O bioma Cerrado está cada vez mais fragmentado devido à ocupação agrícola e antrópica. Para a manutenção da biodiversidade, corredores de vegetação devem ser criados com o auxílio da revegetação e recuperação de áreas degradadas. Isto é facilitado pelo conhecimento da distribuição e dinâmica natural dos solos. O objetivo deste trabalho foi caracterizar o funcionamento físico-hídrico dos solos distribuídos em uma toposseqüência sob vegetação nativa. A área de estudo foi localizada dentro de uma parcela permanente instalada na Estação Ecológica de Assis, SP, Brasil, com vegetação predominante de cerradão ou savana florestada. Para a caracterização do funcionamento físico-hídrico dos solos foram realizados inicialmente estudos morfológicos, a partir da técnica da análise estrutural e da descrição de perfis de solo dispostos em cinco posições-chave da encosta. Amostras deformadas de solo foram utilizadas em análises químicas, granulométricas e densidade de partículas. Amostras indeformadas coletadas em anéis cilíndricos definiram as curvas de retenção de água e a densidade do solo. Blocos de solo foram impregnados e polidos para análise de imagens, obtendo-se a distribuição de poros em número, forma e tamanho. Em poços perfurados em três setores da toposseqüência, foi determinada a condutividade hidráulica saturada de campo. O monitoramento da umidade do solo “in situ” foi obtido por sensores instalados nos principais horizontes das trincheiras, calibrados para cada horizonte, durante o período de novembro de 2003 a novembro de 2004. Foram também utilizados os dados de precipitação mais próximos. Fotografias digitais adquiridas nos perfis de solo determinaram a distribuição das raízes. Os solos foram classificados, de montante a jusante, em Latossolo Vermelho, Latossolo Vermelho-Amarelo, Latossolo Amarelo e Gleissolo Háplico, com transição homogênea de cor e predomínio de textura franco-arenosa. No horizonte de superfície da toposseqüência, pequeno número de poros complexos de diâmetro equivalente superior a 1000µm ocupou quase a área total da imagem, representando uma estrutura de empilhamento de grãos simples com porosidade maior que em profundidade. Este comportamento provocou uma menor retenção hídrica, apesar do maior teor de matéria orgânica, e oscilação da umidade do solo após cada evento chuvoso. Predominaram raízes aglomeradas ou ramificadas nesta camada. Em profundidade, as raízes são mais individuais. Nos Latossolos, maior número de poros complexos de diâmetro equivalente superior a 1000 µm ocupa menor área em Bw do que em superfície. Isto indica a presença de aglomerados de microagregados em Bw que conferem maior retenção de água, maior número de microporos e menor oscilação da umidade do solo do que em superfície. No Gleissolo, o horizonte Btg2, mais profundo e mais argiloso, apresentou estrutura mais densa representada por uma porosidade expressiva de forma arredondada ou cavitária de diâmetro de 30 a 1000 µm. Neste horizonte, foi obtida a maior retenção hídrica, drenagem imperfeita e menor condutividade hidráulica. Nos outros horizontes da toposseqüência a condutividade foi elevada. O relevo influenciou nas propriedades físicohídricas e morfológicas dos solos que, por sua vez, determinaram o conteúdo de água limitante na estação seca e em períodos de estiagem. Este comportamento pode definir o padrão florístico de cerradão na parcela permanente. / The “Cerrado” bioma is being fragmented due to the human and agricultural occupation. To maintain the biodiversity, ecological corridors must be created by the revegetation and the restoration of the degraded areas. It can only be ameliorated upon the knowledge of the soil’s natural dynamics and distribution. The aim of this work was to characterize the behavior of soil water flow and soil physical properties, distributed in a toposequence under native vegetation. The study area was in a permanent plot installed in the Assis Ecological Station, São Paulo, Brazil. The predominant vegetation is the closed “cerrado” or savanna woodland. The soil physical, hydraulic characterization depended on soil morphology. The morphological study was carried out by structural analysis and by description of soil profiles arranged in five key positions on the slope. Disturbed soil samples were taken for chemical, particle size and soil particle density analyses. Undisturbed samples collected in cylindrical cores were used to define the soil water retention and bulk density. Soil blocks were impregnated and polished for image analysis to obtain the distribution of pores in number, shape and size. In wells perforated in three sectors of the toposequence the field saturated hydraulic conductivity was determined. The soil moisture monitoring “in situ” was obtained by sensors installed in the main horizons of the pits and calibrated for each soil horizon, during the period of November 2003 to November 2004. The nearest rain volume data were collected too. Digital photos of the soil profiles were acquired for the determination of the root distribution. The soils were classified, from the top backslope down to the footslope, as Rhodic Haplustox, Typic Haplustox and Epiaquic Haplustult, with a homogeneous color transition and the predominance of a sandy loam texture. In the soil surface on the toposequence, a little number of complex pores with equivalent diameter over 1,000 µm occupied almost the total pore area, characterizing the predominance of a structure formed by the packing of single grains. The porosity was higher than in the other horizons. This behavior caused lower water retention even with the highest organic matter content. On the surface, the oscillation of the soil moisture is closely related to each rain event. The roots were distributed in ramified or grouped roots in the surface layer and individually in the deeper horizons. In Oxisols, the presence of microaggregates in the B-horizon was characterized by a number of complex pores with equivalent diameter over 1,000 µm larger than in the soil surface but in minor area than in the surface layer. This conferred higher water retention, larger number of micropores and lower oscillation of soil moisture than in soil surface. The structure of the deepest B-horizon of Epiaquic Haplustult was denser, featured by an expressive rounded or vugh porosity with diameters between 30 and 1,000 µm. This conferred the largest content of clay, with the highest water retention, imperfect drainage and lowest hydraulic conductivity. The other soil horizons in the toposequence presented greater hydraulic conductivity. The landscape influences the physical, hydraulic and morphological soil properties in the toposequence. So the water content is limited in the dry season and partially in the humid season too, which can define the floristic pattern of the closed “cerrado” in this permanent plot.

A dinâmica dos herbicidas no solo é influenciada pela umidade e pela quantidade e qualidade da matéria orgânica, que são variáveis nos agregados organominerais. Os objetivos foram avaliar a influência do grau de umidade na mineralização e sorção do 2,4-D (ácido fraco) e Diuron (não ionizável), em quatro latossolos com diferentes quantidades de matéria orgânica do solo (M.O.S.), avaliar a influência do tamanho do agregado (> 150, 54 – 150, 21 – 53, 2 – 20 e < 2 mm) na sorção dos herbicidas e determinar o grau de humificação para explicar possíveis diferenças na sorção. Foram utilizadas amostras superficiais (0 - 0,2 m) de um Latossolo Amarelo distrófico (LAd) (Piracicaba/SP), de um Latossolo Amarelo ácrico (LAw) (Uberlândia/MG), de um Latossolo Vermelho ácrico (LVw-1) (Uberlândia/MG) e de um Latossolo Vermelho ácrico (LVw-2) (Canoinhas/SC). Foram determinados os valores de pH (em H2 O, KCl 1,0 mol L -1 e CaCl2 0,01 mol L -1 ), a quantidade de M.O.S., de fósforo, de K + , de Ca 2+ , de Mg 2+ , de Al 3+ e estimada a soma H+Al. Os óxidos de ferro, de alumínio e de silício foram quantificados após extração com ácido sulfúrico, os óxidos de ferro “livre” e mal cristalinizado também foi determinado e a análise granulométrica foi efetuada pelo método do densímetro, sendo quantificada também a argila dispersa em água (ADA). Foi determinada a mineralogia por difração de raio-X. Foram quantificadas as frações organominerais dos solos. Foram dispersos 40 g de solo em 160 mL de água destilada, que foram agitados a 160 agitações min -1 por 16 h e sonificada por 15 min. Após disperso, o solo foi peneirado para separar os agregados > 150 mm e entre 53 e 150 mm. Os agregados menores que 53 mm foram separados por sedimentação. Foi determinado o carbono orgânico dos agregados e do solo por combustão. A atividade microbiana dos solos foi determinada pelo método da radiorespirometria. Amostras dos solos foram incubadas com 14 C-2,4-D e 14 C-diuron por 42 dias umedecidas a 25, 50 e 75 % da capacidade de campo em sala climatizada semi-escura a 22 ± 2 o C, após foram realizadas três extrações com CaCl2 0,01 mol L -1 . O solo foi então fracionado após oxidação para determinar o os herbicidas sorvidos no solo e, posteriormente nos diferentes agregados. O grau de humificação das amostras foi determinado por fluorescência. A mineralização do 2,4-D foi de 62 % no LAd a 75 % da capacidade de campo. A difusão foi responsável pela sorção dos herbicidas. O 2,4-D foi menos sorvido no LAd, que tinha maior pH e menor quantidade de M.O.S.. Os solos apresentaram maior quantidade de agregados > 150 mm. Os agregados organominerais de diâmetro menores que 53 mm apresentaram maior acúmulo de carbono. A exceção do LAd, os herbicidas foram mais sorvidos pelos agregados maiores que 53 mm. A sorção só aumentou nos agregados menores que 53 mm, quando a amostra foi incubada a 75 % da capacidade de campo. Porém, no caso do diuron, isto só foi verificado no LAw e LVw-1. As sucessivas extrações alteraram a estabilidade dos agregados. O LAd que se localiza em uma área de cultivo tem maior grau de humificação que o LVw-2 localizado em uma área não cultivada. Os agregados de diâmetro entre 53 e 150 mm, foram os que tiveram maior grau de humificação nos solos. / The dynamic of herbicides in soils is influenced by soil moisture and organic matter contents and also by their quality, which are variable in the organic-mineral aggregates of the soils. The aims of this research were to evaluate the effects of soil moisture on the mineralization and sorption of the herbicides 2,4-D (weak acid) and diuron (non-ionic), in four Oxisols with different contents of soil organic matter (SOM), as well as to evaluate the influence of aggregate sizes (> 150, 54 – 150, 21 – 53, 2 – 20 and < 2 mm) and degree of humification in the sorption of these herbicides. Surface samples (0 – 0.2 m) of one Xanthic Hapludox (LAd, from Piracicaba/SP), one Xanthic Acrudox (LAw, from Uberlândia/MG), and two Anionic Acrudox (LVw-1 from Uberlândia/MG and LVw-2 from Canoinhas/SC) were collected. SOM, phosphorus, K + , Ca 2+ , and Mg 2+ contents and pH values (in H2 O, in KCl 1.0 mol L -1 and in CaCl2 0.01 mol L -1 ) were measured, whereas H+Al was calculated. Fe, Al, and Si oxides were quantified after soil extraction with H2SO4. Free and amorphous Fe oxides were determined by DCB and oxalate method, respectively. Granulometric analysis and water dispersed clay (WDC) were quantified by the densimeter method. The mineralogy was evaluated by X-ray diffraction. In order to quantify soil organic-mineral aggregates, 40 g of soil was added to 160 mL of distilled water in centrifuge tubes, which were shaken for 16 h at 160 rpm and sonicated for 15 min at 240 W. The aggregates > 150 and 53 – 150 mm were obtained by sieving, whereas the aggregates < 53 mm were obtained by sedimentation. Soil and aggregate organic carbon contents were obtained by combustion. The soil microbial activity was obtained by the radiorespirometry method. Soils were incubated with 14 C-2,4-D and 14 C-diuron, for 42 d at 25, 50 and 75 % of the field capacity and remained in a semi-dark room at controlled temperature of 22 ± 2 o C. Then, the pesticides were extracted three times with CaCl2 0.01 mol L -1 and, afterwards, the soil samples were fractionated in order to quantify the amount of herbicides in the aggregates. In these, the degree of humification was obtained by fluorescence. Diffusion markedly affected the herbicides sorption. For example, 2,4-D mineralization was 62 % on LAd only at 75 % field capacity. As expected, 2,4-D was less sorbed on LAd that had higher pH and lower SOM content. In general, the soils presented higher amounts of aggregates > 150 mm. The organic-mineral aggregates < 53 mm presented higher organic carbon content. However, the herbicides were more sorbed in the aggregates > 53 mm, except for LAd. When the soil were at 75 % of the field capacity, the sorption increased in the aggregates < 53 mm for 2,4-D, but it was only verified for LAw and LVw-1 for diuron. The successive extractions altered the aggregate stability. The LAd located in a tilled area had higher degree of humification than the LVw-2 located in a non-tilled area. The soil aggregates between 53 and 150 mm presented higher degree of humification.

Made available in DSpace on 2017-07-10T19:24:40Z (GMT). No. of bitstreams: 1 Juliana Fenner Ruas Lucas.pdf: 7353201 bytes, checksum: 171282273d86ea92304991a62a946fc6 (MD5) Previous issue date: 2010-07-13 / The soil water content is related to the soil matrix ability to retain the water, characterized by the water matric potential. Moisture and matric potential are factors functionally interrelated and represented by the soil-water retention curve. This relationship allows inferring moisture from the matric potential measurement and vice versa, as well as deducing several soil and water in soil properties. The traditional method for determining the retention curve employs the Richards pressure plate apparatus. For practical reasons, the search for alternatives to the Richards apparatus that are financially more accessible and faster is needed. In this regard, this study aimed at evaluating the use of two devices: the triaxial compression chamber and the filter paper. Therefore, soil was initially collected and physical-chemically characterized. Undisturbed soil samples were prepared and tested in the Richards chamber, using pressures of 0, 10, 30, 60, 100, 300, 500, 1,000 and 1,500 kPa. In the triaxial compression chamber test, soil samples were submited to pressures of 0, 10, 30, 60, 100, 300, 500 and 1,000 kPa, and for each pressure, it was measured the volume of drained water and calculated the sample moisture at that pressure. In the filter paper test, it was measured the water matric potential in samples for which moisture levels were established using an appropriated calibration curve. The three tests were repeated five times, resulting in points of pressure versus moisture that were adjusted by the RETC program, using to the model of van Genuchten. It was performed a comparative analysis of the triaxial chamber and the filter paper estimated soil moisture values with the adjusted retention curve obtained by the Richards apparatus. This comparison allowed to verify the applicability of the filter paper method for determining the water retention curve in agricultural soils and the inadequacy of triaxial compression chamber for this purpose. / O teor de água no solo está relacionado com a capacidade da matriz do solo em reter a água, caracterizada pelo potencial matricial da água. Umidade e potencial matricial são fatores funcionalmente inter-relacionados e representados pela curva de retenção da água no solo. Esta relação possibilita inferir a umidade a partir da medida do potencial matricial e vice-versa, assim como estimar outras propriedades do solo e da água no solo. O método tradicional para a determinação da curva de retenção emprega a câmara de pressão de Richards. Por questões práticas, a busca por métodos alternativos ao de Richards, financeiramente mais acessíveis e menos morosos, faz-se interessante. Diante disso, desenvolveu-se o presente trabalho com o objetivo de avaliar o uso de dois dispositivos: a câmara de compressão triaxial e o papel filtro. Para tanto, realizou-se inicialmente coleta e caracterização físico-química do solo, preparo de amostras indeformadas e ensaio na câmara de Richards, utilizando pressões de 0, 10, 30, 60, 100, 300, 500, 1000 e 1500 kPa. No ensaio com a câmara de compressão triaxial, submeteu-se amostras de solo às pressões de 0, 10, 30, 60, 100, 300, 500 e 1000 kPa e, para cada pressão, foi mensurado o volume de água drenado, o que permitiu calcular a umidade da amostra àquela pressão. Com o papel filtro, mediu-se o potencial matricial da água em amostras cujas umidades foram previamente estabelecidas, utilizando-se curva de calibração adequada. Os três ensaios foram executados em quintuplicata e resultaram em pontos de pressão versus umidade que foram ajustados pelo programa RETC, usando o modelo de van Genuchten. Realizou-se uma análise comparativa de valores de umidade volumétrica estimados pelo modelo ajustado nos ensaios com a câmara triaxial e o papel filtro com a curva de retenção ajustada obtida pela câmara de Richards. Através dessa comparação, verificou-se a aplicabilidade do método do papel filtro para a determinação da curva de retenção de água em solos agrícolas e inadequação da câmara de compressão triaxial para esta finalidade.

O objetivo deste trabalho é avaliar a influência da variação do teor de umidade no valor do índice de suporte CBR de uma brita estabilizada granulometricamente e de seis solos coletados em rodovias do interior do Estado de São Paulo. Os seis solos estudados foram divididos em três pares, com curvas granulométricas próximas, mesma classificação HRB e USCS, sendo cada par formado por um solo de comportamento laterítico e um solo de comportamento não-laterítico. Os corpos-de-prova foram moldados na umidade ótima e massa específica seca máxima obtidos com os resultados do ensaio de Proctor normal. Os materiais foram analisados sob quatro condições de umidade: sem imersão, após alcançar metade da umidade de estabilização, após quatro e oito dias de imersão. Observou-se a distribuição da umidade interna dos corpos-de-prova para cada uma das situações. Foi analisada a influência do envelhecimento dos materiais solto e compactado por quatro dias e sem imersão, nos resultados dos ensaios de CBR. Com os resultados pôde-se correlacionar a influência da granulometria e da gênese dos materiais nos resultados dos ensaios de índice de suporte CBR nas diversas condições de umidade avaliadas. / The aim of this dissertation is to evaluate the variation influence of the moisture content on the value of the CBR support index of a granulometrically stabilized crushed stone and six soils. The soils studied were divided into three pairs with similar particle size distribution curves and same HRB and USCS classification. Each pair is formed by a soil of lateritic and non-lateritic behaviors. The specimens were moulded in the optimum moisture content and maximum dry density obtained from the results of the standard Proctor tests. The materials were analysed under four moisture conditions: without immersion, after reaching half of the stabilization moisture, and after four and eight days of immersion. The internal moisture distribution of the specimens was observed for each situation. The internal distribution moisture was observed for each situation. The influence of the aging of the loose and compacted materials was analysed for four days without immersion in the test results of CBR. According to the results it was possible to correlate the influence of both granulometry and genesis of the materials on test results of CBR support index in the diverse moisture conditions evaluated.

For roughly the past 200 years land-managers have used the practice of “muirburning” to manipulate the structure of heather (Calluna vulgaris) to create a patchwork of habitat structures able to provide forage and nesting sites for red grouse (Lagopus lagopus scoticus) as well as grazing for sheep (Ovis aries) and red deer (Cervus elaphus). This thesis investigates both the behaviour and impact of management fires in recognition of the need to develop multi-aim land management practices that ensure both continued productivity and protection of biodiversity in the face of climatic and environmental change. Fuel structure and loading are crucial controlling factors on both fire behaviour and impact governing both rate of spread and heat release to the ground surface. A visual obstruction method is developed that estimates total and fine fuel loading as well as the structure of the heather canopy. In order to adequately understand fire impact a dimensional analysis approach is taken to estimating the mass of burnt heather stems. Experiments at a number of spatial and temporal scales relate variation in heather fuel moisture content to stand structure and variation in weather conditions. Monitoring shows moisture contents to be relatively stable temporally, but spatially variable. Periods of extreme low moisture contents in early spring are associated with frozen ground, winter cuticle damage and physiological drought. Such conditions may have contributed to the large number of wildfires in 2003. A replicated plot design was used to investigate the effect of weather conditions and fuel loading on fire behaviour. An empirical approach is taken to fire behaviour modelling with equations describing rate of spread and fireline intensity being developed on the basis of fuel structure descriptors and windspeed. The theoretical negative correlation between fuel bed density and rate of spread is demonstrated to hold true for heather stands, while the impact of heterogeneity in fuel bed structure is also investigated. Redundancy Analysis is used to investigate the influence of multiple predictors on a number of aspects of fire behaviour including: rate of spread, fireline intensity, flame length and ground surface heating. Data from this and previous studies are used to ground-truth a number of fire behaviour prediction systems including BehavePlus and the Canadian Fire Behaviour Prediction System. Finally linkages between fire behaviour, fire severity and heather regeneration are investigated. A number of proxy measures of ‘Immediate Severity’ are tested and used to examine the influence of fires on plant regeneration. The post-fire development of stands is shown to relate primarily to stand age and structure before burning, and to post-fire substrates rather than variation in fire behaviour and severity.

Made available in DSpace on 2017-05-12T14:48:03Z (GMT). No. of bitstreams: 1 Juliana Fenner Ruas Lucas.pdf: 7353201 bytes, checksum: 171282273d86ea92304991a62a946fc6 (MD5) Previous issue date: 2010-07-13 / The soil water content is related to the soil matrix ability to retain the water, characterized by the water matric potential. Moisture and matric potential are factors functionally interrelated and represented by the soil-water retention curve. This relationship allows inferring moisture from the matric potential measurement and vice versa, as well as deducing several soil and water in soil properties. The traditional method for determining the retention curve employs the Richards pressure plate apparatus. For practical reasons, the search for alternatives to the Richards apparatus that are financially more accessible and faster is needed. In this regard, this study aimed at evaluating the use of two devices: the triaxial compression chamber and the filter paper. Therefore, soil was initially collected and physical-chemically characterized. Undisturbed soil samples were prepared and tested in the Richards chamber, using pressures of 0, 10, 30, 60, 100, 300, 500, 1,000 and 1,500 kPa. In the triaxial compression chamber test, soil samples were submited to pressures of 0, 10, 30, 60, 100, 300, 500 and 1,000 kPa, and for each pressure, it was measured the volume of drained water and calculated the sample moisture at that pressure. In the filter paper test, it was measured the water matric potential in samples for which moisture levels were established using an appropriated calibration curve. The three tests were repeated five times, resulting in points of pressure versus moisture that were adjusted by the RETC program, using to the model of van Genuchten. It was performed a comparative analysis of the triaxial chamber and the filter paper estimated soil moisture values with the adjusted retention curve obtained by the Richards apparatus. This comparison allowed to verify the applicability of the filter paper method for determining the water retention curve in agricultural soils and the inadequacy of triaxial compression chamber for this purpose. / O teor de água no solo está relacionado com a capacidade da matriz do solo em reter a água, caracterizada pelo potencial matricial da água. Umidade e potencial matricial são fatores funcionalmente inter-relacionados e representados pela curva de retenção da água no solo. Esta relação possibilita inferir a umidade a partir da medida do potencial matricial e vice-versa, assim como estimar outras propriedades do solo e da água no solo. O método tradicional para a determinação da curva de retenção emprega a câmara de pressão de Richards. Por questões práticas, a busca por métodos alternativos ao de Richards, financeiramente mais acessíveis e menos morosos, faz-se interessante. Diante disso, desenvolveu-se o presente trabalho com o objetivo de avaliar o uso de dois dispositivos: a câmara de compressão triaxial e o papel filtro. Para tanto, realizou-se inicialmente coleta e caracterização físico-química do solo, preparo de amostras indeformadas e ensaio na câmara de Richards, utilizando pressões de 0, 10, 30, 60, 100, 300, 500, 1000 e 1500 kPa. No ensaio com a câmara de compressão triaxial, submeteu-se amostras de solo às pressões de 0, 10, 30, 60, 100, 300, 500 e 1000 kPa e, para cada pressão, foi mensurado o volume de água drenado, o que permitiu calcular a umidade da amostra àquela pressão. Com o papel filtro, mediu-se o potencial matricial da água em amostras cujas umidades foram previamente estabelecidas, utilizando-se curva de calibração adequada. Os três ensaios foram executados em quintuplicata e resultaram em pontos de pressão versus umidade que foram ajustados pelo programa RETC, usando o modelo de van Genuchten. Realizou-se uma análise comparativa de valores de umidade volumétrica estimados pelo modelo ajustado nos ensaios com a câmara triaxial e o papel filtro com a curva de retenção ajustada obtida pela câmara de Richards. Através dessa comparação, verificou-se a aplicabilidade do método do papel filtro para a determinação da curva de retenção de água em solos agrícolas e inadequação da câmara de compressão triaxial para esta finalidade.

This document reports the results of 4 studies of subalpine ecosystem ecology, describing ways that spatial heterogeneity in soils and plant communities mediate ecosystem responses to environmental change. Ecosystem responses to environmental change are also mediated by regional climate patterns and interannual variability in weather. In the first chapter we report the results of an experiment to test for the mediating effects of associational resistance in a forest community that experienced wide-spread beetle kill. We found that Engelmann spruce were more likely to survive a beetle outbreak when growing in low densities (host dilution) and not through other types of associational resistance that relate to higher tree-species richness or greater phylogenetic diversity of the forest community. In the second chapter we report the effects of early snowmelt on soil moisture in subalpine meadow and aspen communities. We found that soil organic matter, soil texture, and forest cover mediated the effects of early snowmelt and were more important drivers of growing-season soil moisture than was snow-free date. In the third chapter we report the effect of early snowmelt on growth and seed production of early-season and midsummer herbaceous species. We found that the primary effect that snowmelt timing had on plant growth was through its effect on species distribution. Changes in the timing of snowmelt had limited effect on the growth, flowering, and seed count of species after they were established. In the final chapter, we report the effect of early snowmelt on soil respiration, microbial biomass, dissolved organic carbon and soil organic carbon. We found that early snowmelt resulted in warmer soil temperatures compared to neighboring snow-cover plots, and that microbial biomass and soil respiration showed no signs of a snowmelt legacy effect during the growing season. Soil organic carbon in rapid and slow-turnover pools was affected more by plant community than by snowmelt timing, and the primary drivers of soil respiration during the snow-free period were first soil organic matter and second soil temperature. Taken together, this dissertation reports our findings that subalpine ecosystems are resilient to environmental change in part because organisms in these systems are adapted to environmental conditions that are highly variable between sites, seasons, and years.

<p>Economics is about the management of scare resources. In agricultural production, water stress and excess heat are the main constraints. The three essays of this dissertation try to improve our understandings of how climate and water resources interact with agricultural markets, and how global changes in agricultural markets may affect water resources. I construct empirical and simulation models to explain the interplay between agriculture and water. These models integrate economic theories with environmental sciences to analyze the hydroclimatic and economic information at different geospatial scales in a changing climate. </p> <p>In the first essay, I illustrate how irrigation, as a potential adaptation channel, can reduce the volatility of crop yields and year-on-year variations caused by the projected heat stress. This work includes estimation of yield response to climate variation for irrigated and rainfed crops; and global projections of change in the mean and the variation of crop yields. I use my estimated response function to project future yield variations using NASA NEX-GDDP climate data. I show that the impact of heat stress on rainfed corn is around twice as big as irrigated practices. </p> <p>In the second essay, I establish a framework for estimating the value of soil moisture for rainfed production. This framework is an extension of Schlenker and Roberts (2009) model enabled by the detailed soil moisture information available from the Water Balance Model (WBM). An important contribution is the introduction of a cumulative yield production function considering the daily interaction of heat and soil moisture. I use this framework to investigate the impacts of soil moisture on corn yields in the United States. However, this framework can be used for the valuation of other ecosystem services at daily basis.</p> <p>In the third essay, I have constructed a model that explains how the global market economy interacts with local land and water resources. This helps us to broaden the scope of global to local analysis of systems sustainability. I have employed SIMPLE-G-W (a Simplified International Model of agricultural Prices, Land use, and the Environment- Gridded Water version) to explain the reallocation across regions. The model is based on a cost minimization behavior for irrigation technology choice for around 75,000 grid cells in the United States constrained by water rights, water availability, and quasi-irreversibility of groundwater supply. This model is used to examine the vulnerability of US land and water resources from global changes.</p>

De nos jours, l'humidité dans les bâtiments est une problématique majeure car elle impacte simultanément la consommation énergétique, le confort des occupants, ainsi que les risques de moisissures dans l'envelope du bâtiment. Les matériaux de construction ont la capacité d'absorber et de libérer de grandes quantités de vapeur d'eau et peuvent par conséquent amortir les variations d'humidité relative intérieure. Cette proporiété est appelée tampon hygrique. Elle est liée aux échanges de vapeur d'eau entre l'air intérieur et les parois, à la ventilation, et aux sources de vapeur. Cet effet a été précédemment mis en évidence à l'échelle du matériau et de la paroi par des expériences de laboratoire et des modèles numériques. Cependant, peu de modèles décrivent de manière réaliste les sources intérieures dues à la présence et aux activités des occupants. Dans ce travail, un modèle hygrothermique à l'échelle de la pièce a été développé en Python afin d'investiguer l'influence du scénario d'occupation, et l'impact du tampon hygrique des parois sur l'air intérieur. Ce modèle regroupe les transferts couplés d'énergie et de masse dans les parois, ainsi que les sources intérieures décrites par un système de conditionnement d'air et par la présence et les activités des occupants. Ce dernier étant modélisé de manière stochastique par un modèle implémenté dans une plateforme nommée No-MASS. Des indicateurs de performance sur les besoins énergétiques, le confort hygrique intérieur, et les risques liés aux moisissures dans les parois ont été définis pour quantifier la performance hygrothermique d'une pièce. La sensibilité des indicateurs de performance vis-à-vis du scénario d'occupation a été évaluée en simulant des scénarios stochastique, déterministe et constant. Les résultats ont montré une influence marginale du scénario à l'échelle de l'année. [...} / Humidity in buildings has nowadays become a major concern as it impacts simultaneously the energy consumption, the occupants' comfort and the moisture related risks in the buildings envelope. Buildings materials have the ability to absorb and release large amounts of moisture and therefore they may dampen the indoor relative humidity variations. This is called the moisture buffering capacity. It depends on the vapour exchanges between the air and the walls, the ventilation and the indoor moisture sources. This property was previously highlighted at material and wall scales through laboratory experiments and numerical models. However, few models describe the indoor sources due to the occupants' presence and activities in a realistic way. In this work, a hygrothermal room model was developed in Python to investigate the influence of the occupancy scenario and of the impact of the walls moisture buffering on indoor air balance. This model regroups the coupled heat and mass transfer in the walls, as well as the indoor sources depicted by the air-conditioning system and the occupants' presence and activities. The numerical modelling of the latter relies on a stochastic occupancy model implemented in a platform called No-MASS. Performance indicators on the energy demand, the indoor hygric comfort and the moisture related risks in the walls were defined to quantify the hygothermal performance of a room. The sensitivity of the performance indicators towards the occupancy scenario was assessed by simulating a stochastic occupancy scenario, a deterministic one and a constant one. Results showed a marginal influence of the scenario at year scale. However, at smaller time scales (seasonal or monthly), their impact on the indoor relative humidity dampening was not negligible, mainly due to the consideration of a seasonal effect for the stochastic scenario. [...]

Le béton de chanvre est un matériau de construction biosourcé pouvant répondre aux problématiques environnementales actuelles. Utilisé comme matériau de remplissage avec une bonne capacité isolante, il possède également la capacité de réguler l'humidité relative intérieure. Son comportement hygrothermique complexe résulte notamment de performances thermiques et hydriques interdépendantes. La prédiction de ces effets est réalisée à l'aide de modélisation et simulation de transferts hygrothermiques. Toutefois, l'utilisation de données d'entrée les plus représentatives possibles de la réalité est nécessaire. Les méthodes de caractérisation courantes ont souvent été développées pour des matériaux conventionnels et peuvent montrer des limites dans le cas de matériaux biosourcés. L'objectif principal de ces travaux est de déterminer les propriétés hygrothermiques d'un bloc de béton de chanvre préfabriqués à l'échelle industrielle, de mieux appréhender cette caractérisation et de décrire son comportement hygrothermique via des simulations numériques. Le matériau étudié est formulé à partir d'un liant pouzzolanique et de granulats de chènevotte. Une partie de ce travail de thèse a donc porté sur la caractérisation des propriétés physiques, thermiques et hydriques du béton de chanvre étudié ainsi que sur les méthodes de mesure. Pour chaque paramètre hygrothermique étudié, plusieurs méthodes ont été confrontées afin d'en évaluer l'impact. Dans la mesure du possible, l'influence de la température et de l'humidité sur les différents paramètres a également été estimée. Un modèle de transferts hygrothermiques est proposé avec une évaluation d'ordre de grandeur dans le cas du béton de chanvre à partir des propriétés de la littérature. Ce modèle est appliqué à une étude expérimentale à l'échelle de la paroi, dans une enceinte bi-climatique, mettant en avant l'impact de la sorption et du changement de phase sur les transferts de chaleur. En ce qui concerne les propriétés thermiques, l'étude expérimentale à l'échelle du matériau met en évidence l'impact significatif du protocole expérimental sur le résultat de mesure, en particulier pour la chaleur massique. Pour les propriétés hydriques, les essais mettent en avant l'intérêt de réaliser une étude paramétrique de type round-robin sur les matériaux biosourcés. [...] / Hemp concrete is a bio-based construction material able to meet current sustainable issues. Used as filling and insulating material, it has the capacity to regulate the indoor relative humidity. Its complex hygrothermal behavior results on interdependent thermal and hydric performances. The prediction of the hygrothermal effect is performed through heat and moisture transfer modeling and simulation. However, the use of representative inputs is necessary. Standard characterization methods have often been developed for usual building material and can show some limitations in the case of bio-based material. The main objective of these works is to determine the hygrothermal properties of a precast hemp concrete produced at industrial scale, have a better understanding of this characterization and describe its hygrothermal behavior through numerical simulations. The studied material is based on pozzolanic binder and hemp aggregates. One part of this work deals with the characterization of the physical, thermal and hydric properties of the studied material and with the measurement methods. For each hygrothermal properties, several methods have been confronted. If possible, the temperature and humidity influences have been appraised. A heat and moisture transfer model is proposed with a scale analysis based on hemp concrete properties from the literature. This model has been applied to wall scale experiments highlighting the impact of sorption and phase change phenomena on the heat transfers. With regards to the thermal properties, the experimental study at material scale highlights the significant impact of the experimental protocol on the result of the measure, particularly for the specific heat capacity. For hydric properties, the studies put forward the interest of performing a parametric round-robin test dedicated to bio-based materials. An air permeability measurement protocol designed for regular concrete has been adapted in order to evaluate the performance of a very permeable material such as the hemp concrete. The numerical model is validated on a test from a standard and a test from the literature. It manages to describe test with usual ambient solicitations performed in the bi-climatic chamber.