Prior research has concluded that climate change is having an overall negative impact on rice production worldwide. The vast majority of climate change impacts on rice production result from fluctuations in precipitation and temperature, which lead to flooding, water scarcity, and increases in insects and pests, diseases, and weeds. As a small developing country, Guyana is highly vulnerable to climate change despite its insignificant contribution to global warming. Guyana heavily relies on rice cultivation for food, employment, and export earnings. While generally increasing, rice yields have fluctuated over the last two decades. For example, in 2016, rice yields declined by 12.7 percent due to a drought. This dissertation explores the relationship between fluctuating yields and climate change, and how farmers are adapting. Of particular importance are the impacts of climate change on small farmers (those cultivating less than 4.45 hectares or 11 acres) and their ability to successfully adapt. Small farmers are especially vulnerable to a changing climate because they often lack the necessary knowledge, support, and resources to effectively respond and adapt. Given the large percentage of rice farmers engaging in small-scale production in Guyana, this study investigates the impacts of climate variability on rice production and the extent to which the production and productivity of small farmers are affected. It also identifies the coping strategies small farmers employ to combat the effects of climate change and the extent to which these strategies are successful. Given that climate change is expected to vary across different regions of the world, the first aim of this study is to show how the climate in Guyana has changed. At the country level, evidence from descriptive statistics, a linear trend model, and a two-sample t-test shows that minimum and maximum temperatures have increased over the last 111 years. The aggregate data is less clear on changes in precipitation over the last 111 years. However, analysis of farm-level data provides strong evidence of shifts in rainfall patterns. Among 189 small farmers interviewed, 182 (96.3%) perceived changes in rainfall patterns, 170 (89.9%) perceived changes in temperature, 169 (89.4%) perceived changes in extreme weather events, 185 (97.9%) perceived changes in insects and pests, 73 (38.6%) perceived changes in diseases, and 168 (88.9%) perceived changes in weeds. Changes in precipitation have included an increase in intensity and out of season rainfall, which has impacted harvesting due to poor dams, wet fields, and the lodging of plants. The primary responses farmers have adopted include adjusting planting dates based on water availability and the cultivation of different rice varieties. Changes in temperature have resulted in hotter days, accelerating the evaporation of water from fields. In response, farmers replenish water in their fields, when available. Excess rainfall and resulting flooding, drought, and heavy winds have been the primary extreme weather events observed. Excess rainfall and associated flooding submerges, uproots, and/or kills young plants. The lodging of plants due to heavy winds and flooding has been the main impact. In response to flooding, farmers have pumped water out of their fields. There is very little that farmers can do in response to heavy winds. The primary change in insects and pests reported by farmers has been an increase in paddy bug infestations, which cause damage to the grains resulting in lower quality and quantity at harvest. As a result, farmers are engaging in more preventative spraying. An increase in brown spot disease was also reported. Brown spots are primarily found on the leaves, damaging and/or stunting the growth of the plants by reducing the amount of food they manufacture through photosynthesis. Farmers have responded by engaging in preventative spraying and the rotation of fungicides. Increases in red rice and duckweed have been the major changes in weeds observed. Both weeds compete with rice for space, sunlight, nutrients, and water. Additionally, red rice reduces the quality and by extension the price farmers receive. Farmers are responding by spraying more herbicide and using a contact chemical to burn red rice. Multivariate analysis of farm-level data found that land tenure, tractor ownership, membership in an agricultural organization(s), secondary non-agricultural income, and farms located in regions two and four have positive correlations with annual yields. Perceived changes in rainfall, farm size, livestock ownership, participation in rice extension training, and household members help with rice farming were found to have negative correlations with annual yields. Policy recommendations to improve rice production and farmers' resilience include improving research and development capacity; tax exemption for agricultural inputs and equipment; improving extension services; improving the management of irrigation systems and water resources; enhanced access to credit, insurance, and subsidies; improving weather forecasting and climate monitoring; and improving the management of drainage infrastructure. The analytical framework used in this research produced a rich dataset and interesting results that are important to our understanding of farm-level impacts and responses to climate change. As such, it may prove useful for studying climate change impacts in other developing countries that have similar characteristics and face similar risks from climate change as Guyana. / Doctor of Philosophy / The vast majority of climate change impacts on rice production result from variations in rainfall and temperature that lead to flooding, water shortage, and increases in insects and pests, diseases, and weeds. Guyana is highly exposed to climate change. More importantly, the country relies heavily on rice farming for food, employment, and foreign income. Of particular importance are the impacts of climate change on small farmers (growing less than 4.45 hectares) and their ability to successfully adapt. Small farmers are especially helpless because they often lack the necessary knowledge, support, and resources to effectively respond and adapt. Given the large percentage of rice farmers engaged in small-scale production in Guyana, this study explores the impacts of climate variability on rice production and the extent to which the production and output of small farmers are affected. Analysis of farm-level data shows that changes in rainfall have included an increase in intensity and out of season rainfall which has affected harvesting due to poor farm-to market roads, wet fields, and lodging of plants. The main responses involved adjusting planting dates based on water availability and the cultivation of different rice varieties. Changes in temperature resulted in hotter days which increased the loss of water from the field. In response, farmers replenish water in their fields, when available. Excess rainfall and resulting flooding, drought, and heavy winds have been the main extreme weather events observed. Excess rainfall and associated flooding submerges, uproots, and/or kills young plants. The lodging of plants due to heavy winds and flooding has been the main impact. In response to flooding, farmers have pumped water out of their fields. There is very little that farmers can do in response to heavy winds. An increase in paddy bug infestations damaged the grains resulting in lower grain quality while an increase in red rice and duckweed increased the competition for space, sunlight, nutrients, and water. Farmers engaged in more defensive spraying and used a contact chemical to burn red rice.

Land alterations including deforestation, unsustainable land management practices and an increase in cultivated areas have occurred in the Upper Ruvu watershed in recent decades threatening water and natural resources. This study, which used a combination of remote sensing techniques, field experiments, watershed monitoring, and modeling was designed to investigate impacts of environmental changes on hydrology and soil erosion. The objectives were to: map the extent of land use and land cover change and its influence on soil erosion; correlate the contribution of climate variability and human activities to the changes in hydrology at headwater and watershed scales; estimate surface runoff, sediments and Curve Number at plot scale, and model streamflow responses to changes in land use and land cover using the SWAT watershed model. Results indicate that areas covered by forest decreased from 17% in 1991 to 4% of the total watershed area in 2015. However, areas covered by cropland increased from 14% to 30% of the total watershed area from 1991 to 2015, respectively. Further, results indicate that site characteristics affect runoff and sediment yield as higher soil loss was estimated from cropland with a mean of 28.4 tha-1 in 2015 from 19.8 tha-1 in 1991. Results from monitoring show high sediment loads were from the most disturbed watersheds, compared to Mbezi. Analysis of trends for the long term records at the watershed showed that rainfall had significant decreasing trends. At annual scale, climate variability contributed 46% and human activities contributed 54% of the changes in streamflow. Results from the rainfall simulation experiments show upland rice had higher runoff (48 mmh-1) and soil loss (94 gm-2) compared to grassland and forest. Results from the model outputs showed that average streamflow decreased by 13% between 1991 and 2015. Average peak flows increased by 5% and 12% for 2000 and 2015, respectively compared to the baseline. Land alterations had impacts on surface runoff which increased by 75% and baseflow decreased by 66% in 2015 from the baseline. These results highlight the main areas of changes and provide quantitative information to decision makers for sustainable land and water resources planning and management. / Ph. D.

Frequent climatic shocks have presented challenges for rainfed agriculture in sub-Saharan Africa. Appropriate water management practices are among the solutions to the challenges. The role of water harvesting in achieving sustainable agricultural intensification and specified resilience was explored. Suitable areas for water harvesting in the Upper Blue Nile basin were identified. The usefulness of the Curve Number method for surface runoff estimation was evaluated, and was found to perform satisfactorily. The impact of climate change in the Lake Tana sub-basin was studied. A decision support system was developed for locating and sizing of water harvesting ponds in the SWAT model. Methodological developments enabled analysis of the implications of water harvesting intensification in a meso-scale watershed in the Lake Tana sub-basin. Results suggest that water harvesting can increase agricultural productivity, sustain ecosystems and build specified resilience, and thereby contribute to sustainable agricultural intensification. There is considerable potential for water harvesting in the Upper Blue Nile Basin. Rainfall may increase in the Lake Tana sub-basin due to climate change. Supplementary irrigation from water harvesting ponds and better nutrient application increased staple crop production by up to three-fold. Moreover, a substantial amount of cash crop was produced using dry seasonal irrigation. Water harvesting altered the streamflow regime, and reduced sediment loss from the watershed.       Water harvesting can play an important role in food security. It showed potential to buffer climatic variability. In the watershed studied, water harvesting will not compromise the environmental water requirements. Instead, increased low flows, and reduced flooding and sediment loss may benefit the social-ecological systems. The adverse effects of disturbance of the natural flow variability and sediment influx to certain riverine ecosystems warrant detailed investigation. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 5: Epub ahead of print. Paper 6: Manuscript.</p> / Water resources management and social-ecological resilience

Understanding the conflict potential of climate variability is critical for assessing and dealing with the societal implications of climate change. Yet, it remains poorly understood under what circumstances – and how – extreme weather events and variation in precipitation patterns affect organized violence. This dissertation suggests that the impacts of climate variability on organized violence are conditional on specific climate patterns, the sensitivity of livelihoods, and state governance. These theoretical conjectures are subjected to novel empirical tests in four individual essays. Three essays investigate the relationship between climate variability and communal and civil conflict through sub-national quantitative analysis focusing on Sub-Saharan Africa. The fourth essay sheds light on causal mechanisms leading to participation in land-related conflict based on interview material on 75 ex-participants in violence from Mt. Elgon, Kenya. Essay I suggests that the exposure of vulnerable agricultural livelihoods to sustained drought increases the risk of civil conflict violence. Essay II indicates that rainfall anomalies increase the risk of communal violence, an effect which is amplified by political marginalization. Essay III finds support for the proposition that volatility in resource supply increases the risk of communal conflict over land and water in remote regions, which tend to have limited state presence. Essay IV proposes that individuals depending on agriculture are prone to participate in land-related conflict as they face impediments to leaving a conflict zone, and additionally have high incentives to partake in fighting for land. Taken together, the dissertation furthers our understanding of the specific economic and political context under which climate variability impacts armed conflict. This knowledge is important for conflict-sensitive adaptation to climate change and conflict prevention efforts.

Central America is a region regularly affected by natural disasters, with most of them having a hydro-meteorological origin. Therefore, the understanding of annual changes of precipitation upon the region is relevant for planning and mitigation of natural disasters. This thesis focuses on studying the precipitation variability at annual scales in Central America within the framework of the Swedish Centre for Natural Disaster Science. The aims of this thesis are: i) to establish the main climate variability sources during the boreal winter, spring and summer by using different statistical techniques, and ii) to study the connection of sea surface temperature anomalies of the neighbouring oceans with extreme precipitation events in the region. Composites analysis is used to establish the variability sources during winter. Canonical correlation analysis is employed to explore the connection between the SST anomalies and extreme rainfall events during May-June and August-October. In addition, a global circulation model is used to replicate the results found with canonical correlation analysis, but also to study the relationship between the Caribbean Sea surface temperature and the Caribbean low-level jet. The results show that during winter both El Niño Southern Oscillation and the Pacific Decadal Oscillation, are associated with changes of the sea level pressure near the North Atlantic Subtropical High and the Aleutian low. In addition, the El Niño Southern Oscillation signal is intensified (destroyed) when El Niño and the Pacific Decadal Oscillation have the same (opposite) sign. Sea surface temperature anomalies have been related to changes in both the amount and temporal distribution of rainfall. Precipitation anomalies during May-June are associated with sea surface temperature anomalies over the Tropical North Atlantic region. Whereas, precipitation anomalies during August-September-October are associated with the sea surface temperature anomalies contrast between the Pacific Ocean and the Tropical North Atlantic region. Model outputs show no association between sea surface temperature gradients and the Caribbean low-level jet intensification. Canonical correlation analysis shows potential for prediction of extreme precipitation events, however, forecast validation shows that socio-economic variables must be included for more comprehensive natural disaster assessments.

Les influences respectives de l’anthropisation et de la variabilité climatique sur l’histoire de la végétation méditerranéenne sont difficiles à différencier et peuvent être variables d’une région à une autre. Ce travail de recherche a pour objectif de mieux caractériser l’influence des populations humaines et de la variabilité climatique sur la mise en place des environnements du nord-ouest de la Méditerranée (i) en apportant une contribution inédite à l’étude de l’histoire de la végétation de cette région et (ii) en développant de nouveaux outils de traitement des données paléo-environnementales. Pour cela, deux nouvelles séquences polliniques à haute résolution temporelle situées dans le Languedoc (France) et dans la région de Murcie (Espagne) ont été acquises. Elles couvrent respectivement les 7800 et 6500 dernières années. Dans le Languedoc, la végétation est dominée par des taxons plutôt mésophiles pendant la majeure partie de la séquence, notamment le hêtre qui forme des forêts à basse latitude en zone méditerranéenne. Ce dernier régresse sous l’effet d’une aridification croissante du climat, combinée à des crises d’aridités centennales. D’un autre côté, la végétation sclérophylle méditerranéenne s’installe progressivement depuis le Néolithique en lien avec une anthropisation croissante. Dans la région de Murcie, l’impact du climat sur la végétation est plus équivoque, c’est l’impact de l’Homme qui est le plus nettement visible. Les formations arbusitives et pionnières montrent clairement des phases de développement et de régression reliées aux variations de l’anthropisation du territoire. D’autre part, un travail de calibration du signal pollinique par rapport à la végétation a été initié. Le modèle de transport des grains de pollen, REVEALS, a été adapté aux environnements de dépôts côtiers tels que ceux étudiés dans cette thèse. De plus, des données en vue de la quantification de la production pollinique de douze des principaux taxons méditerranéens ont été collectées et traitées. Pour finir, l’analyse spectrale de séries temporelles paléoclimatiques a permis de caractériser l’influence de l’activité solaire, de la circulation thermohaline atlantique et de la variabilité climatique tropicale sur le climat du nord-ouest de la Méditerranée. La variabilité spatiale du signal climatique à l’Holocène en Méditerranée a également été discutée grâce à une remise en contexte des résultats de cette thèse à l’échelle de l’ensemble du bassin Méditerranéen. / Holocene climate fluctuations and human activities since the Neolithic have shaped present-day Mediterranean environments. Separating anthropogenic effects from climatic impacts to better understand Mediterranean paleoenvironmental changes over the last several millennia remains a challenging issue. This work aims to characterize the influence of human activities and past climate variability over the development of north western Mediterranean environments by (i) providing new data about the vegetation history of this region and (ii) developing new tools for paleoenvironmental data processing. Two high-resolution pollen sequences from Languedoc (France) and the Murcia region (Spain) are presented, covering the last 7800 and 6500 years, respectively. In Languedoc, the past vegetation is dominated by mesophilous forests during most of the sequence, in particular beech forests growing at low altitude within the Mediterranean area. However, recurrent abrupt climate changes, the late Holocene aridity trend, and human deforestation caused beech forests to decline. On the other hand, evergreen Mediterranean vegetation has developed gradually since the Neolithic due to the increasing human impact. In the Murcia region, the influence of past climate variability on the environment is less obvious. Changes in human activities are clearly driving most of the observed vegetation changes. Shrubs and pioneer plants show spread and decline phases alternatively in relation to archeological and historical records. Work to adapt pollen based land-cover reconstruction methods developed in northern Europe to the Mediterranean area was also initiated. REVEALS model of pollen dispersal and deposition was adapted to coastal sedimentary basins such as those studied in this PhD. However, to apply such pollen based land-cover reconstruction methods, pollen productivity estimates are needed. Thus, the data necessary to quantify the pollen productivity of 12 Mediterranean plant taxa were collected and processed. Finally, spectral analysis of paleoclimate time series using wavelets allowed us to characterize the influence of solar variability, the Atlantic thermohaline circulation, and tropical climate variability on the past climate of the north-western Mediterranean. The spatial variability of past climate changes in the Mediterranean is also highlighted by comparing our results obtained for the north western Mediterranean with paleoclimate data from the whole Mediterranean basin.

Sur la période 2006-2008, les prix de la plupart des produits agricoles ont connu une hausse spectaculaire. Un des facteurs explicatifs de cette flambée des prix est le changement climatique. En effet, l’instabilité pluviométrique et les températures extrêmes affectent négativement les récoltes agricoles et entraînent une baisse de l’offre alimentaire sur les marchés internationaux qui contribue à la hausse des prix agricoles. La flambée des prix agricoles et le changement climatique soulèvent de sérieuses préoccupations en ce qui concerne l’inflation et le bien être des populations dans le monde et surtout dans les pays pauvres dépendants des marchés internationaux. Dans un premier chapitre, nous montrons à partir de modèles économétriques sur séries temporelles que la hausse du prix du pétrole et les fluctuations du dollar américain sont les principaux facteurs de la hausse des prix internationaux agricoles. Dans un deuxième chapitre, à l’aide d’un modèle de cointégration non linéaire, nous mettons en évidence le fait que les hausses du prix du riz sur le marché international se transmettent plus rapidement aux marchés intérieurs du Burkina Faso que les baisses. Dans un troisième chapitre, nous montrons que la hausse du prix international du riz a un effet négatif sur la pauvreté et les inégalités de revenu au Burkina Faso. Le quatrième chapitre met en évidence l’effet négatif et significatif de la variabilité climatique sur la sécurité alimentaire dans les pays en développement. Cet effet apparait plus élevé dans les pays africains. Il ressort de cette thèse que les pays en développement et plus particulièrement les pays africains sont fortement vulnérables aux chocs de prix alimentaires et au changement climatique. Cette vulnérabilité s’explique par le fait que ces pays dépendent des importations alimentaires et ont un secteur agricole sensible au climat. Des initiatives de protection sociale des populations pauvres sont nécessaires compte tenu de l’accès limité à la nourriture engendré par la flambée des prix alimentaires. Des investissements viables pour une croissance agricole soutenue sont aussi nécessaires. Il peut s’agir d’investissements pour l’amélioration des infrastructures rurales et des services agricoles ainsi que pour la recherche de nouvelles pratiques agricoles moins sensibles aux aléas climatiques. / Over the period 2006-2008, the prices of most of agricultural commodities considerably increased. One of the explanatory factors of this surge in prices is climate change. Indeed, rainfall instability and extreme temperatures negatively affect agricultural crops and lead to reduced food supply in international markets, which contributes to the rise in food prices. Soaring food prices and climate change raise serious concerns regarding inflation and welfare of households in the world and especially in poor countries that depend on food imports. In a first chapter, using econometric models applied to temporal series, we show that rising oil prices and fluctuations in the U.S. dollar are the main causes of the rise in world food prices. In a second chapter, using the threshold cointegration tests, we highlight the fact that the imported rice prices in the local markets of Burkina Faso respond more rapidly to increases than to decreases in the world price. In a third chapter, we show that the increase in the world rice price has a negative effect on poverty and income inequality in Burkina Faso. The effect is lower in the rice-producing areas but remains negative. The fourth chapter highlights the significant and negative effect of climate variability on food security in developing countries. The effect is higher in African countries than in other countries. The main message of this thesis is that developing countries and especially African countries are highly vulnerable to food price shocks and to climate change. This vulnerability might be explained by the fact that these countries depend on food imports and have an agricultural sector sensitive to climate variability. Initiatives for the social protection of poor households are required due to limited food access caused by soaring food prices. Investments for sustained agricultural growth are also required. These are for example investments for the improvement of rural infrastructure and agricultural services as well as development of new agricultural practices less sensitive to climate.

Submitted by Celso Magalhaes (celsomagalhaes@ufrrj.br) on 2017-05-19T13:33:19Z No. of bitstreams: 1 2016 - Jair Figueiredo do Carmo.pdf: 2232723 bytes, checksum: fe83db2be94c1c93b2be3e9af0a35856 (MD5) / Made available in DSpace on 2017-05-19T13:33:19Z (GMT). No. of bitstreams: 1 2016 - Jair Figueiredo do Carmo.pdf: 2232723 bytes, checksum: fe83db2be94c1c93b2be3e9af0a35856 (MD5) Previous issue date: 2016-02-25 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / The objective of this research was to study the growth and wood properties of Copaifera langsdorffii trees in an open rain forest, under a forest management system in the state of Mato Grosso, Brazil. Therefore, samples from 20 trees were collected, and the development of the research was divided into two stages. In the first one, a dendrochronological study for the species was carried out and in the second one, a study of the effect of forest management on the anatomical, chemical and physical properties of C. langsdorffii wood. The area where the trees were collected, has as main characteristic the fact that had occurred the first lumbering in 1987 and reaching his second cutting cycle in 2013. During the dendrochronological study, a master chronological series of the tree species and also an analysis of the cambium sensitivity to climatic variations (temperature and precipitation) were done. Furthermore, weather effects of El Ni?o event were found in the growth of those trees. The study of the effect of forest management on the properties of wood, was carried through the anatomical, physics and chemistry characterization of woods that were formed 10 years before and 10 years after the first cutting cycle that had occurred in 1987. It was also analyzed the effect of the distance of the trees studied in relation to the glade (remaining stub) opened in the year of the first lumbering, in 1987. The results indicated that C. langsdorffii has potential to the dendrochronological studies, presenting a significant correlation between the width of the rings within and among those trees. The forest management led to diametrical higher increases than those observed before the first lumbering. It was observed that the higher diametrical growth of trees occurred during periods of the year in which the precipitation rate is higher. The study indicated a significant change in anatomical structure of the wood, by the increased frequency of vessels and decreasing width of rays formed on wood after lumbering in1987. Those results were also observed for the trees distances in relation to the glade. The changes into anatomical structure showed a decrease in the density of the wood formed after 1987. By chemical analysis, 10 chemical elements were found, 4 macro and 6 micronutrients. There was no significant difference in the assimilation of minerals into the wood as a result of forest management. Thus, there was no negative effect on the availability of nutrients to the C langsdorffii. Overall the results showed that forest management was beneficial to the C. langsdorffii, growth because that action led to possible and considerable gains in growth after forest intervention, without incurring significant losses in the anatomical, physical and chemical structure in the wood species. / O objetivo deste trabalho foi estudar o crescimento e propriedades da madeira em ?rvores de Copaifera langsdorffii de uma floresta ombr?fila aberta, sob regime de manejo florestal, no estado de Mato Grosso. Para tanto, foram coletadas amostras de 20 ?rvores, e o desenvolvimento do trabalho foi dividido em duas etapas. Na primeira, foi realizado um estudo dendrocronol?gico para a esp?cie e, na segunda, um estudo do efeito do manejo florestal nas propriedades anat?micas, qu?micas e f?sica da madeira de C. langsdorffii. A ?rea, onde foram coletadas as ?rvores, tem como principal caracter?stica o fato de ter ocorrido a primeira explora??o florestal no ano de 1987 e atingindo seu segundo ciclo de corte no ano de 2013. No estudo dendrocronol?gico, foi constru?da uma s?rie cronol?gica mestre da esp?cie e an?lises da sensibilidade cambial ?s varia??es clim?ticas (temperatura e precipita??o). Al?m disso, verificou-se os efeitos clim?ticos do evento El Ni?o no crescimento das ?rvores. O estudo do efeito do manejo florestal nas propriedades da madeira foi realizado atrav?s da caracteriza??o anat?mica, f?sica e qu?mica dos lenhos formados10 anos antes e 10 anos depois do primeiro ciclo de corte ocorrido em 1987. Foi tamb?m analisado o efeito da dist?ncia das ?rvores estudadas em rela??o ? clareira (toco remanescente) aberta no ano da primeira explora??o de 1987. Os resultados obtidos indicaram que a C. langsdorffii apresenta potencial para estudos dendrocronol?gicos, apresentando uma correla??o significativa da largura dos an?is dentro e entre ?rvores. O manejo florestal propiciou incrementos diametrais superiores aos observados antes da primeira explora??o. Observou-se que os maiores incrementos diametrais das ?rvores ocorreram nos per?odos do ano em que o ?ndice de precipita??o ? maior. O estudo indicou altera??es significativas na estrutura anat?mica da madeira, atrav?s do aumento da frequ?ncia de vasos e redu??o largura dos raios na madeira formada ap?s a explora??o florestal de 1987. Esses resultados tamb?m foram encontrados na an?lise de dist?ncia da ?rvore estudas em rela??o ao toco remanescente. As altera??es na estrutura anat?mica denotaram uma diminui??o da densidade aparente da madeira formada p?s 1987. Atrav?s da an?lise qu?mica foram encontrados 10 elementos qu?micos, sendo 4 macros e 6 micronutrientes. N?o houve diferen?a significativa na assimila??o de minerais na madeira decorrentes do manejo florestal. Assim, n?o houve efeito negativo na disponibilidade de nutrientes para a C. langsdorffii. De modo geral, os resultados encontrados demonstraram que o manejo florestal foi ben?fico para a C. langsdorffii, pois possibilitou ganhos consider?veis de incremento ap?s a interven??o florestal, sem acarretar preju?zos relevantes na estrutura anat?mica, f?sica e qu?mica no lenho da esp?cie.

Thesis (MSc. (Geography)) -- University of Limpopo, 2018 / In spite of the widespread scientific debate on the impacts of climate variability, not much is known about smallholder farmers’ perceptions towards climate variability and the impacts thereof on their agricultural practices. This is especially true for smallholder farmers in Sub-Saharan Africa in general and South Africa in particular. Literature contends that an understanding of the farmers’ perceptions of climate change and variability is indispensable for effective policy formulations and adaptive strategies. This current study posits that discrepancies between farmer perceptions and climatological evidence will negatively impact on farmer adaptation options and outcomes. The objectives of the study were to; (1) assess climate variability in Molemole Local Municipality, Limpopo Province, (2) investigate farmers’ perceptions of climate variability, (3) compare farmers’ perceptions of climate variability with climatological data and (4) appraise farmers’ adaptive strategies to climate variability. A total of 125 farmers from Botlokwa Village participated in the study. The village was selected because it is the largest village in the municipality and it comprises mainly of rural farmers that are involved in rain-fed subsistence agriculture. In addition, the village receives limited government intervention and is in close proximity to a functional climate station (Polokwane Airport Weather Station). Based on purposive sampling, focus group discussions and a three-part closed ended questionnaire was administered to the farmers. Mean annual temperature and rainfall data (30 years) was used to assess climate variability in the study area. Farmers’ perceptions to climate variability was assessed using descriptive statistics based on summary counts of the responses with Statistical Package for Social Science (SPSS) program. Logistic regression analysis was used to compare differences in perception (mean responses). Comparison of farmers’ perceptions of climate variability against climatological evidence was restricted to mean annual temperature and rainfall data over the past 5 – 10 years). To appraise farmers’ adaptive strategies, the Adaptation Strategy Index (ASI) and the Weighted Average Index (WAI) were employed. vi Farmers’ perceptions of climate variability were consistent with recorded meteorological data. Based on the ASI and WAI computations, use of indigenous knowledge systems (IKS) and crop management approaches were highly important adaptation strategies while the use of insurance and subsidies were least employed by the farmers. The results from the study also showed that the age of the household head, gender, level of education, farming experience and access to information on climate variability were crucial factors in influencing the likelihood of farmers to perceive climate variability. Given the overwhelming dependence on IKS for weather forecast, and adaptation to climate variability, it is recommended that IKS take centre stage in government initiatives and policies on climate change and variability, especially for smallholder farmers in rural settings. Sensitisation on the use of technology such as cellular phones to receive weather forecast is also recommended.

The eastward winds that form each winter in the Arctic stratosphere are intermittently disrupted by planetary-scale waves propagating up from the surface in events known as stratospheric sudden warmings. It is shown here that following roughly half of these sudden warmings, the winds take as long as three months to recover, during which time the polar stratosphere evolves in a robust and predictable fashion. These extended recoveries, termed here Polar-night Jet Oscillation (PJO) events, are relevant to understanding the response of the extratropical troposphere to forcings such as solar variability and climate change. They also represent a possible source of improvement in our ability to predict weather regimes at seasonal timescales. Four projects are reported on here. In the first, the approximation of stratospheric radiative cooling by a linear relaxation is tested and found to hold well enough to diagnose effective damping rates. In the polar night, the rates found are weaker than those typically assumed by simplified modelling studies of the extratropical stratosphere and troposphere. In the second, PJO events are identified and characterized in observations, reanalyses, and a comprehensive chemistry-climate model. Their observed behaviour is reproduced well in the model. Their duration correlates with the depth in the stratosphere to which the disruption descends, and is associated with the strong suppression of further planetary wave propagation into the vortex. In the third, the response of the zonal mean winds and temperatures to the eddy-driven torques that occur during PJO events is studied. The collapse of planetary waves following the initial warming permits radiative processes to dominate. The weak radiative damping rates diagnosed in the first project are required to capture the redistribution of angular momentum responsible for the circulation anomalies. In the final project, these damping rates are imposed in a simplified model of the coupled stratosphere and troposphere. The weaker damping is found to change the warmings generated by the model to be more PJO-like in character. Planetary waves in this case collapse following the warmings, confirming the dual role of the suppression of wave driving and extended radiative timescales in determining the behaviour of PJO events.