U.S. Joint Fire Science Program


Date of this Version


Document Type



Fire Science Brief, Issue 148, December 2011


US government work.


Allometric equations, which express biomass as a function of tree size, are often used to estimate the amount of fuel in a site’s canopy. Most managers assume that one allometric equation per species is suffi cient, or that any error introduced by extrapolation is irrelevant. This work showed, however, that the allometric biomass relationship for ponderosa pine likely changes over space and time. The researchers concluded that for maximum accuracy, allometric equations for ponderosa pine should account for stand management history and site productivity. Thinned trees replaced their foliage within about 4 years, and 8–10 years post-thinning, growth had stabilized. This indicates that using allometric equations to estimate fuel loads can result in miscalculation of the potential for active crown fi re.