Dissertations / Theses: 'Aridità'

1

Burgess, Tony L. "Agave Adaptation to Aridity." University of Arizona (Tucson, AZ), 1985. http://hdl.handle.net/10150/554187.

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To show features of Agave taxa adapting to arid habitats, comparative studies at three taxonomic levels in the genus are presented. There is a brief review of Agave physiology and some aspects of recent evolution are discussed. Comparisons among species groups within the genus show several traits differentiating desert species from related taxa. Related taxa in the Deserticolae group are examined over a transect in Baja California, revealing patterns linking leaf shape to climate. In a comparison of leaves of A. desert] Engelm. along an elevational gradient, high intrapopulation variation obscures differences between the sites. Results are summarized as hypotheses to be tested.

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Fouet, Caroline. "Caractérisation de quelques phénotypes liés à l'aridité et à la température chez Anopheles gambiae sensu stricto (Giles, 1902)." Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20155/document.

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Grâce aux progrès expérimentaux permettant d'étudier deux phénotypes qui sont d'un intérêt majeur dans la compréhension des capacités d'adaptation d'A. gambiae s.s. à son environnement. Les différences de résistance à la dessiccation mises en évidence entre les différents caryotypes liés à l'inversion chromosomique 2La et entre les formes moléculaires M et S offrent des pistes intéressantes pour l'identification de facteurs génétiques impliqués dans la divergence écologique au sein de ce complexe d'espèces
Thanks to progress in sequencing, the genomes of many organisms are known and available. Thus, functional genomics, the elucidation of gene function in sequenced genome, is currently booming. However, there is a gap between our growing knowledge in genetic and the current sparse information on phentoypic data ( "phenotype gap"). All organisms whose genome has been sequenced are facing this problem, including Anopheles gambiae.Anopheles gambiae sensu lato is a complex of sibling species, indistinguishable from a morphological point of view, present on almost the entire African continent. A. gambiae demonstrates an extreme environmental ubiquity and the characterization of phenotypes associated with adaptation to varying environments as well as the identification of genes involved in this adaptation is one of the main research axes in the post-genome area of this major malaria vector.We have studied some phenotypes associated with aridity and temperature in the nominal species of the A. gambiae complex. These two parameters are discriminent in the distribution of molecular forms and chromosomal inversions that characterize this species and may be involved in ecological divergence and speciation. We first measured desiccation resistance of adult mosquitoes of A. gambiae s.s. and we then studied the preferred temperatures of larvae in a choice device set-up (the shuttlebox). We compared the thermoregulation behavior and thermal preferences of a laboratory strain with field larvae of A. gambiae s.s. We also presented preliminary data on the preferred temperatures measured in field larvae of the S and M molecular forms.From a technical point of view, we improved an existing device for testing the survival of mosquitoes in highly desiccated conditions by coupling it with a video surveillance system, which help to increase the accuracy in determining the survival time, to avoid disturbing the system during the experiment and allow to test relatively large numbers of individuals. This study revealed a significant association between the 2La chromosomal inversion and resistance to desiccation in A. gambiae and highlighted the role of body size in the survival of this mosquito in dry environments.We also adapted a new device to study experimentally the thermopreference of A. gambiae s.s. larvae. The results showed that laboratory larvae and field M molecular form larvae had similar thermal preferences, consistent with the values of temperature usually found in natural breeding sites. In addition, the S molecular form larvae from southern Cameroon had preferences similar to those of northern Cameroon, regardless of karyotypes related to chromosomal inversions. In addition, the comparison of data for the M and S molecular forms larvae revealed that there was no significant difference in thermal preferences or in thermoregulatory behavior.Our results have contributed to the development of two experimental devices to study two phenotypes that are of major interest in understanding the adaptation of A. gambiae s.s. to its environment. The differences in desiccation resistance between the different karyotypes associated with the 2La chromosomal inversion and between the M and S molecular forms offer interesting new possibilities for the identification of genetic factors involved in their ecological divergence

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Gortan, Emmanuelle. "Misura dello stato idrico di fraxinus ornus L. quale biomonitor dell'aridità ambientale in siti diversi del carso triestino." Doctoral thesis, Università degli studi di Trieste, 2008. http://hdl.handle.net/10077/2658.

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2006/2007
L'aridità è una condizione ambientale che comporta una ridotta disponibilità d'acqua per le piante all'interno del suolo. La disponibilità d'acqua rappresenta, unitamente alla temperatura, il fattore ambientale che più di ogni altro condiziona la distribuzione e la produttività primaria della vegetazione. Poiché una prolungata aridità ambientale ha serie conseguenze sulla produttività degli ecosistemi forestali e sulla sopravvivenza di alcune specie vegetali meno competitive di altre in tali condizioni, è di fondamentale importanza quantificare il livello di aridità ambientale per poterne prevedere l'impatto attuale e le tendenze in atto. Il progetto di ricerca si poneva quindi l’obiettivo di individuare e definire un indice di aridità ambientale, che consentisse di rappresentare le relazioni che la pianta contrae con l’acqua presente nell’ambiente in funzione della risposta fisiologica della pianta al variare del contenuto idrico del suolo, attraverso un valore unico a significato ecofisiologico. L'individuazione di un parametro ecofisiologico in grado di stimare in modo affidabile l'impatto dello stress idrico poneva le basi per valutare possibili correlazioni con parametri ottenibili con il telerilevamento. Un'altra finalità del lavoro era, infatti, l'individuazione di un parametro di riferimento mediante l'utilizzo di tecniche di telerilevamento da satellite da applicare nello “scaling up” ecologico, che a partire dallo studio dell'impatto dello stress idrico su singole specie potesse indagare sistemi di vegetazione sempre più grandi nell'ottica di sviluppare una visione olistica di grandi aree in relazione all'aridità ambientale. La specie vegetale che è stata scelta come potenziale biomonitor è Fraxinus ornus L. ossia l'orniello, che è stato selezionato in quanto trattasi di una specie vegetale che si distingue per la notevole capacità di resistenza a condizioni di stress idrico e proprio per questa sua capacità, è una specie diffusa in una grande varietà di ambienti. L'area di studio scelta è stata la provincia di Trieste ed in particolare l'area carsica. Questa zona, infatti, offre l'opportunità di eseguire significativi biomonitoraggi per valutazioni quantitative e qualitative sull'ambiente, in quanto presenta una elevata variabilità di substrati litologici, costituiti da rocce soggette a fenomeni di dissoluzione da parte delle acque meteoriche chimicamente aggressive (rocce carsificabili), a cui sono associati diversi tipi di circolazione idrica. La presenza di una fitta rete di fessure e fratture nei substrati geologici a tratti determina un forte drenaggio dell'acqua all'interno del suolo dovuto a percolamento della stessa verso gli strati più profondi. Nella zona del Carso triestino, sono state selezionate 21 stazioni in base ad un criterio geomorfologico noto come carsificabilità, che misura in modo indiretto e qualitativo la capacità di campo di un suolo, e in modo tale da ricoprire tutto il territorio dell'area carsica all'interno della provincia di Trieste. Al fine di identificare quale fosse il parametro fisiologico o morfologico che meglio si addicesse allo scopo della ricerca, sono stati misurati nel periodo da Maggio a Settembre i parametri relativi alle relazioni pianta-acqua generalmente correlati allo stress idrico e cioè la conduttanza fogliare al vapore d'acqua (gL), il potenziale dell'acqua della foglia (Ψfoglia) e la conduttanza idraulica della foglia (Kfoglia). Contestualmente, sono stati misurati anche i diametri dei vasi xilematici. Grazie all'analisi di questi parametri è stato possibile eseguire uno studio biofisico accurato del comportamento idraulico dell'orniello in condizioni di limitazione della disponibilità d'acqua. Da questi dati emerge che la conduttanza fogliare al vapore d'acqua (gL) è il parametro più affidabile a rappresentare l'indice di aridità ambientale, in quanto è risultato essere il più sensibile alle variazioni nella disponibilità d'acqua. Il tentativo di integrare i dati di campo relativi a gL con quelli ottenuti mediante elaborazione di immagini satellitari non ha portato ai risultati sperati. L'indice ottenuto da dati telerilevati è risultato poco promettente come indice di riferimento per la realizzazione di uno “scaling-up”, in quanto non è risultato essere in grado di rilevare condizioni di stress idrico in aree caratterizzate da forte drenaggio dell'acqua (aree ad alta carsificabilità). L'applicabilità delle tecniche di telerilevamento da satellite nel monitoraggio dell'aridità ambientale risulta quindi fortemente limitata dalla struttura geomorfologica del territorio oggetto di studio.
XX Ciclo
1973

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Touzeau, Alexandra. "L'Egypte ancienne, une civilisation face à un changement climatique : le message isotopique (C, N, O, S) des tissus vivants momifiés." Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10104.

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L'Egypte, territoire aride, dépend essentiellement du Nil pour l'irrigation de ses terres agricoles. La variabilité temporelle de la crue du fleuve a donc pu affecter directement la dynamique de la population égyptienne. Ici, cette hypothèse est testée en étudiant la variation du climat pendant l'Egypte ancienne parallèlement à des indicateurs du mode de vie des égyptiens. La variation dans le temps du δ18Ow de l'eau du Nil est reconstituée à partir des valeurs de δ18Op du phosphate de l'apatite de momies égyptiennes. L'augmentation de +3 ‰ du δ18Ow de l'eau du Nil entre la période Prédynastique (5500BP) et la période Gréco-Romaine (2000BP) est causée par une modification des conditions de précipitation au-dessus des sources du Nil. Elle traduit soit une hausse de température proche de 2°C soit une baisse des précipitations mensuelles d'environ 140 mm. Ici, l'hypothèse d'une aridification est privilégiée : en effet des mesures de δ18Op sur des poissons du Nil permettent de calculer une température du Nil à la période Gréco-Romaine comparable à l'actuelle. Le changement climatique constaté semble avoir peu d'impact sur la civilisation égyptienne. En effet la population égyptienne s'accroît nettement pendant la période considérée et le régime alimentaire est resté fondé sur les plantes en C3, peu adaptées aux milieux arides, avec une consommation rare de poissons et de protéines animales. La réduction de la crue a sans doute été compensée par les progrès technologiques de la civilisation égyptienne (chadouf, drainage) qui ont rendu possible la mise en culture de nouvelles terres
Egypt is an arid territory, which essentially depends on the Nile river for the irrigation of its agricultural lands. The temporal variability of the river flood thus may have affected directly the dynamics of the Egyptian population. Here, this hypothesis is tested by studying the variation of the climate during Ancient Egypt concurrently to indicators of the life habits of the Egyptians. The variation with time of the δ18Ow of the Nile water is reconstructed from the δ18Op of the apatite phosphate of Egyptian mummies. The increase of +3 ‰ in the Nile water δ18Ow between the predynastic period (5500BP) and the Greco-Roman Period (2000BP) is caused by a change in the conditions of precipitation above the Nile sources. This increase can be the result of an increase in temperature of about +2 °C or of a decrease in the monthly amount of precipitation of about 140 mm. Here, the hypothesis of aridification is preferred: in effect, δ18Op measures on Nile fishes permit to infer a Nile water temperature at the Greco-Roman Period similar to the present-day one. The climatic change seems to have had little impact on the Egyptian civilization. In effect the Egyptian population increases considerably during the selected period and its diet remains funded on C3- plants, feebly adapted to arid environments, with a rare consumption of fishes or other animal protein. The decrease of the flood was admittedly compensated by the technological advances of the Egyptian civilization (shaduf, drainage) which allowed the cultivation of newly reclaimed lands

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Reyes, Serrano Héctor Fabian. "La tierra se mueve : les transformations de la propriété agricole dans une zone aride : la province du Limarí (Région de Coquimbo, Chili)." Phd thesis, Université d'Orléans, 2009. http://tel.archives-ouvertes.fr/tel-00455240.

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La terre agricole du Limarí change de mains, parfois très lentement, parfois très rapidement. La concentration de la propriété de la terre, initiée avec les mercedes de tierra faites par la couronne espagnole à partir du 16ème siècle, ne sera interrompue que par la réforme agraire des années 1960. Le courant économique néolibéral confirmé avec force au Chili à partir de 1973, marque le début d'une nouvelle période de transformation de la propriété et de la production agropastorale qui se maintient actuellement. De nouveaux propriétaires et de nouvelles dynamiques économiques et sociales se développent dans le Limarí. Dans le contexte politique qui a mis en évidence le problème de paysans sans terre dans l'Amérique latine, l'accès à la terre agricole donne t'elle un meilleur accès à la croissance ? Le fait qu'un plus grand nombre devienne propriétaire de la terre transforme-t-il la relation entre l'agriculteur, la terre et la production ? La relation entre l'accès à la terre, la production et le bien-être des agriculteurs les moins favorisés n'est pas homogène mais présente une vaste gamme de nuances. L'accès à l'eau, au financement, à l'information et à la formation sont tout aussi déterminants. L'avenir des propriétaires-agriculteurs actuels, et de ceux qui aspirent à le devenir, n'est pas tout tracé et dépend de facteurs devenus imprévisibles. A travers les données des recensements agro-pastoraux et les données fiscales, et à travers des exemples détaillés, ce travail aborde l'évolution de la structure foncière dans une province dont l'agriculture s'est développée de façon spectaculaire malgré ou grâce à l'aridité, malgré ou grâce au néolibéralisme.

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Neilson, Julia W., Katy Califf, Cesar Cardona, Audrey Copeland, Treuren Will van, Karen L. Josephson, Rob Knight, et al. "Significant Impacts of Increasing Aridity on the Arid Soil Microbiome." AMER SOC MICROBIOLOGY, 2017. http://hdl.handle.net/10150/625716.

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Global deserts occupy one-third of the Earth's surface and contribute significantly to organic carbon storage, a process at risk in dryland ecosystems that are highly vulnerable to climate-driven ecosystem degradation. The forces controlling desert ecosystem degradation rates are poorly understood, particularly with respect to the relevance of the arid-soil microbiome. Here we document correlations between increasing aridity and soil bacterial and archaeal microbiome composition along arid to hyperarid transects traversing the Atacama Desert, Chile. A meta-analysis reveals that Atacama soil microbiomes exhibit a gradient in composition, are distinct from a broad cross-section of nondesert soils, and yet are similar to three deserts from different continents. Community richness and diversity were significantly positively correlated with soil relative humidity (SoilRH). Phylogenetic composition was strongly correlated with SoilRH, temperature, and electrical conductivity. The strongest and most significant correlations between SoilRH and phylum relative abundance were observed for Acidobacteria, Proteobacteria, Planctomycetes, Verrucomicrobia, and Euryarchaeota (Spearman's rank correlation [r(s)] = >0.81; false-discovery rate [q] = <= 0.005), characterized by 10- to 300-fold decreases in the relative abundance of each taxon. In addition, network analysis revealed a deterioration in the density of significant associations between taxa along the arid to hyperarid gradient, a pattern that may compromise the resilience of hyperarid communities because they lack properties associated with communities that are more integrated. In summary, results suggest that arid-soil microbiome stability is sensitive to aridity as demonstrated by decreased community connectivity associated with the transition from the arid class to the hyperarid class and the significant correlations observed between soilRH and both diversity and the relative abundances of key microbial phyla typically dominant in global soils. IMPORTANCE We identify key environmental and geochemical factors that shape the arid soil microbiome along aridity and vegetation gradients spanning over 300 km of the Atacama Desert, Chile. Decreasing average soil relative humidity and increasing temperature explain significant reductions in the diversity and connectivity of these desert soil microbial communities and lead to significant reductions in the abundance of key taxa typically associated with fertile soils. This finding is important because it suggests that predicted climate change-driven increases in aridity may compromise the capacity of the arid-soil microbiome to sustain necessary nutrient cycling and carbon sequestration functions as well as vegetative cover in desert ecosystems, which comprise one-third of the terrestrial biomes on Earth.

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Rey, Carine. "Détection de l’évolution convergente à l’échelle génomique : développement de méthodes et étude des adaptations indépendantes à la vie en milieu aride chez les rongeurs." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEN060.

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La convergence phénotypique, c’est-à-dire l’acquisition indépendante de caractères similaires par des espèces différentes, est omniprésente dans la nature et a été souvent étudiée. Mais ce processus évolutif n’est pas bien compris. Par exemple, de nombreux chercheurs cherchent à comprendre s’il existe des bases génétiques convergentes sous-jacentes à ces convergences phénotypiques.Quelques substitutions convergentes corrélées à un phénotype convergent ont été décrites dans la littérature, mais il existe peu d’études à l’échelle génomique. Ceci peut s’expliquer par deux problèmes méthodologiques : 1/ D’une part, la difficulté de créer des jeux de données multi-espèces pour des analyses comparatives. 2/ D’autre part, le manque de méthodes dédiées à la détection de la convergence à l’échelle génomique.Au cours de ma thèse, j’ai proposé des solutions à ces deux défis. Dans un premier temps, j’ai créé un programme (CAARS) permettant d’automatiser l’assemblage de jeux de données composés de familles d’orthologues à partir de données RNA-Seq. Puis, j’ai créé un outil (PCOC) pour étudier les substitutions convergentes au sein de séquences codantes, basé sur l’identification de changements de profils d’acides aminés. Ces outils ont été développés dans un souci de reproductibilité et de facilité d’utilisation. J’ai ensuite étudié la capacité de différentes méthodes, dont PCOC, à détecter des substitutions convergentes en présence de facteurs confondants. Enfin, j’ai appliqué ces méthodes à un cas biologique où j’ai cherché à caractériser les bases génomiques de l’adaptation aux milieux arides chez les rongeurs
Phenotypic convergence, the independent acquisition of similar characters by different species,is widespread in nature and has been extensively studied. But this evolutionary process is not well understood. For example, many researchers seek to understand whether there are convergent genetic bases underlying these phenotypic convergences.Some convergent substitutions correlated with a convergent phenotype have been described in the literature, but there are few studies at the genome scale. This can be explained by two methodological problems : 1 / On the one hand, the difficulty of creating multi-species datasets for comparative analyses. 2 / On the other hand, the lack of dedicated methods to detect convergence at the genomic scale.During my thesis, I proposed solutions to these two challenges. As a first step, I created a program (CAARS) to automate the assembly of datasets composed of orthologous families from RNA-Seq data. Then I created a tool (PCOC) to study convergent substitutions within coding sequences, based on the identification of amino acid profile changes rather than strict amino acid changes. These tools have been developed for the sake of reproducibility and ease of use. I then studied the ability of different methods, including PCOC, to detect convergent substitutions in the presence of confounding factors. Finally, I applied these methods to a biological case where I sought to characterize the genomic bases of adaptation to arid environments in rodents

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8

Spinks, Andrew Charles. "Sociality in the common mole-rat, Cryptomys hottentotus hottentotus : the effects of aridity." Doctoral thesis, University of Cape Town, 1998. http://hdl.handle.net/11427/23681.

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This study addresses the extrinsic factors which have shaped the evolution and maintenance of sociality in the African mole-rats. Specifically, the common mole-rat was used as a model to assess the Aridity Food-Distribution Hypothesis (AFDH), as an explanation for the evolution of bathyergid sociality. The AFDH correlates mole-rat sociality with habitat aridity and the pattern of food distribution. Aspects relating to ecological constraints, foraging behaviour, population demography, reproductive biology and aggressive behaviour were compared between an arid and a mesic population of C. h. hottentotus, to assess how inter-habitat divergence in ecological attributes has influenced social behaviour within these two populations. In evaluating the AFDH as an explanation for the evolution of sociality within C. h. · hottentotus two broad questions were addressed: (1) do the assumptions of the AFDH hold true i.e. do arid and mesic habitats exhibit ecological differences, specifically with regard to the pattern of resource dispersion and the energetic costs of foraging, which influence foraging risks and consequently the costs of dispersal? and (2) do these inter-habitat differences have implications for bathyergid social evolution i.e. do the common mole-rat populations inhabiting arid and mesic areas exhibit regional differentiation in social behaviour? Substantial inter-site divergence in ecological characteristics, notably climate and resource attributes, were revealed in this study. Rainfall at the arid site was markedly lower and more sporadic, and evaporation levels significantly higher, than at the mesic site. Moreover, thermal constraints were more limiting at the arid site. These features will greatly elevate the costs of soil excavation and the risks of hyperthermia, severely restricting the occurrence of suitable burrowing opportunities at the arid locality. Consequently, foraging will be severely constrained in this area. At the mesic site, higher, more predictable rainfall, low evaporation rates and reduced thermal constraints will translate into more suitable burrowing opportunities for much, if not all, of the year. Regional differentiation in food resource characteristics was also evident. Although geophytes were clumped at both study localities, the density of geophytes was lower and the distance between geophytes or geophyte clumps concomitantly greater at the arid relative to the mesic site. Differences in resource dispersion in turn influenced the patterns of foraging. In response to the low geophyte density and associated longer foraging distances, burrow systems were notably longer and more linear at the arid site. Furthermore, food storage and in situ harvesting were essential components of cooperative foraging in C. h. hottentotus as they minimised the risks of starvation, particularly in arid habitats. Thus, resource characteristics together with the climatic restrictions on burrowing in arid areas may have a marked impact on foraging behaviour, imposing severe constraints on the mole-rats occurring there and ultimately shaping their foraging responses. Together, these factors satisfactorily account for the underlying premise of the AFDH, that arid and mesic habitats exhibit ecological differences with regard to the pattern of resource dispersion and the energetic costs of foraging, which are likely to influence foraging risks and the costs of dispersal. In evaluating the AFDH, the second question which needed to be addressed was whether the study populations exhibited divergence in their social behaviour. The populations revealed no differences in absolute group size or in reproductive characteristics which were related to the effects of aridity per se. However, distinct inter-population divergence was readily apparent in phenotypically plastic traits such as dispersal behaviour and xenophobia. Clear differences were evident between the arid and mesic sites in both the quantitative and qualitative nature of dispersal; dispersal was markedly constrained at the arid site and colonies demonstrated greater temporal stability, with more predictable temporal group membership. The ecological constraints on successful foraging at the arid site will curb opportunities for dispersal and promote cooperation in the C. h. hottentotus occurring there. Colony members should therefore maximise their inclusive fitness by natal philopatry, delayed dispersal and cooperative foraging. Inter-site differences were also apparent in the response of colony members to foreign conspecifics. Common mole-rats from the arid site were markedly more xenophobic than those from the mesic site, and aggressively rejected foreigners. For arid-occurring populations, the fitness penalties for failing to exclude foreigners from the colony burrow system and associated resources, will be more severe than for mesic-occurring populations, resulting in heightened levels of xenophobia. Again, colony cohesion and cooperation in arid areas are essential to individual survival and inclusive fitness. The regional differences in dispersal patterns and xenophobia revealed in this investigation may reflect adaptive variation in social behaviour between the study populations, and the results suggest that delayed dispersal and cooperation may be more crucial to individual survival in arid than in mesic areas. As such these findings provide support for the underlying contention of the AFDH that ecological constraints on foraging in arid areas have promoted a greater degree of social elaboration in mole-rats occurring there. This study provides persuasive support for the AFDH as an explanation for the adaptive significance of social behaviour and cooperation in the common mole-rat, and together with other investigations, suggests that the AFDH provides a valid explanation for the evolution of group-living in the Bathyergidae.

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Mpofu, Khulekani. "Evaluation of the performance of community-based natural resources management (CBNRM) projects along an aridity gradient in Botswana." Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1006063.

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The Botswana Community Based Natural Resources Management (CBNRM) programme started in 1989. Its aims were to promote sustainable development through sustainable natural resources management and utilisation to improve rural livelihoods. The country CBNRM programme has recorded mixed outcomes and this has raised questions on the programme performance throughout the country. Since the programme has been recognised as one of the eight main livelihood strategies for rural communities in Botswana, there was a need to evaluate the programme performance and determine the factors that influence it. This thesis therefore evaluated the performance of CBNRM projects along an aridity gradient in Botswana and by so doing answered the two research questions of: (1) What factors influence the performance of CBNRM? And (2) how does aridity influence the performance of CBNRM programmes? Performance was determined in terms of financial benefits generated by CBNRM projects and the projects adherence to the CBNRM principles. Data were collected from seven selected CBNRM projects covering three aridity zones (wet, medium rainfall and dry areas) in the country. Data were also collected from key informants and community based organisations (CBO) project managers. Research findings have indicated differences in the performance of CBNRM projects across the identified three aridity zones. Factors that influenced the performance of CBNRM projects varied among the three aridity zones. These factors included: existence of complimentary rules and regulations for managing CBNRM projects; literacy levels of communities involved in CBNRM; ethnic composition of the project communities; historic and current socio-economic trends within communities; collaboration between CBNRM institutions and other local level institutes; amount of benefits generated through the projects; ability of institutions to resolve outstanding issues in time and type of CBNRM project. Research results also indicated that there was variation in the performance of CBNRM projects across the three aridity zones. Aridity was found to directly influence the performance of CBNRM projects through its influence on the amount of revenues that projects generated.

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Ben, Brahim Mohamed. "Le sillon de Boudenib (SE-Maroc) : structuration morphotectonique, hamadas tertiaires et paléoaltérations associées, morphogenèse quaternaire et aridité actuelle." Paris 1, 1994. http://www.theses.fr/1994PA010597.

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Le but de cette thèse est d'étudier le rôle de la tectonique et du climat dans l'élaboration des reliefs de grande et de moyenne échelle. L'approche pluridisciplinaire y constitue le cadre méthodologique. Il est montré que le sillon de Boudenib se situe au croisement de trois unités géotectoniques majeures : planafricaine, hercynienne et atlasique. Cette structuration transparait dans la dissymétrie des formes de relief. Le remplissage sédimentaire a enregistré la totalité des phénomènes qui se sont succédés à l'interieur du bassin et sur ses bordures. L'évolution préturonienne est marquée par le contrôle des facteurs tectoniques, climatiques et eustatiques. À partir du crétacé supérieur, seuls les facteurs tectoniques ou climatiques rythment l'évolution. L'étude du Piémont hamadien de Boudenib apporte des faits nouveaux sur la tectonique atlasique, la nature des dépôts et les alterations associées dont les silicifications y font l'originalité. Deux grands types de silicification ont été distingués : silicification pédogénétique associée à La Hamada de Boudenib I (eocene inférieur) et silicification de nappe affectant la Hamada du Guir (néogene). Enfin, la morphogeneèse tertiaire est marquee par la juxtaposition d'un Piémont d'accumulation à un Piémont d'érosion. La phase fini-pliocène ? met en place les unités de relief majeurs, mais les conditions morphogeniques quaternaires sont plutôt placées sous le contrôle du climat, évoluant vers l'aride, et ce malgré une néotectonique active jusqu'au. .
The purpose of this research is to study the role of tectonic and climat in the elaboration of reliefs of high and middle scale. The pluridisciplinary approch constitues the methodologic frame. It is shown that boudenib grooc is situated in the intersection of three major geotectonic units : panafrican, hercynian and atlasic. The dissymetry of topographical features reflects this structure. The sedimentation recorded the total phenomenon which succeeded inside the basin as well as on the borders. Therefore, dissymetry between eastern and western parts of the boudenib groov has been constant in the evolution. The preturonian evolution was caracterized by the control of tectonic factors, climat and eustatic ones. However, from the upper cretaceous only tectonic and climatic factors predominated. The study of hamadas deposits on the piedmont of boudenib brings new factors about the atlasic tectonic, the kind of deposits and associeted paleoweathering in which silicification makes the originaly. Two types of silicification were difined : pedogenetic silicification in the lower part of "hamada de boudenib" (lower eocene) and ground water silicification in the "hamada de guir" (neogene). Eventually, the tertiary morphogenisis is caracterized by the juxtaposition of two piedmonts : accumulation and erosion. .

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11

Frenette-Dussault, Cédric. "L'assemblage des communautés en milieu aride : une approche fonctionnelle." Thèse, Université de Sherbrooke, 2012. http://hdl.handle.net/11143/6546.

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La survie des, populations humaines est directement reliée à la préservation de leur environnement, principalement par le maintien des services écosystémiques. Cependant, depuis les débuts de l'industrialisation, plusieurs actions anthropiques ont fortement modifié les écosystèmes et les services écosystémiques en découlant, sur une échelle temporelle relativement courte. Cette situation est d'autant plus préoccupante pour les milieux arides dédiés au pastoralisme. Un surpâturage des terres de parcours combiné à des précipitations faibles et erratiques menacent la pérennité de la végétation et la sécurité alimentaire des populations locales qui dépendent de ces milieux pour leur survie. Pour ces raisons, il est primordial d'acquérir des connaissances sur le fonctionnement écologique des milieux arides et de s'attarder à leur devenir. Au cours de mon projet de doctorat, je me suis penché sur les relations entre les conditions environnementales et l'écologie fonctionnelle des communautés de plantes et de fourmis des steppes de l'Oriental marocain. Dans un premier temps, je me suis intéressé au changement dans la composition fonctionnelle de la végétation en fonction de l'aridité et du pâturage. Une approche fonctionnelle permet de suggérer des mécanismes explicites de l'assemblage des communautés en plus de pouvoir être utilisée peu importe les espèces et le type de milieu considérés. Les résultats ont mis en évidence trois groupes de traits fonctionnels qui rappellent la théorie C-S-R de Grime. La végétation a montré une stratégie d'évitement du pâturage plutôt qu'une réponse de résistance au pâturage en favorisant les espèces annuelles à croissance rapide, de petite taille et avec des graines de faible masse. L'aridité a sélectionné une végétation composée d'espèces ligneuses avec des feuilles succulentes et une teneur élevée en carbone isotopique 13. Malgré l'existence de corrélations significatives entre les traits fonctionnels et l'environnement, la force de ces corrélations était relativement faible. Le gradient d'aridité et le temps de mise en défens des exclos considérés n'étaient probablement pas suffisamment contrastés afin d'observer un filtrage environnemental net. Dans un deuxième temps, j'ai utilisé un modèle statistique novateur (MaxEnt) pour prédire les abondances relatives des espèces des communautés de plantes actuelles dans un contexte de changements climatiques. On prévoit une augmentation de l'aridité dans l'Oriental marocain pour la période 2080-2099. Le modèle MaxEnt s'appuie sur un principe clé de l'écologie fonctionnelle, soit le filtrage environnemental par les traits, et sur des outils empruntés à la mécanique statistique et à la théorie de l'information pour faire de telles prédictions. Les résultats ont montré que les prédictions d'abondances relatives des communautés actuelles sont plus précises lorsque les traits agrégés observés sont utilisés. Pour la période 2080-2099, le modèle MaxEnt suggère que les communautés passeront d'une dominance d'espèces annuelles à des espèces ligneuses tolérantes au stress. Ceci suggère un processus de désertification. Les prochaines études devront se pencher sur la définition du pool d'espèces et sur l'évolution des activités pastorales. Finalement, j'ai intégré les traits fonctionnels de fourmis à l'étude des communautés de plantes afin de suggérer une approche multitrophique à l'assemblage des communautés. Les résultats ont montré que la végétation a un effet direct sur la structure des communautés de fourmis et que l'environnement a un effet indirect sur ces mêmes communautés via la végétation. Ce modèle était supporté autant par les données de composition taxonomique que par les données de composition fonctionnelle des plantes et des fourmis. Ceci constitue un développement pour l'écologie des communautés, car ce type d'approche fonctionnelle est encore peu utilisé en écologie animale. Le développement d'un cadre conceptuel similaire à celui de la théorie C-S-R de Grime pourrait être très utile pour mieux comprendre les mécanismes d'assemblage des communautés animales.

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12

van, Dijk Jeroen. "Size and Abundance of Late Pleistocene Reticulofenestrid Coccoliths from the Eastern Indian Ocean in Relation to Temperature and Aridity." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-325273.

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Measurements on coccolith abundance and mass can be used as a signal of primary productivity and pelagic calcification in response to environmental change. The Leeuwin Current (LC) is known to transport warm and low-salinity waters from the Indo-Pacific Warm Pool (IPWP) southwards along the coast of West Australia. Along with the onset of continental aridity during late Neogene, increased strength of the LC may have played a role in reef expansion on the Northwest Shelf. In this study the morphological variation in size and mass of reticulofenestrid coccoliths was assessed in material from IODP Site U1461 in the eastern Indian Ocean spanning the past 500 ka. Both the absolute abundance of all reticulofenstrid coccoliths (Emiliania huxleyi, Reticulofenestra spp., Gephyrocapsa spp. and Pseudoemiliania spp.) was determined, as well as the relative abundance of large versus small coccoliths. Coccolith size and mass were measured quantitatively under circularly polarized light. The data was compared to variations in sea surface temperatures (SST) of the LC, and to continental aridity of Australia. SST fluctuations could influence coccolithophore productivity by affecting their metabolic rate, whereas continental aridity may influence the influx of terrestrial matter by wind. The investigated interval is dominated by small species of Gephyrocapsa. Peak values of absolute abundance and mass were observed during Marine Isotope Stage (MIS) 11, an interglacial period of extended warmth and humidity. These results coupled with high densities of aragonite needles in the same samples indicate the sediments were diluted by material overflowing from the adjacent shallow- water carbonate platform, analogous to the whiting events observed in the modern-day Bahamas. A decrease in abundance of Gephyrocapsa caribbeanica at 240 ka can be linked to the timing of their last common occurrence (LCO), within MIS 7. The subsequent shift to Gephyrocapsa oceanica as the dominant large species may indicate an ecological replacement of G. caribbeanica, or signify warm and low-salinity waters.
Mätningar av abundans och massa hos coccoliter kan användas som en signal för primärproduktion och pelagisk förkalkning som resultat av miljöförändringar. Leeuwin Current (LC) är känd för att transportera varmt vatten och vatten med låg salthalt från Indo-Pacific Warm Pool (IPWP) söderut längs kusten i västra Australien. Tillsammans med början av kontinental torka under sen Neogen kan ökad styrka hos LC ha spelat en roll i expansionen av rev på nordvästsockeln. I denna studie bedömdes den morfologiska variationen i storlek och massa hos coccoliter i material från IODP plats U1461 i östra Indiska oceanen från de senaste 500 000 åren. Både den absoluta abundansen av alla reticulofenstridcoccoliter (Emiliania huxleyi, Reticulofenestra spp., Gephyrocapsa spp. och Pseudoemiliania spp.) bestämdes, liksom den relativa abundansen av stora jämfört med små coccoliter. Storlek och massa av coccoliter mättes kvantitativt under cirkulärt polariserat ljus. Uppgifterna jämfördes med variationer i havsytans temperatur (SST) hos LC, och med kontinental torrhet i Australien. SST-fluktuationer kan påverka produktiviteten hos coccolitoforider genom att påverka deras metabolism, medan kontinental torrhet kan påverka inflödet av markmaterial med vind. Det undersökta intervallet domineras av små arter av Gephyrocapsa. Toppvärden av absolut abundans och massa observerades under marinisotopsteget (MIS) 11, en interglacial period med förlängd värme och fuktighet. Dessa resultat kombinerat med hög densitet av aragonitnålar i samma prover indikerar att sedimenten späddes ut med material som svämmade över från den intilliggande grunda karbonatplattformen, vilket är jämförligt med de vitningshändelser som har observerats i dagens Bahamas. En minskning i abundans av Gephyrocapsa caribbeanica vid 240 ka kan kopplas till tidpunkten för deras senaste gemensamma förekomst (LCO) inom MIS 7. Den efterföljande övergången till Gephyrocapsa oceanica som den dominerande stora arten kan indikera en ekologisk ersättning av G. caribbeanica, eller indikera varmt vatten med låg salthalt.

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Kheir, Maya. "Fonctionnement des sols méditerranéens sous changement climatique : effet de la préexposition au stress, de la mixité des litières et de l'identité de l'espèce végétale." Thesis, Aix-Marseille, 2020. http://theses.univ-amu.fr.lama.univ-amu.fr/200710_KHEIR_495pzb687n410mxugdf923oaivtm_TH.pdf.

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Ce travail se situe dans un contexte du changement climatique. L’objectif est d’explorer le fonctionnement des communautés microbiennes de litières végétales dépendant des contrastes climatiques (sub-humide vs semi-aride) Nord/Sud de la Méditerranée mais aussi selon le contexte côtier/continental,et d’évaluer leur réponse au stress d'aridification en considérant les effets i) du type de litière (identité de l’espèce végétale et mixité) et ii) de la préexposition au stress intrinsèques des milieux côtiers. Le stress d’aridité a été appliqué en laboratoire (cycles de séchage/réhumectation) et in natura via des transferts de «litter bags» de France vers l’Algérie. Les résultats montrent que la biomasse microbienne et la respiration basale dépendent des traits chimiques de la litière (C/N et lignine/N): lorsque ces ratios augmentent la biomasse microbienne diminue, alors que l’effet sur la respiration dépend des contrastes climatiques. L’effet de la mixité binaire des litières sur les microbes dépend du contexte climatique et de la composition du mélange: certains mélanges semblent limiter le relâchement du carbone par respiration hétérotrophique en contexte aride Algérien. En outre, un fonctionnement microbien particulier des environnements côtiers a été mis en évidence: i) la préexposition aux contraintes côtières a limité l’effet du stress sur les structures cataboliques microbiennes en laboratoire ii) l’expérience in natura a montré que les réponses microbiennes au stress dépendent du contexte (côtier/continental) mais aussi du type de la litière, mettant en valeur une influence de la litière qui dépasse l’échelle locale pour s’imposer même à une large échelle spatiale
This work takes place in the context of climate change. We aimed to explore plant litter microbial communities' functioning depending on climate contrasts Northern/Southern Mediterranean but also according to inland/coastal context, and to assess their response to aridification stresses, considering the effect i) of the type of litter (plant species identity and mixture) and ii) of the preexposure to stress intrinsic of coastal environments. Aridity stress was applied in the laboratory (drying /rewetting cycles) and in natura via "litter bags" transfer from France to Algeria. Results show that microbial biomass and basal respiration depend on litter chemical traits (C/N and lignin/N): when these ratios increase, microbial biomass decreases, while the effect on respiration depends on the climate contrasts. The effect of binary litter mixtures on microbes depends on the climate context and the mixture composition: some mixtures seem to limit carbon release through heterotrophic respiration in Algerian arid context. In addition, a particular microbial functioning of coastal environments was highlighted: i) preexposure to coastal constraints limited the effect of stress applied in the laboratory on microbial catabolic structures ii) the in natura experiment showed that microbial responses to stress depend on the context (coastal/inland) but also on litter type, highlighting litter influence even at large spatial scales

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O'Connor, Peter W. "Aeolian activity and environmental change in the Central Mega Kalahari : implications for the timing, nature and causes of late Quaternary aridity." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284355.

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15

Tatsumi, Chikae. "Nitrogen cycling driven by soil microbial communities in exotic black locust plantations and native oak forests in the drylands of East Asia." Kyoto University, 2020. http://hdl.handle.net/2433/253313.

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Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第22477号
農博第2381号
新制||農||1074(附属図書館)
学位論文||R2||N5257(農学部図書室)
京都大学大学院農学研究科森林科学専攻
(主査)准教授舘野隆之輔, 教授北島薫, 教授德地直子
学位規則第4条第1項該当

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16

Rueff, Henri. "Optimizing dryland afforestation : prospects and limitations : minimum carbon payment for non-annex I dryland countries on an aridity gradient with stochastic weather and prices." Aix-Marseille 3, 2009. http://www.theses.fr/2009AIX32045.

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Des études récentes ont montré que les arbres dans les zones arides forment d’importants puits de carbone. On ne connait cependant pas le prix du carbone à partir duquel un agriculteur serait indifférent entre son activité agricole coutumière et une activité de plantation d’arbres. La production de carbone séquestré par les arbres a été simulée sur le modèle CO2FIX v3. 1 pour le pin d’Alep. Les récoltes de blé et la production des pâturages pour les activités agricoles renoncées ont été simulées par des modèles quadratiques semblables, se basant sur les engrais azotés et utilisant 30 ans de données climatiques pour simuler le déficit hydrique. Les deux modèles ont été développés pour les conditions des zones arides. Leur calibrage a été fait sur des données observées en Israël, sur 8 stations, distribuées le long d’un gradient d’aridité (de 200mm à 900mm de précipitation). Les valeurs obtenues pour les récoltes ont été adaptées à une fonction de distribution de probabilité gamma. Les prix de production et de vente, ont eux été adaptés à une distribution normale. Une méthode itérative a permis de simuler l’effet stochastique du prix et du climat sur un flux de trésorerie pendant 30 ans avec 10'000 itérations. Les résultats montrent qu'en dépit de la capacité élevée de l’afforestation dans les zones arides à séquestrer le carbone, son commerce est peu lucratif, quel que soit le niveau d’aridité et l’activité renoncée. En effet, le prix du carbone doit augmenter sensiblement, et les coûts de certifications doivent fortement diminuer, sans quoi, l’afforestation des zones arides dans les pays ne faisant pas partie de l’annexe I ne sera pas un mécanisme adopté
Recent findings demonstrate that dryland trees are efficient carbon sinks. The price of carbon at which a farmer would be indifferent between his customary activity and the plantation of trees for the trade of carbon credits remains however unknown. Carbon yields were simulated by means of the CO2FIX v3. 1 model for Pinus halepensis. Wheat yields and pasture yields were predicted on somewhat similar nitrogen-based quadratic models, using 30 years of weather data for the simulation of moisture stress. Both models were developed for dryland conditions, while calibration and validation were done with data collected in Israel on 8 stations (from 200mm to 900mm of annual precipitation). No-till wheat and pasture yield values were then fitted to a gamma probability distribution function, to enable iterative stochastic production simulation. Input and output prices were, however, fitted to a normal distribution. Stochastic production, input and output prices were afterwards simulated on a Monte Carlo matrix with 10,000 iterations on a 30 years cash flow. Results show that, despite the high levels of carbon uptake by dryland trees, carbon trading by afforesting is unprofitable anywhere along the aridity gradient. Indeed, the price of carbon will have to raise unrealistically high, and the certification costs will have to drop significantly, to make afforestation under the clean development mechanism a worthwhile activity for non annex I dryland countries

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Tran, Hoa Thi. "Integration of Geospatial Technologies in Monitoring Drought Events in a Coastal Area of Vietnam (Case study: Binh Thuan Province)." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/95471.

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Drought is a climatic event regarding prolonged "drier than normal" conditions. Precipitation deficits, crop-moisture stress, soil-water unbalance, sudden stream flow cut-offs and low carrying capacity of ecosystems are responses to drought. Drought can occur in humid to arid climates, however, drought is more severe in arid and semi-arid areas due to the fact that in those distinctive areas, water resources are extremely limited and restricted. Additionally, local ecologies and ecosystems in arid regions are very fragile. Once a water competition occurs, critical services of ecosystems such as pure water, recreation, and land productivity will be threatened. This research focuses on prolonged drought events that have been occurring more frequently in a coastal province of South Central Vietnam – named Binh Thuan. The study area is distinctive because its climate is characterized as one of the driest provinces in Vietnam. Annual rainfall in the North and near the coast of the province is less than 800 mm per year. During 6 months of dry season, there is almost no rain, or less than 50 mm. Due to precipitation deficits and high surface temperatures in recent years, meteorological droughts have occurred more frequently, and lasted longer, thereby stressing water resources for vegetation, wildlife, households, and industry. The occurrence of prolonged droughts has constrained economic activities in the coastal areas, especially agriculture and aquaculture. Furthermore, a long duration of dry conditions coupled with unsustainable land management (such as overgrazing), "drought-sensitive" soils in areas with sand and barren lands may introduce and accelerate risks of desertification processes (land productivity deterioration and unable to recover). This research uses geospatial technologies to monitor drought severity and drought impacts on land use and land cover. Chapter 1 is a brief introduction and literature review of the drought context in Binh Thuan Province to place the research questions and objectives in content. Chapter 2 discusses the occurrence of meteorological droughts in Binh Thuan Province, then proposes climatic indices able to monitor this type of drought. Chapter 3 focuses on explaining and assessing uneven dry conditions that stressed vegetation health in the study area. This chapter investigates spatiotemporal distributions and frequencies of prolonged agricultural droughts using remotely sensed data and anomalies of precipitation distribution. Results indicate that coastal areas in the North of Binh Thuan are subject to severe droughts. Chapter 4 assesses human impacts on land management and practices in the study area during drought periods. Results show that in recent years (2010 to present), local governments and residents have implemented strategies to prevent sand dominance and to adapt to water shortages during dry seasons, such as vegetative cover, crop rotation with drought-tolerant plants and wind breaks. Accuracy was assessed using field data collected in the summer of 2016, in conjunction with Google Earth imagery. In summary, this dissertation enhances understanding of drought events and impacts in Binh Thuan Province by considering different types of drought - meteorological and agricultural drought, and interactions of drought and human impacts upon land management and land practices during dry periods. Furthermore, findings and results of this research have demonstrated the effectiveness of remotely sensed datasets, and other geospatial technologies, such as geographic information systems, in modeling drought severity and in examining efforts and drought-adaptive practices of local residents. This work is a valuable foundation on which further studies can build to support policy development to protect and reserve soil-land productivity in Binh Thuan and other coastal regions of Vietnam affected by prolonged droughts.
Doctor of Philosophy
Drought is a temporal climatic event with "drier than normal" conditions. While drought can occur in any climates, it can be more extreme in arid and semi-arid areas where annual rainfall and water resources are limited. Depending on types of drought, its presences and impacts may differ: (1) meteorological drought relates to a decrease of average rainfall/snowfall may resulting in moisture stress, (2) hydrological drought leads to a reduction of streamflow and groundwater, and (3) agricultural drought influences soil-water-crop balance or vegetation health. Prolonged drought – abnormally long duration of dry conditions, coupled with unsustainable management in water and land practice may cause losses of land productivity, promote soil erosion, and result in sand dominance in coastal areas. These land degradation processes can lead to "a desert-like condition" in impacted areas. This research concerns drought and its impacts in a coastal province in South central Vietnam, Binh Thuan. The study area is distinctive because its climate is characterized as one of the driest provinces in Vietnam. Annual rainfall in the North and near the coast is less than 800 mm per year, and during the 6 months of the dry season, there is almost no rain, or less than 50 mm. Due to precipitation deficits and high surface temperatures in recent years, meteorological droughts have occurred more frequently and lasted longer, stressing water resources for vegetation, wildlife, households, and industry. Additionally, unsustainable land management, such as overgrazing, coupled with movements of sand and barren lands from the coast inland, have accelerated the risks of land degradation. This research applies an integration of geospatial technologies for monitoring drought severity and impacts on land management and illustrates how local people have adapted to droughts.

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Fabris, Beatrice <1990&gt. "Evoluzione della rete di impollinazione lungo il gradiente di successione dei prati aridi." Master's Degree Thesis, Università Ca' Foscari Venezia, 2017. http://hdl.handle.net/10579/11713.

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L’ultima frontiera della conservazione della biodiversità prevede di mantenere le specie prendendo in considerazione i rapporti che queste instaurano con gli altri organismi e che ne consentono in definitiva la sopravvivenza a lungo termine. Obbiettivo del presente lavoro di tesi è stato quello di valutare come cambiassero i rapporti interspecifici per l’impollinazione a seguito dell’abbandono delle pratiche di gestione delle praterie aride. La conservazione delle praterie aride dipende dal mantenimento delle pratiche di gestione tradizionali quali sfalcio e pascolamento. Per ottemperare a questo obbiettivo abbiamo monitorato i rapporti di impollinazione tra specie entomofile ed insetti di praterie aride a diverso grado di successione (abbandono). Dal calcolo di parametri classici nello studio delle reti di impollinazione è emerso come nelle praterie gestite la rete di impollinazione sia più nested e più modulare. Le reti delle praterie gestite quindi risultano più stabili e meno soggette a estinzioni secondarie.

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ALVES, Telma Lúcia Bezerra. "Avaliação do nível de degradação das terras (desertificação) no alto curso da bacia hidrográfica do rio Paraíba." Universidade Federal de Campina Grande, 2016. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/978.

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A desertificação é um problema ambiental que atinge várias regiões no mundo, sendo definida como a degradação das terras nas zonas áridas, semiáridas e subúmidas resultante de vários fatores, incluindo variações climáticas e atividades humanas. O objetivo desse estudo foi avaliar o nível de degradação das terras (desertificação) no alto curso da bacia hidrográfica do Rio Paraíba, através da dinâmica temporal e espacial de aspectos climáticos, biofísicos e socioeconômicos. O alto curso da bacia hidrográfica engloba total ou parcialmente, a área de 18 municípios, distribuídos entre as microrregiões do Cariri Ocidental e Oriental do estado da Paraíba. Foram utilizados dados climáticos do período de 1950 a 2013 para as variáveis: precipitação pluvial e índice de aridez (Ia), dados de sensores orbitais - Moderate Resolution Imaging Spectro radiometer (MODIS), período de 2000 a 2013, visando à obtenção do albedo da superfície e do índice de vegetação ajustado ao solo (IVAS) e dados censitários (demográficos e agropecuários) para quantificação do índice socioeconômico e do nível de degradação na região. O teste de Mann-Kendall (MK) foi utilizado para identificação da tendência temporal das variáveis, ao nível de significância de α = 0,05, o método de Sen para quantificação da tendência e a krigagem para análise da dinâmica espacial das variáveis. Os principais resultados evidenciam que há uma tendência crescente da precipitação pluvial e decréscimo da aridez no alto curso da bacia como um todo, durante o período estudado. Pode-se inferir que estas condições não contribuem para desencadear o processo de degradação das terras (desertificação), sugerindo que as causas desse problema ambiental não são climáticas. A precipitação média anual aumenta na direção nordeste-noroeste da bacia, com mínimo (320 mm) em Cabaceiras e máximo (680 mm) nas localidades de Ouro Velho e Prata; o albedo da superfície e o índice de vegetação têm seus valores influenciados pela sazonalidade climática da região. A precipitação pluvial é o elemento que condiciona o aumento do índice de vegetação e diminuição do albedo da superfície, considerando-se que estas duas variáveis têm comportamento inverso. A região central do alto curso da bacia hidrográfica (municípios de Congo, Camalaú e Caraúbas) apresentou baixo índice de vegetação e elevado albedo da superfície, caracterizando possivelmente um processo de degradação das terras. Ao longo do período analisado (2000-2013), estas variáveis apresentaram tendência decrescente, mas não significativa, evidenciando um aumento pouco significativo da degradação das terras. Em relação ao índice socioeconômico geral de cada município – Isem observa-se que sete apresentaram “Moderada” degradação, dez “Baixa” degradação e apenas o município de Boqueirão apresentou situação de “Acentuada” degradação das terras. Os valores médios do Isem por município revelam que está havendo degradação das terras em todo o alto curso da bacia, porém em níveis Moderados e Baixos, sendo a região noroeste a área com maior pressão antrópica. Há uma tendência de aumento do índice socioeconômico - Iseb no alto curso da bacia hidrográfica com valor médio que indica uma situação de degradação “Moderada” das terras. Esse aumento é resultante do crescimento econômico, de programas sociais implantados e das melhorias nas condições de vida da população ao longo dos anos.
Desertification is an environmental problem that affects several regions in the world, defined as the land degradation of arid, semi-arid and sub-humid areas resulting from various factors, including climatic variations and human activities. The aim of this study was to evaluate the level of land degradation (desertification) in the upper course of the watershed of Paraíba River, through the temporal and spatial dynamics of climatic, biophysical and socio-economic aspects. The upper reaches of the watershed encompasses all or part of the area of 18 municipalities, distributed among the micro-regions of Western and Eastern Cariri state of Paraiba. Period of climatic data were used in 1950 the 2013 for the variables: rainfall and aridity index (Ia), orbital data from sensors - MODIS (Moderate Resolution Imaging Spectro radiometer), from 2000 to 2013, to obtain the surface albedo and Vegetation Index adjusted to the ground (SA VI) and census data (population and agricultural) to quantify the socio economic index and the level of degradation in the region. The Mann-Kendall test (MK) was used to identify the time trend variable, the level of significance o f α = 0.05, the Sen method to quantify the trend and Kriging for analyzing spatial dynamics of the variables. The main results show that there is an increasing trend of rainfall and decrease dryness on the upper course of the watershed as a whole, during the period studied. You can infer that these conditions do not contribute to trigger land degradation process (desertification), suggesting that the causes of this environmental problem is not climate. The average annual precipitation increases in the north-northwest direction of the watershed, with minimum (320 mm) in Cabaceiras and maximum (680 mm) in Ouro Velho and Prata localities; the surface albedo and vegetation index have their values influenced by the seasonality of the region. Rainfall is the element that determines the increase in vegetation index and decrease in surface albedo, considering that these two variables have opposite behavior. The central region of the upper course of the watershed (municipalities of Congo, Camalaú and Caraúbas) showe d a low rate of vegetation and high albedo surface, possibly featuring a land degradation process. Throughout the period analyzed (2000-2013), these variables showed a downward trend, but not significant, showing a slight increase of land degradation. Rega rding the general socioeconomic index of each municipality – Isem it is observed that seven had "moderate" degradation ten "Low" degradation and only the municipality of Boqueirão presented situation of "Severe" land degradation. The municipality by Isem average values reveal what's going on land degradation across the upper course of the watershed, but in Moderate and Low levels, and northwest region of the area with increased human pressure. There is a tendency to increase the socioeconomic index - Iseb in the upper course of the watershed with an average value indicating the degradation of situation "moderate" land. This increase is the result of economic growth, implemented social programs and improvements in the living conditions of the population over the years.

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Scarpace, Michelle Rose. "The effects of tillage and long-term irrigation on dynamic soil properties and genesis of Aridic Argiustolls in western Kansas." Thesis, Kansas State University, 2016. http://hdl.handle.net/2097/32834.

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Master of Science
Department of Agronomy
Michel D. Ransom
Soil is a dynamic resource that can undergo many changes due to altering conditions (Tugel et al., 2005). With that, humans can have a great effect on the conditions of a landscape and contribute to soil change. As soils change, the function of soils can be altered which would affect the ability of soils to support ecosystem services. The objective of this thesis is to access how management affects dynamic and inherent soil properties in western Kansas soils. Eight sites in Sheridan County, KS mapped as Keith 1-3% slopes (fine-silty, mixed, superactive, mesic Aridic Argiustolls) were described and sampled. Of the eight sites, four are in ST (ST) management and four are in no-till (NT) management. All sites have been irrigated under center pivot irrigation systems since the 1970s. Soil samples of the A horizon were taken at each site to analyze total carbon, aggregate stability, bulk density, pH and microbial respiration to assess the impacts of tillage management on dynamic soil properties. Additionally, pedons were described from the ST sites in the irrigated areas as well as outside the pivot track to represent dryland conditions. Particle size data, field descriptions, and the micromorphology of thin sections were analyzed to determine if the classification of Keith soils are affected by irrigation. Significant differences between NT and ST management were seen in microbial respiration, select water stable aggregate sizes, and pH and bulk density at certain depths. It was also found that irrigation did not affect clay illuviation nor carbonate leaching. Overall, it was concluded that inherent soil properties such as soil map unit composition and parent material can have a greater impact on soil change and prevent the recognition of changes in soil properties over a human time scale.

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Carvalho, Vitor Celso de. "Structure et dynamique de la végétation en milieu tropical semi-aride : la Caatinga de Quixaba (Pernambouc, Brésil) du terrain à l'analyse des données MSS/LANDSAT." Toulouse 2, 1986. http://www.theses.fr/1986TOU20031.

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Parmi les différents moyens de surveillance des milieux tropicaux semi-arides, la télédétection satellitaire est amenée à jouer un rôle de plus en plus important. L’objectif de ce travail est d'évaluer les limites et les possibilités de l'outil satellitaire à partir des images mss landsat sur un périmètre-pilote du nordeste brésilien, situe au nord de Petrolina (pe). Dans une première étape, un système de classification structurale de la steppe nordestine (Caatinga) est établi et applique au périmètre-pilote. Puis, des cartographies au 1 100 000e du périmètre, effectuées à partir des missions aériennes 1955, 1965, 1983, permettent de discuter la perception des objets sur photographie aérienne et, ensuite, d'analyser l'évolution 1955-1983 de la caatinga. Enfin, le pouvoir de discrimination des images, à partir du traitement numérique de quatre scènes (1973,1974 et 1983), est évalué, par comparaison avec les cartographies précédentes : 7 classes seulement au maximum (contre 15) sont distinguables. Concrètement toutes les analyses montrent que, de 1955 à 1983, l'évolution se caractérise essentiellement par une extension des surfaces cultivées (surtout depuis 1974) et une grande stabilité structurale de la Caatinga
Satellite remote sensing is more used as a tool for monitoring the tropical semiarid ecosystems. In this work we propose to do an estimation of practicability and limits of mss landsat datas, from a test region of brazilian nordeste, north of Petrolina (pe) the first part deals with the finalization of a structural classification of the steppe (Caatinga) vegetation and its application to the test region. Then, a 1 100 000 scale structural mapping, drawn from the 1955,1965 and 1983 aerial photographs, allows to discuss the signification of aerial photographic structure perception, and to analyse the 1955-1983 caatinga evolution. At last, the results of four mss landsat scenes (1973,1974 and 1983) numerical processing, are estimated, by comparison to vegetation structure maps : while in these maps, 15 thematic classes are distinguished, only 7 are available on the classified picture. In practice, the whole analysis show that the main characteristics of 1955-1983 landcape evolution are : a clear expansion of agricultural area (mainly after 1974) and, in all probability, a notable stability of Caatinga

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Toureiro, António José Pequito. "Estudo da desertificação no Alentejo: causas, consequências e estratégias atenuadoras (caso do Concelho de Arraiolos)." Master's thesis, Universidade de Évora, 2006. http://hdl.handle.net/10174/15854.

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A desertificação assume cada vez maior importância, pela degradação do meio ambiente e pela redução das produções agrícolas, que para além do sustento da população, são o motor da indústria e do comércio. O clima e o Homem, são as causas do fenómeno de desertificação. Pelos seus efeitos, sente-se cada vez mais necessidade de perceber e atenuar este fenómeno, através do uso sustentável do solo. A desertificação ocorre em muitos pontos do planeta. Também entre nós, em Portugal, e especialmente no Alentejo. O concelho de Arraiolos, situado no Alentejo Central, não é exceção, e sofre, nos dias que correm de desertificação, como resultado do despovoamento, do abandono da terra (já desflorestada e erosionada), do uso incorreto do solo (que com a atuação dos fatores climáticos, se degrada e desertifica). ***/Abstract - The desertification assumes every time larger importance, because of the degradation of the environment, and because of the reduction of the agricultural productions, that are the human sustain and the motor of the industry and trade. Both climate and Man are the causes of the desertification phenomenon. Because of them it’s necessary to notice and to lessen this phenomenon more and more, through the maintainable use of the soil. The desertification happens in many points of the planet. Also among us, in Portugal, and especially in Alentejo. The region of Arraiolos, located in Alentejo Central, is very affect for the desertification, happening the depopulation, for the abandonment of the earth, already deforested and erosion, for the use inaccurate of the soil, that with the acting of the climatic postman’s, it is degraded and desertific.

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Wu, Liuliu. "Similarity of Climate Control on Base Flow and Perennial Stream Density in the Budyko Framework." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5727.

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Streams are classified into perennial, intermittent, and ephemeral streams based on flow durations. Perennial stream is the basic network, while intermittent or ephemeral stream is the expanded network. Connection between perennial stream and base flow at the mean annual scale exists since one of the hydrologic functions of perennial stream is to deliver runoff even in low flow seasons. The partitioning of precipitation into runoff and evaporation at the mean annual scale, on the first order, is captured by the ratio of potential evaporation to precipitation (Ep/P called climate aridity index) based on the Budyko hypothesis. The primary focus of this thesis is the relationship between base flow and perennial stream density (Dp) in the Budyko framework. In this thesis, perennial stream density is quantified from the high resolution National Hydrography Dataset for 185 watersheds; the climate control (represented by the climate aridity index) on perennial stream density and on base flow is quantified; and the correlation between base flow and perennial stream density is analyzed. Perennial stream density declines monotonically with the climate aridity index, and an inversely proportional function is proposed to model the relationship between Dp and Ep/P. This monotonic trend of perennial stream density reconciles with the Abrahams curve, and the perennial stream density is only a small portion of the total drainage density. The dependences of base flow ratio (Qb/P) and the normalized perennial stream density on the climate aridity index follow a similar complementary Budyko-type curve. The correlation coefficient between the ratio of base flow to precipitation and perennial stream density is found to be 0.74. The similarity between the base flow and perennial stream density reveals the co-evolution between water balance and perennial stream network.
M.S.
Masters
Civil, Environmental, and Construction Engineering
Engineering and Computer Science
Civil Engineering; Water Resources Engineering

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Puig-Gironès, Roger. "Estudi dels patrons de colonització postincendi en vertebrats al llarg de gradients ambientals i espacials." Doctoral thesis, Universitat de Girona, 2016. http://hdl.handle.net/10803/416576.

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Wildfires are natural perturbations that affect the structure of the landscape and biodiversity. In the Mediterranean basin, wildfires occur especially in hot seasons. However, in recent years the number of fires with the size of them has been increasing, associated with human intervention. In this thesis, I analyse how the gradient of regional aridity in Catalonia affects the recovery of vegetation, the richness of bird species and shrubland warbler abundance. The relative role of two hypotheses on the abundance of rodents in the first moments after a wildfire is evaluated. These opposite hypotheses make reference to the ability of rodents to resist the fire into refuges or, on the other hand, to colonize burnt areas from the unburnt area. Finally, I study how the postfire and the management of burnt wood can affect the recolonization of rodents
Els incendis forestals són alteracions naturals que afecten l'estructura del paisatge i la biodiversitat. A la conca mediterrània, els incendis forestals es donen especialment en les estacions caloroses. Tanmateix, en els darrers anys tant el nombre d’incendis con la mida dels mateixos ha anat en augment, associat amb la intervenció humana. En aquesta tesi s’analitza com el gradient d'aridesa regional de Catalunya afecta a la recuperació de la vegetació, la riquesa d'espècies d'aus i l’abundància de tallarols de matollar. S’avalua el paper relatiu de dues hipòtesis sobre l'abundància de rosegadors en els primers moments després d'un incendi forestal. Aquestes hipòtesis contraposades fan referència a la capacitat dels rosegadors a resistir el pas del foc en refugis o, per altre banda, a la colonitzar des de l'àrea no cremada. Finalment, s’avalua com la tala postincendi i la gestió de la fusta cremada poden afectar la recolonització de rosegadors

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Konaté, Nianguiri Moussa. "Diversité interspécifique de l'efficience d'utilisation de l'eau des acacias sahéliens et australiens." Thesis, Nancy 1, 2010. http://www.theses.fr/2010NAN10044/document.

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Le principal objectif de ce travail était de déterminer l’efficience d’utilisation de l’eau (WUE) de diverses espèces d’acacias d’origine Australienne et Sahélienne par la discrimination isotopique au niveau de la feuille (Δ13Cf) et par différentes techniques de mesure. Les acacias ont montré une forte variabilité interspécifique de Δ13Cf. Cette variabilité a été confirmée par les mesures directes d’échanges gazeux au niveau des feuilles (efficience intrinsèque d’utilisation de l’eau, Wi) et par des mesures effectuées au niveau de la plante entière (efficience de transpiration, TE). Une forte variabilité interspécifique des traits foliaires(densité stomatique DS, proportion d’azote dans les feuilles %N, surface massique SLA, assimilation nette du CO2 à la saturation Asat, conductance stomatique en vapeur d’eau à la saturation gssat) et de la croissance (ratio biomasse racinaire sur biomasse aérienne R/S) a également été constatée entre les espèces. WUE était pratiquement contrôlée par gssat.L’hypothèse selon laquelle les espèces se développant dans les zones arides présenteraient une WUE plus élevée n’a pas été vérifiée. Au contraire, les espèces des zones semi-humides ont présenté une WUE plus élevée que celles de zones semi-arides et arides
The main objective of this work was to compare water use efficiency (WUE) among various Australian and Sahelian acacia species using isotope discrimination at leaf level (Δ13Cf) and various methods of measurement. Acacia species exhibited a large inter-specific variability of Δ13Cf. This variability was confirmed by direct leaf gas exchange measurements (intrinsic water use efficiency, Wi) and by measurement at the whole plant level (transpiration efficiency, TE). A large interspecific variability of leaf traits (stomatal density DS, leaf nitrogen concentration %N, specific leaf area SLA, net CO2 assimilation of the saturation Asat, stomatal conductance for water vapor of the saturation gssat) and growth characteristics (root shoot biomass ratio R/S) has also been reported. WUE was controlled for gssat. The hypothesis that the species from arid areas exhibit higher WUE was not confirmed. In contrast, the species from semi-wet area exhibited a higher WUE than those from semi-arid and arid zones

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Gigliotti, Alessandro. "Groundwater recharge estimation in a data sparse arid catchment of westbank. Stima della ricarica delle falde acquifere in bacini aridi e carenti di osservazioni idrometriche: il Darga in Cisgiordania." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5959/.

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Il seguente elaborato è frutto del lavoro di ricerca, della durata di cinque mesi, svolto presso il Department of Catchment Hydrology del centro di ricerca UFZ (Helmholtz-Zentrum für Umweltforschung) con sede in Halle an der Saale, Germania. L’obiettivo della Tesi è la stima della ricarica della falda acquifera in un bacino idrografico sprovvisto di serie di osservazioni idrometriche di lunghezza significativa e caratterizzato da clima arido. Il lavoro di Tesi è stato svolto utilizzando un modello afflussi-deflussi concettualmente basato e spazialmente distribuito. La modellistica idrologica in regioni aride è un tema a cui la comunità scientifica sta dedicando numerosi sforzi di ricerca, presentando infatti ancora numerosi problemi aperti dal punto di vista tecnico-scientifico, ed è di primaria importanza per il sostentamento delle popolazioni che vi abitano. Le condizioni climatiche in queste regioni fanno sì che la falda acquifera superficiale sia la principale fonte di approvvigionamento; una stima affidabile della sua ricarica, nel tempo e nello spazio, permette un corretta gestione delle risorse idriche, senza la quale il fabbisogno idrico di queste popolazioni non potrebbe essere soddisfatto. L’area oggetto di studio è il bacino idrografico Darga, una striscia di terra di circa 74 km2, situata in Cisgiordania, la cui sezione di chiusura si trova a circa 4 kilometri dalla costa del Mar Morto, mentre lo spartiacque a monte, ubicato a Nord-ovest, dista circa 3 kilometri dalla città di Gerusalemme.

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Bell, Benjamin. "Advancing the application of analytical techniques in the biological chemistry of sporopollenin : towards novel plant physiological tracers in Quaternary palynology." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/advancing-the-application-of-analytical-techniques-in-the-biological-chemistry-of-sporopollenin-towards-novel-plant-physiological-tracers-in-quaternary-palynology(59605f2b-642a-4ea9-8921-4c926217e6f2).html.

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Palynology, the study of organic microfossils, is an important tool for improving our understanding of past environments and landscapes. Palynology provides a wealth of information from which climatic and environmental conditions can be inferred. However, inferred climatic and environmental conditions are often open to interpretation. Assumptions made about past climate conditions from pollen assemblages often rely on qualitative understanding of modern-day vegetation distributions, rather than empirical relationships. Historic anthropogenic impact on the environment must also be inferred, and assessments made as to whether vegetation changes are a result of climate change or human impact. This study seeks to address some of the questions that arise through the interpretation of pollen assemblages, by establishing empirical relationships between the geochemistry of modern pollen and climate or environmental controls. It focuses on the pollen of the climatically sensitive montane conifer Cedrus atlantica, which is distributed across the mountains of Morocco and Algeria. The study investigates aspects of modern pollen geochemistry and morphology and finds a strong relationship between the stable carbon isotope composition of modern pollen and mean annual precipitation (r2 = 0.54, p <0.001) and summer precipitation (r2 = 0.63, p <0.0001). Furthermore, a stronger relationship exists with aridity measured using the self-calibrating Palmer Drought Severity Index (r2 = 0.86, p <0.0001), suggesting that the stable carbon isotope composition of Cedrus atlantica pollen is influenced by environmental moisture availability. The study also finds there is an increased abundance of ultraviolet absorbing compounds (UACs) in modern Cedrus atlantica pollen with increasing summer UV-B flux. This relationship was evident with samples growing in their native range (r2 = 0.84, p <0.0001), but not with samples from outside this range (r2 = 0.00, p = 0.99), suggesting a possible genetic influence. Lastly, the study finds that grain size of Cedrus atlantica pollen is highly variable within and between samples, and we rule out climatic control on pollen grain size. These results suggest that quantitative relationships can be established between the geochemistry of Cedrus atlantica pollen and environmental and climatic influences. Stable carbon isotope analysis of fossil pollen could be used as a proxy for reconstruction of summer moisture availability, while analysis of UACs in fossil pollen could be used as a proxy for the reconstruction of summer UV-B flux. These proxies will enhance our understanding of climatic and environmental change in Northwest Africa and will complement existing palynological techniques for environmental and climate reconstruction. Palynology, the study of organic microfossils, is an important tool for improving our understanding of past environments and landscapes. Palynology provides a wealth of information from which climatic and environmental conditions can be inferred. However, inferred climatic and environmental conditions are often open to interpretation. Assumptions made about past climate conditions from pollen assemblages often rely on qualitative understanding of modern-day vegetation distributions, rather than empirical relationships. Historic anthropogenic impact on the environment must also be inferred, and assessments made as to whether vegetation changes are a result of climate change or human impact. This study seeks to address some of the questions that arise through the interpretation of pollen assemblages, by establishing empirical relationships between the geochemistry of modern pollen and climate or environmental controls. It focuses on the pollen of the climatically sensitive montane conifer Cedrus atlantica, which is distributed across the mountains of Morocco and Algeria. The study investigates aspects of modern pollen geochemistry and morphology and finds a strong relationship between the stable carbon isotope composition of modern pollen and mean annual precipitation (r2 = 0.54, p <0.001) and summer precipitation (r2 = 0.63, p <0.0001). Furthermore, a stronger relationship exists with aridity measured using the self-calibrating Palmer Drought Severity Index (r2 = 0.86, p <0.0001), suggesting that the stable carbon isotope composition of Cedrus atlantica pollen is influenced by environmental moisture availability. The study also finds there is an increased abundance of ultraviolet absorbing compounds (UACs) in modern Cedrus atlantica pollen with increasing summer UV-B flux. This relationship was evident with samples growing in their native range (r2 = 0.84, p <0.0001), but not with samples from outside this range (r2 = 0.00, p = 0.99), suggesting a possible genetic influence. Lastly, the study finds that grain size of Cedrus atlantica pollen is highly variable within and between samples, and we rule out climatic control on pollen grain size. These results suggest that quantitative relationships can be established between the geochemistry of Cedrus atlantica pollen and environmental and climatic influences. Stable carbon isotope analysis of fossil pollen could be used as a proxy for reconstruction of summer moisture availability, while analysis of UACs in fossil pollen could be used as a proxy for the reconstruction of summer UV-B flux. These proxies will enhance our understanding of climatic and environmental change in Northwest Africa and will complement existing palynological techniques for environmental and climate reconstruction.

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Deblauwe, Vincent. "Modulation des structures de végétation auto-organisées en milieu aride." Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210121.

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À l’échelle macroscopique, à savoir celle du paysage, la couverture végétale des milieux arides apparaît comme fortement hétérogène. Cette organisation spatiale des peuplements est habituellement attribuée aux processus de facilitation et de compétition qui opèrent à l’échelle microscopique des individus végétaux. Le qualificatif d’auto-organisées fut donc attribué à ces végétations qui se structurent en l’absence d’hétérogénéité préexistante du milieu physique.

L’auto-organisation de la végétation fut particulièrement bien étudiée dans le cas des structures périodiques connues dès les années '50 sous le nom de brousses tigrées. Depuis les années '90, un pas en avant dans la compréhension de ce phénomène fut accompli grâce au développement de modèles mécanistes de la dynamique de la phytomasse et des ressources, émanant du cadre théorique de l'auto-organisation des structures dissipatives. Ces modèles se rejoignent sur un ensemble de prédictions robustes et vérifiables concernant la formation, le maintien et la modulation par l'environnement des structures macroscopiques. Durant le même laps de temps, notre niveau d’analyse a connu une expansion sans précédent, à la fois dans le temps et dans l’espace, grâce au développement de l’imagerie satellitaire et des outils d’analyse spatiale. Nous nous trouvons dès lors à un moment charnière pour la validation macroscopique des théories d’auto-organisation des végétations en milieu aride.

Le présent travail s'articule en quatre études, chacune traitant d'une prédiction différente. Nous avons mis en évidence les principales variables responsables de la formation des structures et de leur modulation en termes d’échelle et de géométrie. Enfin avons démontré la mobilité des structures sous l’effet d’une pente de terrain.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

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Fazel, Modares N. (Nasim). "The role of climate and land use change in Lake Urmia desiccation." Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526221021.

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Abstract Wetlands in arid and semi-arid regions are complex fragile ecosystems that are critical in maintaining and controlling environmental quality and biodiversity. These wetlands and specially closed lake systems depend on support processes in upstream parts of the basin or recharge zone, as small changes in river flow regime can cause significant changes in lake level, salinity and productivity. Recent strong alterations in river flow regimes due to climate and land use change have resulted in ecosystem degradation and desiccation of many saline lakes in arid and semi-arid regions. Because of the low economic value of these lakes, their hydrology has not been monitored accurately, making it difﬁcult to determine water balance and assess the role of water use and climate in lake desiccation. Furthermore, available data are usually of coarse resolution on both spatial and temporal scale. New frameworks using all available data and refining existing information on lake basins were developed in this thesis to assess regional differences in water resource availability, impacts of human activities on river flow regime alteration and agricultural land use change. The frameworks were applied to study causes and impacts of desiccation of a major lake, Lake Urmia, one of the largest saltwater lakes on Earth. This highly endangered ecosystem is on the brink of a major environmental disaster resembling that around the Aral Sea. The spatial pattern of precipitation across the Lake Urmia basin was investigated, to shed light on regional differences in water availability. Using large numbers of rainfall records and a wide array of statistical descriptors, precipitation across space and time was evaluated. Another important research component involved examining streamflow records for headwaters and lowland reaches of the Lake Urmia basin, in order to determine whether observed changes are mainly due to climate change or anthropogenic activities (e.g. water withdrawal for domestic and irrigation purposes). Principal component and clustering analyses of all available precipitation data for the lake basin revealed a heterogeneous precipitation pattern, but also permitted delineation of three homogeneous precipitation areas within the region. Further analysis identified variation in seasonal precipitation as the most important factor controlling the spatial precipitation pattern in the basin. The results showed that climate change impact on headwaters is insignificant and that irrigation is the main driving force for river flow regime alterations in the basin. This is supported by evidence that the headwaters have relatively remained unaffected by agriculture and by lack of significant changes in the historical records. The approach presented, involving clear in terpretation of existing information, can be useful in communicating land use and climate change information to decision makers and lake restoration planners
Tiivistelmä Kuivilla aridisilla ja semiaridisilla alueilla sijaitsevat kosteikot ovat hauraita ekosysteemejä. Ne ovat myös tavallista tärkeämpiä, koska ne ylläpitävät ja säätelevät ympäristön laatua sekä luonnon monimuotoisuutta. Nämä kosteikot, kuten valtaosa muistakin kosteikoista, ovat riippuvaisia vesistöalueen ylemmillä osilla tehdyistä toimista kuten vesistöjen säännöstelystä. Jopa pienet muutokset jokien virtauksissa voivat aiheuttaa merkittäviä muutoksia järvien vedenpinnan korkeuteen, suolapitoisuuteen ja tuottavuuteen. Viimeaikaiset ilmastonmuutoksen ja maankäytön muutosten aiheuttamat voimakkaat muutokset jokien virtaamiin ovat johtaneet ekosysteemien rappeutumiseen sekä monien suolajärvien kuivumiseen kuivilla ja puolikuivilla alueilla. Kuivilla alueilla sijaitsevien suolajärvien hydrologiaa ei ole tarkkailtu riittävästi niiden alhaisemman taloudellisen arvon vuoksi. Se hankaloittaa vesitaseen määrittämistä. Tarkkojen tietojen puuttuessa on vaikea arvioida myös sitä, miten vedenkäyttö ja ilmasto ovat vaikuttaneet järvien kuivumiseen. Lisäksi saatavilla olevat tiedot ovat yleensä sekä ajallisesti että alueellisesti epätarkkoja. Analysointiin tarvittavien tietojen ja välineiden puute saattaa pahimmillaan johtaa ristiriitaisiin oletuksiin. Väitöstyön päätavoite on tarjota puitteet, joilla parannetaan ymmärrystä vesivarojen alueellisista eroista, ihmisen toiminnan vaikutuksista jokien virtausten muutoksiin ja maatalouden maankäytön muutoksista käyttäen kaikkea saatavilla olevaa dataa sekä täsmentäen samalla vesistöistä jo olemassa olevaa tietoa. Väitöskirja tutkii yhden suuren järven kuivumisen syitä ja seurauksia. Urmiajärvi on yksi maapallon suurimmista suolajärvistä sekä erittäin uhanalainen ekosysteemi. Järvi on samankaltaisen ympäristökatastrofin partaalla, joka aiheutti Araljärven kuivumisen. Väitöskirja antaa tietoa veden saatavuuden alueellisista eroista tutkimalla sademäärien alueellista jakautumista Urmiajärven valuma-alueella. Tutkielmassa arvioidaan sadannan ajallista ja paikallista vaihtelua erilaisten tilastollisten menetelmien avulla. Tutkielman toinen tärkeä osa keskittyy vesialtaan latvavesistön ja tasankoalueiden valumatietoihin. Tämän osuuden päätavoite on määritellä johtuvatko havaitut muutokset järvessä pääasiassa ilmastonmuutoksesta vai ihmisen toiminnasta kuten kastelusta. Sadantatietojen pääkomponentti- ja ryhmittelyanalyysien tulokset osoittavat, että Urmiajärven allas on sadannaltaan heterogeeninen alue. Analyysi johti seudun jakamiseen kolmeen homogeeniseen sadanta-alueeseen. Analyysi osoitti, että sademäärien kausittainen vaihtelu on merkittävin järvialtaan alueellisiin sademääriin vaikuttava tekijä. Tulokset osoittavat, että ilmastonmuutoksen vaikutukset latvavesistöön eivät olleet merkittäviä ja keinokastelu on ylivoimaisesti merkittävin järvialtaan jokien virtausten muutoksiin vaikuttava tekijä. Tätä johtopäätöstä tukee se tosiseikka, että maanviljelys ei ole juurikaan vaikuttanut latvavesistöihin eikä niissä näy historiallisten lähteiden perusteella merkittäviä muutoksia. Tutkimuksen hyöty on siinä, että se tulkitsee saatavilla olevan tiedon selkeästi, joka on avuksi, kun maankäyttöön ja ilmastonmuutokseen liittyviä tietoja välitetään päättäjille ja järven kunnostusta suunnitteleville tahoille

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Ag, Atteynine Solimane. "Changement climatique et rongeurs ravageurs des cultures : effet attractif des cultures de saison sèche sur les espèces du genre Arvicanthis au Mali." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0130.

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Au Mali, pendant la saison sèche se pose la question de l’effet attractif exercé par les cultures de saison sèche sur les rongeurs ravageurs; lequel serait d'autant plus marqué sur le gradient latitudinal d’aridité soudano-sahélien GECS (1100 mm à 200 mm). Ces hypothèses sont testées chez le genre Arvicanthis (A.ansorgei,A.niloticus). Les résultats de la prospection cytogénétique antérieure 1994-1999 & une prospection élargie 2009-2014, révèle des changements récents des aires de distribution des 2 espèces; suggérant un rôle fort de leur adaptation chronobiologique dans le déterminisme de leur distribution. Cette approche horizontale suivie d'une approche verticale (2009-2016) compare 4 indicateurs de l'effet attractif des CSS vs les MNC dans les 5 régions climatiques du GECS (Sikasso, Koulikoro, Ségou, Mopti, Gao). Les densités de populations des 2 espèces sont plus élevées dans les CSS vs les MNC ; et cet effet attractif des CSS augmente avec l’aridité dans l'aire d'A.niloticus. Le ratio de "stratèges migrateurs" au sein des populations démontre l’effet tampon des CSS et confirme la fréquence de ces épisodes. L’étude du régime alimentaire confirme leur régime phytophage. En milieu naturel, l’aridité induit une baisse de la consommation de plantes compensées par celle d'Arthropodes non orthoptères; et la diversité des plantes consommées diminue avec l’aridité chez A.ansorgei vs augmente avec l’aridité chez A.niloticus. L'effet tampon des CSS "neutralise" les différences interspécifiques et chez les 2 espèces, dans les CSS, la diversité des adventices consommés diminue au détriment des plantes cultivées en particulier le riz.et la consommation en Orthoptères augmente
In Mali, during the dry season, there is the issue of the attractive effect of dry season crops on rodent pests, which would be all the more marked in the latitudinal gradient of Sudan-Sahel aridity GECS (1100 mm to 200 mm). These hypotheses are tested in the genus Arvicanthis (A.ansorgei, A. niloticus). The results of the previous cytogenetic survey 1994-1999 and an expanded survey 2009-2014 reveal recent changes in the distribution areas of both species; suggesting a strong role of their chronobiological adaptation in the determinism of their distribution. This horizontal approach followed by a vertical approach (2009-2016) compares four indicators of the attractiveness of the CSS vs. the MNC in the five climatic regions of GECS (Sikasso, Koulikoro, Ségou, Mopti, Gao). The population densities of both species are higher in the CSS vs. the MNC; and this attractiveness of the CSS increases with aridity in the area of A. niloticus. The ratio of "migratory strategists" within populations demonstrates the buffering effect of the CSS and confirms the frequency of these episodes. The diet study confirms their phytophagous diet. In a natural environment, aridity induces a decrease in the consumption of plants compensated by that of non-orthopterous Arthropods; and the diversity of plants consumed decreases with aridity in A.ansorgei vs increases with aridity in A. niloticus. The buffering effect of CSS "neutralizes" inter-specific differences, and in both species, in the CSS, the diversity of weeds consumed decreases to the detriment of crops, especially rice and the consumption in the Orthoptera increases

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Myslíková, Tereza. "Ztráty vody výparem u gekonů rodu Paroedura." Master's thesis, 2020. http://www.nusl.cz/ntk/nusl-410608.

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Keeping a balanced state in terms of liquids in an organism, especially evaporative water loss regulation, is essential for all terrestial animals, including reptiles. Respiratory water loss and cutaneous water loss account for the highest percentage of total water loss. For this reason, the degree of evaporative water loss in reptiles can be primarily influenced by body dimensions, metabolism intensity and morphology of body surface scales. This thesis focuses on water loss through evaporation in Madagascan Paroedura geckos. The Paroedura are suitable for this research because they represent a monophyletic genus with a strongly supported hypothesis about phylogenetic relationships. The thesis adds some facts to this theory. At the same time, individual Paroedura species differ in body dimensions and habitat preference. The aim of the thesis was to find out whether individual representatives of Paroedura differ in TEWL, to specify the characteristics of the ancestral state of TEWL in this genus and to test which morphological and physiological factors influence TEWL. Further aim was to measure cutaneous water loss. Measuring was carried out by flow- through respirometry. The results show that individual representatives of Paroedura differ remarkably in TEWL figures. The reconstruction of the...

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Taylor, D. "Tree leaf-and branch-trait coordination along an aridity gradient." Thesis, 2008. http://hdl.handle.net/10453/36066.

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University of Technology, Sydney. Faculty of Science.
NO FULL TEXT AVAILABLE. Access is restricted indefinitely. The hardcopy may be available for consultation at the UTS Library.
NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- Functional attributes of leaves and branches have a significant influence on a plant’s establishment, survival and fitness to particular environments. A major environmental variable to which plants must adapt is annual rainfall, or soil water availability. This thesis presents an analysis of variation in leaf- and branch-traits of trees across a rainfall gradient within NSW, Australia. In particular, it quantifies relationships amongst five leaf-traits: C0₂ assimilation rate, stomatal conductance to water vapour (gs), foliar nitrogen (N) concentration, specific leaf area, and foliar carbon isotope ratio (δ¹³C) (a measure of leaf water-use-efficiency and intercellular C0₂ concentration; Cᵢ), and three branch-traits: branch hydraulic conductivity, wood density and the ratio of leaf area to sapwood area (LA:SA), across a total of 16 perennial tree species across 13 native woodland sites spanning a mean annual rainfall gradient of 455 to 1310 mm. The generality of the trends found within tree species of NSW are then compared with the ‘global’ leaf-trait relationships of data obtained through Wright et al. (2004a) (referred to as the GLOPNET dataset), including comparisons among phenological and plant functional groups. Increased gs and foliar N concentration were associated with increased C0₂ assimilation rate. Higher foliar N concentrations were also associated with reduced Cᵢ and higher δ¹³C, suggesting that increased N concentration increases water-use-efficiency. Trees growing at low rainfall sites had lower mean gs, allocated more N to leaves, and consequently had higher foliar δ¹³C, suggesting a water conservation strategy at low rainfall sites. Similarly, reduced sapwood-specific hydraulic conductivity (ks) was correlated with reduced gs, higher foliar N concentration, a lower Cᵢ, but, most importantly, a statistically similar average rate of C0₂ assimilation as branches with higher ks. Overall, these results suggest that trees or species subject to water limitation, either by reduced rainfall or through a lower water transport capacity (a lower ks) ‘substitute’ water for N to achieve a given rate of leaf-level carbon gain. This mechanism represents an optimisation strategy for the use of limited supplies of water and N. Consequently, trees growing at low rainfalls sites, with low ks, maximise water-use-efficiency and minimise any decrease in C0₂ assimilation rate. This is achieved by these low rainfall trees operating at low Cᵢ which increases the diffusional gradient of C0₂ into the leaf. Branch wood density was inversely correlated with leaf area per branch, per unit branch length and per unit sapwood area, consistent with a reduced hydraulic capacity of denser wood. However, leaves of branches with high wood density and low LA:SA exhibited higher rates of C0₂ assimilation per unit leaf area and had a lower average Cᵢ. Thus, whilst branches with low ks invested more carbon in sapwood (higher density wood and more sapwood area per unit leaf area), this investment was supported by maximising C0₂ assimilation per unit leaf area. The patterns of correlation amongst gs, foliar N concentration and C0₂ assimilation observed in NSW were replicated in an analyses of the global data contained in the GLOPNET dataset. Thus, species with low gs had higher foliar N concentration for any given C0₂ assimilation rate, demonstrating the broad generality of water and N substitution. More importantly this pattern was observed only within certain functional groups. Evergreen species, trees, shrubs and N-fixing species exhibited this pattern but functional groups with short leaf lifespan, including deciduous species and grasses, did not display resource substitution. These differences suggest that species which utilise limited quantities of water and N over a long leaf lifespan use water and N sparingly and optimise resource use. In contrast, species with short leaf-lifespan use water and N in a more profligate manner and do not optimise resource use. In addition, N-fixing species were capable of substituting water for N to a greater degree than non-N-fixers, by allocating more N to foliage at low gs. The greater plasticity of N-fixers (such as Acacias) to substitute the two resources to achieve a given rate of carbon assimilation might explain their relative success in low rainfall environments.

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Wang, Lixin. "Soil biogeochemistry, aridity and plant adaptation responses in southern Africa savannas." 2008. http://wwwlib.umi.com/dissertations/fullcit/3362902.

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Coleman, Joy Carol. "Integrated physiology and behaviour of Thallomys nigricauda along an aridity gradient." Thesis, 2008. http://hdl.handle.net/10413/10795.

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Climate change predictions suggest that the continent most vulnerable to climate change is Africa. The impacts of potential changes which include increases in air temperatures and rainfall variability are negative with potential species extinctions projected throughout southern Africa. A number of climate models have been applied to examine the consequences of climate change for ranges of South African animal species. One such model frequently predicted range shifts from west to east, which is realistic considering the marked aridity gradient in an east-west direction across the country, but the authors suggested that these shifts may not be as marked if species are able to use physiological and behavioural methods to adapt to an increase in aridity. Information on the degree to which behavioural and physiological flexibility affect species range in southern Africa is scant which is surprising given its importance with regard to climate change. Thallomys nigricauda occurs along an east-west aridity gradient in southern Africa, inhabiting mesic, semi-xeric and xeric regions. One would expect phenotypic flexibility in physiological and behavioural traits in response to the diverse environmental conditions to be related to the success and range of the species. The wide distribution and arboreal habits, suggesting that T. nigricauda is exposed to greater extremes of temperature than fossorial rodents, makes T. nigricauda an ideal species to test this assumption. Hence I expected that T. nigricauda would exhibit variation in physiological and behavioural traits measured along an aridity gradient. This has important implications in predicting the survival of small mammal species in the light of climate change in southern Africa. Thallomys nigricauda were live-trapped in winter 2006 and 2007 and summer 2007 using Elliot traps in three sites: mesic site Weenen Game Reserve (KwaZuluiv Natal Province, South Africa); semi-xeric site Haina Game Farm (Botswana) on the northern boundary of the Central Kalahari Desert and xeric site Molopo Nature Reserve (southern Kalahari savannah, North-West Province, South Africa). I studied the home-range size of T. nigricauda by radiotracking 12 males and 16 females in winter 2006, 2007 and summer 2007. Home ranges were estimated using 100% and 95% minimum convex polygons and 95% and 50% fixed kernels. Home ranges varied widely, from 166 to 80199m2 for males and from 46 to 8810m2 for females. Males had larger home ranges than females, which supports a promiscuous mating system reported for the species. Although range size was reduced in both sexes in winter, this was not significant. I found no significant difference in home range size along the aridity gradient. It is suggested that a combination of precipitation, habitat productivity and breeding system influences the size of home range of the species, and that this species displays phenotypic flexibility in terms of its behavioural responses to these factors. I measured the urine concentrating ability (UCA), as indicated by urine osmolality and relative medullary thickness (RMT), and water turnover rate (WTR) of T. nigricauda. There was no significant difference in RMT between sites or sex and no difference in osmolalities when site, season and sex were taken into account. In addition, specific WTR was not significantly influenced by season. Lack of significant differences could be the result of the high degree of individual variation in the traits measured, an indication of the flexibility in UCA and WTR. However, higher urine osmolality and lower WTR’s were recorded in the dry winter months. I quantified the thermal environment perceived by a small, arboreal, mammalian endotherm using a number of methods at three study sites in winter and summer. Our area of interest was how well these methods accurately portrayed the actual temperatures that small mammals are exposed to. Temperature differences between the methods were largest during the midday, when temperatures were highest. All methods recorded a greater range of temperatures during photophase than during scotophase. Black-bulb and model temperatures produced more accurate, rapid measurements when compared to measurements produced by direct temperature recording devices, particularly during photophase, when solar radiation is the major influence of heating. Other methods lagged behind black-bulb measurements. Although the mean temperatures of some of the methods were significantly different, there was a high degree of correlation between all methods, even after randomization and generation of 25% and 10% subsamples. Computed thermal indices and blackbulb temperatures produced similar thermal profiles. In studies requiring accurate time series measurements, it is suggested that black-bulb or copper models be employed rather than direct temperature recording devices. Simpler measurement devices would suffice for studies requiring an estimate of the temperature variation and trends in the microclimate of small mammalian endotherms, particularly arboreal or cavity dwelling species. In the wild, across an aridity gradient, I measured abdominal body temperarture (Tb) of T. nigricauda using implanted iButtons®. All but three T. nigricauda displayed significant 24 h Tb rhythmicity. The Tb range for free-living T. nigricauda was 32.33-40.63 oC (n = 13) and 32.69-40.15 oC (n = 17) in winter and summer respectively. Although there was variation in Tb profiles, T. nigricauda generally displayed a bimodal distribution of Tb, with high and low Tb values during scotophase and photopase respectively. Body temperature range was significantly greater in winter, when T. nigricauda reduced its minimum Tb. It was shown that the maximum amplitude of circadian rhythms of body temperature was on average 259.6% of expected values. To determine the extent to which the microclimate of T. nigricauda cavities assists in the maintenance of Tb, I measured the temperatures of cavities across the gradient, providing an indication of the degree of buffering provided by refugia. I measured the temperatures of shallow and deep regions of cavities using iButtons® in summer and winter and recorded operative and shade temperatures for comparison. Compared with operative temperature, cavities had stable microclimates, displaying smaller ranges in temperature. Mean minimum and maximum cavity temperatures differed significantly to operative temperature and between seasons, whereas there was no significant difference between shallow and deep measurements in cavities. Differences in the buffering capacities of the cavities between seasons were not significant. To determine whether T. nigricauda alter its length of exposure in response to lower ambient temperatures in winter as a means of maintaining Tb, I measured the activity of T. nigricauda, defined as the proportion of fixes outside the home cavity of the individual. Males spent a greater proportion of the active phase away from their home cavity in summer, and significantly in winter when compared with females, but there were no differences between seasons. It is suggested that T. nigricauda realize energy savings by lowering its Tb during their rest phase during the day, allowing them to maintain nocturnal activity and overall energy balance. Thus, besides the larger male home range, a result of the reproductive pattern, the physiological and behavioural traits of T. nigricauda measured in this study did not differ between aridity sites or seasons. The results of this study, in highlighting the variation in physiological and behavioural responses of subpopulations of T. nigricauda to diverse conditions, suggest that this variation is due to phenotypic flexibility. Understanding the extent and nature of this flexibility is critical to our comprehension of the consequences climate change. By defining the presence and extent of intraspecific variation in physiology and behaviour, this study resolved the necessary first step towards this understanding for the widely distributed T. nigricauda in southern Africa.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

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35

Rose, Cassaundra Ashley. "Late Cenozoic Evolution of Aridity and C4 Vegetation in North Africa." Thesis, 2015. https://doi.org/10.7916/D8NK3DS6.

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Northern Africa has experienced major shifts towards aridity and extensive C4 vegetation over the late Cenozoic, but due to a scarcity of spatially and temporally extensive paleoenvironmental records, the timing, patterns, and causes of these shifts are still under debate. Both long-term aridification and large amplitude orbital-scale climate variability have been recognized, with little understanding of how these two patterns relate to each other over time. African’s climate and environmental history of the last 7 Myr is of particular interest because hydrological and vegetation variability is considered the driving selection mechanism for human evolution. In addition, the age of the initiation of desert conditions in the modern Sahara desert, Earth’s largest warm desert and the largest source of dust to the modern atmosphere, is unknown. The stable isotope ratios of carbon and hydrogen in sedimentary plant leaf wax biomarker compounds have recently been shown to quantitatively track source vegetation photosynthetic pathways and the hydrogen isotope composition of plant source water, which is dominantly controlled by the amount of precipitation in Africa. These proxies have been applied to reconstruct long-term vegetation changes in East Africa and SW Africa over the last 14 Ma, as well as orbital-scale variability from various locations around the African continent, but they have not been extended further back in time or combined in tandem to robustly assess both long-term and orbital-scale climate and vegetation variability and how they relate to each other. In this thesis, I have utilized quantitative plant leaf wax stable isotope proxies to examine both orbital-scale and long-term changes in North African aridity and vegetation from a variety of regions over the last 25 Ma, with particular emphasis on the last 4.5 Ma. In Chapter 2, I investigated the evolution of hydrological and vegetation gradients from the equator to the sub-Sahara in NW Africa over the last 25 Myr using leaf wax stable isotopes at two marine sediment core locations, producing the longest existing leaf wax stable isotope record in Africa to my knowledge, and one of the longest such records globally. In this study I found that NW African environments were remarkably similar at both latitudes from 25 – 10 Ma, but at 10 Ma C4 vegetation abruptly expanded in the north, indicating sudden aridification in the Sahara region at that time. The hydrogen isotope record was stable long-term, with variability similar to that of known orbital-scale cyclicity in the Pliocene and Pleistocene, possibly suggesting that orbital-scale cyclicity or other factors obscured or were larger than any long-term changes in the hydrogen isotope ratio of precipitation. Saharan aridification at 10 Ma is consistent with climate model predictions of aridity due to the closure of the Tethys Seaway connection between the Indian Ocean and Mediterranean Sea near that time. The 10 Ma expansion in C4 vegetation is earlier than most other regions globally. To examine long-term changes in orbital-scale variability in the Eastern Sahara and Mediterranean Sea, I constructed a record of eastern Mediterranean sedimentary leaf wax carbon and hydrogen isotopes, leaf wax abundance, lignin biomarkers, and oxygen isotope ratios of planktonic foraminifera G. ruber during two 100-kyr periods of equal eccentricity near 3.0 and 1.7 Ma (Chapter 3). I found that precession-scale variability dominates the record during both periods, and Eastern Saharan precipitation and the vegetation assemblage, which was C4-dominated, do not change on average between the two periods. Chapter 4 extended the eastern Mediterranean record of Chapter 3 by sampling leaf wax stable isotopes in sapropel sediments (deposited during North African humid periods) at ~0.25 Myr resolution back to 4.5 Ma, placing the orbital-scale Chapter 3 results in long term context. I found that Eastern Saharan environments were persistently C4-dominated (>68%) throughout the entire interval, and that long-term hydrogen and carbon variability were similar in magnitude to orbital-scale cycles back to 4.5 Ma, strongly indicating that orbital-scale variability has been the dominant environmental control in NE Africa since the early Pliocene. This record contrasts sharply with observations of a transition from C3-C4 mixed vegetation to abundant C4 grasslands in East Africa over the same period of time. The results may suggest that long-term precipitation shifts did not occur in NE Africa since the Pliocene, or that the resolution of this approach is not sufficient to detect long-term shifts. It is likely that NW Africa also experienced similarly large hydrological variability over the same period of time, which may explain the unclear long-term hydrological signal in Chapter 2. The results emphasize that East Africa has not been representative of northern Africa as a whole since the Pliocene.

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Paquette, Jesseca. "Tendances environnementales en Afrique de l’Est au Plio-Pléistocène : étude des isotopes stables de carbone et d’oxygène de l’émail des herbivores." Thèse, 2018. http://hdl.handle.net/1866/21909.

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Boyers, Melinda Frances. "A comparative study of behavioural and thermoregulatory responses of blue wildebeest and gemsbok to aridity." Thesis, 2018. https://hdl.handle.net/10539/25834.

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A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg, 2018.
Future climate change scenarios predict that many arid and semi-arid ecosystems within southern Africa, will get warmer and drier with increased frequency of droughts. Although the effects of climate change may only be apparent over a few decades, understanding the physiological and behavioural flexibility of individuals currently inhabiting hot and dry climates provides an analogue for conditions likely to become prevalent in the future. To enhance our understanding of how a species may respond to future hotter and drier environments, I set out to investigate seasonal variation in behaviour and thermoregulation of two ungulate species with differing water dependency in a semi-arid savanna. I focused on thermoregulatory (body temperature) and behavioural responses (activity and microclimate selection) of the water-dependent blue wildebeest (Connochaetes taurinus), and the arid-adapted gemsbok (Oryx gazella gazella) free-living in the Kalahari. Both species prioritised behavioural thermoregulation in the form of cool microclimate selection during the heat of the day and reduced both diurnal and 24 h activity, particularly when conditions were hot and dry. Both species experienced high maximum 24 h body temperature when conditions were hot and low minimum 24 h body temperatures when conditions were dry, resulting in a large amplitude of 24 h body temperature rhythm during the hot dry period. Yet, wildebeest appeared to be more sensitive to changes in aridity with a larger amplitude of 24 h body temperature rhythm compared to gemsbok (3.1 ± 0.2 °C vs. 2.1 ± 0.5 °C), during the drought. These seasonal analyses imply that the species behavioural and thermoregulatory responses were influenced by seasonal changes in water and forage availability. Low minimum 24 h body temperatures may result from an energy deficit during the dry season, but no study to date has explicitly linked changes in body temperature of free-living ungulates, to forage quality within the environment. I therefore investigated the influence of vegetation greenness on body temperature and activity of blue wildebeest and gemsbok inhabiting the same environment. I then investigated if the responses of gemsbok were heightened in a more arid environment. I used Normalized Difference Vegetation Index (NDVI) as a standardized index of vegetation greenness, which can be considered a proxy for vegetation productivity and quality. Both species reduced total 24 h activity and became hypothermic when exposed to brown vegetation but when exposed to brown vegetation minimum 24 h body temperatures were lower for blue wildebeest compared to gemsbok. When exposed to more extreme aridity, gemsbok showed an exaggerated lowering of minimum 24 h body temperatures. Under conditions of low food availability, the cost of thermoregulation may become too demanding. Therefore, when food resources are limited in quality, wildebeest and gemsbok in arid regions appear to prioritize the conservation of energy over the maintenance of a high body temperature. Within seasonal environments, access to water is often the limiting factor for plants and animals. I therefore investigated how distance to water (i.e., how frequently animals were likely to have accessed drinking water) during the hot season influenced microclimate selection, activity and body temperature of blue wildebeest and gemsbok. Both species selected similarly cool microclimates during the heat of the day, with slight enhancement in the quality of microclimates selected when they were further from water. Both species decreased activity during the heat of the day when they were further from water. Gemsbok were able to compensate for their reduced activity during the heat of the day and showed little change in total 24 h activity, but wildebeest showed a more exaggerated decline in activity during the heat of the day for which they were unable to compensate, i.e. total 24h activity of wildebeest declines when they were further away from water sources. Both species displayed higher maximum 24 h body temperatures when they were further away from water, with the hyperthermia being exaggerated for the wildebeest compared to gemsbok. Hyperthermia in both species resolved following the first rains and likely access to drinking water. Access to water appears to be the primary driver towards hyperthermia in the wildebeest, potentially resulting from dehydration during thermal stress. In summary, I have investigated behavioural and thermoregulatory flexibility that large African ungulates currently inhabiting hot and dry climates currently employ. I have shown that ungulates in the Kalahari may differ in their use of microclimate selection and activity patterns to buffer thermal, energetic and water stressors. My study is unique in that I have looked at where the animal was in space and time and linked it to their physiological and behavioural responses. I have, therefore, quantified microclimate selection, activity and body temperature responses in relation to NDVI and distance to water and have shown that the driving mechanisms behind the seasonal changes of body temperature and activity patterns is access to energy and water. I have further enhanced our existing knowledge and created the link between body temperature, vegetation quality and distance to surface water for antelope of the Kalahari and effectively assessed a functional trait. With climate change predicted to increase ambient temperatures and have less predictable rainfall in the semi-arid Kalahari, wildebeest will be forced to remain within the Kalahari, because historical migratory paths have been blocked by fences, and they may not have the behavioural and physiological flexibility to survive a hotter and drier future.
LG2018

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Fitzsimmons, Kathryn Elizabert. "The late Quaternary history of aridity in the Strzelecki and Tirari Desert dunefields, South Australia." Phd thesis, 2007. http://hdl.handle.net/1885/151056.

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Koloadin, Leah S. "Intraspecific and interspecific variation in the xylem functional traits of Callitris species growing along an aridity gradient." Thesis, 2020. http://hdl.handle.net/1959.7/uws:67022.

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More severe and prolonged drought events as a result of climate change, have the potential to cause broad scale forest and woodland dieback worldwide. The Australian continent is primarily comprised of arid biomes. However, rapid climate change-induced desertification threatens these surprisingly diverse ecosystems. Callitris is Australia’s most successful conifer genus, yet they remain they remain vulnerable to drought-induced decline. Given Callitris are the primary structural component of vegetation in many Arid-Australian ecosystems, their persistence is the most important factor preventing the collapse of these ecosystems. Resistance to drought-induced xylem cavitation has emerged as a key physiological trait determining the survival of tree species under water-limited conditions. Under the influence of aridity, Callitris have evolved the world’s most cavitation resistant xylem, yet little is known about the xylem anatomy liable to convey this. The main objective of this thesis was to identify the anatomical xylem traits and attributes associated with cavitation resistance in Callitris. The main body of work in this thesis involved analysis of microscopic anatomical traits through the use and development of several microscopy techniques. An inter-specific study produced a complementary dataset of xylem anatomical traits for branches of 15 Callitris and closely related species, building on the physiological dataset by Larter et al. (2017). An intraspecific study among five C. glaucophylla populations required the physiological and anatomical traits measurements. An intraspecific increase in cavitation resistance with aridity was found among the five populations in both the primary branches and roots. To understand whole plant hydraulic function, variability in xylem anatomical traits in the tertiary branches, secondary branches and trunks, of C. glaucophylla, in relation to the primary branches and roots was also explored. A greenhouse experiment tested the plasticity of anatomical traits in C. glaucophylla seedlings grown under contrasting water treatments. Mainly, among seedlings grown under well-watered conditions, height growth and more hydraulically efficient roots are prioritised, while more mechanically reinforced tracheids and safer but less efficient pit traits are favoured among seedling grown under water deficit.

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Potgieter, Henriette Cornelia. "Avian ecology of arid habitats in Namibia / Henriette Cornelia Potgieter." Thesis, 2015. http://hdl.handle.net/10394/15505.

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Examination of bird assemblages along an environmental gradient which encompasses both climate and habitat change is needed if we are to better understand the potential effects of these changes for avians and the ecological process that depend upon them. Climate change is predicted to have a significant impact on deserts and desert margins, resulting in distributional shifts of entire ecosystems and new community associations. This study explores the probable responses of avian communities to increasing desertification. In general, species richness and numbers of birds in arid zones are low compared to more mesic areas. Different combinations of habitat types and the variety of patches in a landscape influence the diversity and community structures of avians in that landscape. The role of vegetation structure in avian habitat selection in semi-arid areas is dictated by horizontal habitat density as well as vertical structure. Although bird distribution is determined by habitat boundaries, most birds are flexible and can disperse across small habitat barriers. The hypothesis tested, was that bird species assemblages along an aridity gradient are affected primarily by rainfall and secondarily by habitat type. Assessing the impacts of rainfall and habitat on bird variables, such as species richness, abundance, diversity, biomass, and life history traits, were the objectives of the study. An east-west aridity gradient of 300 mm, stretching over 370 km, was chosen in central Namibia for the study area. The climate is harsh with localised rain and considerable daily fluctuations in temperature. Grasses, and trees and shrubs up to 7 m in height are the co-dominant life-forms. Surveys were conducted over three years; one winter and one summer survey in each year. Rainfall, seasons and vegetation height were recorded as environmental variables. Three structurally different habitat types were selected for stratified sampling: open areas, rivers and thickets. Open areas were dominated by grass; river refers to ephemeral dry river lines with mature trees; and thickets comprise woody shrubs and trees. At each site, the same three habitats were used for bird sampling, resulting in 15 sample units. Sampling took place on 51 discontinuous line transects of 1km in length and without a width limit. Univariate analyses included ANOVA and t-tests. Multivariate analyses consisted of cluster analysis, MRPP tests, indicator analysis, Shannon diversity index and NMS ordinations. NMS bi-plots were used to define avian community structures responding to aridity, habitat, migration and life history traits. The results showed that bird species richness, abundance, and diversity remained relatively constant across the aridity gradient, until they declined significantly once a certain aridity threshold was crossed at the most arid site. There were significantly more bird species and individual birds at the wetter sites than at the drier sites. Rivers contained more birds than thickened or open habitat types, suggesting the importance of riparian habitat types for maintaining avian diversity. The three more mesic sites included higher numbers of species from the nesting and feeding guilds, regardless of habitat type, than the two more arid sites. The aridity threshold had a significant effect on bird community structures: more migrant and nomadic species, and omnivore and insectivore species persisted in very arid conditions. From the results it was predicted that climate change will cause avian species to undergo range shifts from west to east, resulting in community composition changes and a reduction in diversity. Life history traits affect the adaptive capabilities of bird species and it is predicted that nomadism, flexibility in diet, and adaptability of nesting requirements will contribute to species persistence in the drier conditions predicted under current climate change scenarios. Dry river lines will act as refugia for avian diversity, but crucial habitat types that currently contain less diversity are also important for maintaining unique avian assemblages.
MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

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Loehr, Victor J. T. "The ecology of the world's smallest tortoise, Homopus signatus signatus: effects of rainfall." Thesis, 2008. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_3016_1259833196.

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Tortoises appear to be successful in arid ecosystems, where they depend on primary production for their predominantly herbivorous diets. The low primary production of arid regions is exacerbated by priodic droughts, so that iteroparous species such as chelonians require mechanisms to overcome resource shortages. The smallest of all tortoises, Homopus signatus signatus, occurs in a dry winter rainfall area in northwestern South Africa that is threatened with aridification due to regional climate change. The overall aim of this study is to understand the ecology of H. s. signatus, particularly in reference to the importance of rainfall.

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Saladino, Saverio Salvatore. "INCREMENTO DELLA FERTILITA’ DEI SUOLI COME CONSEGUENZA DI PRATICHE COLTURALI PER LA GESTIONE SOSTENIBILE DEI VIGNETI IN CLIMI SEMI-ARIDI." Doctoral thesis, 2012. http://hdl.handle.net/10447/94585.

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Turton, Anthony Richard. "The hydropolitics of Southern Africa: the case of the Zambezi river basin as an area of potential co-operation based on Allan's concept of virtual water." Diss., 1998. http://hdl.handle.net/10500/16231.

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Southern Africa generally has an arid climate and many hydrologists are predicting an increase in water scarcity over time. This research seeks to understand the implications of this in socio-political terms. The study is cross-disciplinary, examining how policy interventions can be used to solve the problem caused by the interaction between hydrology and demography. The conclusion is that water scarcity is not the actual problem, but is perceived as the problem by policy-makers. Instead, water scarcity is the manifestation of the problem, with root causes being a combination of climate change, population growth and misallocation of water within the economy due to a desire for national self-sufficiency in agriculture. The solution lies in the trade of products with a high water content, also known as 'virtual water'. Research on this specific issue is called for by the White Paper on Water Policy for South Africa.
Political Sciences
M.A. (International Politics)

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Dissertations / Theses on the topic 'Aridità'

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