Recently CORRIM published their Trillion Trees Report which aims to flesh out the concept, and advocates for using timber as carbon storage. Unfortunately, right at the beginning of the report the bias of CORRIM is displayed with three assertions that are used to justify the remainder of the report:
- the rate of a forest’s growth declines with age as more suppressed trees die, reducing the net rate of CO2 removal as the forest matures (Gholz, 1982; Lippke et al., 2011a; McArdle et al., 1961).
- Carbon (C) in wood from dead forest trees and other organic matter combines with O2 by decomposing or burning to re-form CO2 that is released back to the atmosphere (Oneil & Lippke, 2010).
- Consequently, in aging forests, CO2 sequestration rates slow down and may even release more CO2 than they are removing, especially if fires occur. In effect, growing forests provide a one-time reduction in CO2, not a sustained reduction.
Now what is really interesting is that when we look at the literature there is a divergence between climate scientists who posit that forests continue to sequester carbon with age, and forestry researchers who claim sequestration rates peak and decline within 100 years. Obviously this has huge implications for forestry management, and EPDs for timber based products. This is a serious discrepancy that has important implications for policy development. Deforestation accounts for 15% of global emissions and it is imperative that we get the balance right.
This difference appears to me to have arisen due to differences in methodology, climate scientists use Eddy-Covariance to measure carbon flux over large areas, whereas forestry research measures the total board-feet of saleable timber within individual stands and tries to extrapolate from there. Thus forestry research deliberately excludes biomass from the understorey and below ground. This paper attempts to reconcile this discrepancy.
Leaving aside that logging practices increase risks of fire and infestation, the figures used in the CORRIM report appear erroneous, the report references Lippke et. al. 2014 which claims that forest sequestration reaches a maximum of 200 TCO2-e/ha, however in surveys conducted in the 1970s Waring & Franklin, 1979 measured old growth forests in the same study region had biomass densities between 600 to 3,500 tons/ha - so roughly 300 to 1,750 TCO2-e/ha.
Forestry research also tries to impose limits on forest carbon sequestration on the basis of limited nitrogen availability, completely ignoring the nutrient exchange of nitrogen and carbohydrates between mycorrhizal networks and trees. Established and old growth forests can be thought of as giant carbon pumps that are continuously pushing carbon into the soil. It should also be recognized that these ecosystems take centuries to establish and cannot be simply replanted with genetically limited stock in a matter of a few decades.
Bellassen and Luysseart, 2014 provide a great summary and pragmatic analysis of the situation. In the meantime, the following should be made very clear:
- Biogenic sequestration must include consideration of the feedstock of timber, and conversion of old growth forests would result in vastly increased embodied carbon of timber products. This also needs to consider the proportion of timber that makes its way into long term use compared to short term products / fuel, I have seen a figure of only 20% of logged timber is used for long term products. Other affects of logging operations (road clearing, degradation, etc.) should also be included.
- FSC actually allow old growth timber to be certified as sustainable when there is no other economic opportunities for the local people, this is a perverse extension of the colonial mindset, effectively the west can extract resources from peoples that it has severely disadvantaged.
- Reliable supply chain information is absolutely imperative and specifiers should require that timber products are only ever sourced from sustainable plantation forests (or better yet salvaged timber).