2024 Abstracts

Effects of Fire and Fire-Induced Changes in Soil Properties on Post-Burn Soil Respiration


Thea Whitman1* (twhitman@wisc.edu), Dana B. Johnson1*, Kara M. Yedinak2, Benjamin N. Sulman3, Timothy D. Berry1, Kelsey Kruger1


1University of Wisconsin–Madison, WI; 2Forest Products Laboratory, USDA Forest Service, Madison, WI; 3Oak Ridge National Laboratory, Oak Ridge, TN



Boreal forests cover vast areas of the northern hemisphere and store large amounts of carbon (C). Wildfires affect soil C via combustion and transformation of organic matter during fire and via changes in plant growth and microbial activity postfire. Wildfire regimes in many boreal forests of North America are shifting towards more frequent and severe fires. As wildfire regimes shift, there is a need to link fire-induced changes in soil properties to changes in microbial functions such as respiration to better predict the impact of future fires on C cycling. The team used laboratory burn simulations characteristic of boreal crown fires on both organic-rich and sandy soil cores collected from Wood Buffalo National Park in Alberta, Canada, to measure the effects of burning on soil properties including pH, total C, and total nitrogen (N). Researchers used 70-day soil incubations and two-pool exponential decay models to characterize the impacts of burning on soil properties and respiration. Laboratory burns successfully captured a range of soil temperatures that were realistic for natural wildfire events. Burning increased pH and caused small decreases in the C to N ratio in organic soil. Overall, respiration per gram total (post-burn) C in burned soil cores was 16% lower than in corresponding unburned control cores, indicating that soil C lost during a burn may be partially offset by burn-induced decreases in respiration rates. Simultaneously, burning altered remaining C cycles, increasing the proportion of C represented in the modeled slow-cycling versus fast-cycling C pool as well as increasing fast-cycling C decomposition rates. Together, these findings imply that C storage in boreal forests following wildfires will be driven by the combination of C losses during the burn itself as well as burn-induced changes to the soil C pool that modulate postfire respiration rates. The team will also discuss next directions for this project.