Thèse (M.Ress.Renouv.) -- Université du Québec à Chicoutimi, 2003. / Bibliogr.: f. 36-38. Document électronique également accessible en format PDF. CaQCU

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The landscape of the boreal forest in north-central Canada is characterised by mosaics of broad-leaved deciduous trees (aspen, Populus; birch, Betula), evergreen conifers (black spruce, Picea mariana; jack pine, Pinus banksiana; and larch, Larix), fens and lakes. The forest has been cited as the possible location of a global carbon sink, and its likely response in the event of global climate change remains unclear. To improve our current understanding of the links between the boreal forest ecosystem and the lower atmosphere, the Boreal Ecosystem-Atmosphere Study (BOREAS) was executed in a series of field experiments in 1994 and 1996. This thesis documents the efforts made to characterise and map temporal and spatial distributions of the fluxes of heat, water vapour and CO2 over two 16 km x 16 km heterogeneous sites at the BOREAS study sites. / Most of the data in this thesis were obtained from the airborne observations by the Canadian Twin Otter Aircraft, operated by the Institute for Aerospace Research of the Canadian National Research Council, at the BOREAS Northern Study Area (NSA), and Southern Study Area (SSA). The research aircraft was flown at a fixed altitude of about 30 m agl. The data acquired in 1994 were primarily used to develop an objective deterending scheme in eddy-correlation flux estimates, that took into consideration the physical nature of turbulent transport during convective daytime conditions, and to map the spatial distribution of sensible heat, latent heat and CO2 fluxes over three intensive field campaigns. Maps of spatial patterns of the surface characteristics, such as the surface temperature excess over air temperature (Ts-T a) and Greenness index (GI), were also constructed. The mapping procedure involved generation of an array of grid points by block averaging the parameter of interests along the flight lines, spaced 2 km apart, over 2 km windows, with 1 km overlap between adjacent windows. The (Ts-Ta) maps showed, not surprisingly, that surface temperatures were relatively cooler over the mature forests than over the disturbed, regenerating and burn areas. However, they also showed a decoupling between sensible heat flux and T s-Ta not seen in less complex terrain. By contrast, close correspondence was observed between maps of CO2 flux and greenness, suggesting that the potential to infer CO2 exchange from remote sensing observations of the surface is higher than that for energy exchange. (Abstract shortened by UMI.)

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The effect of species, parent material, and stand age on nitrogen mineralization were examined during aerobic lab and field incubations. The experimental design consisted of 3 tree species (birch (Betula papyrifera Marsh.); poplar (Populus tremuloides Michx.); and conifers (Abies balsamea (L.) Mill. and Picea glauca (Moench) Voss.)); two parent materials (lacustrine clay and glacial till); and three stand ages (50, 75, and 124 years of age). The strongest determinant of nitrogen mineralization potential was species. The effects of parent material and stand age were variable. Total nitrogen, pH, and soil moisture also affected N mineralization. Nitrogen mineralization dynamics may be largely affected by annual changes in quality of organic matter or climate. Available nitrogen inherent in forest stands must be taken into consideration when replacing hardwood stands with softwoods, because eliminating stages of boreal mixedwood succession could have detrimental effects on available nitrogen and forest productivity in the long-term.

A comparison of the soil fertility and relationships between soil fertility and early regenerating vegetation were examined following clearcut harvesting and wildfire in the black spruce-feathermoss zone of west-central Quebec. During the summer of 1997, sampling was conducted in wildfires burnt 2, 14, and 21 years ago, stands clearcut within +/-3 years of each fire, and undisturbed control stands. At each site an estimation of vegetative cover of each species present and a volumetric sample of the forest floor (FH), and mineral soil (0--10 cm) were collected from at least 8 fire and cut sites and at least 4 control sites in each study area. The comparison between the soil fertility of stands clearcut and burnt suggested that important differences exist following these two disturbance types in the boreal forest. The forest floor of clearcut sites had greater dry mass, mass of total nutrients and mineralized N than fire or control sites, whereas fire sites generally had higher pH and concentrations of total nutrients than clearcut or control sites. Partitioning of the variance of the vegetation data between soil fertility and general site characteristic variables was carried out to evaluate the direct influence of post-disturbance soil fertility on the composition of regenerating vegetation. All explanatory variables accounted for 53.6% of the variance, of which 23.2% was exclusively attributed to soil fertility variables. Disturbance severity is suggested as an important factor, directly affecting the initial composition of the regenerating vegetation, and indirectly affecting soil fertility and stand productivity in the later stages of regeneration.

Medicinal plants, as part of traditional ingestion practices, may contain antioxidants to combat the oxidative stress which is implicated in prediabetes as well as many of the complications of diabetes, As Indigenous Peoples move further from their traditional lifestyles, and therefore their use of medicinal plants, incidence of diabetes has increased dramatically, Those medicinal plants of the boreal forest that have been used for 3 or more symptoms of diabetes or its complications were selected for analysis. Three different assays (DPPH, NBT/xanthine oxidase and DCF/APPH) determined the antioxidant activity of 35 medicinal plant species. The majority of the species (89%) had free radical scavenging activity significantly greater than the market produce tested (Tukey, P < 0.05), 63% had superoxide scavenging activities similar to vitamin C, and eight species had free radical scavenging activity similar to green tea. Considering that many of these species are also used for food or beverage they represent an antioxidant benefit to the traditional lifestyle. Among the parts used medicinally, roots and barks were used the most frequently with activity in the order of fruit > bark > leaves > roots. The perennials selected had activity in rank trees > shrubs > herbs and the activity associated with habitat found rocky areas > woodland > wet/boggy habitats. Species used for symptoms such as diarrhea, rheumatism, tonic and heart/chest pain were typically high in antioxidant activity. Using cluster analysis it was determined that species used for diarrhea and heart disease as well as those used for a combination of tonic, sores, urinary, blood, pregnancy and boils could also be species with high antioxidant activity. The greater the number of symptoms a species was used for, the greater the activity. Three species with high antioxidant activities, Rhus hirta, Cornus stolonifera and Solidago canadensis, inhibited TNF production in human macrophage cells suggesting a po

Mémoire (M.Ress.Renouv.)-- Université du Québec à Chicoutimi, 1991. / Bibliogr.: f. 63-67. Document électronique également accessible en format PDF. CaQCU

Mémoire (M.Ress.Renouv.)--Université du Québec à Chicoutimi, 1996. / Document électronique également accessible en format PDF. CaQCU