> I would have guessed that any kind of forests have quite limited cap how much carbon it could retain in dead wood
The article says, "We found that a forest that's developing toward old-growth condition is accruing more wood in the stream than is being lost through decomposition" and "The effect will continue in coming decades, Keeton said, because many mature New England forests are only about halfway through their long recovery from 19th- and 20th-century clearing for timber and agriculture".
Ah, overlooked they actually acknowledge the "cap" directly in the preceding paragraph, and even put it into "coming decades" time frame. Makes much more sense now, thanks for the pointer!
Still a bit confused about the emphasis in wood deposits in "streams" – reportedly way more effective, but I'd guess with very limited capacity to really "lock" the mass – compared to regular hummus – not that effective, but for forest with couple of centuries of growth ahead I'd guess way more capacious. Good news either way, though!
Reading between the lines in the article (which is of course always subject to incorrect interpretation) I think the reason for the focus on streams is just that nobody else has looked at that before and thus it is a factor not previously accounted for. Other sources have already been accounted for - they may be worth more than what is in streams, but it is already known so the article didn't mention them.
“Coming decades” is an understatement. It depends on local conditions but douglas fir pines in the PNW take 200-300 years to decay completely, so that’s centuries more of carbon capture as long as we let our forests rewild. Realistically a forest becomes old growth once there are at least three generations of trees in various states of decay. That may decades in warmer climates but much longer in the north.