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.

No description available.

The purpose of this study is to 1: Get an updated population estimate for the regionally endangered alpine specialist plant Phippsia concinna in Sweden and 2: Explore the ecological dependencies that limits the distributions of this species to late melt-out alpine snowbeds on calcareous soils, and 3: Explore if climate change in the southern part of the Scandes mountain range is causing a decline in the population numbers of P. concinna. The majority of the sites in Sweden where P. concinna occurred historically was inventoried in 1992. This study presents the results of a re-inventory of the same snowbeds after 22 years, along with measurements of abiotic soil factors and records of abundance and composition of associated vegetation at the sites. The main findings are 1: Population number of P. concinna has increased but one third of the original populations has disappeared since 1992, and 2: Soil pH appears to limit the distributions of P. concinna while slope aspect and soil Nitrogen concentrations affects this species competitive abilities in the Swedish Scandes. 3: Presence of P. concinna is negatively correlated to cover of other graminoids and bryophytes. These results suggests that snowbeds are melting earlier following increased temperatures and precipitations in summer, resulting in longer vegetation periods that favours plant species with stronger competitive abilities over specialised snowbed species. The observed rate of change in P. concinna populations during 22 years is evidence of fast occurring vegetation changes and highlights the need to monitor rare plant species in alpine environments.

Nutrient dynamics of two sub-types of peat swamp forest, mixed swamp forest and low pole forest, in the upper catchment of the Sebangau River in Central Kalimantan, Indonesia were studied. Three permanent study plots, 50 x 50 m, were established in each forest sub-type to facilitate collection of throughfall, stemflow, litterfall, decomposition, above ground and below ground biomass, peat and water samples. Graphical presentation, Wilm's method, and analysis of variance were carried out for both sub-types of forest in order to analyse data to detect any significant differences. Rainfall is slightly acid (pH 5.96+0.35) with a predominance of NH4-N, Ca and K. Throughfall and stemflow are enriched in most elements analysed compared to rainfall and the pH values are lower. Throughfall pH is 4.76±0.33 in mixed swamp forest and 4.37±0.33 in low pole forest. Stemflow pH is 4.03±0.19 in mixed swamp forest and 3.57±0.11 in low pole forest. Greater litter production was obtained in mixed swamp forest (8,411 kg ha-1 yr-1) than in low pole forest (6,534 kg ha-1 yr-1). Dry weight of the different fractions of litterfall (leaves, branches, reproductive parts and other debris) for MSF and LPF were 6216,1246, 460 and 489 kg ha-1 and 4864,1251,169 and 251 kg ha-1, respectively. Decomposition rates (k) in the MSF and LPF are 0.396 yr-1and 0.285 yr-1 respectively. Above ground biomass in MSF and LPF are 313,899 and 252,547 kg ha-1 respectively, while below ground (root biomass) is 26,533 and 14,382 kg ha respectively. Nitrogen is the predominant nutrient in peat soil at 50 cm depth in both MSF and LPF, while manganese is the lowest. Calcium is the element in greatest amount in water run off in MSF and LPF at 8,15 and 7.15 kg ha-1 yr-1 respectively, while manganese was the lowest at 0.01 and 0.02 kg ha-1 yr-1, respectively. Nutrient inputs were higher than nutrient losses during the 1-year study period with the greatest nutrient gain for calcium while manganese was the lowest in both sub-types of forest. Moreover, the results of this study highlight that nutrient concentrations in peat soils are low and the substrates are acidic. These factors are likely to be strongly limiting to agricultural development, including plantations of estate crops and trees. Under such conditions the maintenance of intact forest for natural ecosystem services (e. g. carbon storage, watershed, biodiversity maintenance, timber production in certain time period) is likely to be a far wiser land use from a long-term perspective.

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.

Thesis (M. Sc.) (Hons.)--University of Western Sydney, Hawkesbury, 1994. / Includes bibliographical references.

Thesis (Ph.D.)--University of Wollongong, 2006. / Typescript. Includes bibliographical references: p. 262-287.

Thesis (M.Sc.)(Botany)--University of Pretoria, 2007. / Includes summary. Includes bibliographical references.

Thesis (M.Sc. (Centre for Wildlife Management)) -- University of Pretoria, 2002. / Summary in English. Includes bibliographical references.

Thesis (Ph.D.) - Carleton University, 2003. / Includes bibliographical references (p. 164-177). Also available in electronic format on the Internet.