Biomass Harvesting and Soil Productivity: Is the Science Meeting our Policy Needs?

Biomass harvesting and associated management practices increase the availability of forest-based feedstocks for emerging bioproduct and energy markets. Concerns about the sustainability of these practices have led to the development of biomass harvesting guidelines (BHGs) by state, national, and international agencies and nongovernmental organizations. Site productivity BHG provisions include retaining specific proportions of harvested residues and restricting biomass harvesting on some sites. Field experiments have shown that forest responses to biomass harvesting vary widely and are often counterintuitive. With site-specific data lacking, BHGs tend to rely on default assumptions supported by best professional judgment. These include (i) the natural or unmanaged state is an ideal frame of reference, (ii) conventional harvesting retains and distributes most residues across the site, (iii) biomass harvesting removes virtually all residues, (iv) decomposing residues always enhance soil C and site productivity, (v) biomass harvesting is conducted in the absence of operational practices that alleviate site deficiencies and sustain productivity, and (vi) changes in forest state are equivalent to changes in forest function. Effective BHGs are science based, operationally feasible, and protect values of interest while allowing managers the flexibility to prevent or mitigate potential impacts within constraints imposed by best management practices and forest certification provisions. While harvesting-induced nutrient deficiencies can be prevented or corrected with fertilizers or other soil amendments, soil disturbance and exposure may warrant greater attention. Policy-relevant field studies should incorporate operational practices, examine linkages between indicators and values of interest, and evaluate and improve prevention and mitigation options.