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Increasing Wildfires and the Carbon Balance of Boreal Forests

Speaker: Dr. Xanthe Walker, Northern Arizona University

One of the most rapid pathways through which climate warming could alter the structure and function of high-latitude ecosystems is through intensification of wildfire disturbance. More severe and frequent wildfires can shift these ecosystems across a carbon (C) cycle threshold: from a net accumulation of C from the atmosphere over centuries and fire cycles to a net loss. This shift can occur when organic soil C that escaped burning in previous fires or that has accumulated over centuries, termed ‘legacy carbon’, combusts.

The burning of legacy C is not only an important determinate of the C balance over the disturbance cycle, but also sets the conditions that control tree seedling recruitment, and therefore successional dynamics and species dominance. Species dominance, in turn, has the potential to exert strong control over the plant-soil-microbial feedbacks that determine C and nutrient coupling, C storage, and ultimately, replacement of combusted C. In this presentation, Walker will discuss research results on the vulnerability of legacy C to combustion, changes in successional dynamics, and the consequences of shifting species dominance on the long-term C balance of North American boreal forests.