Fire-Derived Charcoal Along an Ecological Gradient in the Colorado Front Range

Terrestrial ecosystems are shaped by natural disturbances such as wildland fire. In the intermountain western United States, forests, shrub and grasslands adapt to repeated fires. An important long-term legacy of wildland fires is black C (BC) commonly referred to as char or charcoal. Black C is a recalcitrant C form that has been long known to influence soil physical, chemical, and biological processes that they vary across landscapes and over time. The objective of this research is to address two key areas in the emerging field of ecosystem BC research; 1) how much BC as charcoal C is formed per fire at a watershed scale and 2) how much charcoal C and total soil organic C are in mineral soil pools in the predominant Colorado Front Range vegetation types. For the former, we combined fire model results for fuel consumption with published charcoal conversion constants to create maps of predicted charcoal C per fire. These maps represent the first spatial estimates shown at a watershed scale. For the latter, we measured charcoal C pools in surface soils (0-10 cm) at mid-slope positions on east facing aspects in five continuous shrublands and forests from grassland to tundra. We found a significant statistical effect of vegetation type on soil charcoal C pools along this ecological gradient, but not a linear pattern of increasing charcoal C amounts with elevation gain. This study yielded the largest collection of soil samples analyzed for charcoal C in the United States. The geospatial data and thermo-chemical analysis methods developed here are an advance in the framework for evaluating the two critical phases in ecosystem black C cycling. Future modeling and field-based efforts are called for after revealing a landscape-pattern of SOC and charcoal C pools