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Après une vingtaine d'année de mise en œuvre, les mesures agro-environnementales n'ont pas permis d'enrayer le déclin de la biodiversité des paysages agricoles. Des études récentes défendent l'idée que des mesures efficaces demanderaient non seulement de développer des pratiques favorables à la biodiversité à l'échelle de la parcelle mais aussi de favoriser des usages et des agencements spatiaux de ces usages qui accroissent l'hétérogénéité des paysages. Toutefois, on dispose à ce jour de peu de quantifications des relations entre production et conservation de la biodiversité en milieux agricoles. L'objectif de cette thèse est d'analyser à différentes échelles spatiales et temporelles l'arbitrage entre production agricole et conservation d'oiseaux dans un agroécosystème prairial exploité par des élevages bovins viande. La démarche de recherche s'appuie sur le développement de plusieurs modèles basés sur le cadre mathématique de la viabilité. Ces modèles formalisent à trois échelles spatiales emboitées (parcelles, exploitation, paysage) les interactions entre les pratiques de pâturage et de fauche et les dynamiques écologiques de deux espèces d'oiseaux prairiaux. Cette thèse apporte cinq résultats principaux. A l'échelle de la parcelle (1) Les périodes et les intensités de pâturage sont des déterminants majeurs de l'arbitrage entre production et conservation. (2) Les meilleures performances écologiques sont atteintes aux niveaux intermédiaires de performances productives. (3) Des variations interannuelles de modes de gestion permises par des mesures agro-environnementales à objectif de résultat améliorent les performances écologiques tout en augmentant la flexibilité de la gestion des prairies. (4) A l'échelle de l'exploitation agricole, la proportion des différents usages agricoles est un levier majeur de l'arbitrage entre production et conservation mais la conservation des oiseaux a toujours un coût en termes de production. (5) A l'échelle du paysage, l'agencement spatial des usages améliore les conditions de l'arbitrage entre production et conservation. L'ensemble de ces résultats révèle des leviers d'arbitrage spécifiques aux différentes échelles. A chacune de ces échelles, l'interaction entre une diversité de modes d'exploitation est à la base des mécanismes d'arbitrage entre production et conservation. L'importance de l'agencement spatial des modes d'exploitation suggère que la conciliation entre production et conservation pourrait fortement bénéficier de coordinations accrues entre exploitations agricoles.

The vast majority of terrestrial plant species live in symbiosis with arbuscular mycorrhizal fungi (AMF). AMF and plants live in complex networks, with roots of individual plants hosting multiple AMF, and single AMF colonizing multiple plants concurrently. Through the exchange of resources, the two partners of this symbiosis can have great effects on each other, effects which can ripple through both communities. What determines the patterns of associations between the partners is still largely unknown. In this dissertation, I examine a variety of factors, and in particular host identity, that could drive the community composition of AMF in roots. I began by surveying the diversity of AMF in roots of 12 plant species at a remnant bunchgrass prairie in Oregon, U.S.A. (Chapter 2). To do that, I first designed new primers for use in polymerase chain reaction (PCR) to specifically amplify DNA from all Glomeromycota species. Using those primers, I found 36 distinct AMF phylogenetic groups, or operational taxonomic units (OTUs) in the roots from the prairie. The proportion of OTUs in the basal order Archaeosporales was greater than in many other environmental surveys. I also conducted an in silico analysis to predict how effectively previously published primers would detect the whole diversity of OTUs I detected. I then assayed AMF community composition in the roots of 50 plants from nine plant species (Chapter 3). To do that, I designed primers specific to 18 of the OTUs detected in the initial field survey and used them to test for the presence of each OTU in the roots individual plants. I used that data to test if AMF community composition in individual roots correlated with host identity, spatial distribution, or soil characteristics. I found host identity was associated with both the richness and the structure of root AMF communities, while spatial distribution and soil characteristics were not. Finally, I performed an experimental test of the effect of host identity and community context on AMF community assembly (Chapter 4). I grew plants from four native perennial plant species, including two common and two federally endangered plants, either individually or in a community of four plants (with one plant of each species). I analyzed the AMF community composition in the roots of all plants after 12 weeks of growth with exposure to a uniform mix of field soil as inoculum. I found that host species identity affected root AMF richness and community composition, and community context affected AMF richness. Only one of the endangered species was highly colonized by AMF, and I did not detect unique AMF communities associated with it. This dissertation provides information on the diversity of AMF at a remnant bunchgrass prairie, an ecosystem which has been the subject of very few studies of AMF. Although a complex mix of factors interact to determine AMF community composition in roots, this work provides strong evidence that host identity plays a major role in that process. / Graduation date: 2013

The introduction of pen-reared Attwater's prairie-chickens (APC, Tympanuchus cupido attwateri) into the wild to supplement existing populations has met with marginal success. Flight characteristics, predator avoidance behavior, and rearing methods are possible factors contributing to post-release mortality of pen-reared birds. To evaluate flight characteristics and predator avoidance behavior of pen-reared APC's released onto the Attwater Prairie Chicken National Wildlife Refuge, flight characteristics and predator avoidance behavior of pen-reared APC's was compared to wild greater prairie-chickens (GPC, T. c. pinnatus) in Minnesota and Kansas using a radar gun and a trained dog. There was no difference (P = 0.134) in flight speed for pen-reared APC and wild GPC. However, wild GPC had greater (P < 0.001) flight distances than did pen-reared APC. Wild GPC and pen-reared APC that had survived in the wild for at least a year flushed at a greater (P < 0.001) distance from an approaching human than did pen-reared APC that had been released for less than 3 months. A trained dog was able to approach closer (P < 0.001) to APC than GPC before birds flushed, and APC did not fly as far as GPC after being flushed by the dog. Pen-reared APC displayed flight endurance deficiencies and were more approachable by humans and a dog before they flushed when compared to wild GPC, which could explain their increased mortality when released into the wild. To determine if APC chicks could be reared without daily human contact, pelleted food, and water in founts, a greenhouse was used to rear chicks in a semi-natural environment. Planted vegetation and commercial insects provided hiding cover and a food source for the APC chicks. An underground heat source provided chick warmth, and water misters and a sprinkler system simulated dew (a water source for chicks) and rain. The greenhouse provided chicks protection from predators and adverse weather conditions (before they could thermo-regulate) while exposing chicks to natural sunlight, day length, and temperature fluctuations. This technique allowed chicks to be reared in a semi-natural environment which reinforced their natural foraging behavior for food and water, and reinforced their hiding and avoidance behaviors, creating a wilder pen-reared bird.

De nos jours, la production agricole est soumise à certaines restrictions avec l'objectif de contrôler limpact environnemental et les volumes de production. Ces restrictions ont entrainé des modifications du niveau d'intensification de la production. En ce qui concerne lélevage des ruminants, le niveau d'intensification est défini par le chargement (animaux/ha) et la fertilisation minérale (kg/ha). La réforme de la Politique Agricole Commune (PAC) en 1992 a instauré des « méthodes de production agricole compatibles avec les exigences de la protection de l'environnement ainsi que l'entretien de l'espace naturel » (Règlement (CEE) N° 2078/92 du Conseil du 30 juin 1992, J.O.C.E. N°L 215 du 30/7/92 ; MRW, 1997). La réduction du niveau d'intensification de la production se trouvait parmi ces mesures. En élevage viandeux, elle était encouragée par l'octroi de primes aux éleveurs ne dépassant pas un seuil de chargement de 2 UGB/ha. Ces primes permettaient de compenser la perte de production due à la réduction du niveau dintensification. De plus, des primes à l'extensification pouvaient être obtenues pour les chargements inférieurs à 1,4 UGB/ha. Ces mesures, conjointement au système des quotas, ont permis de maîtriser aussi le volume de la production à grande échelle. Actuellement, suite au principe du découplage décidé lors de la réforme à mi parcours de lAgenda 2000 en juin 2003 et qui correspond aux dernières réformes de la PAC, loctroi de primes nest plus lié au volume des productions, mais bien à la surface. Chaque exploitant doit disposer de « droits » quil doit activer en justifiant les superficies correspondantes. Ces droits sont calculés sur base des superficies et des animaux qui ont donné lieu à un paiement daides directes au cours des années de références 2000, 2001 et 2002. Une fois les droits justifiés et un ensemble de conditions appelées « conditionnalité », liées à lenvironnement (Directive Nitrate), à la sécurité alimentaire et au bien-être des animaux, respectés, lexploitant pourra obtenir le «paiement unique». Les Etats Membres peuvent choisir de découpler certaines productions comme cest le cas pour les vaches allaitantes en Belgique. De plus, les règlements liés à la « Directive Nitrate » ont permis de mieux prendre en compte les effluents délevage et ont provoqué une diminution de la fertilisation azotée susceptible de diminuer la production, lazote étant le premier minéral limitant pour la croissance végétale. Cependant, dans les prairies pâturées, on constate souvent un bilan azoté positif. Lazote en excès est susceptible de sortir du système en étant lessivé sous forme de nitrate avec un risque de pollution environementale. La réduction de l'intensification de la production obtenue soit par une réduction de la fertilisation azotée soit par la réduction du chargement ou les deux facteurs conjugués, peut provoquer une diminution des déjections déposées sur les parcelles et une réduction du bilan azoté. On peut ainsi obtenir une réduction de la pollution des eaux (notamment par les nitrates) ainsi que les émissions des composants azotés volatils (ammoniac et oxyde nitreux). Les résultats dune série d'essais menés pendant six années consécutives sur des prairies pâturées par les principaux types de spéculation bovine, la vache allaitante, la vache laitière et le taurillon, sont présentés et discutés dans cette thèse. Le fil conducteur des essais a été un protocole semblable dans ces trois spéculations. Ce protocole visait à comparer d'une part, la réduction de 33% de la fertilisation azotée sans réduction du chargement et d'autre part, le rapport entre ces deux systèmes et un système sans apport d'azote minéral. Les paramètres étudiés ont été les performances zootechniques, phytotechniques, le bilan azoté et, pour les spéculations des vaches laitières et des taurillons, les reliquats azotés dans le sol. En plus, dans la spéculation "taurillon", les trois lots soumis au pâturage ont été comparés à un lot engraissé en stabulation.

The Prairie Pothole Region (PPR) of North American contains millions of wetlands in shallow depressions that provide important hydrological and ecological functions. To assess and model these functions it is important to have accurate methods to quantify wetland water volume storage. Hayashi and van der Kamp (2000) developed equations suitable for calculating water volume in natural, regularly shaped wetlands when two coefficients are known. This thesis tested the robustness of their full and simplified volume (V) area (A) depth (h) methods to accurately estimate volume for the range of wetland shapes occurring across the PPR. Further, a digital elevation model (DEM) derived from light detection and ranging (LiDAR) data was used to extract the necessary data for applying the simplified V-A-h method at a broad spatial scale. Detailed topographic data were collected for 27 wetlands in the Smith Creek Research Basin and St. Denis National Wildlife Area, Saskatchewan that ranged in surface area shape. The full V-A-h method was found to accurately estimate volume (errors <5%) across wetlands of various shapes and is therefore suitable for calculating water storage in the variety of wetland shapes found in the PPR. Analysis of the simplified V-A-h method showed that the depression (p) and size (s) coefficients are sensitive to the timing of area and depth measurements and the accuracy of area measurements. Surface area and depth should be measured concurrently at two points in time to achieve volume errors <10%. For most wetlands this means measuring area and depth in spring when water levels are approximately 70% of hmax, and also in late summer prior to water depths dropping below 0.1 m. The wetted perimeter of the deepest water level must also be measured accurately to have volume errors less than 10%. Applying the simplified V-A-h method to a LiDAR DEM required GIS analysis to extract elevation contours that represent potential water surfaces. From these data the total wetland depth and s coefficient were estimated. Volume estimates through this LiDAR V-A-h method outperformed estimates from two volume-area equations commonly used in the PPR. Furthermore, the process to extract the wetland coefficients from the LiDAR DEM was automated such that storage could be estimated for the entire St. Denis National Wildlife Area. Applying the simplified V-A-h method according to the guidelines and data sources recommended here will allow for more accurate, time-effective water storage estimates at multiple spatial scales, thereby facilitating evaluation and modelling of hydrological and ecological functions.

The intensification of land-water management due to agriculture, forestry, and urbanization is a global phenomenon increasing the pressure on worlds water resources and threatening water security in North America. The Prairie Pothole Region of North America covers approximately 775,000 km2 and contains millions of wetlands that serve important hydrological and ecological functions. The unique hummocky topography and the variable effect of different processes contribute to high spatio-temporal variability in soil water, posing major challenges in hydrological studies. The objectives of this study were to a) examine the spatial pattern of soil water storage and its scale and location characteristics; and b) to identify its controls at multiple scales. Soil water content at 20 cm intervals down to 140 cm was measured along a transect extending over several knolldepression cycles in a hummocky landscape. High water storage in depressions and low water storage on the knolls created a spatial pattern that was inversely related to elevation. Spatial patterns were strongly similar within any given season (intra-season rank correlation coefficient as high as 0.99), moreso than between the same season over different years (inter-annual rank correlation coefficient as high as 0.97). Less similar spatial patterns were observed between different seasons (inter-season rank correlation coefficients as high as 0.90). While the intra-season and inter-annual spatial patterns were similar at scales >18 m, the inter-season spatial patterns were similar at much large scales (>72 m). This may be due to the variations in landform elements and micro-topography. The similarity at scales >72 m were present at any time and depth. However, small- and medium-scale spatial patterns changed with depth and with season due to a change in the hydrological processes. The relative dominance of a given set of processes operating both within a season and for the same season over different years yielded strong intra-season and inter-annual similarity at scales >18 m. Moreover, similarity was stronger with increasing depth, and was thought to be due to the dampening effect of overlying soil layers that are more dynamic. Similarity of spatial patterns over time helps to identify the location that best represents the field averaged soil water and improves sampling efficiency. Change in the similarity of scales of spatial pattern helps identify the change in sampling domain as controlled by hydrological processes. The scale information can be used to improve prediction for use in environmental management and modeling of different surface and subsurface hydrological processes. The similarity of spatial pattern between the surface and subsurface layers help make inferences on deep layer hydrological processes as well as groundwater dynamics from surface water measurements.

An acoustic frequency-swept wave was investigated as a means for determining Snow Water Equivalent (SWE) in cold wind-swept prairie and sub-alpine environments. Building on previous research conducted by investigators who have examined the propagation of sound in snow, digital signal processing was used to determine acoustic pressure wave reflection coefficients at the interfaces between 'layers' indicative of changes in acoustic impedance. Using an iterative approach involving boundary conditions at the interfaces, the depth-integrated SWE was determined using the Berryman equation from porous media physics. Apparatuses used to send and receive sound waves were designed and deployed during the winter season at field sites situated near the city of Saskatoon, Saskatchewan, and in Yoho National Park, British Columbia. Data collected by gravimetric sampling was used as comparison for the SWE values determined by acoustic sounding. The results are encouraging and suggest that this procedure is similar in accuracy to SWE data collected using gravimetric sampling. Further research is required to determine the applicability of this technique for snow situated at other geographic locations.

Depressions in the prairie pothole region (PPR) are commonly referred to as sloughs and were formed during the most recent glacial retreat, ~10-17 kyrs ago. They are hydrologically isolated, as they are not permanently connected by surface inflow or outflow channels. Extreme thunderstorms are common across the prairies and the hydrologic response of isolated wetlands to intense rainfall events is poorly understood. The purpose of this study was to compare the response of different landscape/ecological elements of a prairie wetland to snowmelt and extreme rainstorms. Comparisons were completed by investigating the spring snowmelts of 2005 and 2006 and the rainstorm event of June 17 - 18, 2005, in which 103 mm fell at the St. Denis National Wildlife Area (NWA) Saskatchewan, Canada (106°06'W, 52°02'N). The wetland was separated into five landscape positions, the pond center (PC), grassed edge (GE), tree ring (TR), convex upland (CXU), and concave upland (CVU). Comparison of the rainfall of June 17 18, 2005 with the spring snowmelts of 2005 and 2006 indicates that the hydrologic consequences of these different events are similar. Overland flow, substantial ponding in lowlands, and recharge of the groundwater occur in both cases. Analysis of this intense rainfall has provided evidence that common, intense rainstorms are hydrologically equivalent to the annual spring snowmelt, the major source of water for closed catchments in the PPR.

Hydrological models have been developed to estimate snow accumulation, snowmelt and snowmelt runoff on the Canadian Prairies; however, their proper scale of application is unknown in the Prairie environment. The first objective of this thesis is to examine the proper scale for pre-melt snow accumulation as snow water equivalent (SWE) and snowmelt in a Prairie first order basin. Spatially distributed and spatially aggregated approaches were used to calculate SWE and snowmelt at St. Denis National Wildlife Area (SDNWA). Both approaches used models with similar physics, but differed in the model scale at which calculations were carried out. The simulated pre-melt SWE, cumulative seasonal SWE, and daily snowmelt from the two modelling approaches were compared to field observations of pre-melt SWE, cumulative seasonal SWE, and daily snowmelt; comparisons of areal cumulative seasonal SWE, areal snowmelt, snowmelt duration, and snow-covered area were also conducted between two modelling approaches. Results from these comparisons showed that both approaches had reasonable and similar accuracy in estimation of SWE and snowmelt. The spatially aggregated approach was more computationally efficient and was selected as a modelling scale for small-sized prairie basins. <p>Another objective of this thesis is to derive a snow hydrology model for the Canadian Prairies. Physically-based hydrological models were assembled in the Cold Regions Hydrological Model Platform (CRHM) using the aggregated approach. Tests of pre-melt SWE and surface snowmelt runoff were conducted at two basins in Saskatchewan Creighton Tributary of Bad Lake and Wetland 109, St. Denis. Results showed that the snow hydrology model had a reasonable capability to simulate SWE and snowmelt runoff to the stream and wetland. <p>Droughts are natural hazards that develop frequently on the Canadian Prairies. Analyzing the impact of drought on hydrological processes and water supply is another objective of this thesis. Synthetic drought scenarios were proposed for the Creighton Tributary of Bad Lake and the corresponding impacts on the snowmelt runoff-related processes were examined. Results indicated that wind redistribution of snow was very sensitive to drought conditions, sublimation of blowing snow and snow-covered period were sensitive to drought, but winter evaporation and infiltration did not show strong trend. The results also showed that drought conditions had magnified effects on the snowmelt runoff and could cause cessation of streamflow. Also, the impacts of the recent 1999-2005 drought on the snowmelt hydrology were investigated at St. Denis. Results illustrated that three-years (1999-2002) of severe winter drought were followed by a normal year (2002-03) and then a two-year (2003-05) recovery period, and then returning to normal (2005-06). Results showed that both snowfall and rainfall during hydrological winter were consistently low for severe drought and surface snowmelt runoff was very much lower during severe drought, about 45-65 mm less compared to that in the normal periods.