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Early Palaeocene floras from twenty seven sites within the Raton, southern Powder River and south-western Williston Basins of the western interior of North America were collected, and their leaf physiognomy, ecological character and depositional setting compared. Such a spread of samples enabled the study of spatial and temporal vegetational and climatic variations in the region, following the Cretaceous-Tertiary boundary event. Climatic changes are observed across the Cretaceous-Tertiary boundary. Precipitation increased dramatically, and remained relatively high throughout the earliest Palaeocene. Temperatures were somewhat lower, compared to those of the Late Cretaceous, and seasonality in climate increased. Climatic and vegetation zones shifted southwards as latitudinal climatic equability decreased. Palaeotemperature and palaeoprecipitation were determined using CLAMP and leaf margin analysis. Experiments carried out to assess the robustness of CLAMP to loss of foliar physiognomic data revealed that this data loss did not drastically effect palaeoclimatic determinations but that information about leaf size and margin type had the most effect on results. Vegetation was of low diversity directly after the boundary event, but recovered to stable, but still relatively low levels, within a short time. Changes in diversity are difficult to interpret due to masking by taphonomic biases, which are important within the depositional environments analysed in this study. Climatic deterioration and the prevalence of disturbed environments ultimately facilitated expansion of the angiosperms, although their aspect was changed with a general increase in deciduous forms, in relation to increased seasonality and decreased equability. These trends cannot be related merely to the impact of a bolide at the Cretaceous-Tertiary boundary, but reflect the more global and wide-ranging changes of the period, which were punctuated by this brief, deleterious event. Previous work has tended to concentrate on the North American continent but a more global perspective reveals that the Cretaceous-Tertiary boundary event was not a world-wide catastrophe within terrestrial environments.

In arctic tundra ecosystems mosses dominant the vegetation in terms of productivity and diversity.  Despite this, mosses are often overlooked in studies of tundra ecology.  However, evidence from this thesis suggests that mosses maybe integral to the functioning of these systems.  Mosses insulate soil keeping it cooler than air temperature, an effect more apparent under deeper moss.  The effects of the moss layer on soil characteristics alter conditions for microbial populations resulting in higher nitrogen availability in soil under shallow moss.  This thesis shows that the role of mosses in determining vascular plant success may dictate many higher plant interactions.  There are both positive and negative effects of the moss layer on vascular plant growth.  The relationship between positive and negative impacts of the moss layer on vascular plants is species specific, meaning that moss cover may be a key determinate of vascular plant community structure.  Climatic warming and herbivory are important drivers of vegetation change in the Arctic.  This thesis shows that grazing by reindeer and grubbing by geese is detrimental to moss cover.  As mosses insulate the soil, a reduction in depth or integrity increases soil temperatures and enhances microbial activity and thus nitrogen availability.  This in conjunction with addition of nutrients from faeces enhances vascular plant productivity to the further detriment of mosses.  Warming increases soil temperature and accelerates decomposition, but has little affect on either biomass of moss or vascular plants.  Moss grubbing has a greater negative effect on mosses in a warmed environment.  This thesis concludes that mosses are integral to the current functioning of tundra heaths.

Thesis (Ph. D. - Geosciences)--University of Arizona, 1983. / Includes bibliographical references (leaves 150-166).

Thesis (M. Sc.)--University of New South Wales, 2001. / Also available online.

Thesis (M. Sc.)--Carleton University, 2003. / Includes bibliographical references (p. 141-146). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographic references (leaves [111]-127).

Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 48-51.

Thesis (M. SC.)--Carleton University, 2007. / Includes bibliographical references (p. 147-157). Also available in electronic format on the Internet.