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Highlights • We size-fractioned PyC from a burned California mixed conifer forest soil. • PyC particles >2 mm represented 5–10% of mineral soil PyC in recently burned areas. • PyC particles >2 mm represented 3% of mineral soil PyC in unburnt areas. • The C concentration in the >2 mm charcoal particles was greater in burned areas. 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. [ABSTRACT FROM AUTHOR]

Pyrogenic carbon (PyC) is hypothesized to play an important role in the carbon (C) cycle due to its resistance to decomposition; however, much uncertainty still exists regarding the stocks of PyC that persist on-site after the initial erosion in postfire forests. Therefore, understanding how fire characteristics influence PyC stocks is vital, particularly in the context of California forests for which an increase of high-severity fires is predicted over the next decades. We measured forest C and persistent PyC stocks in areas burned by low-to-moderate and high-severity fire, as well as in adjacent unburned areas in a California mixed-conifer forest, 2 to 3 years after wildfire. We measured C and PyC stocks in the following compartments: standing trees, downed wood, forest floor, and mineral soil (0-5 cm), and we identified PyC using the weak nitric acid digestion method. We found that the total stock of PyC did not differ among fire severity classes (overall mean 248 ± 30 g C m−2); however, fire severity influenced the distribution of PyC in the individual compartments. Areas burned by high-severity fire had 2.5 times more PyC stocked in the coarse woody debris ( p < 0.05), 3.3 times more PyC stocked in standing trees ( p < 0.05), and a lower PyC stock in the forest floor (−22%, p < 0.05) compared to low-to-moderate fire severity areas. These results have important implications for the permanence time of PyC, which is putatively higher in standing trees and coarse woody debris compared to the forest floor, where it is susceptible to rapid losses through erosion. [ABSTRACT FROM AUTHOR]

Forest fires create pyrogenic carbon (PyC), which is present in charred biomass and whose characteristics can vary within an individual fire. The purpose here was to investigate the influence of position in a tree on post-fire element concentrations and ratios from charred Pinus banksiana Lamb. tree bark after a stand-replacing prescribed burn in Michigan, USA. We felled five fire-killed trees and collected charred bark from the main tree stem at the base and upper crown and from inner and outer crown locations, and analyzed bark samples for element concentrations. N and H concentrations were greater in bark from the crown than from the tree base, whereas there were no differences in C or O concentrations. There were no statistically significant differences (at p < 0.05) in element concentrations between the inner and outer crown. Van Krevelen diagrams indicated relatively greater charring in bark from the tree base than bark from the tree crown, and in bark from the inner crown than the outer crown. The study shows that physical location in a tree influences PyC characteristics and provides further evidence of the variability that exists in the physicochemical properties of natural PyC material. [ABSTRACT FROM AUTHOR]

The weak nitric acid digestion method (also known as KMD) is a method to quantify black carbon (BC) in mineral soil. Here we extended the use of this methodology from mineral samples to organic matrices. We tested this methodology on known mixtures of pyrolyzed pine wood and needles (at 300 °C and 550 °C) and non-pyrolyzed pine needles and measured: (1) the fraction of pyrolyzed material identified as BC by the methodology, (2) the fraction of non-pyrolyzed pine needles identified as BC, and (3) the precision of the method. We found that the fraction of pyrolyzed-C identified as BC ranges from 10% (needles at 300 °C) to 90% (wood at 550 °C), indicating that the weak nitric acid digestion method can be extended to measure BC in organic matrices and that the methodology can be used in studies aimed to quantify BC stocks in post-fire environments. [ABSTRACT FROM AUTHOR]

Pyrogenic carbon (PyC) is produced by the thermal decomposition of organic matter in the absence of oxygen (O). PyC affects nutrient availability, may enhance post-fire nitrogen (N) mineralization rates, and can be a significant carbon (C) pool in fire-prone ecosystems. Our objectives were to characterize PyC produced by wildfires and examine the influence that contrasting types of PyC have on C and N mineralization rates. We determined C, N, O, and hydrogen (H) concentrations and atomic ratios of charred bark (BK), charred pine cones (PC), and charred woody debris (WD) using elemental analysis. We also incubated soil amended with BK, PC, and WD at two concentrations for 60 days to measure C and N mineralization rates. PC had greater H/C and O/C ratios than BK and WD, suggesting that PC may have a lesser aromatic component than BK and WD. C and N mineralization rates decreased with increasing PyC concentrations, and control samples produced more CO2 than soils amended with PyC. Soils with PC produced greater CO2 and had lower N mineralization rates than soils with BK or WD. These results demonstrate that PyC type and concentration have potential to impact nutrient dynamics and C flux to the atmosphere in post-fire forest soils. [ABSTRACT FROM AUTHOR]