Este trabalho visa dar uma importante contribuição à pesquisa de novos materiais, através da determinação de condições otimizadas para obtenção pela técnica LHPG de fibras monocristalinas de compostos óxidos. Com esse objetivo fibras foram obtidas com êxito para compostos que podem ser utilizados como meios ativos para lasers de estado sólido (CaNb2O6 e GdTaO4), em aplicações de óptica de raios X (cristais gradientes dos sistemas GdTaO4-ErTaO4 e GdTaO4-YbTaO4) e também compostos que apresentam supercondutividade (EuNbO3, Yb2NbO5, Sm2NbO5 e Er2NbO5). A preparação dos pedestais se mostrou uma etapa muito importante na preparação das várias fibras. A caracterização estrutural por técnicas de difração de raios X mostrou que fibras monocristalinas de CaNb2O6 e GdTaO4 podem ser obtidas rapidamente e com alta qualidade cristalina sendo altamente adequadas para aplicações em óptica. Adicionalmente resultados de medidas espectroscópicas mostraram que as fibras CaNb2O6 dopadas com Nd+3 são boas candidatas para desenvolvimento de micro-lasers. Monocristais com gradiente controlado de parâmetro de rede foram obtidos pela primeira vez para os sistemas GdTaO4- ErTaO4 e GdTaO4-YbTaO4. A estratégia aplicada aqui possibilitou a obtenção de um gradiente composicional e de parâmetros de rede com ótima linearidade. Para o sistema GdTaO4- ErTaO4 foi obtido um gradiente de espaçamento de rede de 1,24%/cm para a reflexão (4 -4 4). Para os cristais GdTaO4- ErTaO4 um gradiente de 2,9%/cm para a reflexão (6 -4 0) foi obtido, sendo este o maior valor já observado em cristais gradientes. Através de uma inovação, utilizando Nb metálico em pó na preparação dos pedestais, fibras do composto EuNbO3 foram obtidas pela primeira vez, ao nosso conhecimento, através de uma técnica utilizando fusão. A aplicação desta mesma inovação buscando a obtenção de fases com esta mesma estrutura para outras terras raras, proporcionou a descoberta de três fases inéditas, Yb2NbO5, Sm2NbO5 e Er2NbO5. A estrutura destas novas fases foi determinada e através de caracterizações magnéticas e elétricas iniciais observou-se que estas apresentam supercondutividade com temperaturas de transição, Tc, iguais a 12,5K, 6,5K e 14,9K respectivamente para Yb2NbO5, Sm2NbO5 e Er2NbO5 / This work aims to give an important contribution to the research of new materials, by determining optimized conditions for obtaining of single crystal fibers of oxide compounds by LHPG technique. With this objective fibers were successfully obtained for compounds which can be used as solid state lasers (CaNb2O6 e GdTaO4), for X-ray optics applications (gradient crystals of GdTaO4-ErTaO4 e GdTaO4-YbTaO4 systems) and also as superconducting compounds. The preparation of the pedestals was a very important stage in the obtaining of the various fibers, with influence in growth experiments and quality of the fibers. The structural characterization by X-ray diffraction techniques showed that CaNb2O6 and GdTaO4 single crystal fibers presenting high crystalline quality can be quickly obtained. These fibers can be highly suitable for optics applications. In addiction the results of spectroscopic measurements showed Nd+3 doped CaNb2O6 fibers are good candidates for development of micro-lasers. Single crystals with controlled lattice parameter gradient were obtained for the first time for GdTaO4- ErTaO4 e GdTaO4-YbTaO4 systems. The applied approach in here enabled to obtain a compositional and lattice parameters gradient presenting optimized linear behavior. For the GdTaO4- ErTaO4 system a lattice spacing gradient of 1.24%/cm for (4 -4 4) reflection was obtained. For GdTaO4-YbTaO4 crystals a gradient of 2.9%/cm was observed. This is the largest value of lattice spacing gradient up to this moment. By an innovation, using metallic Nb in the form of powder in preparing the pedestals, fibers of the EuNbO3 compound were obtained, being the first report by a fusion technique. The application of this innovation to obtain phases with this structure for others rare earth enabled the discovery of three new phases, namely Yb2NbO5, Sm2NbO5 and Er2NbO5. The structure of these new phases was determined and by magnetic and electric characterizations it was observed that the phases are superconductor materials with transition temperatures, Tc, equals to 12,5K, 6,5K and 14,9K respectively for Yb2NbO5, Sm2NbO5 and Er2NbO5. compounds

O objetivo do presente trabalho é analisar a eficácia de um desenho em campo e o quanto este pode facilitar a implantação, avaliação e manutenção dos experimentos, principalmente se estes necessitam de uma grande área para a instalação. O delineamento sistemático é aplicado em áreas, tais como, horticultura, solo, irrigação e vem sendo abordado nas pesquisas florestais que se preocupam em oferecer respostas aos gradientes de espaçamentos que uma espécie apresenta em campo. O trabalho, mostra uma revisão bibliográfica de vários estudos realizados com delineamento sistemático em uma gama de aplicações em distintas áreas, revelando suas dificuldades, vantagens e desvantagens sobre os chamados delineamentos clássicos. Os desenhos em campo podem seguir dois diferentes tipos de delineamentos sistemáticos, em \"leque\" ou linhas paralelas. Para cada um existem regras que devem ser seguidas para a instalação dos experimentos em campo. Com o objetivo de retratar o comportamento da espécie Eucalypus dunni, submetida a diferentes tratamentos, sendo estes os espaçamentos entre as plantas, foi constatada a vantagem em empregar o delineamento sistemático, que reduziu a área utilizada e os custos de produção, melhorando a avaliação e a sobrevivência das espécies. Esse estudo possibilitou identificar o espaçamento ideal para a instalação desta espécie em campo, por meio da análise de regressão. / The objective of the present work is to analyze the effectiveness of a drawing in the field and how much it can facilitate the implantation, evaluation and maintenance of the experiments, especially if they require a large area for the installation. The systematic design is applied in areas such as horticulture, soil, irrigation and has been approached in the forest researches that are concerned with providing answers to the gradients of spacing that a species presents in the field. This work presents a bibliographical review of several studies carried out with systematic design in a range of applications in different areas, revealing their difficulties, advantages and disadvantages on the so - called classic designs. Field designs can follow two different types of systematic, fan-like or parallel lines. For each one there are rules that must be followed for the installation of field experiments. With the aim of portraying the behavior of the species Eucalypus dunni, submitted to different treatments, these being the spacings between plants, it was observed the advantage of using the systematic design, which reduced the area used and the production costs, improving the evaluation and survival of the species. This study made it possible to identify the ideal spacing for the installation of this species in the field, through regression analysis.

Propiciado pela construção de uma pista experimental inteiramente instrumentada com medidores de deformação e de temperatura na Cidade Universitária, este trabalho buscou o entendimento de inúmeros fatores intervenientes no desempenho do whitetopping ultradelgado, recente técnica de manutenção de pavimentos asfálticos com a utilização de delgadas placas de concreto, sob tráfego característico urbano, em condições tipicamente tropicais de uso, sobre uma pequena espessura de concreto asfáltico remanescente de fresagem. Com o intuito de nortear o problema em questão, além da revisão bibliográfica, foram realizados levantamentos periódicos das condições estruturais e funcionais deste pavimento; leituras contínuas de temperaturas e deformações obtidas por meio de um sistema automatizado de captação de dados junto aos instrumentos colocados no interior das placas; caracterização dos gradientes térmicos presentes nas placas durante as diferentes estações climáticas do ano. Foram realizadas provas de carga, estáticas e dinâmicas, com intuito de verificar os reais níveis de deformação aos quais as placas estariam sujeitas quando da interação com o tráfego; posteriormente, realizou-se modelagem numérica por meio de um programa de elementos finitos objetivando uma comparação com os dados obtidos nas provas de carga, analisando inclusive o posicionamento da linha neutra neste pavimento composto. Por fim, em uma sucinta abordagem sobre as deflexões antes e depois da execução do whitetopping ultradelgado, observou-se o tipo de comportamento estrutural do pavimento nas condições em que o experimento foi realizado. Ao término da pesquisa, inferiu-se que os gradientes térmicos dependem de vários fatores climáticos que não somente a temperatura ambiente, importando também a irradiação solar, o número de horas de sol, a velocidade de crescimento e decréscimo da temperatura ambiente; os gradientes térmicos encontrados não são importantes para o acréscimo nos níveis de tensões nas placas, não alterando assim a vida à fadiga do whitetopping ultradelgado, considerada a magnitude destes gradientes, as diminutas dimensões das placas e ainda a presença de aderência na interface concreto e concreto asfáltico. Em provas de carga, concluiu-se que os valores de tensões obtidos em campo mantêm grandezas semelhantes com os provenientes de modelos numéricos e ainda observou-se o vasto potencial de utilização das provas dinâmicas. Dado o excelente desempenho observado nas condições do experimento, mesmo com as placas aderidas a uma delgada camada asfáltica, fator que diferentemente do relatado no exterior não comprometeu o desempenho, não foi possível fazer uma avaliação em termos funcionais do desempenho deste tipo de pavimento. Verificou-se a significativa redução nas deflexões após a execução das placas, visualizando inclusive a transferência de cargas entre sucessivas placas, quando mantida a integridade estrutural das demais camadas do pavimento. / In this work, several factors affecting behavior and performance of ultra-thin whitetopping were evaluated taking advantage of a full scale experimental pavement, restored by applying such technique. Temperatures and thermal gradients in concrete thin slabs were evaluated by almost one year, comprising al the seasons. Load tests were carried out to allow strains measurements on concrete as well to define the deflection basins on whitetopped pavements. The experimental research has permitted to verify the dependence of thermal gradients on air temperature and solar radiation among other factors. It was observed that the thermal gradients practically do not affect behavior of the thin slabs. Stresses received from load tests compared to finite element generated stresses shown to maintain a good and closed relation. Due to good performance observed along the experiment it became not possible to establish patterns of functional performance. Expressive decrease of deflection level was observed over concrete overlays allowing to infer some load transfer on joints when the slabs are to be laid over non distressed old asphalt pavements.

Submitted by Jean Medeiros (jeanletras@uepb.edu.br) on 2016-02-25T17:54:47Z No. of bitstreams: 2 PDF - Paulo Sérgio Monteiro Ferreira.pdf: 2116190 bytes, checksum: a97029f785ad5bd7d572650db6aa3e29 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Secta BC (secta.csu.bc@uepb.edu.br) on 2016-03-10T15:13:43Z (GMT) No. of bitstreams: 2 PDF - Paulo Sérgio Monteiro Ferreira.pdf: 2116190 bytes, checksum: a97029f785ad5bd7d572650db6aa3e29 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2016-03-10T15:13:43Z (GMT). No. of bitstreams: 2 PDF - Paulo Sérgio Monteiro Ferreira.pdf: 2116190 bytes, checksum: a97029f785ad5bd7d572650db6aa3e29 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-02-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The study of how species behave in relation to environmental gradients is an established tool in the ecology, being investigated since the pioneering studies in this field. Cactaceae is established as an important constituent family of plant communities of the Brazilian semiarid, and the change in the distribution of many genres and modes of life of this family coincides with the transition between wet and dry environments. In this context, this study aimed to test the hypothesis that the structure and diversity of cactaceas communities will be differentiated in relation to different areas of the semiarid of Paraiba, because the genera and species of this family present distinct environmental preferences. To carry out the study were selected four areas (A1, A2, A3 and A4) with pluviometric precipitations decreasing (650, 550, 450 and 350 mm respectively) in the semiarid of Paraiba. We assessed a total of 3,660 individuals of Cactaceae, distributed in six species: Cereus jamacaru DC., Melocactus zehntneri (Britton & Rose) Luetzelb, Opuntia inamoena K. Schum, Pilosocereus gounellei (F. A. C. Weber) Byles & G. D. Rowley, Pilosocereus pachycladus F. Ritter and Tacinga palmadora (Britton & Rose) N.P. Taylor & Stuppy. A1 presented 196 individuals divided into three species (C. jamacaru, O. inamoena and P. pachycladus); A2 was represented by 642 individuals, A3 presented 1,447 individuals and A4 1,375 individuals divided among the six species mentioned. The cactaceas species demonstrated patterns of Importance Value Index (IVI) and Relative Volume (VR) between the different areas. A1 presented the highest individuals (mean height = 4.96 m) and with bigger DAS (mean DAS = 13,34 cm), and having the largest volume of cactaceas (21.42 m 3 ); A2 showed more diversity (H '= 1.39) and equability (J' = 0.83); A3 had the lowest values of DAS (mean DAS = 4.33 cm), height (mean height= 0.85 m), diversity (H'= 0.58), equability (J'= 0.39) and volume of cactaceas (4.92 m ); and A4 presented, in most cases, intermediate values between A2 and A3. The greatest richness and abundance of species were related to the locations with low rainfall and more clayey soils had greater diversity of cactaceas. The nMDS (non-Metric Multidimensional Scaling) produced by the environmental variables separated the samples into four groups and the cluster analysis showed differentiated configurations of these attributes within their own areas. The groups differed significantly according to the permutation of Monte Carlo test that were between the Areas 1 and 2; 1 and 4; 2 and 4; and 3 and 4. Of these environmental variables, the predictive model given by BIO-ENV (Biotic-Environmental) suggested that the percentage of clay in the soil and EVI (Enhanced Vegetation Index) are those that best explain the variations of cactaceas communities. The CCA diagram (Canonical Correspondence Analysis), produced 3 with the predicted variables by BIO-ENV showed that the cactacea species that occurring in of Paraiba semiarid have different environmental preferences, revealing that the species P. pachycladus and C. jamacaru were positively related to areas with higher indices of EVI and rainfall; M. zehntneri and P. gounellei adapted better in areas with soils with higher proportion of clay and silt; O. inamoena, was negatively related with higher proportions of medium sand; and T. palmadora, showed no patterns related to variables given by the BIOENV. The significant correlations between the axes of the CCA and the attributes of the structure of the species (abundance, height and DAS), were some times moderate (r 0.40 to 0.69) and most of the times stronger (r ≥ 0.70) and the species that presented best linear associations with the variables tested were M. zehntneri, P. gounellei and P. pachycladus. / O estudo de como as espécies se comportam em relação aos gradientes ambientais é uma ferramenta estabelecida na ecologia, sendo investigado desde os estudos pioneiros nesse campo. Cactaceae, estabelece-se como uma importante família constituinte das comunidades vegetais do semiárido brasileiro, e a mudança na distribuição de muitos gêneros e formas de vida dessa família coincide com a transição entre ambientes secos e úmidos. Nesse contexto, o presente estudo buscou testar a hipótese de que a estrutura e diversidade das comunidades de cactáceas serão diferenciadas em relação às diferentes áreas do semiárido paraibano, pelo fato dos gêneros e espécies dessa família apresentarem preferências ambientais distintas. Para a realização do estudo foram selecionadas quatro áreas (A1, A2, A3 e A4) com precipitações pluviométricas decrescentes (650, 550, 450 e 350 mm respectivamente) no semiárido paraibano. Foram aferidos ao todo 3.660 indivíduos de Cactaceae, distribuídos em seis espécies: Cereus jamacaru DC., Melocactus zehntneri (Britton & Rose) Luetzelb, Opuntia inamoena K. Schum, Pilosocereus gounellei (F. A. C. Weber) Byles & G. D. Rowley, Pilosocereus pachycladus F. Ritter e Tacinga palmadora (Britton & Rose) N.P. Taylor & Stuppy. A1 apresentou 196 indivíduos divididos em três espécies (C. jamacaru, O. inamoena e P. pachycladus); A2 foi representada por 642 indivíduos, A3 apresentou 1.447 indivíduos e A4 1.375 indivíduos divididos entre as seis espécies citadas. As espécies de cactáceas demonstraram padrões de Índice de Valor de Importância (IVI) e Volume Relativo (VR) distintos entre as Áreas. A1 apresentou os indivíduos mais altos (Alt. med. = 4,96 m) e de maior DAS (DAS med. = 13,34 cm), possuindo também o maior volume de cactáceas (21,42 m 3 ); a A2 demonstrou maior diversidade (H’ = 1,39) e equabilidade (J’ = 0,83); A3 apresentou os menores valores de DAS (DAS med. = 4,33 cm), altura (Alt. med.= 0,85 m), diversidade (H’ = 0,58), equabilidade (J’ = 0,39) e volume de cactáceas (4,92 m ); já A4 apresentou, na maioria das vezes, valores intermediários entre A2 e A3. As maiores riquezas e abundâncias estiveram relacionadas aos locais de menores precipitações e os solos mais argilosos foram os que comportaram maior diversidade de cactáceas. O nMDS (Escalonamento Multidimensional não-Métrico) produzido através das variáveis ambientais separou as amostras em quatro grupos e a análise de agrupamento demonstrou configurações diferenciadas desses atributos dentro das próprias Áreas. Os grupos que diferiram estatisticamente segundo a permutação do teste de Monte Carlo foram entre as Áreas 1 e 2; 1 e 4; 2 e 4; e 3 e 4. Destas variáveis ambientais, o modelo preditivo dado pelo BIO-ENV (Biotic-Environmental) sugeriu que a % de Argila no solo e o EVI (Índice de Vegetação 3 Aprimorada) são as que melhor explicam a variação das comunidades de cactáceas. O diagrama de CCA (Análise de Correspondência Canônica), produzido com as variáveis preditas pelo BIO-ENV, demonstrou que as espécies de cactáceas ocorrentes no semiárido paraibano apresentam preferências ambientais distintas, revelando que as espécies P. pachycladus e C. jamacaru foram positivamente relacionadas às áreas com maiores índices de EVI e Precipitação; M. zehntneri e P. gounellei, foram melhor adaptadas a habitarem em ambientes com solos com maior proporção de Argila e Silte; O. inamoena, esteve negativamente relacionada às maiores proporções de Areia média; e T. palmadora, não demonstrou padrões relacionados as variáveis dadas pelo BIO-ENV. As correlações significativas entre os eixos da CCA e os atributos da estrutura das espécies (abundância, altura e DAS), foram algumas vezes moderadas (r 0,40-0,69) e na maioria das vezes fortes (r ≥ 0,70) e as espécies que apresentaram melhores associações lineares com as variáveis testadas foram M. zehntneri, P. gounellei e P. pachycladus.

The red-headed woodpecker is a primary cavity excavator found throughout the Eastern Deciduous Forest and parts of the Great Plains. Although widespread, the red-headed woodpecker is generally considered uncommon, with patchily distributed populations. Over the past 50 years, this species has experienced precipitous, range-wide declines. The red-headed woodpecker uses a variety of cover types to meet resource needs across the annual cycle, ranging from oak savannas and wetlands, to mature beech forests and urban parks. Given their apparent adaptability to such a wide range of habitats, causes of declines are perplexing. To understand and stem declines, recent studies have focused on quantifying this species’ habitat requirements. Most of these studies have focused on a single cover type, often open forests, during the breeding season. However, effective management requires comprehensive knowledge of red-headed woodpecker habitat needs in a variety of cover types across the annual cycle. My thesis seeks to address this knowledge gap. I studied red-headed woodpecker habitat selection during both the breeding and non-breeding seasons at Fort A.P. Hill (FAPH) in Caroline County, Virginia. FAPH contains a variety of cover types that red-headed woodpeckers are known to use for breeding and overwintering, including: wetlands, open forests and closed forests. In Chapter 1, I investigated winter roost-site selection of red-headed woodpeckers in a burned forest stand. My study was the first to quantify winter habitat selection for this species. My aim was to identify variables driving winter roost-site selection at two relevant spatial scales, and estimate their parameter weights using logistic regression. I found that red-headed woodpeckers preferred habitat around the roost tree that contained a higher basal area of snags and mast-producing trees. They differentially selected roost trees based on taxon and decay state. My results indicate that managers should adopt practices that promote snag generation and retention, and mature oak recruitment. In chapter 2, I focused on red-headed woodpecker breeding season habitat requirements, as many other studies have done. However, unlike other studies that investigated habitat selection within a single cover type, I found and characterized nest-sites in three distinct cover types (wetlands, closed forests, open forests). I used a comparative approach to identify cover-type specific nest-habitat thresholds at the landscape, patch and tree scales using boosted regression trees (BRT). Although models at the landscape scale inadequately discriminated between nest and available sites, models at the patch and tree scales achieved excellent discrimination ability. I found that red-headed woodpeckers are consistent in their preference for a number of habitat features at the patch (high medium/large snag density, open canopy) and tree (large diameter tree with less bark) scales, irrespective of cover type context. However, I also found cover-type specific habitat preferences at the patch scale, indicating red-headed woodpeckers are flexible in their selection of features surrounding the nest and responsive to the broader habitat context. My findings suggest that there are a number of habitat features that facilitate breeding for red-headed woodpeckers generally, and management that promotes these features will be effective in a variety of habitat contexts. They also indicate that management can be tailored to provide the most suitable habitat for each of these three commonly used cover types. Together, Chapters 1 and Chapter 2 expand our knowledge of this declining keystone species’ habitat needs across the full annual cycle. But there is still much to know. The choices of habitat selection have consequences. Determining the conditions under which habitat features function to either help or harm populations is a necessary next step. While not a part of this thesis, I am currently investigating the factors that drive nest success among cover types, linking breeding-site selection to population dynamics. I also have behavioral data that will help reveal the mechanisms that either facilitate or constrain the exploitation of food resources across cover types. Finally, the red-headed woodpecker is a facultative migrant that often shifts habitat associations to take advantage of seasonally available resources. Data from my point count surveys—conducted over two successive winter and summer seasons—allow for development of dynamic occupancy models. Modeling shifts in occupancy across seasons will show the habitat factors underlying seasonal shifts. Site-specific differences in colonization, extinction and frequency of occupancy, within seasons but across years, will further our understanding of what constitutes habitat quality for this species, in both the breeding and non-breeding seasons.

Choosing a stationary phase is the first step in developing a liquid chromatography (LC) separation method, where the selectivity is governed by the differential interactions of the analytes with the stationary and mobile phases. Introducing a gradient in stationary phase functionality allows for tuning of analyte retention, translating to a possible improvement in selectivity and an increase in resolution versus that offered by uniform stationary phases. In this work, C18-silica, phenylbutyl-silica, and phenylbutyl-ammonium opposed continuous stationary phase gradients were fabricated using controlled rate infusion (CRI) on particle packed LC columns. Characterization of the stationary phase was carried out using spectroscopy and LC analysis to relate the ligand density gradient profile to the observed chromatographic parameters. C18-silica gradients were created with a time-dependent acid hydrolysis infusion and demonstrated an increase in resolution when combined with a mobile phase gradient. Phenylbutyl-silica and phenylbutyl-ammonium gradients were produced using an in-situ silanization CRI method. Phenylbutyl-silica gradients were confirmed to be stable and reproducible; however, produced tailing peak shapes. Phenylbutyl-ammonium gradients were utilized to incorporate an ion exchange model into a simulator built by Jeong et al. The phenylbutyl-ammonium gradient was not reproducible but did exhibit an increase in resolution when combined with a mobile phase gradient. Also, the ion exchange model was successfully added within the simulator, with percent differences for retention prediction all under 5 %. This dissertation serves as a proof-of-concept for gradient stationary phases on particle packed LC columns.

The isothermal movement of liquid water in saturated soil has been intensively studied, and a sound theoretical basis has been developed. Considerably less is known about the flow of water in unsaturated soils, but a general theory based on Darcy's law of flow is beginning to develop. A good theoretical basis exists for the vapor diffusion under isothermal conditions. Inconsistent data and theories are found in the literature concerning the movement of water in both the vapor and liquid phases, under the influence of thermal fields.

Global climate change is a real-time problem that presents threats to many species. Climate change can alter ecosystems and may lead to species extinction. Species can respond to climate change by moving to a better environment or adapting. Therefore, it is necessary to rely on several approaches and perspectives to anticipate ecological impacts of climate change. A common strategy uses models to understand how populations respond to different climate scenarios. Ecological models have helped usunderstand population persistence, but they often ignore how populations adapt to environmental stress. Adaptive evolution has been ignored because it was assumed that evolution was too slow to have any effect on ecology. Current research has shown that some populations are able to rapidly adapt to novel environments and this is essential for population persistence. We used a population genomics approach to understand how different precipitation regimes affect the perennial bunchgrass, Pseudoroegneria spicata, in the eastern Idaho sagebrush steppe. Our objective was to determine how genetic diversity changes under manipulated precipitation regimes and whether these changes were consistent with patterns of genetic diversity under natural precipitation regimes. The manipulated precipitation regimes consist of three precipitation treatments: control, drought with 50% ambient precipitation, and irrigation with 150% ambient precipitation. The natural precipitation regimes consist of two treatments: low elevation (drier than the experimental site) and high elevation (wetter). We collected plant tissue to isolate plant DNA and then used sequenced DNA for analyses. We used a hierarchical Bayesian model to estimate genotypes and allele frequencies across all loci. We found that there were low levels of genetic variation across all experimental precipitation treatments. When examining genetic differentiation, we found there was stronger differentiation in the natural precipitation regimes. Our study focuses on the short-term responses to climate to understand how environmental stress influences genetic diversity.

Plant spatial patterns have been studied to gain insight into plant interactions such as competition and facilitation (positive plant interactions). The stress gradient hypothesis predicts that as environmental stress increases facilitation dominates, while competition dominates in less stressful conditions. Beneficial plants (nurses) can create favorable abiotic conditions for subanopy plants. Additionally, palatable herbaceous species growing under nurse shrub canopies benefit from physical protection. I investigated spatial associations between Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and three native grasses (Poa secunda, Elymus elymoides, and Pseudoroegneria spicata) across a rainfall gradient in the Great Basin, USA. I also explored the effect of grazing on grass-shrub spatial associations. I hypothesized that positive shrub-grass spatial associations would become more frequent at lower rainfall levels; I further hypothesized that 1) at intermediate levels of stress, positive grass-shrub spatial associations would dominate and 2) at extreme levels of stress, positive grass-shrub spatial associations and interactions would no longer dominate. At high moisture stress, the addition of grazing stress may limit the nurse’s ability to provide to benefits to subcanopy plants. Cover of P. secunda was greater in shrub canopy microsites than interspaces at low to moderate levels of rainfall. Cover and density of E. elymoides were greater in sagebrush canopies over most rainfall levels. Elymus elymoides and P. spicata were taller and narrower in basal width and less likely to be grazed in canopy versus interspace microsites. I next investigated the effects of grazing intensity over a rainfall gradient and found a significant interaction of rainfall and microsite on P. secunda cover. Poa secunda formed positive interactions with A. tridentata at lower rainfall levels, regardless of grazing intensity. Its cover was significantly greater in interspaces at high rainfall compared to low rainfall sites. Elymus elymoides density was greater in canopy vs. interspace microsites, regardless of rainfall level or grazing intensity. Plant spatial associations can indicate which nurse microsites are favorable to plant growth and may improve seeding or planting success during ecological restoration. My results suggest that exploiting sagebrush canopy microsites for restoration of native perennial grasses would improve plant establishment, growth or survival particularly in drier areas.

The objective of this research is to help better understand the effects of exit face inclinations on critical gradients. This will lead to more practical ways to predict critical hydraulic gradients and slope stability using soil properties and exit face conditions. Current geotechnical engineering does not consider these factors because they are not thoroughly understood. Despite the attempts to better predict critical gradients, methods developed over 70 years ago to model the heave mechanism are used to model failure mechanisms such as backward erosion (or piping). This critical hydraulic gradient is only calculated by means of the buoyant unit weight of the soil. While modern engineering estimates critical piping gradients near unity, research has shown that calculated critical gradients can largely under-predict actual piping gradients. The results of this thesis research will help provide an empirical, but mechanism-based, grain-scale model that takes into account the effect of non-horizontal exit faces, and soil properties while assessing the potential for piping initiation to occur. This research is expected to help the understanding of the internal erosion mechanism known as piping, and eventually help to develop more practical ways of predicting and preventing conditions which are susceptible to this type of erosion. This research should be used to initiate more research, develop better methods, and eventually increase public safety with regards to designing and improving earth structures such as dams and levees.