Holocene environmental change at the subarctic alpine treeline in northern British Columbia and the southern Yukon Territory, Canada
Dates
Year
2001
Citation
Pisaric, Michael Frederick Joseph, 2001, Holocene environmental change at the subarctic alpine treeline in northern British Columbia and the southern Yukon Territory, Canada: Queen's University (Canada).
Summary
Recent temperature compilations suggest that 20th century temperatures have been anomalously high in some regions of the world, especially in the context of the last several hundred years. Increases in anthropogenically produced greenhouse gases are believed to be the primary cause behind the warmer temperatures during the 20 th century. Because instrumental temperature records are normally very short, they are insufficient for assessing the impact of anthropogenic activity on climate. Therefore, knowledge of past climatic variation across longer timescales is needed to assess the natural variability of climate and to determine how vegetation may respond to further warming during the next century. This thesis investigates, (1) the [...]
Summary
Recent temperature compilations suggest that 20th century temperatures have been anomalously high in some regions of the world, especially in the context of the last several hundred years. Increases in anthropogenically produced greenhouse gases are believed to be the primary cause behind the warmer temperatures during the 20 th century. Because instrumental temperature records are normally very short, they are insufficient for assessing the impact of anthropogenic activity on climate. Therefore, knowledge of past climatic variation across longer timescales is needed to assess the natural variability of climate and to determine how vegetation may respond to further warming during the next century. This thesis investigates, (1) the relationship between modern vegetation and pollen and stomate dispersal, and (2) treeline dynamics and vegetation-climate relationships at the subalpine treeline in northwestern Canada, with a focus on the northern Canadian Rocky Mountains. Four hypotheses were tested to assess the objectives: (1) Major vegetation assemblages can be distinguished from one another based on their respective pollen and stomate signatures; (2) Postglacial treeline fluctuations the northern Rocky Mountains been driven by changes in the seasonal and latitudinal duistribution of solar radiation; (3) Postglacial development of subalpine forests was the result not only of differential migration in response to changing climatic conditions, but disturbance factors such as fire were important as well; and (4) 20 th century temperature increases in northeastern British Columbia and southeastern Yukon Territory have exceeded the natural variability of temperature in this region during the past centuries and these temperature increases are in direct response to increasing levels of greenhouse gases. The results indicate that (1) climate-growth relationships are complex and that the factors controlling them have changed through time; (2) the response of Picea glauca populations to changing climatic conditions during the Holocene have been manifested as increases in treeline elevation and higher density of trees at or near treeline; (3) vegetation development, although driven by climate, is also related to higher fire activity; and (4) early 20 th century temperatures have been anomalously high compared to the past 300 years, likely reflecting increased levels of greenhouse gases.