Forest Carbon Management: Let's Brainstorm The Trade-offs


Image credit:USDOE, pdf file, Emissions of Greenhouse Gases In The United States, 2008.

Often lately when I post numbers, and especially if I offer a definitive analysis on climate, I get blasted by some of you data-drivens, and endure a few silly personal attacks. Let's try something different this time. I'll put up my brainstorming list - regarding the above graphic - and you tell me what conclusions would be valid or if I missed any trade-offs.

Let's start with basic concepts. The total US forest-carbon pie can not increase significantly, inside a decade, based on organic growth. Some uses of one or more slices can reduce the total carbon stored in a few years, however. Individual slices can be increased to make up for decreases elsewhere.I begin with above-ground biomass in the USA, and brainstorm from the graphic, clockwise, discussing the millions of metric tons carbon in storage and possible tradeoffs.

  1. Bring up forest carbon and most people think you are talking only about the 50% of forest carbon as above-ground, living biomass (452 MMT). Note: Logging subtracts instantaneously from this category, but in northerly forests, the Candian boreal especially, stumps, roots, and leaf litter stay around for many years due to the cooler climate and acid soils. The opposite is true in more southerly forests. We should not compare northerly (apple) and southerly (orange) forests without making this very clear.
  2. Once you put wood in any form into a landfill (64 MMT/7%), the carbon stays there for decades, maybe centuries. Recycling and re-use keeps the carbon roughly the same: stored. Conversely, diverting wood from the landfill to a biomass burner, whether for building heat of electricity generation or both, pulls that carbon out of the storage pie.
  3. You can make wood a more common building material - LEED buildings often do - diverting carbon from the above ground slice and into the wood products slice, keeping the carbon locked up (37 MMT/4%). If wood is imported, above ground slice stays as it is. If harvested locally it goes down. Only way to keep the pie size constant in global terms is to require replanting regardless of source.
  4. Soil organic carbon - this would be in addition to root material - accounts for 159 MMT/18% of the stored carbon in the pie. Remaining northern forest soils generally are of poor quality for farming due to rocks, acidity, and short growing seasons. The opposite is often true for more southerly forests, at least in the short term. Analogous to the apples and oranges idea presented for above-ground biomass carbon.
  5. Forest litter accounts for a 71MMT/8% slice of the carbon pie. Given a chance, someone would probably propose harvesting it and burning or feeding into a cellulosic ethanol plant. Let's hope not, as it would open up the soils for rapid erosion.
  6. Dead wood is 37 MMT/4% and likely rising rapidly in the USA due to the pine bark beetle and other invasive Asian insects. Given our metaphorical habit of "getting rid of the dead wood" I suspect there will always proposals afoot to log dead wood, either for product manufacture or for burning. Arguably, manufacturing is the better option as it keeps carbon in storage longer; but, to the extent that living disease-resistant trees are planted to replace the dead wood, use of dead wood as biofuel or as ethanol feedstock displaces fossil fuels and is thus a second place "good."
  7. Below ground biomass (91 MMT/10%) would be stumps and roots of course. Generally, these are grubbed out and/or burned in preparation for farming or highway and building construction. If the intent is to keep it as forest, below ground stays. It is definitely a possibility to make roots and stumps biofuel feedstock. Doing that as a logging adjunct eliminates the slice. See point 1 for discussion.
Update: looking these slices over, it's easy to see why reporters (and the reading public) get confused over the various studies that have come out on forest versus "tree" carbon storage. If a politician favors logging to bring jobs and expand the tax base, he'll cite a study that only measures above ground living biomass. If an environmental interest favors wilderness preservation, they'll add up all the slices they can, which is objectively sensible, but which leads observers wondering if anyone is "right." Add to that the apples and oranges problem I described and it's a formulae for political spin and management gridlock.

OK have at it.

Tags: Buildings | Forestry