Should the accounting period begin as the biomass source is originally created, or should the accounting period begin at harvest and fuel use? For example, there is a big difference between (1) harvesting an old growth forest versus (2) growing energy crop trees on marginal lands that only had weeds before tree planting.
While the topic of life-cycle carbon accounting is complex, two key carbon capture components that we rarely see in this discussion are (1) below ground carbon sequestration and greenhouse gas emissions (primarily, NOx); (2) biochar created through biomass gasification technology.
Through our field work in Florida (i.e., growing energy crop trees on marginal mined lands) our collaborative work with the University of Florida and Oak Ridge National Lab documented that in accumulating total carbon:
(A.) 62% was contained above ground (harvestable trees) and,
(B.) 38% was below ground (i.e., root systems).
Also, according to the U.S. Department of Energy's NETL, approximately 50% of the biomass harvested feedstock (i.e., the 62%) could be captured in biochar (31% of the total biomass) through gasification pyrolysis.
Clearly, biochar has the potential to be a "major player" in carbon cycle accounting ranging from the gasification process to its ability to capture NOx emissions from soils. The problem is that so little empirical data exists outside of laboratory study (the need for commercial scale field documentation).
(1) Per UF/ORNL field measurements of eucalyptus tree plantation (62% + 38% = 100% total tree mass).
(2) Per NETL estimates of 50% biochar carbon capture through gasification.
(3) Assumes biogas would be scrubbed downstream from the gasifier through a Wet ESP (electrostatic precipitator), emitting almost no greenhouse gas nitrous oxide emissions (and also no sulfur emissions).
(4) Lehmann (Cornell) research that biochar may capture ~80% of NOx and ~100% of methane (CH4).
(5) Current Proxy of ~10% using Life Cycle Assessment developed by University of Michigan, SUNY (Heller, Keoleian, Volk, July, 2002)