Understanding how fire impacts soil carbon and nutrient cycling: Toward standardized reporting of fire metrics for the integrated plant-soil system

Fire events impact soil carbon (C) and nutrient stocks immediately due to combustion of biomass and organic matter and set up additional post-fire changes to ecosystem inputs and losses. The literature on this topic is expanding rapidly as large and intense wildfires are increasingly affecting communities globally. However, many of these studies do not describe initial post-fire soil conditions adequately or consistently, nor do they link the impacts of fire on C and nutrient cycling to key soil properties and soil inputs, stocks and fluxes. Here we conduct a systematic analysis of 56 review- papers published in 2010 or later that address fire impacts to C and nutrient cycling and integrate relevant research from the fire ecology and soil carbon cycling literature. We begin with a conceptual framework that ties belowground changes to the soil system with aboveground changes. The extent to which fire modifies or perturbs the plant-soil system is related to the properties of the fire and its alteration of plants and soil. However, we found inconsistent or a lack of reporting of fire intensity or fire severity, and soil burn severity. Therefore, we offer a set of definitions and methods based on the fire ecology literature to encourage the soil science community to report distinct metrics of the energy or impact delivered by fire to plants and soil. We also suggest a set of essential soil properties that should always be measured as they strongly impact C and nutrient cycling post-fire. Our review will aid the soil science community in tying fire severity and frequency to the mechanisms of post-fire impacts on soil C and nutrient cycling in a way that integrates above and belowground processes. Implementing our approach will also facilitate more consistent cross-study measurements and allow future research, especially meta-analyses, additional power to test hypotheses regarding the factors that control the impact of fire on soil C and nutrient cycling.