Canadian Forest Service Publications

Charcoal in forest floor and surface mineral soil in a boreal forest fire chronosequence of Western Quebec: stocks, depth distribution, chemical properties and a synthesis of related studies. 2017. Front. Earth Sci. 5:98.

Year: 2017

Available from: Pacific Forestry Centre

Catalog ID: 38998

Language: English

CFS Availability: PDF (download)

Available from the Journal's Web site.
DOI: 10.3389/feart.2017.00098

† This site may require a fee.

Abstract

Wildfires are a major driver of carbon stocks and ecosystem development in Canadian boreal forests, but there is little information on amounts and properties of the charcoal produced. Using data and samples available from a previous study, we determined amounts, depth distribution and chemical properties of visually-determined charcoal (>2 mm) in a boreal chronosequence in the Abitibi region of Quebec, Canada. Sites ranged from 24 to 2,355 years since fire (ysf) and originated from low- and high-severity soil burns (>5 or <5 cm organic horizon unburned, respectively). Two or three pits were sampled at 1-cm depth intervals from 20 jack pine (Pinus banksiana) sites (one low severity and 19 high severity) and 31 black spruce (Picea mariana) sites (12 low severity and 19 high severity). Site-level charcoal stocks ranged from 50 to 5,527 kg ha−1 with high within-site variability and lower stocks for the oldest sites. Depth distributions typically peaked around the organic-mineral interface, but some low-severity sites also had charcoal layers within the organic horizon. Means from 30 charcoal samples were 569mg g−1 total C, 4.1mg g−1 total N and 140 C/N (molar), with total C and C/N showing a trend of decline with time since fire, and total N showing an increase. Solid-state 13C CPMAS NMR spectra of nine samples showed high variability among the younger samples, but a trend to higher aromaticity for the older ones. A literature survey focusing on boreal forests similarly showed highly variable stocks and chemical properties of charcoal in organic horizon and upper mineral soil, with reduction of variance and lower stocks after several hundred years. This initial variation was also consistent with reports of highly variable temperatures and duration of charring in wildfires. Adding reports available for char production, and considering that most studies of char stocks and production are limited to the organic horizon (forest floor), suggests that initial production of charred material from boreal wildfires might be around 5–10 tons ha−1.

Plain Language Summary

Wildfires are the predominant disturbance in boreal forests, with blackened charcoal an obvious product. This Pyrogenic Carbon (PyC) is expected to resist decomposition more than other dead organic matter, and also affects soil and forest floor properties, However, there is little information on amounts and properties of charcoal (i.e., visually determined PyC) in boreal forests. We used data and samples from a previous fire chronosequence study in the Abitibi region of Quebec (51 sites, 24 to 2355 y), This gave charcoal amounts (>2 mm) by 1 cm increments in forest floor and upper mineral soil, and enough samples for essential chemistry. Amounts of charcoal were greatest 'around the organic-mineral interface. Amounts and chemical properties were highly variable up to around 200 years since fire, but with time, properties tended to converge and amounts decrease. We added much more value by compiling data from similar studies in boreal Canada and Scandinavia, that show similar trends to ours. Comparing the limited data on production suggests that initial charcoal production on stems, down coarse wood and forest floor might reasonably be around 5000-10000 kg/ha. Our data have value for C budget modelling and identify knowledge gaps.

Date modified: