Pyrogenic Carbon production in eucalypt forests: implications for the carbon cycle in fire-prone ecosystems

Wildfires play an important role in the carbon cycle, influencing both atmospheric carbon concentrations and terrestrial carbon storage. Pyrogenic carbon (PyC) derived from incomplete biomass combustion during wildfires is currently considered a relevant carbon sink at the global level. In order to assess the quantitative importance of PyC production, accurate data on PyC generation in different ecosystems and under a range of fire conditions are needed. In this study, we focus on the fire-prone continent of Australia, specifically on eucalypt forests, which are the most common type of native forests. Eucalypt forests, subjected frequently to both wildfires and human-prescribed fires, provide an important context for understanding PyC dynamics.
We conducted comprehensive pre-fire and postfire fuel inventories and quantified all pyrogenic materials generated in three representative eucalypt forests in Sydney, Melbourne, and Perth. Experimental fires, simulating low to medium-severity wildfires, were used to quantify PyC conversion rates in the main fuel components: forest floor, understory, down wood, and overstory (comprising only tree bark as these fires did not affect the crowns).
Our results show an average pyrogenic carbon conversion rate of 24% for eucalypt forests. This translates to 9 t C ha^-1 of the carbon affected by the fire being emitted to the atmosphere, while 3 t C ha^-1 is transformed into PyC, underscoring the relevance of PyC in carbon budgets from eucalypt forest fires. The conversion rates varied substantially among fuel components, with the bark component exhibiting the highest conversion rate, at approximately 40%, and the down wood component displaying the lowest rate at around 15%. Intermediate conversion values were reported for forest floor and understory components. 
Given the recurrent nature of fires in eucalypt forests in Australia, both naturally and under human-prescribed conditions, our findings suggest that PyC production plays a significant role in the carbon cycle, of sufficient magnitude to be considered in global carbon budget estimations.