Climate forcing and the response of vegetation and disturbances during the ‘Populus Period’, 2000-4000 cal yr BP.

Abstract:

Paleoecological proxies, such as charcoal and pollen, are valuable tools for reconstructing previous fire regimes, vegetation change and ecosystem resilience. This study attempts to analyze fire severity and ecosystem response using lake sediments from southeastern Wyoming, during a unique period of time coined the ‘Populus period’ (Carter et al., 2013). The ‘Populus period’ (3,100-4,000 cal yr BP) was a time when vegetation composition changed from a lodgepole pine dominant system to a quaking aspen system. This change in vegetation altered the fire regime from a low frequency regime to a high disturbance regime. This study investigates 12 fire events from 2000-4000 cal yr BP to determine the ecological response associated with the fire events and to identify driver(s) associated with vegetation change and fire regimes. In order to determine fire severity, this study compares high-resolution charcoal and pollen data to peak magnitude data from CharAnalysis (a statistical treatment program). Linear discriminant analysis (LDA) is used to set a threshold by which pollen taxa are associated with low or high severity fires. Preliminary LDA results suggest that low severity fires have a peak magnitude lower than 200 particles/cm²/episode and high severity fires have a peak magnitude higher than 200 particles/cm²/episode. Superposed epoch analysis (SEA) will be used to model pollen behavior through fire sample intervals to determine the ecology response associated with each of the 12 fires events. Statistical analysis using LDA and SEA can potentially be used in combination to determine fire severity and thus ecosystem resilience. Long-term reconstructions of fire severity can be beneficial for informing land managers in the 21^st century.