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Abstract Wildfires have the potential to dramatically alter the carbon (C) storage potential, ecological function, and the fundamental mechanisms that control the C balance of Pacific Northwest (PNW) forested ecosystems. In this study, we explored how wildfire influences processes that control soil C stabilization and the consequent soil C persistence, and the role of previous fire history in determining soil C fire response dynamics. We collected mineral soils at four depth increments from burned (low, moderate, and high soil burn severity classes) and unburned areas and surveyed coarse woody debris (CWD) in sites within the footprint of the 2020 Holiday Farm Fire and in surrounding Willamette National Forest and the H.J. Andrews Experimental Forest. We found few changes in overall soil C pools as a function of fire severity; we instead found that unburned sites contained high levels of pyrogenic C (PyC) that were commensurate with PyC concentrations in the high severity burn sites—pointing to the high background rate of fire in these ecosystems. An analysis of historical fire events lends additional support, where increasing fire count is loosely correlated with increasing PyC concentration. An unexpected finding was that PyC concentration was lower in low soil burn severity sites than in control sites, which we attribute to fundamental ecological differences in regions that repeatedly burn at high severity compared with those that burn at low severity. Our CWD analysis showed that high mean fire return interval (decades between fire events) was strongly correlated with low annual CWD accumulation rate; whereas areas that burn frequently had a high annual CWD accumulation rate. Within the first year postfire, trends in soil density fractions demonstrated no significant response to fire for the mineral-associated organic matter pool but slight increases in the particulate pool with increasing soil burn severity—likely a function of increased charcoal additions. Overall, our results suggest that these PNW forest soils display complex responses to wildfire with feedbacks between CWD pools that provide varying fuel loads and a mosaic fire regime across the landscape. Microclimate and historic fire events are likely important determinants of soil C persistence in these systems.
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Yukon-Kuskokwim River Delta 2015 fire burn depth measurements and unburned soil and vegetation organic matter and carbon content collected in 2019.
Tundra environments in Alaska are experiencing elevated levels of wildfire, and the frequency is expected to keep increasing due to rapid warming of the Arctic. Because of large amounts of carbon stored in permafrost soils, tundra wildfires may release significant amounts of carbon to the atmosphere that ultimately influence the Earth’s radiative balance. Therefore, accounting for the amount of carbon released from tundra wildfires is important for understanding the trajectory of climate change. We collected data in the Yukon-Kuskokwim River Delta during the summer of 2019 for the purpose of determining organic matter and carbon lost during the 2015 fire season. Organic matter and carbon lost from combustion were determined by combining burn depth measurements with organic matter and carbon content measurements from unburned tundra. Burn depth measurements were taken opportunistically across different levels of burn severity. Three vegetative markers, Sphagnum fuscum, Eriophorum, and Dicranum spp., that survived the fire event were used to measure the difference between the pre and post fire soil height in unburned and burned areas respectively, defined here as burn depth. All burn depth measurements are accompanied with coordinate locations so that they can ground truth and be upscaled by remote sensing data of burn severity. Organic matter and carbon content of the dense live vegetation layer and fibric soil layer were measured in the lab from vegetation and soil cores taken from four different sites in unburned tundra areas.
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- Award ID(s):
- 1915307
- PAR ID:
- 10438456
- Publisher / Repository:
- NSF Arctic Data Center
- Date Published:
- Subject(s) / Keyword(s):
- tundra fire ecology carbon
- Format(s):
- Medium: X Other: text/xml
- Sponsoring Org:
- National Science Foundation
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