Can you expand a bit on that, since it doesn't match my understanding? Where does the carbon come from that young forests emit?
My understanding is:
A tree is a carbon sink, i.e. it captures carbon as long as it is growing (the carbon goes into its organic matter). Once it stops growing it has a constant amount of organic matter, a constant amount of carbon, and no net exchange of carbon. That is until it burns, or decomposes, or parts of it are eaten by animals, or whatever.
The same, but on a larger scale, goes for a forest, or any ecosystem really: when total organic matter increases carbon is captured from the atmosphere; when total organic matter decreases carbon is emitted.
Still to my understanding, young forests are forests that grow pretty rapidly and are therefore excellent in capturing carbon.
What am I missing?