Old growth red and white pine forest stands in Temagami retain a significant amount of sequestered atmospheric carbon dioxide which has accumulated over millennia. The living trees contain a huge biomass of heartwood, foliage, and other living tissue but that is not the most substantial reservoir of bound carbon. Giant standing snags (aka dead or dying tree) and downed logs composed of carbon-based organic matter fixed in centuries past decompose slowly in the closed forest environment releasing CO2very gradually over many decades. But the largest stock of stored greenhouse gas resides in the forest soil, duff, litter, and the coarse woody debris that accumulates on the forest floor. Although net productivity is low in these ancient systems, it is well established in the scientific literature that old growth stands continue to accumulate and sequester carbon until they undergo major disruption.
Harvesting old growth (even utilizing the shelterwood cut system) disrupts ecosystem structure and function and results in the release over a period of weeks or months of substantial amounts of the carbon that has been accumulating in these stands. The large amount of carbon stored within the soil component is exposed to oxidation and accumulated dead woody debris rapidly decomposes on the surface of the harvested landscape along with the harvesting residuals, all of which release CO2. Such greenhouse gas emissions would not be equivalent to fossil fuel emissions, but they would be releases of carbon captured pre-industrial revolution that would contribute to the current crisis.
It has been emphasized that some portion of the carbon in harvested wood products will remain stored for many decades as manufactured goods. There is some truth to this, however, the amount of carbon stored in this manner does not represent a large portion of the original organic matter present. On average, timber removed from a site is only about 50% of the living biomass. Of this quantity, bark, sawdust, cutting wastes, and finishing residues are disposed of resulting in a very small portion of the original carbon in the stand being fixed into long-lasting wood products.
The arguments that regenerating forest take up carbon rapidly or that manufactured wood products sequester some carbon for long periods are debatable in this context because they are only relevant if we cut the old growth and have to mitigate the release of the accumulated carbon. If we don’t cut the old growth in the first place, the forest will continue to retain the large amounts of carbon present for decades to come and continue to fix more CO2 in modest amounts.
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