Reburning pyrogenic organic matter: a laboratory method for dosing dynamic heat fluxes from above

Background Pyrogenic organic matter (PyOM) represents a relatively persistent component of soil carbon stocks. Although subsequent fires have the potential to combust or alter preexisting PyOM stocks, simulating soil heating faces important methodological constraints. In particular, methods for estimating the effects of subsequent fire on preexisting PyOM in soil have important limitations. Aims We aimed to design a laboratory method to effectively simulate soil heating from above, to investigate the impacts of subsequent fires on PyOM at different soil depths while addressing key limitations of previous methods. Methods Jack pine (Pinus banksiana Lamb.) log burns were used to parameterise realistic heat flux profiles. Using a cone calorimeter, these profiles were applied to buried jack pine PyOM to simulate variable reburn fire intensities. Key results In general, higher heat fluxes and shallower depths led to more mass loss of PyOM. Conclusions We offer a method to simulate specific soil heating profiles. Conditions that result in higher temperatures (higher heat fluxes and shallower depths) are likely to lead to more loss of PyOM in subsequent fires. Implications The method could simulate different fire scenarios to represent spatial variability within a given fire event, or to study the effects of fire on different types of biomass, or organisms such as microbes.