Biochar Application to Forest Soils: A Side Benefit of Mobile Pyrolysis Bioenergy Production.

Biochar is the solid product of biomass pyrolysis that is equivalent to charcoal found naturally in fire ecosystems.  Biochar has tremendous promise as the focal point for building recalcitrant carbon stocks in forest soils since it is resistant to microbial decomposition with thousand-year soil residence times. Agronomists have promoted the use of agricultural crop and land use for biochar applications to maintain or improve soil productive capacity and sequester carbon.  Forest biochar application has similar justifications to that of agronomic applications; however, because forest biomass feedstocks produce biochar there are important economic and environmental arguments for applying biochar back to remote forest sites from which bioenergy feedstocks are derived.  Reapplication returns most nutrients removed with the biomass and enhances soil physical, chemical and biological properties to improve forest soil productivity.   Reapplication will also build recalcitrant soil carbon stocks without having to move material to from the remote locations.  However, before any large-scale program of biochar land application is expanded there are numerous questions that remain, e.g. rates, quality requirements and forest responses.  Our results indicate that nutrient availability with biochar application depends on soil type, and tree growth must be evaluated with similar treatments.  Many questions regarding the impacts of biochar application are unique to forest ecosystems.  The purpose of this review is to identify available knowledge in reference to temperate forest ecosystems.