RAPID: Quantifying post-wildfire carbon retention and cycling in moist, coniferous forests of the Pacific Northwest

Wildfires are increasing in frequency and intensity across the western U.S. and are a major risk to forests in the region. One major impact of wildfires in forests is the release of carbon when forest vegetation and soils burn. This increases atmospheric greenhouse gas concentrations, which in turn drives climate change. However, not all carbon in forest vegetation and soils is released to the atmosphere during wildfires. A large proportion is left in the forest, with part of this carbon being chemically and physically altered to ash and charcoal (called pyrogenic carbon). Pyrogenic carbon can be a large proportion of the carbon that is affected by a wildfire and can have important effects on how forests regrow. Despite this, researchers have never studied pyrogenic carbon formation in the highly productive temperate rainforests of the Pacific Northwest region, where wildfires are predicted to increase in frequency and intensity. This RAPID project will examine pyrogenic carbon production during wildfires in Pacific Northwest forests, as well as how newly formed pyrogenic carbon affects soil carbon cycling during ecosystem regeneration. This is critical for improving our ability to estimate greenhouse gas emissions and understand the vulnerability of forests to wildfires across the Pacific Northwest. Despite the potential importance of pyrogenic carbon for post-wildfire forest recovery and accurate estimations of wildfire emissions, no research on the topic has been done in the temperate rainforests of the Pacific Northwest. From August-October of 2023, the mixed-severity Lookout Fire burned the H.J. Andrews Experimental Forest in the western cascades of Oregon—including forest stands with old growth characteristics—presenting a unique opportunity to close this research gap. This study will build on a unique dataset of fire behavior and pre- and post-fire vegetation conditions collected by the U.S. Forest Service’s Fire Behavior Assessment Team (FBAT) to (i) quantify pyrogenic carbon stocks as a function of total wildfire-affected carbon, and (ii) evaluate the influence of pyrogenic carbon on pathways of soil carbon loss and accumulation. The research will integrate existing datasets with field sampling of pyrogenic carbon stocks, tracking total soil and heterotrophic respiration in addition to water extractable organic carbon throughout the growing season, and laboratory analyses of soil carbon, soil nitrogen, and microbial dynamics. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.