Last fall Antony Pak gave a great presentation on biogenic carbon - which included some statistics on the carbon sink/source balance for BC forests - which showed that forests have an outsized effect on the province’s carbon emissions. Currently emissions due to forest fires and pine beetle infestation are termed natural disturbances and excluded from the accounting. This surprised me, and I decided to do a little more digging.
Is old growth logging sustainable?
Here’s what the literature says about old growth forests:
- To have a shot at keeping planetary warming below 2 degrees (a level required to avoid catastrophic crop failures and biodiversity collapse) intact forests must be maintained [Watson et. al. 2018].
- Assumptions that forests become net carbon emitters are based on observations of even-aged plantations, and in fact old-growth forests continue to sequester carbon both above and below ground [Luyssaert 2008, Wirth 2009, Stephenson 2014].
- Conversion of old growth to secondary growth forests results in net emissions to the atmosphere, even including carbon sequestered in wood products [Nunery & Keeton 2010, Trofymow 2008].
- Logging increases the likelihood of fire for moist forests and rainforests. For dry forests logging increases fire risks unless thinning is aimed at removing fuel loads accumulated unnaturally due to fire suppression [Lindenmayer 2009], releasing massive amounts of CO2 that are not included in carbon accounting.
- Beetle infestations of forests have long been linked to logging activities, where residues provide fertile breeding grounds, leading to outbreaks [Lejeune 1961, Aukema 2016] again the resulting emissions are excluded from carbon accounting.
Given the above, and considering that logging old-growth inherently leads to conversion to secondary growth, current LCA assumptions do not cover logging from old growth forests, e.g.:
WWF Quantis Biogenic Carbon Footprint Calculator, 2020
“The study is limited to managed natural forests and existing forest plantations, where the forest is assumed to regrow after harvesting. Deforestation, followed by land use change (e.g., from natural forest to agriculture), as well as afforestation projects (e.g., conversion of grassland to forest plantation) are outside the scope of this study.”
Therefore, it appears that LCAs for wood products assume that the timber is not being logged from old-growth forests.
How are old-growth forests being protected?
The various forestry certifications take the following stance:
SFI prohibits conversion of one forest cover type to another type except in justified circumstances, such as dealing with disease
CSA Z809-16 requires that ‘conservation of old-growth forest attributes’ is included in the public participation process under Criterion 1. It appears that CSA certification does not preclude logging old-growth forest.
Forest conversion to plantations or non-forest land shall not occur,
except in circumstances where conversion:
a) entails a very limited portion of the Forest Management Unit; and
b) does not occur on High Conservation Value Forest areas; and
c) will enable clear, substantial, additional, secure, long term
conservation benefits across the Forest Management Unit.
The NDP provincial government of BC recently commissioned a strategic review in old forests and has announced that they are deferring 352,739 ha of old forest harvesting. Although this leaves 3.75 million hectares of old forest available for harvest.
What can architects and engineers do?
Salvage timber is clearly the most sustainable, but unlikely to meet demand. For me I will be recommending a preference for SFI and FSC over CSA timber, and where possible specifying plantation harvest timber. I also think it’s necessary to make sure that LCA assumptions are clear, and possibly a separate LCA is required for old-growth harvest (not that I would condone harvesting old-growth).
Aukema, B. H., McKee, F. R., Wytrykush, D. L., & Carroll, A. L. Population dynamics and epidemiology of four species of Dendroctonus (Coleoptera: Curculionidae): 100 years since J.M. Swaine. (2016) The Canadian Entomologist, 148(S1), S82–S110. Cambridge University Press.
Lejeune, R., McMullen, L. and Atkins, M. Influence of logging on Douglas fir beetle populations. Forestry Chronicle, 37(4): 308-314. (1961)
Lindenmayer, D.B., Hunter, M.L., Burton, P.J. and Gibbons, P. Effects of logging on fire regimes in moist forests. Conservation Letters, 2: 271-277. (2009) https://doi.org/10.1111/j.1755-263X.2009.00080.x
Luyssaert, S., Schulze, ED., Börner, A. et al. Old-growth forests as global carbon sinks. Nature 455, 213–215 (2008). https://doi.org/10.1038/nature07276
Nunery, J.S., Keeton, W.S., Forest carbon storage in the northeastern United States: Net effects of harvesting frequency, post-harvest retention, and wood products, Forest Ecology and Management, Volume 259, Issue 8, (2010) Pages 1363-1375,
Stephenson, N., Das, A., Condit, R. et al. Rate of tree carbon accumulation increases continuously with tree size. Nature 507, 90–93 (2014). https://doi.org/10.1038/nature12914
Trofymow, J.A., Stinson, G., Kurz, W.A. Derivation of a spatially explicit 86-year retrospective carbon budget for a landscape undergoing conversion from old-growth to managed forests on Vancouver Island, BC, Forest Ecology and Management, Volume 256, Issue 10, 2008, Pages 1677-1691, https://doi.org/10.1016/j.foreco.2008.02.056
Watson, J.E.M., Evans, T., Venter, O. et al. The exceptional value of intact forest ecosystems. Nat Ecol Evol 2, 599–610 (2018). https://doi.org/10.1038/s41559-018-0490-x
Wirth C. Old-growth forests: function, fate and value–a synthesis. In Old-growth forests (2009) (pp. 465-491). Springer, Berlin, Heidelberg.