A range-wide disturbance history for Quercus alba in the eastern US
Throughout much of the eastern US, forests are undergoing a transition from Quercus to Acer-Fagus dominance. While the pattern has been reported in many site-specific analyses and is often linked to changes in disturbance regimes, a landscape-level analysis of historical establishment and disturbance throughout the region has not been conducted. I used tree-ring chronologies to analyze the disturbance history from old-growth Q. alba sites located throughout the species' range with the ultimate goal of determining the environmental conditions and disturbance dynamics that existed throughout the latter period of Quercus dominance and early period of Quercus decline. My analysis provided regional- and range-wide data regarding the frequency of disturbance throughout the development of old-growth Q. alba stands. In general, the temporal distribution of tree establishment dates was bimodal and corresponded to the period of Native American depopulation and the period following European settlement. Drought, Castanea dentata decline, and logging activities also significantly contributed to the long-term, range-wide disturbance regime. Regional discrepancies in release characteristics were identified. The Northern Hardwood Forest Region featured the highest level of disturbance as compared to all other regions. The Central Hardwood Forest Region exhibited the second lowest rate of disturbance (as evidenced by the relativized release descriptors). In general, high-magnitude disturbances occurred throughout the Q. alba range every 234-556 years. My findings confirm that Quercus dominance throughout the latter part of the Holocene was maintained, in part, by high magnitude disturbance events ca. every 400 years. Such high magnitude disturbances remove many disturbance-intolerant species, fragment large areas of the canopy, cause significant damage to subcanopy individuals, and allow disturbance-oriented and mid-successional taxa, such as Quercus, to establish. This return interval for high magnitude disturbance events can be imitated by land managers throughout the region in effort to promote Quercus regeneration.
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