A thesis submitted to the Faculty of Science in fulfilment of the requirements for the degree of Doctor of Philosophy. 30 August 2016 in Johannesburg, South Africa. / The presence of Portulacaria afra affects the flow of ecosystem services from the thicket landscapes of the Eastern Cape. Degraded and intact thicket ecosystems deliver different bundles of ecosystem services, and within each bundle the services are linked non-linearly, so that land-use and management decisions which seek to increase a particular service affect the delivery of other services. One of the challenges of restoring the historically degraded thicket areas is understanding the trade-offs between various objectives, including re-establishing biodiversity and critical services such as carbon sequestration, climate regulation, water provision and forage supply. This thesis uses a variety of techniques to assess some of these trade-offs at several spatial and temporal scales. The amount, rate and nature of carbon assimilation by P. afra at a variety of spatial and temporal scales are also explored. Methods At a landscape scale stream flow data from transformed and intact catchments, near Jansenville and Bucklands respectively, are used to compare the freshwater ecosystem services provided by the presence of P. afra. Similarly, at a landscape scale, the new high resolution Multi-angle Imaging SpectroRadiometer (MISR-HR) products are used to explore the differences in the surface energy budget of intact thicket and degraded ecosystems. Two simple radiative transfer models are used to assess the radiative forcing (RF) trade-off between carbon uptake-related global cooling and albedo-related global warming. From samples and measurements taken from a field site 15 km south-west of the town of Kirkwood, radiocarbon and stable carbon isotope analysis, growth ring analysis, dendrometry, infrared thermometry, water use efficiency and eddy covariance data are used to quantify the rate of carbon assimilation by P. afra, and unpack the contribution of C3- and CAM-derived carbon to total carbon sequestration. Results Intact thicket cover results in a higher total yield of water as a fraction of rainfall, fewer extreme high flow events, and a higher volume of low-flow in comparison to landscapes thought to represent transformed former thickets. Intact thickets have a lower albedo than degraded thickets. Restoring to an intact state will result in a mean albedo decrease of 5% (absolute) which constitutes a direct radiative forcing of +0.019 pW m-2 at a global scale. This warming effect overwhelms the climate benefit derived from carbon sequestration related to P. afra growth by a factor of 1.6. The growth data suggests that P. afra produces two growth rings annually on average, with the average growth increment of 0.8mm in diameter. The multi-year and multi-source aboveground relative growth rate mean is 0.006 (±0.005 SD) g DM per g DM per year, which is mean average increment about 1.1% per year. The eddy covariance data highlighted the temporal variability in the system, measuring intact P. afra thicket vegetation as a net source of carbon to the atmosphere 0.018 gC m-2 hr-1, over the three short-duration campaigns. CAM is now understood to come in several variants. The sampled stems, averaged across all rings, had a δ13C signature of -15.8±1.0 ‰ indicative of “strong CAM” behaviour. P. afra plants in the Kirkwood locality over the past decades have derived 61% of their carbon through the CAM pathway and 39% through the C3 pathway, with substantial inter-stem variation. The soil isotope data suggests 51 - 63% C3 derived carbon, with values increasing with sampling depth. There are occasional large excursions, always in a single growth ring, towards more negative δ13C values (-19.0‰); in other words towards the C3 range. Although thought to be related to water stress, it was hard to determine a single trigger for the switching between C3 and CAM modes. This is consistent with findings for other strongly CAM plants. From the dendrometers and infrared thermometry, P. afra shows flexible stomatal behaviour on a range of timescales. For the majority of the study period the stomata were open both day and night. There is variation in stomatal closure over the year, which appears strongly seasonal, and suggests a link to the bimodal rainfall pattern experienced in the region. Using decision tree to classify the photosynthetic mode, this data suggest that the individual plants being measured are spending only 4% of the time in classical CAM mode, and the majority of the time in CAM-cycling. Conclusions Restoration of transformed thicket will improve freshwater ecosystem services associated with useful water yield, sustained supply, and flood control. It is important to include land-atmosphere feedbacks other than carbon assimilation when assessing the climate service delivered by restoration. The negative and positive radiative forcing will operate over different timelines. CAM metabolism plays an important but not exclusive role in carbon gain. Contrasting patterns between plant and soil C3 fraction may relate to allocation issues and the contribution by plants other than P. afra. The growth rates of thickets are not substantially greater than similar water-limited ecosystems. / LG2017

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Thesis (Ph. D.)--University of Wollongong, 2004. / Title from PDF title page (viewed on Aug. 13, 2005). Some ill. and maps lacking from electronic version. Includes bibliographical references (p. 171-191).

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 101-111).

This thesis describes the biogeoclimatic zones on the southwestern British Columbia mainland and gives a detailed analysis of the vegetation-environmental patterns within the Coastal western hemlock zone. Ecosystem classifications are proposed utilizing coordination techniques and stratification. The major underlying causes of variations in the floristic structure among individual ecosystems are identified by four environmental gradients: regional climate, parent material, local climate (exposure), and soil-moisture regime. The orographic influence of Vancouver Island and the Coast Mountains results in a regional climatic gradient from low to high elevations. Natural segments of this gradient, recognized on the basis of zonal (climatic climax) vegetation and mesic soils, constitute the biogeoclimatic zones and subzones. Land types are separated from within the Coastal western hemlock zone on the basis of parent materials. The rock outcrop land type includes a mosaic of peaks, knolls, and crevices characterized by a coincident pattern of the vegetation types. All glacial drift deposits, except those of the swampy habitats, belong to the glacial drift land type. Maximum floristic variations in the glacial drift land type occur along a soil-moisture gradient. A lesser variation in the floristic structure is attributed to a local climatic gradient from cool to warm exposure. These gradients signify different sets of vegetation types in the different subzones of the Coastal western hemlock zone. The spring-water swamp land type includes waterlogged mineral soils and waterlogged woody peats in the vicinity of spring lines. The vegetation of the spring-water swamps has remarkable uniformity throughout both subzones. Narrow valley-like depressions with permanent or semipermanent streamlets and intermittent overflow water constitute the ravine alluvial land type. The vegetation of the ravines shows little variation among the two subzones. The flood-plain communities of the Squamish alluvial plain land type reflect the influence of overflow water and post-flood drainage. The basic unit of classification used is the ecosystem type, a segment in a simple vegetation-environmental gradient. A vegetation-environmental gradient is simple if it consists of a single set of vegetation types along an environmental gradient. Ecosystem type mapping involved approximately 85 acres in the southwestern part of the University of British Columbia Research Forest; a map is enclosed (in the thesis). / Science, Faculty of / Botany, Department of / Graduate

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No description available.

Thesis (Ph. D.)--Oregon State University, 1964. / Typescript. Mounted photographs. Includes bibliographical references (leaves 99-109). Also available on the World Wide Web.

Thesis (Ph.D.)--University of Wollongong, 2009. / Typescript. Includes bibliographical references: leaf182-203.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy