Properties affecting the consumption of sound and rotten coarse woody debris in northern Idaho: a preliminary investigation using laboratory fires

This study evaluates the consumption of coarse woody debris in various states of decay. Samples from a northern Idaho mixed-conifer forest were classified using three different classification methods, ignited with two different ignition methods and consumption was recorded. Intrinsic properties that change with decay were measured including carbon to nitrogen ratio, density, heat content, lignin content, moisture content and surface area-to-volume ratio. Consumption for logs in different stages of decay is reported with characterisation of wood properties. Results indicate very decayed coarse woody debris is likely to be consumed to a substantially greater degree than sound coarse woody debris given similar conditions. High consumption occurred in debris with low-density, high-lignin content and high gravimetric heat content; however, lignin content and density showed the highest correlation with consumption. The Maser classification method grouped very rotten logs with high consumption into decay class 4 and the remainder into class 3. Trends in consumption were similar regardless of ignition; however low-intensity long-duration ignition produced higher consumption values. Focus on physical properties is recommended for predictive purposes over any classification method. Logs of other species and in regions with different decomposition and combustion dynamics may display different property ranges and consumption results.