Components and nutrient concentrations of small-diameter woody biomass for energy

The growing interest in using woody biomass for energy offers a potential opportunity to commercially remove cohorts of small-diameter trees (
<25 cm dbh) during thinning operations that otherwise have little or no economic value. However, there is little information about the quantity of biomass and the nutrients that would be removed during small-diameter harvests in oak stands of the Central Hardwood Region. The objectives of the study were to quantify biomass removals by component (foliage, twigs, bark, and stemwood) and the nutrient concentrations within components for estimating quantities of both wood and nutrients that would be removed under alternative harvest prescriptions. White oak was the most common species harvested; others included post oak, black oak, mockernut hickory, American elm, persimmon, white ash, and dogwood. Sampling indicated that heartwood and sapwood comprised most of the biomass (78 -79%) followed by bark (15%), twigs (4 - 5%), and leaves (about 2%). Estimated nutrient removals during a small-diameter harvest in this region were 1.3-3 times greater than during conventional sawlog harvests. The relatively high nutrient removals that can occur for biomass harvesting compared to traditional sawlog harvests underscore an ongoing need to ensure that nutrient removals during biomass harvesting do not exceed inputs from soil mineral weathering and the atmosphere.