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  • What happens to the biomass of a BC forest after logging?


    WHEN A CUTBLOCK IS LOGGED in BC, approximately 50 percent of the original living biomass is left in the clearcut as roots, stumps, unmerchantable tops, branches, part of the otherwise merchantable stem that are decayed, broken or wasted, small trees that are killed as collateral damage, the understory of plants, dead trees and course woody debris.

    Of the merchantable stems that are removed as logs, what happens to them?

    An unknown fraction are lost along the way, mainly by escaping from booms and/or sinking. But of those that make it to mills, about 52 percent of that volume is turned into wood chips or sawdust, according to the ministry of forests Major Mills Survey. This is used for making pulp and paper and various other short-lived products, like burnable, compressed sawdust pellets. These products account for about 26 percent of the original forests biomass.

    The other 48 percent of the volume of logs is milled into sawn lumber or turned into veneer or panel boards like plywood and OSB. Of these wood products, roughly 80 percent is exported, mainly to 3 countries: the USA, China and Japan. These exports account for about 19 percent of the forests original biomass. 

    The lumber products that are used in BC account for less than 5 percent of the original biomass of the forest that was logged.

     

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    The diagram below is the ministrys account of “fibre flows” that result from BCs logging activity. Keep in mind that this only accounts for about half of the biomass that is killed as a result of logging.

     

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    That graph references an awesome report I was unaware of, so thank you for that. You seem to misquote the amount of fibre used for lumber/sawdust, and I can't find in the report any reference to the volume of the slash left in the forest (whether for other uses or to be burned). Can you please clarify his for me?

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    Thanks for your question David.

    Let’s move left to right across the graph. The green rectangle on the left represents the total biomass of a forest stand before it was clearcut.

    To its right, the gray square represents the biomass of the stand that was killed by logging but was not removed from the clearcut. The different kinds of biomass left behind are described above. The stuff that wasn’t removed amounts to about 50 percent of the total biomass. The ministry of forests does not estimate this fraction (at least not in public), but a few scientists have. The Evergreen Alliance has used a study done by Dr Suzanne Simard to arrive at 50 percent for a BC-wide average. You can read more about that here. The methodology we are using is a work in progress. The percentage would vary from clearcut to clearcut, depending on a number of things like species composition, seral stage and site-specific factors.

    Moving to the yellow rectangle: That reflects the fact that 52 percent of the biomass that is removed from the clearcut as logs becomes wood chips and sawdust. Where does that "52 percent" come from? It’s derived from the ministry’s diagram of “fibre flows,” below the graph.

    Of the 55.3 million cubic metres in 2019 that was trucked out of the woods, here’s how it breaks down into different fates:

    Log exports: 4.7 million cubic metres, or 8.5 percent. We are not including log exports in this account since they are milled overseas and we don’t know what becomes of them. So we are accounting for 50.6 million cubic metres. In 2019 that volume became:

    Sawn lumber: 17.3 million cubic metres, or 34 percent.

    Shakes & Shingles: 0.5 million cubic metres, or 1 percent.

    Veneer & OSB: 6.14 million cubic metres, or 12 percent.

    Other mills: 0.5 million cubic metres, or 1 percent.

    Those add up to 48 percent.

    The rest, 52 percent, became sawdust or wood chips.

    But that’s just 52 percent of the biomass that was removed from the clearcut, which was only 50 percent of the total biomass killed. So 26 percent (.5 x 52) of the original biomass becomes sawdust and wood chips through the milling process. That’s the yellow square.

    As just noted, “lumber” (see list above) accounts for 48 percent of the biomass removed from the clearcut, or about 24 percent (.5 x 48) of the original biomass of the forest. Since about 80 percent of that 24 percent is exported, that gets broken out as 19 percent (.8 x 24) of the original biomass (light blue).

    The remaining 20 percent of lumber is used in BC. That works out to about 5 percent (.2 x 24) of the original biomass of the forest, and that’s shown in orange.

    Clarity, right?

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