Articles | Volume 12, issue 10
Research article
22 May 2015
Research article |  | 22 May 2015

Distribution of black carbon in ponderosa pine forest floor and soils following the High Park wildfire

C. M. Boot, M. Haddix, K. Paustian, and M. F. Cotrufo

Abstract. Biomass burning produces black carbon (BC), effectively transferring a fraction of the biomass C from an actively cycling pool to a passive C pool, which may be stored in the soil. Yet the timescales and mechanisms for incorporation of BC into the soil profile are not well understood. The High Park fire (HPF), which occurred in northwestern Colorado in the summer of 2012, provided an opportunity to study the effects of both fire severity and geomorphology on properties of carbon (C), nitrogen (N) and BC in the Cache La Poudre River drainage. We sampled montane ponderosa pine forest floor (litter plus O-horizon) and soils at 0–5 and 5–15 cm depth 4 months post-fire in order to examine the effects of slope and burn severity on %C, C stocks, %N and BC. We used the benzene polycarboxylic acid (BPCA) method for quantifying BC. With regard to slope, we found that steeper slopes had higher C : N than shallow slopes but that there was no difference in BPCA-C content or stocks. BC content was greatest in the forest floor at burned sites (19 g BPCA-C kg−1 C), while BC stocks were greatest in the 5–15 cm subsurface soils (23 g BPCA-C m−2). At the time of sampling, unburned and burned soils had equivalent BC content, indicating none of the BC deposited on the land surface post-fire had been incorporated into either the 0–5 or 5–15 cm soil layers. The ratio of B6CA : total BPCAs, an index of the degree of aromatic C condensation, suggested that BC in the 5–15 cm soil layer may have been formed at higher temperatures or experienced selective degradation relative to the forest floor and 0–5 cm soils. Total BC soil stocks were relatively low compared to other fire-prone grassland and boreal forest systems, indicating most of the BC produced in this system is likely lost, either through erosion events, degradation or translocation to deeper soils. Future work examining mechanisms for BC losses from forest soils will be required for understanding the role BC plays in the global carbon cycle.

Short summary
Black carbon (BC) includes everything from charred wood to soot, making it difficult to measure and limiting our understanding of the amount in soils. We studied the effects of fire severity and degree of hillslope on BC quantities in forest floor and soil samples after the High Park wildfire that took place in northwestern Colorado, June 2012. Using molecular markers we found that the majority of BC remained in the litter 4 months post fire, regardless of fire intensity or degree of hillslope.
Final-revised paper