Investigating the contribution of the coarse fraction to total pyrogenic carbon stocks in forest soil

Abstract

Pyrogenic carbon (PyC) quantification methods based on visual identification typically measure only the PyC particles >0.5 mm, whereas oxidative methods are usually conducted on the <2 mm soil fraction. To reconcile the discrepancy between these two methods, we used the weak nitric acid digestion method to quantify the PyC mass in the <2 mm soil, and in the charcoal particles >2 mm, in a California dry mixed conifer forest spatially heterogeneous in fire severity. We found that charcoal particles >2 mm represented 5–10% of mineral soil PyC in recently burned areas (three years post-fire in our study) and 3% in the unburnt areas (>100 years since the last fire). We, therefore, stress the importance of considering the size fraction of the charcoal quantified.