Literally two lines later:
> But decaying wood and organic material releases carbon back into the air. A climax forest is close to a steady state: The rate at which it removes carbon from the air is roughly equal to the rate at which it releases this carbon.
Trees keep on growing, yes, but it’s the old, decaying material that releases CO2 back in the air again, compensating tree growth.
Edit: clarity.
https://www.cbc.ca/news/canada/how-old-trees-help-climate-1....
I think the point is that a forest reaches an equilibrium at some point.
The forest has new trees growning and consuming co2, it has old trees still growing and consuming co2, it has dead trees/branches that releases co2. It's mostly at a steady state when it has matured.
Still, if you planted that forest at a place where there was no forest, the co2 it has bound up in the trunks and roots is removed from the atmosphere as long as the forest stands. Which might be tens or hundreds of thousands of years.
A forest can be in any unbalanced state at any age, it obviously depends on the ratio of dead to living trees and their size, as well as the climate. It's not a closed system that would need to reach equilibrium at some point. Forests will keep growing and trees will keep growing as fast as the environment allows and unsurprisingly, additional CO2 will help.
> the research suggests that almost 70 per cent of all the carbon stored in trees is accumulated in the last half of their lives
https://www.nature.com/news/2008/080910/full/news.2008.1092....
http://www.flanderstoday.eu/current-affairs/old-diverse-fore...