Les pâturages constituent un écosystème terrestre important. En France, ils occupent 21% de la superficie totale, ce qui justifie l'effort pour développer un suivi en temps réel de la production de la biomasse au niveau national, en prenant en compte la variabilité spatiale et temporelle des prairies. L'absence de méthodes indirectes de faible coût applicables à des grandes régions conduit à étudier les modèles de simulation du fonctionnement des cultures, comme dans le cas du système ISOP (Information et Suivi Objectif des Praires), et les possibilités offertes par la télédétection pour contribuer à améliorer le diagnostic fourni. Le travail effectué dans cette thèse a pour but d'évaluer ces possibilités. Pour cela, un nombre limité de treize régions fourragères (FR) de France ont été sélectionnées pour leur contexte géomorphologique, climatique et pédologique associé à leur production fourragère. Les données du capteur VEGETATION embarqué sur la plateforme SPOT4 (résolution spatiale de kilométrique) ont été utilisées pour fournir, à partir de modèles de déconvolution, les valeurs de réflectance correspondant à la signature d'une prairie pure. Celle-ci a été mise en relation avec certaines variables de croissance estimées par le modèle STICS-Prairie à l'intérieur du système ISOP. Au delà du bon accord général entre les deux types de données, l'analyse de ces relations a permis d'établir que celle qui lie les indices de végétation basés sur le moyen infrarouge (SWVI) et l'indice foliaire (LAI) était la plus forte. Les résultats obtenus confirment les capacités des données satellitaires à fournir des estimateurs de variables productives complémentaires de celles estimées à partir de modèles de simulation. En particulier les différences spatiales et temporelles entre les informations fournies par le satellite et les estimations du modèle, surtout pendant les périodes de récolte de biomasse dans les systèmes de production, pourraient contribuer à améliorer les estimations du modèle à l'échelle régionale.

Reproduction de : Thèse de doctorat : Géographie : Lille 1 : 2006. / N° d'ordre (Lille 1) : 3840. Titre provenant de la page de titre du document numérisé. Bibliogr. p. 409-449.

No description available.

Cattle are responsible for the deterioration of aquatic and riparian ecosystems throughout the North American prairies. Marked preference for riparian areas has resulted in vegetation loss, stream bank destabilization, changes in sediment particle size, and increased nutrient loads in the streams. A grazing experiment in Grasslands National Park of Canada manipulated the density of cattle to represent a range of grazing intensities (from no grazing to very heavy grazing, 70% forage utilization). This experiment provided the opportunity to study how streams in the semi-arid mixed-grass prairie environment respond to a range of grazing pressure. Nine experimental pastures located on previously ungrazed land within the park boundary and four located within the adjacent community pastures were created, each subjected to a specified grazing treatment. Sampling occurred in the autumn from 2007 to 2009 and included the measurement of 33 physical, chemical, and biological habitat metrics and the characterization of the aquatic invertebrate community. Linear regressions were performed to determine if the habitat variables had a significant relationship to grazing intensity (P < 0.05). Of the habitat variables, two sediment particle size categories were significantly related to grazing intensity: per cent of fine gravel (4-8 mm diameter) (P =0.003) and per cent of medium gravel (8-16 mm diameter) (P = 0.007). The only other habitat variable with a significant linear relationship to grazing intensity was the concentration of suspended carbon in the stream water (P = 0.050). Three invertebrate community metrics were focused on for their expected response to changes associated with cattle impacts: iii per cent Chironomidae (%Chiron), per cent Ephemeroptera, Odonata, and Trichoptera (%EOT), and taxa richness. There was a significant non-linear relationship between %Chiron (P = 0.005) and grazing intensity, no linear or non-linear relationship between %EOT and grazing intensity, and a non-linear trend between richness and grazing intensity (P = 0.083). A Reference Condition Approach was used to test for the effects of grazing on the invertebrate community. Multiple regression was used to create a model predicting the invertebrate community from habitat metrics. Of the three community metrics, only richness resulted in a model with acceptable predictive ability. The predicted richness values for each test site were calculated and their residuals were determined and compared to the distribution of residuals observed in the reference sites. Using this technique, I determined that 73.3% of the sites subjected to grazing deviated significantly for the reference condition and were therefore deemed to be impacted. There was no significant relationship between the test site residuals and grazing intensity. The macroinvertebrate community in this semi-arid environment is already under a lot of stress, the addition of cattle to the environment, even at low intensities, pushed the community beyond the reference condition.

Changing land cover from prairie grasslands to intensive, primarily cereal agriculture, over the North American Great Plains since the mid-19th century, has had a hydrological and climatological impact on that ecosystem (Pielke, Sr., et al., 2011). Agriculture has introduced timed harvest seasons, irrigation, and C3 photosynthesizing crops with poorer water efficiency than the grasses it replaced. All of these changes have been linked to exacerbated drought conditions and warmer temperatures; however, few studies have quantified this relationship at the continental scale. In order to evaluate the change imposed by this shift in land use and land cover, the observation based 20th Century Reanalysis Project (20CR) was used to quantify the climatological differences in temperature and humidity between areas of natural prairie and agriculture over the 20th century. An additional analysis used the Observation Minus Reanalysis (OMR) technique to isolate the surface climate signal found in the 20CR. We find indications that changing land cover had an impact on climate. However, using observation based data returned no evidence of a statistically significant change due to the small land use and land cover change (LULCC) signal within the larger climate noise. Therefore, an idealised modelling experiment was undertaken using the Geophysical Fluid Dynamics Laboratory (GFDL) AM2-LM2 atmosphere-land model to remove these other influences. This experiment compared the results of two model simulations: one where the entirety of the prairie was preserved as grassland (GRASS), and another where the entire prairies had been converted into an agricultural area (AGRIC). Relative to GRASS, the AGRIC simulation has reduced surface albedo and root zone depth, and increased roughness length over the prairies, which collectively cause a significant summer drying. This occurs when the shallower rooting zone limited potential evapotranspiration (PET) forcing the additional energy created by turbulent mixing and a lower surface albedo to warm the air, surpassing PET and reaching drier conditions faster. While not conclusive, the results presented in this thesis represent a step towards filling the gaps in understanding land-atmosphere interactions and connecting LULCC to climate.

No description available.

Un modèle de morphogenèse aérienne de graminées fourragères, nommé L grass, a été développé lors de travaux précédents. Le but de la thèse est de proposer une méthode d'insertion de la morphogenèse racinaire dans ce modèle afin de tenir compte de l'impact des ressources telluriques sur la structure et le fonctionnement de la plante.</br>Un simulateur de plante entière de ray-grass anglais (Lolium perenne L.) incorporant (i) des règles d'autorégulation de l'architecture aérienne, (ii) le développement architecturé du système racinaire, (iii) des processus de coordination entre les parties aérienne et racinaire et (iv) un système d'allocation du carbone a été développé. La nature autorégulée du modèle lui permet de reproduire les réponses à l'intensité d'une défoliation et à la compétition pour la lumière sans nécessiter de contrôle central. Le couplage du modèle avec un modèle de sol permet de simuler le développement de la plante subissant différents scénarios d'apport en eau sans nécessiter de consignes morphogénétiques données a priori.</br>La représentation architecturée du système racinaire présente quelques limites, principalement en termes de ressources informatiques, pour les simulations de peuplements. Afin de pallier ces limites, un modèle continu de dynamique de densités racinaires a aussi été incorporé pour simuler l'enracinement. Les comparaisons entre les deux modèles de système racinaire ont montré l'intérêt indéniable des modèles de densités racinaires notamment pour les études à l'échelle d'un couvert végétal. / A model of the shoot morphogenesis of forage grasses, called L-grass, was developed in previous studies. The aim of this thesis is to propose a method for introducing root morphogenesis in the current model so the effect of telluric resources availability can be taken into account for shaping plant form and functioning.</br>A simulator of perennial ryegrass (Lolium perenne L.) whole plant, which includes (i) the rules of shoot architecture self-regulation,(ii) the architectural development of the root system, (iii) the coordination processes between shoot and root parts and (iv) a system of allocation of carbon, was developed. The self-adaptable character of the model allows the reproduction of the responses to the intensity of defoliation and the competition for sunlight without the need of any central control. The coupling of the model with a soil model enables to recreate the development of the plant undergoing different scenarios of water supply with no requirement of previously established morphogenetic guidelines.</br>The architectural representation of the root system presents some shortcomings, mainly regarding the need in computing power when simulating plant populations. In order to overcome these limitations, a continuous model of the dynamics of root densities has been also incorporated to simulate plant rooting. The comparison between both models of root systems has shown the undeniable interest of modeling root density, especially for the studies at the vegetation cover level.

Le charbon de bois (biochar), est un amendement qui améliore les propriétés physico-chimiques du sol, augmente le stockage du carbone et les productions agricoles. Les anciens sites de production de charbon permettent d'évaluer son impact directement sur le terrain et sur le long terme. Dans les Alpes italiennes on a échantillonné une série de charbonnières daté de 1858 ainsi que les sols de prairies adjacents, ne contenant pas de charbon. 80±21% du carbone provenant de la production du charbon est toujours présent dans le sol et a un temps de résidence moyen de 650±139 ans. Le contenu des nutriments et leur biodisponibilité sont plus élevés dans les charbonnières par rapport à la prairie alentour et, sont plus élevés aujourd'hui qu'en 1858. L'ajout de charbon apporte des nutriments au sol, mais à court terme les ions Ca2+, K+, SO42- et Mg2+ sont lixiviés sous forme de cendres. Le charbon s'avère capable de retenir les dépositions atmosphériques de PO43-, NH4+, NO3- et, sur le long terme, de K+. L'augmentation du contenu en nutriments, la diminution de l'hydrophobie et de la densité apparente du sol augmentent la productivité et la valeur nutritionnelle des espèces alpines fourragères (Festuca nugrescens Lam. et Trifolium pratense L.). La croissance des plantes est limitée par l'azote sur les charbonnière et par le phosphore dans les prairies non-amendés ou amendés récemment. Nous concluons que le charbon/biochar peut être une stratégie pour stocker le carbone dans les sols, augmenter la production de biomasse et la qualité du fourrage des prairies Alpines à long terme. Toutefois les opérations d'enfouissement peuvent être complexes à cause de la géomorphologie des Alpes. / Charcoal or biochar is proposed as a soil amendment to improve physio-chemical soil properties, increase soil carbon (C) stocks and agricultural yields. Ancient charcoal hearths provide an opportunity to investigate its impact under field conditions and in the long term. A series of charcoal hearths and adjacent charcoal-free soils under grassland in the Italian Alps abandoned in 1858 was sampled.80±21% of the C originating from ancient charcoal is still present in the soil today and has a Mean Residence Time of 650±139 years. The content of total and available nutrients is higher in the hearths soils compared to the surrounding grasslands and it is higher today compared to 1858. The input of charcoal directly adds nutrients to soils but Ca2+, K+, SO42- and Mg2+ are leached in the short term after application, as they are lost in the form of ashes. Charcoal is able to retain atmospheric depositions of PO43-, NH4+, NO3- and in the long term K+.The increase in soil nutrient content and decreases in hydrophobicity and bulk density translated into higher plant growth and nutritional values of two alpine fodder species (Festuca nigrescens Lam. and Trifolium pratense L.). Plant growth was N-limited in the charcoal hearths soils and P-limited in the surrounding grasslands not amended or recently amended with charcoal/biochar.We can conclude that charcoal/biochar is a long term strategy to store carbon in soils, improve biomass productivity and fodder quality in alpine grasslands. However charcoal/biochar incorporation into soil can be complex because of the geomorphology of the Alps.

This thesis discusses American prairie culture through the writings of Thorstein Veblen and Mark Twain.

Hundreds of wetland bird species use ricelands annually in the Gulf Coast Prairie region of Louisiana and Texas. Much of the original ecosystem was transformed for rice and other crops, cattle ranching, flood control, and other human uses. Flooded production and idled ricelands provide critical foraging habitat for breeding, migrating, and wintering wetland birds. Ricelands in coastal Louisiana and Texas provide approximately 42% of the estimated habitat carrying capacity for wintering waterfowl in this region. In 2010, the Deepwater Horizon oil spill in the Gulf of Mexico prompted enactment of the Migratory Bird Habitat Initiative (MBHI) by USDA Natural Resources Conservation Service. The MBHI provided avian habitat, including flooded ricelands, inland from oil impacted areas. My objectives were to: 1) estimate and model variation in biomass of waste rice and natural seeds as potential waterfowl forage in Gulf Coast Prairie ricelands, 2) estimate and model variation in wetland bird use of ricelands, and 3) conduct sensitivity analyses of bioenergetics models by varying foraging thresholds and true metabolizable energy (TME) values. A growing season of ~270 days allows Gulf Coast rice producers to grow two rice crops (i.e., the second termed ratoon). Waste rice was greatest in production fields with harvested and standing ratoon crops, and natural seed biomass was greatest in idled fields with standing vegetation. Wetland bird species richness and waterbird abundance were greatest in shallowly flooded (1–15 cm) ricelands with sparse vertical vegetation (1–20 cm), and duck abundance was greatest in shallow–intermediately (1–30 cm) flooded ricelands with short vegetation (1–15 cm). Shallowly flooded rice fields containing harvested or standing ratoon crops, and shallowly flooded idled fields with standing vegetation provided abundant potential foods for waterfowl and waterbirds. Bioenergetics models indicated that planners in the Gulf Coast Prairie region may be underestimating riceland habitat requirements for waterfowl by 10,000 ha. Models were most sensitive to changes in seed biomass estimates, and less sensitive to changes in foraging thresholds and TME values. Collectively, these results will facilitate conservation partners to refine models for conserving habitats for waterfowl and other waterbirds in the Gulf Coast Prairie.