Big trees grow faster

New paper in "Nature"
Rate of tree carbon accumulation increases continuously with tree size
Stephenson et al.
doi:10.1038/nature12914

You might very well suppose this is obvious. However it is opposed by more than a century of anecdotal forestry.

So, the authors get into the Big Journal for actually making the measurements, and linking them to 'scaling laws' that are seen as providing the (all-important) mechanism.

They don't argue that big trees are growing faster now than they have done in the past. That is treated in other studies and it does appear to to be strongly affected by rising CO2. With about 2000 years of tree-ring data available, that would seem to be a reasonable follow-up. It is (I suppose) related to the 'divergence problem' we have talked about before. Specifically that in recent decades, tree rings don't seem to be recording environmental signals in the same way they did earlier.

Is is not directly related to increased forest mortality, which is also happening now, and the same Stephenson and his (down the list) co author Van Mantgem have studied extensively.

Overall the forest-growth story is that the pluses are outweighing the minuses, and details of the global carbon cycle support that as well. How could that not be good news?

So I want you to notice this, even though it is not my main thing. I work on the other side of the street; decomposition. Dead leaves and wood decompose, thus letting the carbon back out of the forest.

You may compare a youngish forest that has just managed to produce enough leaves to cover the open sky, with one we'd call 'old growth'. Both throw down roughly the same amount of dead leaves each year, while the old one throws down more wood. Also seems obvious yes?

Well, the carbon in that dead wood decomposes 10-20 times slower than the leaves in the same locales. So now let's put it together. Carbon comes in faster and goes out slower from the old growth. Carbon sequestration is one thing that people look to forests to provide. Along with the occasional sheet of paper, stick, or plywood. Younger forests are the ones better suited for that, which I suppose has a lot to do with why foresters like them.

Two more things about old forests with their piles of half-decayed wood laying around. Critters live in that stuff. More often ugly and squishy critters than cute and cuddly ones, but biodiversity nonetheless. We say we like that.

The other thing about old forests is that Charles Darwin wrote about walking around in one, in "The Voyage of the Beagle" . He hated it (and generally, he was not a complainer in that book). I'm sure it was quite unlike the forester-managed woods he was familiar with from home.

Doesn't mean we should plant new trees. But there is some waiting involved, for some of the ecosystem services to get 'fired up'.

 

Eighty readers of my running on drivel. Should be grateful

Here is is an interesting sidelight on wood decomposition. In some oceans, it does get decomposed by unusual critters, by means that are rather different from decomposition on land. That gave Columbus (and later, the Spanish Armada) some problems with their wooden ships.

However in fresh water, teredo worms and gribbles are absent. Sunk wood can be remarkably well preserved. Have a look:

Superior Woods - Recovered Submerged Wood Timbers - Minneapolis

A, they're making money, and B, a brief insight into how forests "used to be"

I have not found a concise description of a similar thing in Ghana. There a reservoir was built (1960s), trees in the bottom, well, they're still there. The valuable species in the surrounding uplands were later cut and sold. Now, the valuable ones are so valuable that a company uses a submarine to cut them down (up?) and float them to the surface. Entertainingly, the sub is called Sawfish.

 

this is the link I should have sent

Triton Logging Inc. | Underwater Harvesting Specialists

interesting website. After I read up and send some emails, it will be clear if they are working with dendrochronogists to get some information from the rings. They really out to be because in a (rapidly) filled impoundment, all the tree die in the same year.