitive to climate drivers. Abundance and spatial clustering were negatively correlated with the importance of density dependence, suggesting that local rarity is a consequence of self-limitation. Our results show that interspecific interactions play a weaker role than intraspecific interactions and climate variability in regulating plant populations. Forecasting the impacts of climate change on populations may require understanding how changes in climate variables will affect the strength of density-dependence, especially for rare species.
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Coppus, Ruben. "Landscape sensitivity to erosion in three semi-arid Central Andean geo-ecosystems." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2002. http://dare.uva.nl/document/63757.
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Honaman, Andrew M. 1958. "The potential and actual evapotranspiration of water-rich ecosystems in arid regions." Thesis, The University of Arizona, 1998. http://hdl.handle.net/10150/291843.
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The well-known and widely accepted Penman combination equation was applied to climatic data collected in a desert environment to predict actual evapotranspiration if the desert region were developed into irrigated agriculture. The Penman evaporation estimates from desert climate data were compared to Bowen ratio ET measurements collected on irrigated alfalfa fields in the general vicinity. Six variations of the wind function in Penman's equation were tested. From these six the best fit-model was determined. surprisingly, Penman's original equation provided the best fit (in mean hourly units W m⁻²) as PLE₁ = 0.953LE + 43. The s.e. was 51 W⁻², r² = 0.953, and n = 298 hourly points. A calibrated wind function was developed and named 'Sonoran'. The Sonoran wind function PLE₆ = 0.954LE + 24, s.e. = 48.8 r² = 0.956 provided virtually imperceptible improvements over Penman's original wind function.
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Bunting, Daniel Paul. "Riparian Restoration and Management of Arid and Semiarid Watersheds." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/228166.
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Riparian ecosystems are valued for ecosystem services which have impacts on the well-being of humans and the environment. Anthropogenic disturbances along rivers in arid and semiarid regions have altered historical flow regimes and compromised their integrity. Many rivers are hydroecologically deteriorated, have diminished native riparian forests, and are pressured for their water supplies. My first study is founded on the premise that river restoration has increased exponentially with little documentation on effectiveness. We designed a conference to discuss lessons learned from past restoration activities to benefit future efforts. Participants, including scientists, managers, and practitioners, agreed that creating measureable objectives with subsequent monitoring is essential for quantifying success and employing adaptive management. Attendees stated that current projects are local and have limited funding and time, whereas future efforts must have longer funding cycles, larger timeframes, should contribute to regional goals, and address factors responsible for ecological decline. Bridging gaps among science, management, and policy in the 21st century is a key component to success. My second study focused on the benefits of long-term monitoring of local riparian restoration. Many efforts include revegetation components to re-establish native cottonwood-willow communities, but do not address how high-density establishment impacts vegetation dynamics and sustainability. Over five years, we documented significantly higher growth rates, lower mortality, and higher cover in cottonwood compared to non-native tamarisk. Cottonwood height, diameter at breast height, growth rates, and foliar volumes were reduced at higher densities. Herbaceous species decreased every year but native shrubs volunteered after two years resulting in a reduction of overall plant diversity from 2007-2009 with a slight increase from 2009-2011.My third study focused on improving basin-scale evapotranspiration (ET), a large component of the water budget, to better inform water resource allocation. My research suggests that multiple models are required for basin-scale ET estimates due to vegetation variability across water-limitation gradients. We created two empirical models using remote sensing, a multiplicative riparian ET model (r²=0.92) using MODIS nighttime land surface temperature (LST(n)) and enhanced vegetation index, and an upland ET model (r²=0.77) using multiple linear regression replacing LST(n) with a precipitation input.
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Honaman, Andrew M. 1958. "Potential and actual evapotranspiration of water-rich ecosystemsn in arid regions." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/192109.
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The well-known and widely accepted Penman combination equation was applied to climatic data collected in a desert environment to predict actual evapotranspiration if the desert region were developed into irrigated agriculture. The Penman evaporation estimates from desert climate data were compared to Bowen ratio ET measurements collected on irrigated alfalfa fields in the general vicinity. Six variations of the wind function in Penman's equation were tested. From these six the best fit-model was determined. Surprisingly, Penman's original equation provided the best fit (in mean hourly units W m⁻² ) as PLE₁ = 0.953LE + 43. The s.e. was 51 W m⁻², r² = 0.953, and n = 298 hourly points. A calibrated wind function was developed and named 'Sonoran'. The Sonoran wind function PLE₆ = 0.954LE + 24, s.e. = 48.8 r² = 0.956 provided virtually imperceptible improvements over Penman's original wind function.
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Routson, Kanin Josif. "Malus Diversity in Wild and Agricultural Ecosystems." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/223381.
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Human-induced land degradation and climate change can reduce agricultural productivity and increase susceptibility to food shortages at local and global scales. Planting perennial crop species, such as fruit and nut crops, may be an intervention strategy because of their beneficial contributions to sustainable agriculture and human nutrition. Many perennial temperate fruit and nut species are however, particularly vulnerable to frost events, drought, insufficient chill hours, and disease and insect outbreaks. Modifying these species to yield harvests under a wider range of biotic and abiotic conditions may increase the value and long-term viability of perennials in agroecosystems. This dissertation examines adaptation and ecogeography in temperate perennial fruit crops, using apple (Malus sensu lato) as an example for case studies. The resilience of feral domestic apple trees in abandoned farmstead orchards throughout the southwestern U.S. indicates plasticity in adapting to local environmental conditions. Dendrochronology reveals these trees tend to persist where they have access to supplemental water, either as shallow groundwater or irrigation. While domestic apples are cultivated under a range of growing conditions, wild relatives of agricultural crops may further expand the cultivable range of the species. Crop wild relatives are species closely related to agricultural species, including progenitors that may contribute beneficial traits to crops. Sampling the genetic variation in crop wild relatives may benefit from ecological genetics and GIS theory to reveal genetic structure. The Pacific crabapple is an example of a wild apple relative that may contain genetic variation useful in apple breeding. Species distribution modeling of the Pacific crabapple identifies a narrow climatic window of suitable habitat along the northern Pacific coast, and genetic fingerprinting reveals a highly admixed genetic structure with little evidence of natural or cultural selection. While the moist coastal Pacific Northwest is not necessarily characteristic of many apple-growing regions, the species may have useful adaptations transferable to domestic apples. Genetic resources offer a promising source of raw material for adapting crops to future agricultural environments; their characterization, conservation, and use may offer important contributions to adaptation and use of perennial crops in agro-ecosystems.
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Lawson, Laurie Linwood. "Epilithic diatoms as indicators of stream condition in arid lotic ecosystems of the american southwest." Diss., The University of Arizona, 1999. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_1999_093_sip1_w.pdf&type=application/pdf.
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Kondoh(Tsuji), Shoko. "Ecophysiological study on drought stress strategy of trees in humid and semi-arid tropical ecosystems." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136824.
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Mendez-Estrella, Romeo, Jose Romo-Leon, Alejandro Castellanos, Fabiola Gandarilla-Aizpuro, and Kyle Hartfield. "Analyzing Landscape Trends on Agriculture, Introduced Exotic Grasslands and Riparian Ecosystems in Arid Regions of Mexico." MDPI AG, 2016. http://hdl.handle.net/10150/621492.
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Riparian Zones are considered biodiversity and ecosystem services hotspots. In arid environments, these ecosystems represent key habitats, since water availability makes them unique in terms of fauna, flora and ecological processes. Simple yet powerful remote sensing techniques were used to assess how spatial and temporal land cover dynamics, and water depth reflect distribution of key land cover types in riparian areas. Our study area includes the San Miguel and Zanjon rivers in Northwest Mexico. We used a supervised classification and regression tree (CART) algorithm to produce thematic classifications (with accuracies higher than 78%) for 1993, 2002 and 2011 using Landsat TM scenes. Our results suggest a decline in agriculture (32.5% area decrease) and cultivated grasslands (21.1% area decrease) from 1993 to 2011 in the study area. We found constant fluctuation between adjacent land cover classes and riparian habitat. We also found that water depth restricts Riparian Vegetation distribution but not agricultural lands or induced grasslands. Using remote sensing combined with spatial analysis, we were able to reach a better understanding of how riparian habitats are being modified in arid environments and how they have changed through time.
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Yavari, Ahmad. "Allocation des ressources naturelles renouvelables et le développement rural dans les milieux montagnards de l'Iran : exemple de modalités du développement rural et la dégradation des ressources naturelles végétales de l'Alborz central." Grenoble 1, 1996. http://www.theses.fr/1996GRE10277.
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Ce travail est une etude en geographie appliquee concernant la gestion des espaces montagnards de pays arides et en voie de developpement ou les montagnes sont des repertoires et lieux de recharge de ressources naturelles et de l'heritage culturel. L'economie de la pluspart des villages de plaines et piedmonts reste dependante des ressources naturelles qui ont subit une degradation intense et de fortes perturbations ecologiques et socio-economiques. La region etudiee est une partie de la chaine d'alborz central choisie de facon a inclure la diversite naturelle et socio-economique de l'espace montagnard de l'iran, tout en restant limitee sur l'etendue (2914 km carres). L'approche adoptee est inspiree par la vision systemique. La gestion de l'espace et son evolution pendant les vingt dernieres annees ont ete etudiees sur place et par des analyses statistiques en tant qu'un systeme uni. L'amenagement de cette region manque d'une gestion rationnelle de l'espace et ceci entraine un rapport desequilibre du developpement entre les montagnes et les pleines adjacentes et la non-integration des specificites montagnardes. Les potentiels agro-sylvo-pastorals sont limites par les contraintes naturelles et par les surexploitations intenses et chroniques. Cependant, il y a des potentiels d'exploitations importants au developpement de la region grace a sa situation geographique exceptionnelle. Le developpement du tourisme, du transport routier, de l'artisanat et de l'industrie legere sont des sources de l'emploi et de revenu et reduisent la pression exercee sur les ressources naturelles mais restent sous-exploites. Etablir l'equilibre (reduction) de l'exploitation de ressources naturelles et le developpement des autres potentiels de l'alborz central sont les premieres mesures indispensables de toutes gestion. La region a besoin d'un amenagement integre base sur les relations complementaires plaines-montagnes au niveau regional dans le respect des specificites des espaces montagnards au niveau local ou micro-regional
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Kgosikoma, Olaotswe Ernest. "Understanding the savanna dynamics in relation to rangeland management systems and environmental conditions in semi-arid Botswana." Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/5874.
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This thesis investigates the effects of rangeland management systems on savanna ecosystems under different environmental conditions in Botswana, Southern Africa. The soil sampling and vegetation assessment were conducted in twenty–three transects located in communal and ranching grazing lands across three sites. Pastoralists were also interviewed on vegetation change on their respective grazing lands. Soil texture, pH, bulk density and soil organic carbon differed between sites, but not between communal and ranching lands. Soil organic carbon was positively affected by soil clay content. The herbaceous vegetation composition showed heterogeneity between sites, but Matlolakgang and Xanagas rangelands were in poor condition, particularly the communal grazing land that had high cover of increasers II species. Higher herbaceous biomass was observed in ranches than communal lands and biomass also increased with increasing soil organic carbon. Bush encroachment was observed in communal and ranching grazing lands at Matlolakgang and Xanagas, but not Goodhope. Woody plant cover, density and diversity increased with decline in soil clay content, but not linearly. Pastoralists indicated that herbaceous vegetation compositions had changed in some areas, with increase of unpalatable grass species and bush encroachment especially in communal land. Pastoralists considered bush encroachment a problem as it suppress herbaceous vegetation productivity, but they also considered woody vegetation as a valuable grazing resource. The long-term indicators of ecosystem degradation (soil and woody cover) showed that communal and ranching grazing did not affect the savanna ecosystem differently. This is contrary to assumptions of Tribal Grazing Land Policy of Botswana, which promote ranching as a more sustainable management system. The results revealed that rainfall and soil clay strongly influence rangeland condition. These results have implications for the management policies of communal grazing lands throughout sub-Saharan Africa and in similar arid habitats across the world.
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Nainggolan, Doan. "On the operationalization of a spatially explicit evaluation of the complexity of land use trajectories in semi-arid Mediterranean agro-ecosystems." Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.659124.
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This thesis aims to unpack the complexity of trajectories of land use change in semiarid Mediterranean agro-ecosystems - illustrated using findings from the Torrealvilla catchment in south-eastern Spain. The research looks at multiple dimensions of land use change and addresses the past, present, and future . It comprises of three key stages. Stage 1 quantifies land use change between 1956 and 2008, assesses the impacts on landscape fragmentation, and identifies important drivers of the detected changes. Stage 2 examines the linkage between farmer heterogeneity and the diversity of agricultural land uses in the studied landscape by developing a typology of farmers. It also investigates how farmers respond to future changes that potentially affect their farming and describes potential future trajectories of agriculture in the area and the implications for agro-ecosystem services provision. Stage 3 models the future trajectories of land use change for the studied landscape using two different approaches: Cellular Automata (CA) and Agent-Based scenario analysis. The research shows that over the past five decades the catchment has undergone significant changes with pronounced effects on landscape configuration. The changes involved three major trajectories (forest expansion, abandonment of rain-fed farming, and intensification) and were attributable to various interacting biophysical and socioeconomic drivers. The study differentiates six types of farmers according to the characteristics of their households and of their farm management. Different types of farmers are expected to pursue different land use directions with important impacts on future provision of agro-ecosystem services. Results from the final stage highlight a diverging future . "'To illustrate, while CA projection suggests scope for further expansion of irrigated farming, the agent-based scenario analysis indicates the opposite. Overall the thesis confirms that land use changes in Mediterranean agro-ecosystems are indeed complex entailing multiple, contrasting, and perhaps competing trajectories and are the manifestation of the interacting effects of various types of drivers. The thesis highlights conceptual and practical challenges in undertaking an integrated evaluation of land use change complexity. Future policy making should consider the various factors that are jointly shaping agricultural land use trajectories.
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Wood, Jamie Russell, and n/a. "Pre-settlement paleoecology of Central Otago�s semi-arid lowlands, with emphasis on the pre-settlement role of avian herbivory in South Island dryland ecosystems, New Zealand." University of Otago. Department of Geology, 2008. http://adt.otago.ac.nz./public/adt-NZDU20080211.142212.
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The vegetation communities that existed in the semi-arid intermontane basins and gorges of Central Otago prior to human settlement ~750 years B.P. are poorly understood. This is because of a lack of fossil evidence and complex restructuring by anthropogenic factors, especially increased fire frequency, and more recently mammalian grazing. There is also little information regarding the effect of the lost fauna on maintaining and structuring presettlement communities, both in Central Otago and throughout the eastern South Island dryland zone. This study aims to provide a clearer understanding of the functioning of pre-settlement ecosystems in dryland Central Otago, particularly the role of the largest vertebrate herbivores, the moa (Aves: Dinornithiformes), and to explore the implications of the extinct fauna for land conservation management across New Zealand.
Late Pleistocene and Holocene vegetation communities of the Central Otago lowlands were reconstructed from plant macrofossils, including seeds, leaves, and wood, excavated from rockshelter, cave, and swamp deposits throughout the region. The macrofossils represent three main vegetation types: late Pleistocene to mid (late?) Holocene basin floor wetland herb associations, Olearia-shrublands surrounding these wetlands, and mid to late Holocene open scrubland and woodland in gorges and on low altitude slopes, dominated by filiramulate Olearia, Coprosma, and Corokia, with abundant lianes (Muehlenbeckia spp. and Rubus spp.) and understorey herbs. Many native tree and shrub species that are presently widespread in the Central Otago lowlands were rare or absent prior to anthropogenic fires (e.g. Discaria toumatou, Kunzea ericoides, Leptospermum scoparium). Other tree and shrub species once present are now extinct in the region (e.g. Coprosma obconica, Plagianthus regius, Pseudopanax ferox). The loss of these indigenous woody vegetation communities was a major factor contributing to the extirpation of many small bird species, and undoubtedly also reptile and invertebrate species, from the region.
Plant macrofossils from rockshelters included remains of bird nests, identifiable by desiccated feathers and eggshell amongst them. These macrofossils include the first described plant remains from the nests of moa, which were constructed from a shallow bed of twigs of locally available shrubs and lianes. Many of the twigs are 25-30 mm in length and show evidence of having been clipped by moa bills.
Desiccated coprolites, mostly of moa, but also specimens attributed to Finsch�s duck (Chenonetta finschi) and red-crowned parakeet (Cyanoramphus novaezelandiae), were recovered from rockshelter excavations. Moa species associated with a sample of coprolites were identified using ancient DNA analysis, and plant macrofossils from these were examined, together with previously unexamined moa gizzard content samples excavated from mires in the eastern South Island dryland zone. The results indicate that, in addition to previously reported browsing, upland moa (Megalapteryx didinus) and heavy-footed moa (Pachyornis elephantopus) also functioned as grazers, and seeds in their coprolites are dominantly of low shrubs and ground-cover herbs. Of particular interest was the higher than expected frequency of seeds from the currently rare and threatened 'spring annual' herbs; Ceratocephala pungens and Myosurus minimus subsp. novae-zelandiae (Ranunculaceae), suggesting further research on potential ecological relationships between moa and these plants would be worthwhile. The results of this study have provided a baseline for future conservation and restoration projects in the Central Otago lowlands.
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Bradford, John B. "The influence of climate, soils, and land-use on primary productivity and cheatgrass invasion in semi-arid ecosystems submitted by John B. Bradford." Access citation, abstract and download form; downloadable file 13.42 Mb, 2004. http://wwwlib.umi.com/dissertations/fullcit/3131658.
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Batista, Leidiane Priscilla de Paiva. "Saberes EtnoictiolÃgicos dos Pescadores Artesanais nos AÃudes do Alto Rio AcaraÃ, CearÃ, Brasil." Universidade Federal do CearÃ, 2012. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=8136.
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A etnoictiologia busca descrever e valorizar os conhecimentos dos pescadores artesanais,
atravÃs de estudos que evidenciam que estes sÃo portadores de conhecimentos bioecolÃgicos
acerca dos peixes que capturam. Desta forma, objetivou-se comparar os conhecimentos
etnoictiolÃgicos dos pescadores artesanais dos aÃudes pÃblicos Araras e Edson Queiroz (bacia
do mÃdio rio AcaraÃ-CE) com a literatura cientÃfica. Com este fim, selecionou-se uma
populaÃÃo representativa para cada um destes aÃudes. Assim, tem-se a Ilha de EsaÃ, para o
aÃude Araras, e Vila SÃo Cosme, para o Edson Queiroz. Foram realizadas observaÃÃo
participante, entrevistas semiestruturadas, estÃmulo visual e turnÃs-guiadas com pescadores
destas populaÃÃes. Foram entrevistados vinte pescadores na Vila SÃo Cosme e vinte e quatro
na Ilha de EsaÃ. As entrevistas abordaram aspectos etnoecolÃgicos das principais espÃcies de
peixes capturadas pelos pescadores. Foram citadas vinte etnoespÃcies de peixes e uma de
camarÃo como sendo capturadas nos aÃudes. Dentre estas, as mais importantes,
economicamente, foram: carÃ-tilÃpia (Oreochromis niloticus Linnaeus, 1758 e Tilapia
rendalli Boulenger, 1897), curimatà (Prochilodus brevis Steindachner, 1874), pescada,
(Plagiossion squamossimus Heckel, 1840), piau (Leporinus sp.), traÃra (Hoplias brasiliensis e
H. malabaricus Bloch, 1794) e tucunarà (Cichla cf. ocellaris Bloch; Schneider, 1801). Na
classificaÃÃo da ictiofauna, os pescadores utilizam aspectos morfolÃgicos e etolÃgicos,
apresentando vÃrias etnoespÃcies com nomes genÃricos e poucas com nomes binomiais. Em
sua dieta, estas populaÃÃes consomem peixes, como principal fonte de proteÃna animal,
havendo restriÃÃes por carÃter social e cultural. Quanto à etnoictiologia, conclui-se que os
pescadores possuem conhecimentos consistentes sobre a ecologia geral, trÃfica e reprodutiva
da ictiofauna capturada, vivenciando empiricamente muitas das informaÃÃes presentes na
literatura acadÃmica. Logo, pela consistÃncia dos saberes dos pescadores da Ilha de Esaà e da
Vila SÃo Cosme, estes conhecimentos podem contribuir para futuros estudos cientÃficos e ser
incorporados na elaboraÃÃo de planos de gestÃo e manejo sustentÃvel dos recursos hÃdricos e
pesqueiros da regiÃo mÃdia do AcaraÃ.The ethnoictiology to describe and use the knowledge of fishermen, by studies that show that they are carriers of bio-ecological knowledge about fish they catch. Thus, the objective was to compare the knowledge of fishermen of public dams Araras and Edson Queiroz (Middle Acaraà River Basin, CearÃ) with the scientific literature. With this end, we selected a representative population for each of these reservoirs. Therefore, there is the Ilha de EsaÃ, for the dam Araras, and Vila SÃo Cosme, to Edson Queiroz. Were performed participant observation, semi-structured interviews, visual stimulus, and guided fishing tours of these populations. Twenty fishermen were interviewed in Vila Sao Cosme and twenty-four on the Ihla de Esaà The interviews aspects ethnoecological of the main fish species caught by fishermen. Were cited twenty ethnospecies fish and shrimp as captured in the reservoirs. Among these, the most important, economically, are carÃ-tilapia [Oreochromis niloticus (Linnaeus, 1758) and Tilapia rendalli (Boulenger, 1897)], curimatà [(Prochilodus brevis (Steindachner, 1874)], pescada [Plagiossion squamossimus (Heckel, 1840)], piau (Leporinus sp.),traÃra (Hoplias brasiliensis e H. malabaricus) and tucunarà [Cichla cf. ocellaris (Bloch; Schneider, 1801)]. In the classification of fishes, fishemen used morphological and ethological aspects, presenting several ethnospecies with generic names and few with binomial names. In your diet, these populations consume fish as the main source of animal protein, with social and cultural restrictions. As for ethnoictiology, it is concluded that the fishermen have consistent knowledge about the general ecology, trophic and reproductive of fishes captured. Therefore, the consistency of the knowledge of fishermen on the Ilha de Esaà and Vila SÃo Cosme, this knowledge can contribute to future scientific studies and be incorporated in the preparation of management plans and sustainable management of water resources and fisheries in the middle region AcaraÃ.
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Sierra-Soler, Andres. "An original GIS and remote sensing protocol to detect agricultural drought effects on rainfed agro-ecosystems in semi-arid developing regions: a case study for Central Mexico." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123308.
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Drought is a silent and pervasive phenomenon, it creeps up over weeks, months, and even years often without any warning, affecting ecosystems and human activity on a global scale. Globally droughts are one of the most devastating natural hazards in terms of the people affected and inflicting directly or indirectly economies, societies and ecosystems. As any natural hazard, the degree of exposure and the ability of systems to be resilient are directly related with the vulnerability of communities. Agricultural drought represents a great threat to poor farmers in semi-arid regions developing regions. For farmers who depend on rainfed agricultural production for self-sufficiency a drought can result in great suffering.As such there is a need to understand how droughts disturb the landscape in such regions. Satellite observations of the Earth have the potential to provide insights on vegetation conditions, crop yield and furthermore to monitor the impact of droughts. The relationship between spectral properties of vegetation and their biomass has been recognized since the first spectrometric field experiments in the 1970s. Satellite remote sensing provides a synoptic view of the land and a spatial context for measuring drought impacts which have proved to be a valuable source of spatially continuous data with improved information on monitoring vegetation dynamics. This thesis had the objective of proposing a new methodology to monitor the development of different vegetation covers in the presence of detected abnormally dry conditions and to compare this with vegetation development in periods with normal precipitation with a particular interest on rainfed agricultural lands. The analysis of the impacts of droughts on vegetation was performed with the use of remote sensing techniques. An original protocol for performing Land Use Land Cover (LULC) classification that combines climatic, topographic and reflectance information from 18 Landsat ETM+ images was applied to subsequently distinguish drought effects in different classes through the selected years. The achieved LULC classification produced overall classification accuracies ranging from 87.88% to 92.42%. Spectral indices for vegetation and soil/vegetation moisture were then used to detect anomalies in vegetation development caused by drought and furthermore, the area of water bodies was measured and compared to detect changes in water availability for irrigated crops. The proposed methodology was tested in Central Mexico to determine which growing season period could be used to detect the evolution of a drought (in this case the year 2005) and which could be applied to other semiarid regions.La sécheresse est un phénomène silencieux et omniprésent , il glisse au fil des semaines , des mois , voire des années souvent sans aucun avertissement , affectant les écosystèmes et les activités humaines à l'échelle mondiale . Sécheresses à l'échelle mondiale sont l'une des catastrophes naturelles les plus dévastatrices en termes de personnes touchées et infliger directement ou indirectement économies, les sociétés et les écosystèmes . Comme toute catastrophe naturelle , le degré d'exposition et la capacité des systèmes de résilience sont directement liés à la vulnérabilité des communautés . La sécheresse agricole représente une grande menace pour les agriculteurs pauvres dans les régions en développement des régions semi-arides . Pour les agriculteurs qui dépendent de la production agricole pluviale pour l'autosuffisance une sécheresse peuvent entraîner de grandes suffering.As comme il est nécessaire de comprendre comment la sécheresse perturbent le paysage dans ces régions. Les observations satellitaires de la Terre ont le potentiel de fournir des indications sur les conditions de végétation, le rendement des cultures et, en outre de surveiller l'impact des sécheresses . La relation entre les propriétés spectrales de la végétation et la biomasse a été reconnue depuis les premières expériences sur le terrain spectrométriques dans les années 1970 . La télédétection par satellite offre une vue synoptique de la terre et un contexte spatial pour mesurer les impacts de la sécheresse qui se sont révélés être une source précieuse de données spatialement continues avec une meilleure information sur le suivi de la dynamique de la végétation . Cette thèse avait pour objectif de proposer une nouvelle méthodologie pour suivre l'évolution des différents couverts végétaux en présence d' détectés conditions anormalement sèches et de la comparer avec le développement de la végétation dans les périodes avec des précipitations normales avec un intérêt particulier sur les terres agricoles pluviales . L'analyse des impacts de la sécheresse sur la végétation a été réalisée avec l'utilisation des techniques de télédétection . Un protocole original pour effectuer l'utilisation des terres de la couverture terrestre (OUS ) classification qui combine des informations climatiques, topographiques et de réflexion de 18 ETM + Landsat images ont été appliqués à distinguer la suite des effets de la sécheresse dans les différentes classes dans les années sélectionnées . La classification LULC atteint produite précision de la classification globale allant de 87,88 % à 92,42 % . Indices spectraux pour la végétation et le sol / humidité de la végétation ont été ensuite utilisés pour détecter des anomalies dans le développement de la végétation causée par la sécheresse et, en outre , la région des masses d'eau a été mesurée et comparée à détecter les changements dans la disponibilité en eau pour les cultures irriguées . La méthodologie proposée a été testée dans le centre du Mexique pour déterminer la période à laquelle la saison de croissance pourrait être utilisé pour détecter l'évolution de la sécheresse ( dans ce cas, l'année 2005) et qui pourrait être appliqué à d'autres régions semi-arides .
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Chaieb, Ghassen. "Variation de l’intensité de la facilitation avec la salinité et l’aridité dans les dépressions salines continentales de Tunisie." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0284.
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L’objectif de ce travail de thèse est de clarifier le débat de la littérature d’écologie des communautés sur les variations d’interactions plante-plante le long de gradients de stress hydrique. Nous nous sommes focalisés sur l’importance du type de stress (ressources vs. non-ressources) et la méthode utilisée (observationnelle vs. expérimentale) pour quantifier les interactions biotiques. Les dépressions salines continentales (Sebkhas) de Tunisie se caractérisant par l’existence d’un gradient marqué de salinité dans des contextes climatiques contrastés est un excellent système modèle pour clarifier ce débat notamment en séparant les effets de la salinité de ceux du stress hydrique.Dans une première étape, nous avons effectué une étude observationnelle à l’échelle de la zone aride tunisienne afin d’identifier les conséquences des interactions possibles existant entre la topographie et le climat et déterminant les variations de stress salin et hydrique et donc la structure, la composition des communautés végétales et le fonctionnement des écosystèmes. Nous avons mis en place un dispositif de terrain croisant un traitement de position topographique (avec quatre habitats) et un traitement de stress hydrique (avec deux situations climatiques, le climat faiblement aride et le climat fortement aride) avec quatre répétitions à l’échelle régionale. Nous avons également effectué deux expérimentations, une première sur les l’effet des voisins par la méthode observationnelle avec transplantation de trois espèces dominantes dans l’ensemble des traitements et une sur l’effet de la méthode (observationnelle vs. expérimentale) avec transplantation de trois Poaceae dans les deux habitats les moins salés.L’étude observationnelle a clairement montré que la salinité est le facteur direct majeur déterminant la composition, la diversité et la structure des communautés, ainsi que la productivité des écosystèmes et leur fertilité. L’aridité a des effets moindres plus subtiles et son effet ne peut être comparé spatialement que dans l’habitat le moins salé entre les zones très et faiblement arides.La première étude expérimentale a montré que le stress salin (facteur direct non de ressource) entrainait un collapse de la facilitation et que ce collapse s’accentuait avec l’aridité croissante, aussi bien temporellement que spatialement. Nous n’avons pas trouvé de retour de la compétition en situation d’aridité extrême comme le prédit la littérature. Ceci est sans doute due à la stratégie faiblement compétitrice des Chaméphytes dominants les habitats les plus salés. La seconde étude expérimentale a montré qu’avant la saison sèche estivale les interactions de court-terme mesurées par la méthode expérimentale (removal method) sont négatives alors que les interactions de long-terme, mesurées par combinaison des méthodes observationnelle et expérimentale sont positives, confirmant nos hypothèses et la littérature. Cependant, après la saison sèche estivale les interactions de court-terme deviennent positives, alors que les interactions de long-terme collapsent par disparition de l’effet tampon du sol végétalisé sur l’humidité.Ces résultats sont cruciaux car ils montrent que dans ce système aride et à important stress salin le collapse de la facilitation est le processus majeur expliquant la structure, la diversité et le fonctionnement des écosystèmes et ce aussi bien le long des gradients de salinité que lorsque que le stress hydrique augmente. D’autre part la combinaison des méthodes observationnelle et expérimentale nous a permis de démontrer que l’augmentation de la facilitation prédite par le SGH lors d’une augmentation modérée de stress hydrique n’est qu’une réponse des plantes à l’effet négatif croissant de l’environnement abiotique, contrairement à l’augmentation de la compétition dans les environnements non stressés et celui de la facilitation des environnements très à moyennement stressés, qui sont des processus d’origine biotiqueWe aim to clarify the debate of the community ecology literature on changes in plant-plant interaction along water stress gradients. We focused on the importance of the type of stress (resources vs. non-resources) and the method used (observational vs. experimental) to quantify biotic interactions. The continental saline depressions (Sebkhas) of Tunisia, characterized by the existence of a strong gradient of salinity in contrasting climatic conditions, is an excellent model system to clarify this debate, in particular by separating the effects of salinity from water stress.In a first step, we carried out an observational study on the scale of the Tunisian arid zone in order to identify the consequences of the possible interactions existing between topography and climate and determining variations in salinity and water stress and ultimately the structure, composition of plant communities and ecosystem functioning. We set up a field design combining a topographic position treatment (with four habitats) and a water stress treatment (with two climate conditions: the wet arid climate and the dry arid climate) with four replicates at the regional scale. We also carried out two experiments, one on the effect of neighbors using the observational method with transplants of three dominant species in all treatments and a second on the effect of the method (observational vs. experimental) with transplantation of three Poaceae in the two least saline habitats.The observational study clearly showed that salinity was the major direct factor determining the composition, diversity and structure of communities, as well as the productivity of ecosystems and their fertility. Aridity has less, more subtle effects, which can only be spatially compared in the least saline habitat between the low and high arid climates.The first experimental study showed that salinity stress (a direct, non-resource factor) induced a facilitation collapse that increased with increasing aridity, both temporally and spatially. The switch to competition in extreme conditions of aridity predicted in the literature was not found. This is very likely due to the weakly competitive strategy of Chamaephytes dominating the most saline habitats. The second experimental study showed that, before the dry summer season, the short-term interactions measured by the experimental method (removal method) were negative whereas the long-term interactions, measured by the combination of the observational and experimental methods were positive, thus, supporting our hypotheses and the literature. However, after the dry summer season, the short-term interactions turned to positive, whereas the long-term interactions collapsed due to vanishing the buffering effect of the vegetated soil on humidity.These results are crucial because they showed that in this arid and saline system, the collapse of facilitation is the major process explaining the structure, diversity and functioning of ecosystems, both along salinity gradients and when water stress increases. On the other hand, the combination of the observational and experimental methods was crucial to show that the increase in facilitation predicted by SGH with increasing water stress is only a response of plants to the increasing negative effect of abiotic environment (environmental-severity effect). This contrasts with the increased competition in unstressed environments and increased facilitation from highly stressed to intermediate environments, both being neighbor-trait effects
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Batista, Leidiane Priscilla de Paiva. "Saberes Etnoictiológicos dos Pescadores Artesanais nos Açudes do Alto Rio Acaraú, Ceará, Brasil." reponame:Repositório Institucional da UFC, 2012. http://www.repositorio.ufc.br/handle/riufc/16625.
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BATISTA, Leidiane Priscilla de Paiva. Saberes Etnoictiológicos dos Pescadores Artesanais nos Açudes do Alto Rio Acaraú, Ceará, Brasil. 2012. 102 f. : Dissertação (mestrado) - Universidade Federal do Ceará, Centro de Ciências e Tecnologia, Programa de Pós-Graduação em Desenvolvimento e Meio Ambiente-PRODEMA, Fortaleza-CE, 2012.Submitted by guaracy araujo (guaraa3355@gmail.com) on 2016-05-03T16:43:04Z No. of bitstreams: 1 2012_dis_ lppbatista.pdf: 14346238 bytes, checksum: cd0e7a424d9c932b857183e761c3733b (MD5)
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The ethnoictiology to describe and use the knowledge of fishermen, by studies that show that they are carriers of bio-ecological knowledge about fish they catch. Thus, the objective was to compare the knowledge of fishermen of public dams Araras and Edson Queiroz (Middle Acaraú River Basin, Ceará) with the scientific literature. With this end, we selected a representative population for each of these reservoirs. Therefore, there is the Ilha de Esaú, for the dam Araras, and Vila São Cosme, to Edson Queiroz. Were performed participant observation, semi-structured interviews, visual stimulus, and guided fishing tours of these populations. Twenty fishermen were interviewed in Vila Sao Cosme and twenty-four on the Ihla de Esaú The interviews aspects ethnoecological of the main fish species caught by fishermen. Were cited twenty ethnospecies fish and shrimp as captured in the reservoirs. Among these, the most important, economically, are cará-tilapia [Oreochromis niloticus (Linnaeus, 1758) and Tilapia rendalli (Boulenger, 1897)], curimatã [(Prochilodus brevis (Steindachner, 1874)], pescada [Plagiossion squamossimus (Heckel, 1840)], piau (Leporinus sp.),traíra (Hoplias brasiliensis e H. malabaricus) and tucunaré [Cichla cf. ocellaris (Bloch; Schneider, 1801)]. In the classification of fishes, fishemen used morphological and ethological aspects, presenting several ethnospecies with generic names and few with binomial names. In your diet, these populations consume fish as the main source of animal protein, with social and cultural restrictions. As for ethnoictiology, it is concluded that the fishermen have consistent knowledge about the general ecology, trophic and reproductive of fishes captured. Therefore, the consistency of the knowledge of fishermen on the Ilha de Esaú and Vila São Cosme, this knowledge can contribute to future scientific studies and be incorporated in the preparation of management plans and sustainable management of water resources and fisheries in the middle region Acaraú.
A etnoictiologia busca descrever e valorizar os conhecimentos dos pescadores artesanais, através de estudos que evidenciam que estes são portadores de conhecimentos bioecológicos acerca dos peixes que capturam. Desta forma, objetivou-se comparar os conhecimentos etnoictiológicos dos pescadores artesanais dos açudes públicos Araras e Edson Queiroz (bacia do médio rio Acaraú-CE) com a literatura científica. Com este fim, selecionou-se uma população representativa para cada um destes açudes. Assim, tem-se a Ilha de Esaú, para o açude Araras, e Vila São Cosme, para o Edson Queiroz. Foram realizadas observação participante, entrevistas semiestruturadas, estímulo visual e turnês-guiadas com pescadores destas populações. Foram entrevistados vinte pescadores na Vila São Cosme e vinte e quatro na Ilha de Esaú. As entrevistas abordaram aspectos etnoecológicos das principais espécies de peixes capturadas pelos pescadores. Foram citadas vinte etnoespécies de peixes e uma de camarão como sendo capturadas nos açudes. Dentre estas, as mais importantes, economicamente, foram: cará-tilápia (Oreochromis niloticus Linnaeus, 1758 e Tilapia rendalli Boulenger, 1897), curimatã (Prochilodus brevis Steindachner, 1874), pescada, (Plagiossion squamossimus Heckel, 1840), piau (Leporinus sp.), traíra (Hoplias brasiliensis e H. malabaricus Bloch, 1794) e tucunaré (Cichla cf. ocellaris Bloch; Schneider, 1801). Na classificação da ictiofauna, os pescadores utilizam aspectos morfológicos e etológicos, apresentando várias etnoespécies com nomes genéricos e poucas com nomes binomiais. Em sua dieta, estas populações consomem peixes, como principal fonte de proteína animal, havendo restrições por caráter social e cultural. Quanto à etnoictiologia, conclui-se que os pescadores possuem conhecimentos consistentes sobre a ecologia geral, trófica e reprodutiva da ictiofauna capturada, vivenciando empiricamente muitas das informações presentes na literatura acadêmica. Logo, pela consistência dos saberes dos pescadores da Ilha de Esaú e da Vila São Cosme, estes conhecimentos podem contribuir para futuros estudos científicos e ser incorporados na elaboração de planos de gestão e manejo sustentável dos recursos hídricos e pesqueiros da região média do Acaraú.
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Grouzis, Michel. "Structure, productivité et dynamique des systèmes écologiques sahéliens (Mare d'Oursi, Burkina Faso)." Paris 11, 1987. http://www.theses.fr/1987PA112339.
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Cette étude traite de la structure, de certains aspects du fonctionnement et de l'évolution des phytocénoses sahéliennes du bassin versant d'Oursi, situé au nord du Burkina Faso. Après avoir· rappelé les conditions sahéliennes (aridité climatique, édaphique, saisonalité, variabilité. . . ) le problème du déséquilibre entre les besoins d'une population en expansion et les ressources limitées du milieu est posé. L'étude aborde ensuite la méthodologie relative à la précision des mesures dans l'estimation des phytomasses épigée et hypogée par les techniques classiques de la récolte et radiométrique. Les résultats recueillis de 1976 à 1984 à l' échelle de la station écologique, du bassin versant et de la région portent sur : ( 1) la structure de la végétation ( spectre floristique et biologique de la strate herbacée, densité et structure démographique du peuplement ligneux) (2) la mise en place du peuplement herbacée (productiondes semences propriétés germinatives, établissement des plantules) ; ( 3) la phénologie, la productivité de la végétation épigée et hypogée et, leur déterminisme écologique. Une expression de la production en fonction des précipitations est proposée pour estimer· la production et la capacité de charge fréquentielles ; ( 4) les conditions de la dégradation et les capacités de régénération de la végétation définies par les effets de la mise en défens sur la flore, la phytomasse, l' efficience en eau, la densité des ligneux et par les effets d'aménagements (travail du sol, reboisement. . . ). Ces caractéristiques de structure et de dynamique actuelle associées à certains aspects de la dynamique historique (évolution climatique, occupation ancienne) permettent d' élaborer un modèle de la dynamique du système écologique sahélien. Celui-ci montre que ce système écologique est d'une grande complexité qui sous une relative homogénéité physionomique masque une grande diversité floristique, structurale, fonctionnelle et évolutive. Sous l'effet conjugué de la persistance de la sécheresse et surtout de l' anthropisation, ce système écologique est le siège de processus de dégradation conduisant à sa désertisation progressive. A l'issue de cette analyse des axes prioritaires de recherches (définition des caractéristiques de l' équilibre écologique, de leur seuil de rupture, des conditions de régénération et de restauration. . . ) sont proposésThis work mainly deals with the spin crossover phenomenon in cobalt (II} molecular chemistry. The synthesis of a series of five and six coordinated complexes, with Schiff bases as equatorial ligands and various apical ones, are reported. The temperature dependances of magnetic susceptibilities and EPR spectra are used to study the influence of the environment on the metal ion spin state. The behaviours observed are interpreted on the basie of simple models. Evidence is provided for thermally induced s = 1/2 - s -= 3/2 spin crossavers. In other respects, a correlation can be established between the geometry and spin state of these complexes and their ability to activate molecular oxygen. In order to specify the spin-crossover mechanism, structural and thermodynamic techniques are used: the ingle-crystal X-ray structure of one of the compounds is reported; the mean variation of metal-ligand diatances upon transition is evaluated by X-ray absorption spectroscopy; enthalpy and heat capacity changes, measured by t ose, are compared with the values calculated on the basis of a phenomenological model. A new means of detecting the crossover, by using its effect r. N he EPR spectrum of a Cu (II)doping ion, is described in the case of an iron(II)complex
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Whittington-Jones, Gareth Morgan. "The role of aardvarks (Orycteropus afer) as ecosystem engineers in arid and semi-arid landscapes of South Africa /." 2006. http://eprints.ru.ac.za/973/.
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