When they are DEAD they begin to emit CO2. It is called decay or rotting. :o) I guess that also constitutes old. While there is still photosenthysis, they are consuming CO2. I suppose there could be scenario when part of the tree is rotting while another part is still consuming CO2. Would that mean the tree is eating itself.
I think I have given myself a headache.
New growth forests use CO2, but OLD growth forests because of the rotting vegetaion below them consume O2 and RELEASE CO2. Does this help your headache. Thats when they should be cut!! LOL
“Would that mean the tree is eating itself.”
Astounding that Nature worked so great for millions of years even without Al Gore.