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Front. Earth Sci. | doi: 10.3389/feart.2018.00041

Quantifying changes in total and pyrogenic carbon stocks across fire severity gradients using active wildfire incidents

 Jessica R. Miesel1*, Alicia Reiner2, Carol Ewell3 and  Bernardo Maestrini1
  • 1Michigan State University, United States
  • 2USDA Forest Service, United States
  • 3Adaptive Management Services, USDA Forest Service, United States

Positive feedbacks between wildfire emissions and climate are expected to increase in strength in the future; however, fires not only release carbon (C) from terrestrial to atmospheric pools, they also produce pyrogenic C (PyC) which contributes to longer-term C stability. Our objective was to quantify wildfire impacts on total C and PyC stocks in California mixed-conifer forest, and to investigate relationships between C and PyC stocks and changes across gradients of fire severity, using metrics derived from remote sensing and field observations. Our unique study accessed active wildfires to establish and measure plots within days before and after fire, prior to substantial erosion. We measured pre- and post-fire aboveground forest structure and woody fuels to calculate aboveground biomass, C and PyC, and collected forest floor and 0-5 cm mineral soil samples. Tree mortality increased with severity, but overstory C loss was minimal and limited primarily to foliage. Fire released 85% of understory and herbaceous C (comprising <1.0% of total ecosystem C). The greatest C losses occurred from downed wood and forest floor pools (19.3±5.1 Mg ha-1 and 25.9±3.2 Mg ha-1, respectively). Tree bark and downed wood contributed the greatest PyC gains (1.5±0.3 Mg ha-1 and 1.9±0.8 Mg ha-1, respectively), and PyC in tree bark showed non-significant positive trends with increasing severity. Overall PyC losses of 1.9±0.3 Mg ha-1 and 0.5±0.1 Mg ha-1 occurred from forest floor and 0-5 cm mineral soil, with no clear patterns across severity. Fire resulted in a net ecosystem PyC gain (0.96±0.98 Mg ha-1) across aboveground and belowground components of these forests, and there were no differences among severity levels. Carbon emissions represented only 21.6% of total forest C; however, extensive conversion of C from live to dead pools will contribute to large downed wood C pools susceptible to release in a subsequent fire, indicating that there may be a delayed relationship between fire severity and C emissions. This research advances understanding of forest C loss and stabilization as PyC in wildfires; however, poor relationships between C and PyC gains or losses and fire severity highlight the complexity of fire impacts on forest C.

Keywords: Wildfire, fire severity, burn severity, Fire effects, carbon stock, pyrogenic carbon, Pyrogenic organic matter, Fire Behavior Assessment Team, Charcoal, black carbon, California, Mixed-conifer forest

Received: 09 Oct 2017; Accepted: 06 Apr 2018.

Edited by:

Cristina Santin, Swansea University, United Kingdom

Reviewed by:

Gustavo Saiz, Imperial College London, United Kingdom
Matthew W. Jones, University of Exeter, United Kingdom  

Copyright: © 2018 Miesel, Reiner, Ewell and Maestrini. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: PhD. Jessica R. Miesel, Michigan State University, East Lansing, United States, mieselje@msu.edu