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.

Ecological and ecophysiological investigations carried out at the ultramafic outcrop near Meikle Kilrannoch, Angus, Scotland are reported. The outcrop is botanically famous for its rare plant species, particularly the endemic Cerastium fontanum ssp. scoticum and the nationally rare Lychnis alnina. The studies were made on the main outcrop (called MK1) which is dome shaped, and on a much smaller low-lying area (called MK1.5) about 300 m from it. The overall aim of the studies was to investigate the relationship between the soil physico-chemical environment and species distribution on the open areas of the ultramafic site and to experimentally test for causality; and to offer an explanation for the open character of the vegetation on the skeletal soils. Variograms which were constructed for soil properties and vegetation data to investigate soil micro-spatial variation and vegetation pattern showed differing levels of spatial dependence, always indicating high intrinsic variability. The cause of this high variability was probably cryoturbation for the soil and morphological characters for plants. The gradient analyses (Principal Components Analysis and its canonical form, Redundancy Analysis) used to study soil - vegetation correlations suggested that A ostis vinealis, Cerastium fontanum ssp. scoticum and Lychnis alpina were most abundant in areas up-slope with lower concentrations of soil magnesium; Cochlearia pyrenaica ssp. alpina and Festuca rubra were associated with bigger stone sizes, and the latter occurred in wetter areas with higher of ions. A comparative solution culture experiment based on the local soil chemistry was used to study the growth responses to magnesium and nickel of Cerastium fontanum ss. scoticum, Cochlearia pyrenaica ssp. al ina and Festuca rubra. The results for Festuca and Cerastium were in agreement with the findings of the gradient analysis: Festuca was indifferent to both magnesium and nickel and Cerastium was susceptible to high magnesium; the reduction of dry weight by nickel in the Cochlearia conflicted with its suggested association with high soil nickel in the gradient analysis. The impacts on the photosynthetic systems of three Cochlearia species of different concentrations of iron and nickel were identifiable only in the non-ultramafic C. pyrenaica where the addition of nickel decreased photosynthesis but the effect could be ameliorated by the addition of high concentrations of iron. The open character of the skeletal soil at the MK1 site was discussed in terms of 'carrying capacity'. Vegetation development was suggested to be controlled at least partly by large stones covering the soil surface. Further factors such as space fragmentation, possible plant-to-plant interactions, and low density of flowering individuals and restricted seed dispersal were also considered. To test if major nutrients were limiting plant growth, major nutrients (NPK) were applied to the MK1.5 skeletal soil. The significantly higher X's and recruitment and change in life history traits (larger rosette sizes, earlier maturing and higher seed production) in the fertilised populations of C. pyrenaica ssp. alpina resulted in a significantly higher plant cover in the fertilised quadrats. The better growth of plants in the fertilised quadrats was reflected in their lower total non-structural carbohydrate (TNC) concentrations in May and their higher TNC in August. The present series of investigations found that magnesium and nickel toxicity had an effect on the intra-site distribution of the ultramafic species and also confirmed earlier reports on the importance of magnesium and nickel toxicity in ultsamafic exclusion. Large stones and low soil phosphorus concentration are proposed as limiting factors for the development of closed vegetation on the skeletal soil areas of the sites.

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This study has investigated how urban vegetation can be used in a multifunctional way to support ecosystem services in urban environments. Nacka municipality is in the start-up phase of building what is to become Nacka city. This provides a unique possibility to study and analyse what role the vegetation play in making the city a healthy living environment and how it needs to be adapted in order to be resilient against changing climate conditions and how the effects of those changes can be regulated. The study further investigates how airborne pollution, caused by urbanization processes, can be regulated or reduced by vegetation or species selection. Methods used in this study were a combination of qualitative interviews and literature studies, seeking to answer the questions: Which specific ecosystem functions are needed in the urban environment and which aspects will influence the ecosystems ability to deliver the functions in demand? And which plant species have the right mechanisms needed to deliver those functions? These questions have been studied and analysed in a local based context where the local conditions ands site specific needs of Nacka define criteria for plant selection. Based on those criteria, a plant list is presented that seeks to find synergies and effectiveness in plant selection with the aim to find plants that support and/or produce multiple ecosystem functions.

and-atmosphere interactions are an important component of climate, especially in semi-arid regions such as the Southern Great Plains. Interactions between soil moisture and vegetation modulate land-atmosphere coupling and thus represent a crucial, but not well understood climate factor. This study examines soil moisture-vegetation health interactions using both in situ observations and land surface model simulations. For the observational study, soil moisture is taken from 20 in situ Oklahoma Mesonet soil moisture observation sites, and vegetation health is represented by MODIS-derived normalized difference vegetation index (NDVI). For the modeling study, the variable infiltration capacity (VIC) hydrologic model is employed with two different vegetation parameterizations. The first is the model default vegetation parameter which is interannually-invariant leaf area index (LAI). This parameter is referred to as the control parameter. The second is MODIS-derived LAI, which captures interannual differences in vegetation health. Soil moisture simulations from both vegetation parameterizations are compared and the VIC-simulated soil moisture’s sensitivity to the vegetation parameters is also examined. Correlation results from the observation study suggest that soil moisture-vegetation interactions in Oklahoma are inconsistent, varying both in space and time. The modeling results show that using a vegetation parameterization that does not capture interannual vegetation health variability could potentially result in dry or wet biased soil moisture simulations.

Climate change will affect Arctic plant communities directly, by altering growth and recruitment, and indirectly, by increasing the frequency of natural disturbance. Since the structure of northern vegetation influences global climate, understanding both temperature and disturbance effects on vegetation is critical. Here, I investigate the influence of temperature and disturbance on Low Arctic vegetation at several spatio-temporal scales in the Mackenzie Delta Region, N.W.T. To disentangle the relative impact of temperature and disturbance on forest-tundra and tundra ecosystems, I sampled microenvironmental variability, plant community composition, and green alder abundance, growth, and reproduction on disturbed (burns and thaw slumps) and undisturbed sites across a regional temperature gradient. Disturbed areas showed increases in alder productivity, catkin production, and seed viability, as well as differences in plant community composition and microenvironment. The magnitude of plot-level responses to disturbance compared to variation across the temperature gradient suggests that in the short-term, increasing the frequency of disturbance may exert a stronger influence on tundra ecosystems than changes in temperature. At the plot level, increases in alder seed viability and recruitment at warmer sites point to the fine-scale mechanisms by which shrub abundance will change. To examine the relative influence of temperature and biophysical variables on landscape-level patterns of shrub dominance, I mapped Low Arctic vegetation using aerial photos. At this broader scale, correlations between temperature and the areal extent of shrub tundra suggest that warming will increase the dominance of shrub tundra. To assess the magnitude of changes in temperature and thaw slump activity, I analyzed climate records and mapped retrogressive thaw slumps using aerial photographs. An increase in thaw slump activity in recent decades, coincident with higher temperatures, suggests that continued warming will change the area affected by thermokarst disturbances like slumps. Taken together, my research indicates that the effects climate change will be magnified by shifts in the frequency of disturbance, initiating changes to Arctic vegetation with significant implications for global climate. My work also shows that to fully understand the influence of patch-landscape feedbacks on Arctic vegetation dynamics, the effects of disturbance must be examined across longer temporal and broader spatial scales.

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Thesis (M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ. 76-90)