Holocene Fire History of the Southeast Yukon Territory
The global climate is dynamic and has undergone many significant changes throughout Earth's history. Since the industrial revolution, anthropogenic activities have released significant amounts of CO2 and other greenhouse gasses (GHG) into the atmosphere, which is believed to be impacting global climate. A change to a warmer climate as is predicted by many scientists will have a profound effect on various ecosystems, such as those in northern regions. To better understand the impacts of climate change and disturbances such as forest fires on vegetation, this study examined proxy data to determine how these factors have interacted during the Holocene. The objectives of the thesis were to determine if fire frequency has changed throughout the Holocene, and if so, what is the relation between fire frequency, climate and vegetation. Three sediment cores from small, closed-basin lakes in the southeast Yukon Territory were analyzed for their macroscopic charcoal content and the resulting data was examined using the Charcoal Analysis Programs (CHAPS). CHAPS statistically distinguishes background levels of charcoal from charcoal peaks that are associated with fire events. The charcoal record was also analyzed against pollen percentage diagrams from the surrounding areas, to study the interactions between fire activity, changes in climate and vegetation. The results from the charcoal records indicate that the fire regime of the southeast Yukon was dynamic and responded to changes in climate throughout the Holocene. Fire frequency increased during the Early Holocene, about ∼10,000 to 7000 yrs BP, when the climate was warmer and drier than present. Pollen diagrams from the surrounding areas indicate the widespread establishment of Picea glauca and Juniperus spp., which is indicative of a warmer and drier climate. Fire frequency decreased during the mid-Holocene, about ∼7000 to 4000 yrs BP when the climate became more cool and moist. Alnus crispa and Picea mariana, which favor such an environment became more abundant at this time. The charcoal record also provides evidence that periods of increased fire frequency were associated with extensive stands of fire-prone species such as Picea mariana and Pinus contorta, despite the onset of a more cool and moist climate at ∼4000 yrs BP to present-day. This study also examined the effect of elevation on fire frequency, which was found to be highest in the lower elevation closed-canopy forests and lowest in the high elevation alpine tundra.
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