Texte remanié de: Diss.--Geschichtswissenschaft--Mainz--Johannes Gutenberg-Universität, 1978. / Notes bibliogr. Bibliogr. p. 507-539. Index.

Th. doct.--Géol.--Caen, 1996. / Bibliogr. p. 186-196. Résumé en français et en anglais.

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This study compared the effect of two contrasting nutrient environments on the growth rates of 12 Carex species from the Mont St. Hilaire Biosphere Reserve, Quebec. All species demonstrated higher growth rates under conditions of high nutrient availability. There was no correlation found between maximum relative growth rate (RGRmax), leaf production, and biomass. High nutrient availability produced a reduction in root/shoot ratio, while leaf production was the trait that showed the greatest response to contrasts in nutrient availability The Carex species were found to be relatively slow growing plants, with growth potential ranging from stress tolerant to competitive. The species from lowlands are more competitive and have higher growth rates; the upland species are more stress tolerant and have lower growth rates. The abundance of a species at Mont St. Hilaire was found to be unrelated to its growth potential.

Species with different requirements can coexist if the environment varies in space; we therefore expect a positive relationship between species diversity and environmental heterogeneity. In this thesis I examine the influence of environmental structure on patterns of fern diversity in one hectare of old-growth forest and compare these patterns to other surveys covering a broad range of scales. The nineteen species recorded in the hectare had non-random spatial distributions and differed in their soil preferences. Diversity was positively related to soil moisture and negatively related to soil fertility, but there was no relationship with environmental variance. The counteracting influence of dispersal may predominate over selection processes at the hectare scale. Both species-area curves and the decreasing correlation of species composition with distance had very similar slopes over quadrat sizes ranging from 1 x 1 m to 50 x 50 km, suggesting that some diversity patterns may be independent of scale.

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Runoff generation refers to the physical processes by which water travels through the landscape, moving through the subsurface or over the ground surface, ultimately arriving at the stream channel. These physical processes vary in both space and time leading to difficulties in mechanistic modelling of storm response, contaminant transport and nutrient fluxes. Runoff generation has been extensively studied at the hillslope scale and in headwater catchments. However, only recently have empirical studies begun to collect similarly detailed datasets across multiple catchments with which to examine how these processes change with scale. This study examines runoff generation from a series of eight small nested forest catchments and focuses specifically on the controlling influences of antecedent moisture conditions and catchment topography. / End-member-mixing-analysis using stream water hydrochemistry from the eight catchments shows changing seasonal and storm-based source water contributions to the stream channel. Analysis identifies hydrochemical solutes with behaviour consistent with the assumptions of the mixing-model approach for all eight catchments. Results indicate that testing of solute selection is critical in the application of this method to multiple catchments. / Runoff generation observed for five storm events shows a strong nonlinear relationship between runoff and antecedent moisture conditions, supporting the hypothesis of varying 'states of wetness'. Detailed hillslope-scale investigation during the different 'states of wetness' indicates that while groundwater and soil moisture profiles show changing active-flow connectivity on a seasonal and storm-base dtime scale, there no significant change in spatial patterns of shallow soil moisture. These results suggest that a priori spatial patterns in shallow soil moisture in forested terrains may not be a good predictor of critical hydrologic connectivity that leads to the threshold change in runoff generation, as has been found in rangeland catchments. / Differences in storm response from the eight catchments are in part attributable to variation in topography and landscape organization. The multiple catchments have similar distributions of topographic index and yet differences in mean values of topographic index lead to significantly different estimates of mean residence time. Scaling of storm response is dominated by the behaviour of the three largest catchments. These three catchments distinguish themselves with larger MRT and larger valley bottom areas. It is these three catchments that, under dry antecedent moisture conditions, show significantly larger amounts of new water delivery to the stream channel, suggesting a significant change in dominant runoff mechanisms related to topography and landscape organization.

The diversity of Brachycera (Diptera) was studied in an old growth beech-sugar maple forest at Mont St. Hilaire, Quebec. Sampling was carried out weekly from early May to late September 2001 using a malaise trap, pan traps, a newly designed trunk trap and sweep netting. Almost 10,000 specimens from 45 families and over 334 species were collected. The most diverse families were Empididae (43 species), Tachinidae (39 species), Syrphidae (35 species) and Dolichopodidae (24 species). Collecting techniques were compared, with particular reference to the trunk trap designed for this study. NMDS ordination showed that a different Diptera assemblage was collected by each method. The greatest number of species was collected using the malaise trap; however, 21 species were collected only in trunk traps. Some of the most abundant species from trunk traps were collected rarely, or not at all, using other methods. These are species which are often considered rare in forests because they are infrequently collected using traditional techniques.