Validating allometric estimates of aboveground living biomass and nutrient contents of a northern hardwood forest

Accurate estimates of tree biomass and nutrient content are essential to the development of budgets for forest ecosystems. Aboveground biomass is typically estimated using allometric equations: nutrient content is calculated by multiplying elemental concentrations times the weight of each tree component. Allometric projections have seldom been compared with direct measurements; yet, such comparisons are necessary to assess the accuracy of forest biomass and nutrient estimates. For three 0.25-ha northern hardwood forest plots we compared allometric estimates with direct measurements of aboveground tree biomass and nutrients. Trees on each plot were skidded to a landing where they were chipped or removed whole. Chip vans and log trucks with material from each plot were weighed and subsampled for moisture and nutrient contents. The allometric and measured estimates of aboveground biomass did not differ significantly. Nutrient contents estimated using allometry were not significantly different from direct measurements for Ca, Mg, P. Mn, and Zn but underestimated K (24%), N (16%), and Fe (70%). The allometric approach proved accurate for estimating aboveground biomass; nutrient estimates were less consistent, requiring validation before they can be used with confidence. The direct measurements provide an estimate of uncertainty in biomass and nutrient contents.