De par sa géométrie et sa situation géographique (2°N-13°N - 8°E-16°E ; ouverture sur l'océan Atlantique), le Cameroun offre l'avantage de proposer un ensemble représentatif des climats régionaux rencontrés en Afrique tropicale. La diminution des cumuls de précipitations enregistrée dans la région pendant la seconde moitié du XXe siècle, est associée à la récurrence de périodes anormalement sèches, essentiellement au coeur de la saison des pluies. Ces conditions ont amplifié la dégradation du couvert végétal au travers ses contraintes socioéconomiques et démographiques (déforestation, extension des surfaces d'activité). Les conséquences souvent dommageables de la variabilité climatique en général, et des sécheresses en particulier, sur les hommes et leurs activités suscitent l'intérêt de développer des études pour mieux comprendre comment le climat et les pressions naturelles et environnementales interagissent localement. Ainsi, l'objectif de cette thèse est de diagnostiquer la variabilité multiéchelle (saisonnière, interannuelle, intra-saisonnière, synoptique) des précipitations et les relations qu'elle entretient avec le couvert végétal au sens large qui, à ces latitudes, est associé directement ou non, à la dynamique d'occupation et d'utilisation du sol, particulièrement sur la période 1951-2002. A partir de données de précipitations observées (CRU/ponctuelles), les modes spatiaux de la variabilité ont été définis aux échelles annuelles et interannuelles, par Analyses en Composante Principale (ACP) et la Classification Ascendante Hiérarchique (CAH). Ces méthodes de classifications ont permis de discriminer cinq zones climatiques, différentes les unes des autres par l'intensité des cumuls et la saisonnalité (unimodal/bimodal). Pour chaque zone, l'attention a été portée sur les paramètres intrasaisonniers qui modulent la variabilité annuelle telle que, les séquences sèches (nombre, longueur, périodes d'occurrence) et les variations des dates de début et de fin des périodes végétatives. La répartition du couvert végétal dans l'espace et dans le temps (1982-2002) a été étudiée, en utilisant des méthodes de classification non supervisée (ISODATA) sur les données de NDVI (Normalized Difference Vegetation index) à 8km de résolution. Enfin, des méthodes statistiques et de télédétection ont permis d'évaluer l'impact des facteurs pluviométriques et anthropogéniques (croissance démographique et utilisation du sol) sur la dynamique du couvert végétal en utilisant des bases de données à plus fine résolution (NDVI/1Km ; Global Land Cover (GLC 2000/1Km)). Ces dernières investigations ont été menées dans le Nord-Cameroun (6°N-13°N - 11°E-16°E), qui est la région la plus sensible des points de vue climatique, économique et environnemental.

Les milieux oroméditerranéens sont considérés comme particulièrement sensibles aux changements climatiques. Deux questions sont posées dans ce contexte : quelles sont la nature et l'ampleur des modifications climatiques à l'échelle régionale (climat et enneigement) au Chili central, depuis les années 70 ? Quels sont les changements de la végétation en montagne (dans la tranche d'altitude 1.500 - 2.500 m), en particulier au niveau de la limite supérieure de la forêt à Kageneckia angustifolia ? La première partie de la thèse présente les spécificités des milieux de montagne et les changements climatiques déjà observés de façon générale et au Chili en particulier. Elle présente aussi les sites d'étude au niveau climatique et biogéographique. La deuxième partie concerne les données et la méthodologie. Une approche scalaire est mise œuvre, avec confrontation et mise en complémentarité de différentes techniques : télédétection, chroniques climatiques et mesures in situ. La troisième partie présente les résultats. Les données climatiques enregistrées les 30 dernières années aux stations d'El Yeso (2.500 m) et de Los Bronces (3.500 m), montre une croissance d'environ 1 °C pour la température moyenne annuelle, réchauffement plus marqué à El Yeso, au niveau des températures minimales. Pour l'enneigement, il est montré une haute variation interannuelle de la couverture de neige et une élévation de la limite de la neige durant les dernières décennies, d'environ 300 m. Ces résultats, sont accompagnés d'une augmentation faible du NDVI. Au niveau de la vallée Yerba Loca, l'étude diachronique de l'écotone supraforestier montre des transformations vers une augmentation de la superficie des espaces forestiers et leur densification. Enfin, l'expérience de germination, à Yerba Loca montre qu'il existe une différence significative entre le pourcentage de germination des graines à l'intérieur des enclos et à l'extérieur, avec un effet négatif de la couverture neigeuse sur la germination des plantules.

Global and local climate patterns may affect barren-ground caribou (Rangifer tarandus groenlandicus) populations. I predicted global climate changes to be correlated with periods of population decline, and local changes to be more pronounced on the habitat of caribou with a declining population. In chapter 1, the Arctic Oscillation (AO), changes in normalized difference vegetation index and phenology were used as measures of global and local climate. In chapter 2 environmental variables and caribou presence points were used to build Maxent habitat models. There was no consistent correlation with the positive AO phase and periods of population decline, or phenology trends and the habitat of caribou with a declining population. Maxent models underestimated the amount of suitable habitat spatially and failed to model suitable habitat temporally. This thesis is the first to look at a range of density-independent variables over a long time period and model suitable habitat for multiple herds.

Anthropogenic disturbance in a landscape can take various forms, including residential development, which has substantial impact on the world’s ecosystems. Exurban development, characterized by low density residential development outside urban areas, was and continues to be one of the fastest growing forms of residential development in North America. It has disproportionately large ecological impacts relative to its footprint, yet is mostly overlooked in scientific studies. Specifically, a lack of spatially explicit (disaggregate) data on exurban development at regional level has contributed to a very limited understanding of this interspersed low density development. The main goal of this dissertation is to provide an increased understanding of exurban development in terms of its location, locating factors, and conservation and ecological implications at regional level, especially to enable incorporation of exurban information in the decision making processes. For this I asked four specific questions in this dissertation: (i) Where exactly is exurban development? (ii) What are the most likely factors that influence exurban development location? (iii) How does current and future development conflict with conservation goals? And (iv) What is the extent of the exurban development’s ecological impacts? Using a heterogeneous landscape, the County of Peterborough (Ontario, Canada), as the case study this dissertation undertook a number of separate yet related analyses that collectively provided the improved understanding of exurban development. The investigation of traditionally used surrogates for development, like roads and census data, and a more direct remote sensing method, using moderate resolution SPOT/HRVIR imagery, provided insights and contributed to development of spatially explicit data on exurban development. The evaluation of several commonly hypothesized locating factors in relation to exurban development revealed some of the major influences on the location of this development, especially in the context of Ontario. This research contributed to our understanding of the future risks of land conversion and identification of potential conflict areas between development and conservation plans in the study area. Lastly, examining the ecological impact of exurban development including associated roads, in terms of functions such as barrier effects and landscape connectivity, highlighted the importance of these seldom included anthropogenic disturbances in land and conservation planning. The contributions of this research to the existing body of knowledge are threefold. First, this dissertation reveals the limitations associated with existing methods used to map exurban development and presents a relatively easy, effective, automated and operational method to delineate exurban built areas at regional level using GIS and remote sensing. Second, the analyses conducted in this dissertation repeatedly highlights the importance of incorporating fine level details on exurban development in land and conservation planning as well as ecological impact assessments and presents methods and tools that can systematically and scientifically integrate this information in decision making framework. Third, this study conducted one of a kind, comprehensive and spatially explicit study on exurban development in Canada, where there is near absence of such research. With the rarely available exurban built footprint data delineated for the study area, this study not only identified the potential locating factors, future conversion risk, and conflict areas between development and conservation plans, but also quantified ecological impact in terms of landscape function, namely barrier effects and landscape connectivity, using a relatively novel circuit theoretic approach that can directly inform land and conservation decision planning process.

Land cover change detection in urban areas provides valuable data on loss of forest and agricultural land to residential and commercial development. Using Landsat 5 Thematic Mapper (1991) and Landsat 7 ETM+ (2000) imagery of Gwinnett County, GA, change images were obtained using image differencing of Normalized Difference Vegetation Index (NDVI), principal components analysis (PCA), and Tasseled Cap-transformed images. Ground truthing and accuracy assessment determined that land cover change detection using the NDVI and Tasseled Cap image transformation methods performed best in the study area, while PCA performed the worst of the three methods assessed. Analyses on vegetative and vegetation changes from 1991- 2000 revealed that these methods perform well for detecting changes in vegetation and/or vegetative characteristics but do not always correspond with changes in land use. Gwinnett County lost an estimated 13,500 hectares of vegetation cover during the study period to urban sprawl, with the majority of the loss coming from forested areas.

Variations in Leaf Area Index (LAI) can greatly alter output values and patterns of various models that deal with energy flux exchange between the land surface and the atmosphere. Customarily, such models are initiated by LAI estimated from satellite-level Vegetation Indices (VIs) including routinely produced Normalized Difference Vegetation Index (NDVI) products. However, the accuracy from LAI-VI relationships greatly varies due to many factors, including temporal and spatial variations in LAI and a selected VI. In addition, NDVI products derived from various sensors have demonstrated variations in a certain degree on describing temporal and spatial variations in LAI, especially in semi-arid areas. This thesis therefore has three objectives: 1) determine a suitable VI for quantifying LAI temporal variation; 2) improve LAI estimation by considering both temporal and spatial variations in LAI; and 3) evaluate routinely produced NDVI products on monitoring temporal and spatial variations in LAI.<p> The study site was set up in conserved semi-arid mixed grassland in St. Denis, Saskatchewan, Canada. One 600 m - long sampling transect was set up across the rolling typography, and six plots with a size of 40 × 40 m each were randomly designed and each was in a relatively homogenous area. Plant Area Index (PAI, which was validated to obtain LAI), ground hyperspectral reflectance, ground covers (grasses, forbs, standing dead, litter, and bare soil), and soil moisture data were collected over the sampling transect and plots from May through September, 2008. Satellite data used are SPOT 4/5 images and 16-day Moderate Resolution Imaging Spectroradiometer (MODIS) 250m, 1km as well as 10-day SPOT-vegetation (SPOT-VGT) NDVI products from May to October, 2007 and 2008. The results show that NDVI is the most suitable VI for quantifying temporal variation of LAI. LAI estimation is much improved by considering both temporal and spatial variations. Based on the ground reflectance data, the r2 value is increased by 0.05, 0.31, and 0.23 and an averaged relative error is decreased by 1.57, 1.62, and 0.67 in the early, maximum, and late growing season, respectively. MODIS 250m NDVI products are the most useful datasets and MODIS 1km NDVI products are superior to SPOT-VGT 1km composites for monitoring intra-annual spatiotemporal variations in LAI. The proposed LAI estimation approach can be used in other studies to obtain more accurate LAI, and thus this research will be beneficial for grassland modeling.

Anthropogenic disturbance in a landscape can take various forms, including residential development, which has substantial impact on the world’s ecosystems. Exurban development, characterized by low density residential development outside urban areas, was and continues to be one of the fastest growing forms of residential development in North America. It has disproportionately large ecological impacts relative to its footprint, yet is mostly overlooked in scientific studies. Specifically, a lack of spatially explicit (disaggregate) data on exurban development at regional level has contributed to a very limited understanding of this interspersed low density development. The main goal of this dissertation is to provide an increased understanding of exurban development in terms of its location, locating factors, and conservation and ecological implications at regional level, especially to enable incorporation of exurban information in the decision making processes. For this I asked four specific questions in this dissertation: (i) Where exactly is exurban development? (ii) What are the most likely factors that influence exurban development location? (iii) How does current and future development conflict with conservation goals? And (iv) What is the extent of the exurban development’s ecological impacts? Using a heterogeneous landscape, the County of Peterborough (Ontario, Canada), as the case study this dissertation undertook a number of separate yet related analyses that collectively provided the improved understanding of exurban development. The investigation of traditionally used surrogates for development, like roads and census data, and a more direct remote sensing method, using moderate resolution SPOT/HRVIR imagery, provided insights and contributed to development of spatially explicit data on exurban development. The evaluation of several commonly hypothesized locating factors in relation to exurban development revealed some of the major influences on the location of this development, especially in the context of Ontario. This research contributed to our understanding of the future risks of land conversion and identification of potential conflict areas between development and conservation plans in the study area. Lastly, examining the ecological impact of exurban development including associated roads, in terms of functions such as barrier effects and landscape connectivity, highlighted the importance of these seldom included anthropogenic disturbances in land and conservation planning. The contributions of this research to the existing body of knowledge are threefold. First, this dissertation reveals the limitations associated with existing methods used to map exurban development and presents a relatively easy, effective, automated and operational method to delineate exurban built areas at regional level using GIS and remote sensing. Second, the analyses conducted in this dissertation repeatedly highlights the importance of incorporating fine level details on exurban development in land and conservation planning as well as ecological impact assessments and presents methods and tools that can systematically and scientifically integrate this information in decision making framework. Third, this study conducted one of a kind, comprehensive and spatially explicit study on exurban development in Canada, where there is near absence of such research. With the rarely available exurban built footprint data delineated for the study area, this study not only identified the potential locating factors, future conversion risk, and conflict areas between development and conservation plans, but also quantified ecological impact in terms of landscape function, namely barrier effects and landscape connectivity, using a relatively novel circuit theoretic approach that can directly inform land and conservation decision planning process.

The feasibility of using optical sensors and non-nitrogen limiting reference crops to determine post-emergent nitrogen fertilizer requirements of canola was evaluated. Normalized difference vegetation index was well suited for estimating yield potential and nitrogen status. Although sensor-based nitrogen management was generally agronomically feasible for canola, the economic benefits of doing so remain uncertain because of the added cost of applying post-emergent nitrogen. / February 2008

Variations in Leaf Area Index (LAI) can greatly alter output values and patterns of various models that deal with energy flux exchange between the land surface and the atmosphere. Customarily, such models are initiated by LAI estimated from satellite-level Vegetation Indices (VIs) including routinely produced Normalized Difference Vegetation Index (NDVI) products. However, the accuracy from LAI-VI relationships greatly varies due to many factors, including temporal and spatial variations in LAI and a selected VI. In addition, NDVI products derived from various sensors have demonstrated variations in a certain degree on describing temporal and spatial variations in LAI, especially in semi-arid areas. This thesis therefore has three objectives: 1) determine a suitable VI for quantifying LAI temporal variation; 2) improve LAI estimation by considering both temporal and spatial variations in LAI; and 3) evaluate routinely produced NDVI products on monitoring temporal and spatial variations in LAI.<p> The study site was set up in conserved semi-arid mixed grassland in St. Denis, Saskatchewan, Canada. One 600 m - long sampling transect was set up across the rolling typography, and six plots with a size of 40 × 40 m each were randomly designed and each was in a relatively homogenous area. Plant Area Index (PAI, which was validated to obtain LAI), ground hyperspectral reflectance, ground covers (grasses, forbs, standing dead, litter, and bare soil), and soil moisture data were collected over the sampling transect and plots from May through September, 2008. Satellite data used are SPOT 4/5 images and 16-day Moderate Resolution Imaging Spectroradiometer (MODIS) 250m, 1km as well as 10-day SPOT-vegetation (SPOT-VGT) NDVI products from May to October, 2007 and 2008. The results show that NDVI is the most suitable VI for quantifying temporal variation of LAI. LAI estimation is much improved by considering both temporal and spatial variations. Based on the ground reflectance data, the r2 value is increased by 0.05, 0.31, and 0.23 and an averaged relative error is decreased by 1.57, 1.62, and 0.67 in the early, maximum, and late growing season, respectively. MODIS 250m NDVI products are the most useful datasets and MODIS 1km NDVI products are superior to SPOT-VGT 1km composites for monitoring intra-annual spatiotemporal variations in LAI. The proposed LAI estimation approach can be used in other studies to obtain more accurate LAI, and thus this research will be beneficial for grassland modeling.

<p>The remote sensing technology is increasingly being used to study land use and vegetation cover changes and identify changes that has occur through different land use activities which may have negative impact on the sustainability of the environment, biodiversity protection and conservation. With increase in population growth rate in Sudan, there has been an increase for food crop production with agriculture playing a prominent role in livelihood security for the increasing population.</p><p> </p><p>The increase use of irrigation and mechanisation has brought about an increase in demand for agricultural land use in Sudan with the conversion of other land use types and vegetation for agricultural land use. This does have effect and impact on the vegetation and environment with the country highly exposed to the incidence of environmental and social hazards and disasters including drought and desertification, deforestations, floods, loss of biodiversity, ethnic conflicts and poverty.</p><p> </p><p>The research study work focused on agricultural land use changes in the country with the aim of investigating the agricultural land use changes that has occurred in the country from 1986 to 2002 using the remote sensing technique. This is important for agricultural land use planning and sustainability monitoring to reduce the negative impact of agricultural land use for crop production and increase long term resource use and environmental sustainability. Two remote sensing methods were used for the classification analysis to identify the land use changes namely the NDVI and the parallelepiped classification techniques. The NDVI method was used to identify the changes in the agricultural land use vegetation cover classes and determine the magnitude of changes in land area use that has occurred from 1986 to 2002 when the former and latter remote sensing images were acquired. The parallelepiped classification technique was however used to identify the aggregate agricultural land use changes in the area of study and conversion to and from other categories of land use. A qualitative analytic technique was also used to identify the possible causes of the changes that have occurred in Sudan in the study period using empirical materials.</p><p> </p><p>The research study result gives information on the role the remote sensing technology can play in analyzing land use cover changes for agricultural land use sustainability monitoring.</p>