Characterizing crown fuel distribution for conifers in the interior western United States

Abstract

Canopy fire hazard evaluation is essential for prioritizing fuel treatments and for assessing potential risk to firefighters during suppression activities. Fire hazard is usually expressed as predicted potential fire behavior, which is sensitive to the methodology used to quantitatively describe fuel profiles: methodologies that assume that fuel is distributed uniformly throughout crowns have been shown to predict less severe fire behavior than those that assume more realistic nonuniform fuel distributions. We used crown fuel data from seven interior western United States conifer species to characterize within-crown fuel distributions. Fuel was shifted upward and concentrated in crowns in crowded stands compared with crowns in open stands, which suggests that the vertical distribution of fuel is shaped by foliage concentration in favorable light environments near the top of crowns and echoes the predictable relationship between crown ratio and stand density. However, unlike crown ratio, the relationship between within-crown foliage distribution and stand density was independent of the shade tolerance of a species. This implies that there is a general relationship between stand density and within-crown fuel distribution for conifers and that species differences in fuel profiles related to shade tolerance are expressed primarily in the relationship between stand density and crown ratio.