Thesis (M.S.)--University of Wisconsin--Madison, 1983. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 65-67).

Thesis (Ph.D.)--University of Western Australia, 2007.

No description available.

No description available.

This thesis explores the role of terrestrial vegetation in the global climate system in a series of modelling studies using the University of Victoria Earth System Climate Model (UVic ESCM). The ways that vegetation affects climate, as well as the feedbacks that operate between changing climate and vegetation distributions, are investigated within the framework of three foci: 1) historical land cover changes that have resulted from human modification of natural vegetation cover; 2) historical land cover change and the dynamics of terrestrial vegetation in the context of anthropogenic and natural climate change; and 3) the role of terrestrial vegetation in the global carbon cycle. First, the radiative effect of changing human land-use patterns on the climate of the past 300 years is discussed through analysis of a series of equilibrium and transient climate simulations using the UVic ESCM. These experiments highlight the biogeophysical effects of historical land cover change on climate: those that result from physical changes to the land surface under altered vegetation cover. Results show a global cooling in the range of -0.06 to -0.22 "C, though this effect is not found to be detectable in observed temperature trends. Using a global carbon cycle the climatic effects of land cover change emissions (the biogeochemical effect of historical land cover change) are assessed. The resultant warming is found to exceed the biogeophysical cooling by 0.15 "C. Second, the effect of historical land cover change is compared with the effects of natural forcings (volcanic aerosols, solar insolation variability and orbital changes) and other anthropogenic forcings (greenhouse gases and sulphate aerosols). Transient model runs from the year 1700 to 2000 are presented for each forcing individually as well as for combinations of forcings. I find that the UVic model reproduces well the global temperature data when all forcings are included. In the context of these anthropogenic and natural climate influences, the response of vegetation distributions to changing climate is explored through the use of a dynamic global vegetation model coupled interactively to the UVic ESCM. Transient simulations of the past 300 years are repeated using this new model so as to isolate the biogeophysical feedbacks that operate between vegetation and climate. Dynamic vegetation is found to act as a positive feedback to climate, amplifying both warming and cooling climate trends. Third, the development of a global carbon cycle model allows for investigation of the role of terrestrial carbon cycle dynamics under past and future climate change. When forced by historical emissions of C02 from fossil fuels and land-use change, the coupled carbon cycle model accurately reproduces historical atmospheric C02 trends, as well as terrestrial and oceanic uptake for the past two decades. Under six 21St century C02 emissions scenarios, both terrestrial and oceanic carbon sinks continue to increase, though terrestrial uptake slows in the latter half of the century. The modelled positive feedback between the carbon cycle and climate is relatively small, resulting in an increase in simulated C02 of 60 ppmv at the year 2100. Including non- C02 greenhouse gas forcing and increasing the model's climate sensitivity increases the effect of this feedback to 140 ppmv. The UVic model does not, however, simulate a switch from a terrestrial carbon sink to a source during the 2lSt century, as earlier studies have suggested. This can be explained by a lack of substantial reductions in simulated vegetation productivity due to climate changes.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Alpine and arctic treelines have been viewed as sensitive indicators of global climate change. While many treelines have advanced under warmer climate regimes in recent decades, the response has not been uniform. Some of this variability may be attributable to the impacts of herbivores. This study investigates the interacting effects of herbivory, climate, and understory vegetation on mountain birch establishment at treeline in the Scandes Mountains of northern Sweden. An extensive dendrochronological database was created to determine periods of establishment, which were then regressed against reindeer (Rangifer tarandus, L.) population data and historical climate data. Vegetation classifications were also created and analyzed to determine if establishment patterns vary by understory vegetation type. I have tested the hypothesis that tree establishment varies within the treeline ecotone and that high reindeer stocking levels negatively impact establishment. Weakly positive responses to herbivory were observed in patterns of tree establishment at treeline. This indicates that reindeer may modestly promote treeline advance at low densities, contradicting some previous research, but many of the results were not statistically significant. The climate variables found to have significant relationships with establishment were inconsistent across herding districts and aggregation levels. No connections between vegetation assemblages and establishment or between vegetation assemblages and reindeer use were observed.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.S. - Hydrology and Water Resources) - University of Arizona. / Includes bibliographical references (leaves 148-150).

Thesis (M.S.)--Eastern Illinois University, 2008. / Includes bibliographical references (leaves 48-59).