Thèse de doctorat : Sciences agronomiques : Vandoeuvre-les-Nancy, INPL : 2005. / Titre provenant de l'écran-titre. Bibliogr.

Reproduction de : Thèse de doctorat : Fonctionnement des écosystèmes et agrosystèmes : Toulouse, INPT : 2007. Reproduction de : Thèse de doctorat : Fonctionnement des écosystèmes et agrosystèmes : Université de sciences agricoles et medecine vétérinaire de Banat Timisoara : 2007. / Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Bibliogr. 255 réf.

Thesis (Ph. D.)--University of Kentucky, 2005. / Includes bibliographical references (p. 203-220). Also available in PDF format via the Internet.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 18, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Mark R. Ryan and Mike Hubbard. Includes bibliographical references.

The objectives of the study were to provide a documented record of the vegetation of the grassland vegetation of the Red River Valley. The native prairies of this Valley are dominated by various combinations of Andropogon gerardi, Andropogon scoparius, Agropyron smithii, Bouteloua curtipendula, Calamagrostis inexpansa, Calamovilfa longifolia, Koeleria cristata, Muhlenbergia richardsonis, Sorghastrum nutans, Spartina pectinata, Sporobolus heterolepis, Stipa comata, Stipa spartea and Stipa viridula. At present only relicts of these grasslands remain. One hundred and fifty-one stands including 299 species, encompassing a wide range of floristic and habitat variability, were selected for study. The species composition frequency) of each stand was sampled by the use of thirty 0.5 X 0.5 m quadrats. A presence list was prepared for each stand and the dominant graminoid species determined by an estimate of cover contribution to the upper strata. The standing crop of green herbage of .34 stands was sampled by clipping five 0.5 X 0.5 m quadrats, and the material oven dried for weight determination. Environmental measurements were taken to determine physiographic position and soil profile characteristics. Soil samples were collected from the "A" horizon of each stand for textural analysis, field capacity, salinity and pH determinations. An analysis based on indicator species determined by physiographic association, indicated that the various species responded in a continuous manner to a moisture gradient. This was suggested by a gradation of importance from one physiographic habitat to another, with its position of peak performance in association with a specific drainage position. Vegetational types were also associated with physiographic position, but the dominant species and to a lesser degree secondary species showed modification of behavior by soil texture. The total number of species and their levels of importance (frequency) within the various vegetational types was used as a measure of diversity. The mid prairie dominance types with high numbers of species, many with high importance, were the most diverse of all types examined. It was further indicated that mid prairie stands in the northern portion of the area studied had higher diversity than all others. Geographic differences in diversity were related to historical development of the grasslands. The yield of green herbage varied according to prairie division, leading dominant, soil texture and geographic location. A high positive correlation between green herbage yield and length of growing season suggested that geographic location was the most effective determinant in production, with southern stands producing about 100% more green herbage than comparable stands in the north. The species comprising the grasslands of the Red River Valley suggest an amalgamation of species of eastern and western origin. The dominant graminoids, however, are most closely associated with the grasslands to the east and suggest the placement of the Red River Valley grasslands within the True Prairie.

This thesis describes aspects of the ecology of West Nile virus (WNV) including factors contributing to the distribution of WNV, possible future distribution, and effects of WNV on host abundance in the Canadian prairies provinces: Alberta, Saskatchewan, and Manitoba. Using mosquito surveillance data collected between 2005 and 2008, models integrating abiotic and biotic factors were constructed to predict the weekly and monthly scales of WNV infection rate in Culex tarsalis, which is the primary vector of WNV in the Canadian prairies. At the weekly scale, the WNV infection rate in Cx. tarsalis increased with increasing Cx. tarsalis abundance and mean temperature lagged from 1 to 8 weeks, but decreased with an increasing mean precipitation lagged from 2 to 6 weeks. Furthermore, precipitation was a ‘distorter variable’ which altered the association between Cx. tarsalis abundance and the WNV infection rate. Study at the monthly scale showed that higher mean temperature and time lagged mean temperature elevated were associated with increased numbers of Cx. tarsalis and higher WNV infection rates. However, increasing precipitation was associated with higher abundance of Cx. tarsalis and lower WNV infection rate. In addition, this study found that increased temperature fluctuation and wetland land cover were associated with decreased WNV infection rate in Cx. tarsalis. Climate change could drive dramatic alterations in the spatial and temporal distribution and overall incidence of vector-borne diseases. The constructed models and biological thresholds were used to predict the distribution of Cx. tarsalis and WNV infection rate in the prairie provinces under a range of potential future climate and habitat conditions. In the current endemic regions, the projected WNV infection rate under the median outcome scenario in 2050 was 18 times higher than under current climate conditions. Seasonal occurence of Cx. tarsalis infected with WNV extended from June to August to include May and September. Moreover, models predicted northward range expansion for Cx. tarsalis and WNV. The declines of susceptible bird abundance caused by WNV may further influence the bird community composition and, in turn, affect the incidence of WNV through a dilution effect. The North American Breeding Bird Survey data was used to evaluate the effect of WNV on the abundance of selected birds in the Canadian prairies, as well as the effects of bird community composition on the WNV risk. There was no significant decline in bird abundances of selected birds following the emergence of WNV. These findings suggest that the effect of WNV on selected bird abundance and bird community composition is insignificant. In addition, there is no evidence to support the association between bird community composition and WNV infection rate in Cx.tarsalis in the Canadian prairies. Lastly, findings in this thesis and current knowledge were integrated to create a decision making flowchart for the prevention of WNV infection in the prairie provinces.

No description available.

To assess the accuracy of the second-generation Prairie Agrometeorological Model (PAM2nd) as an agrometeorological model for spring wheat on the Canadian Prairies, a study was conducted to validate the model using field measurements. Results from model validation indicated soil moisture was being overestimated at most sites during the second half of the growing season, while soil moisture was underestimated during periods that experienced consecutive days of rainfall. Modifications to the model were implemented to improve the model's ability to simulate soil moisture. Evapotranspiration estimates from PAM2nd and the FAO56 Penmen-Monteith method were compared to water balance methods. Both models produced estimates that fell within the range of water balance ET measurement error. The similarity in performance of both models to estimate ET compared to the water balance ET means the adoption of either model could be justified. However, PAM2nd would be more appropriate because it requires fewer, more commonly measured, surface weather parameters.

Prairie restorations in east-central Indiana are commonly accomplished through purposeful planting of prairie vegetation, with the belief that prairie fauna will populate the planting independently at a later time. The objective of this study was to determine whether one assemblage, the ground dwelling beetles, would in fact re-populate tallgrass prairie restorations in a region where tallgrass prairie remnants are rare and highly fragmented. Two prairie remnants and five prairie plantings were sampled using pitfall traps from 21 May to 4 October 2003. Nine hundred forty-three beetles were collected, identified to family, and separated into morphospecies. Shannon diversity was greatest in the CR 575 E Cemetery prairie remnant, and increased linearly with increasing age in the created prairies, with the exception of the 1-year old prairie. TWINSPAN analysis grouped the two remnant prairies together in the first division, indicating that beetle assemblages of remnant prairies are more similar to each other than to created prairies. / Department of Biology

A major challenge facing agriculture is to improve water use and minimize environmental impact while increasing productivity levels. This study, carried out in Winkler, Manitoba, tested four water management treatments: no drainage and no irrigation (NDNI as control), no drainage with overhead irrigation (NDIR), free drainage with overhead irrigation (FDIR), and controlled drainage with subirrigation (CDSI). Each treatment was replicated in three plots during two growing seasons in 2010 and 2011. The monitored variables included soil moisture content, water table depth variation, drainage outflow volume and quality, weather parameters, and agronomic indices. In 2010, yields were 8.48 (NDNI), 10.36 (NDIR), 10.10 (FDIR), and 9.22(CDSI) Mg ha-1 with only the mean yield difference for the NDIR and the CDSI treatments being statistically significant (p = 0.014). In 2011, yields were 9.25 (NDNI), 10.47 (NDIR), 11.28 (FDIR), and 9.49 (CDSI) Mg ha-1 with no statistically significant differences in yield. In 2010, the exports of NO3-N (138 kg ha-1), PO4-P (0.6 kg ha-1) and salts (2.34 Mg ha-1) from the FDIR treatment were significantly larger (p <0.05) than exports from CDSI, which were 0.07 kg ha-1, 0.08 kg ha-1, and 0.41 Mg ha-1, respectively. In 2011, the exports of NO3-N (36 kg ha-1), PO4-P (0.27 kg ha-1), and salts (1.1 Mg ha-1) from FDIR were significantly larger (p < 0.05) than the exports from CDSI which were 10 kg ha-1, 0.08 kg ha-1, and 0.39 Mg ha-1, respectively. These results indicate that irrigation was the main factor driving corn yields under the conditions prevailing in the Canadian Prairies, while subsurface drainage had a beneficial impact when the beginning of the season was wet. Also, this study showed the advantage of controlled drainage over free drainage in reducing the nutrients and salt exports.