Wood Burial and Storage (WBS): Q and A

Q: To bury or to burn: why not burn the wood to displace fossil fuel for energy?

A: One reason in preferring burial to burning is that the energy density of wood is low, in fact, a factor of two lower than the current energy mix (Metzger et al., 2002). So from carbon point of view, it is better to bury wood and burn fossil fuel. Of course there are other issues to consider, and there are likely niches for both methods. The important thing is that, a large amount of wood suitable for burial/storage is decomposed every year, including dead trees that are getting killed by bark beetles. The earlier we can utilize them, the more carbon we can sequester because the production rate of the biosphere is limited. Indeed, burial/storage will save wood in 'carbon/energy banks' that are now carbon sinks, and could serve as energy reserve in the future should bioenergy such as large-scale cellulosic ethanol or advance wood combustion (AWC) become economical and environmentally sound.

Q: The market price of lumber wood is $90-100 for the amount of wood that can sequester a ton of CO₂.  Wouldn't it be foolish to shove it underground for less?

A: The market price of wood is mostly transportation and processing, and typically only 10-30% of the cost is incurred at the origin of wood collection. Estimate based on the cost of harvest/collection only, using data from forest engineering (http://www.cnr.vt.edu/harvestingsystems/Costing.htm) yields a cost of $10-20/tCO₂ sequestered, a competitive price even in the current carbon markets (24 euros on EUETS in 2009). So it is important to bury/store wood in situ to minimize transportation cost.

Q: How much CO₂ can be sequestered this way?

A: Theoretical potential is estimated at 5-15 GtC/y in the form of coarse wood produced in all the world's forests. Competition with other wood usage, land use and accessibility will set practical limits to this potential. Currently the world usage of wood product amounts to 0.9 GtC/y, so there is major extra capacity for carbon sequestration. The practical potential may be 1-5 GtC/y. In the US, WBS could offset 10-25% of the country's fossil fuel emissions. Research will be needed to better quantify these numbers.

Q: How long can the buried wood stay? How long can we maintain the stored wood?

References

Metzger, R. A., G. Benford and M. I. Hoffert, 2002: To Bury or to Burn: Optimum Use of Crop Residues to Reduce Atmospheric CO2, Climatic Change, 54, 3.

Scholz, F., U. Hasse, Permanent Wood Sequestration: The Solution to the Global Carbon Dioxide Problem, ChemSusChem, 2008, DOI: 10.1002/cssc.200800048.
 

Zeng, N., 2008: Carbon sequestration via wood burial. Carbon Balance and Management, 3:1; doi:10.1186/1750-0680-3-1. [Download from CBM]