Heat content variation of interior Pacific Northwest conifer foliage

Abstract

Heat content with and without ash was measured for foliage of three interior Pacific Northwest conifers (Pinus ponderosa, Pseudotsuga menziesii, and Abies grandis/concolor) in five locations in Oregon and Washington. Heat content with ash did not vary by species (20.47–20.59 MJ kg^–1), but ash content did vary, so that heat content without ash varied by species. Heat content also varied by location but, due to confounding with season, these differences should be viewed with caution. Foliar heat content values averaged about 10% higher than those used for surface fuels in standard fire behavior fuel models. If heat content is included in future models of crown fire behavior, errors in using heat contents that are too low may have a larger impact than most errors in estimating foliar moisture content, but sources of error might be overwhelmed by other errors in estimating crown fire energy balance.