I would like to consider an old growth forest ecosystem such as a large part of the Amazonian forest. It is common to refer to such beautiful forests as a source of oxygen for the world. For example, the expression
Amazon: Lungs of the planet is very common (e.g. this BBC article). I would like to question such an expression.
My questions are:
- Does an old growth forest ecosystem produce more oxygen than it consumes?
- Does an old growth forest ecosystem fix more CO$_2$ than it produces?
I understand that such a forest can be an important carbon storage and that if we were to cut the forest down, burn the wood and pour concrete on the soil (to prevent regrowth), then we would definitely release a fair amount of carbon in the atmosphere.
That being said, I am wondering whether, as of today, these forests act as carbon sink or not. It feels to me that while trees accumulate carbon and produce oxygen while growing, this carbon is released when they die and in an old growth forest a tree must die for a new tree to grow. If carbon is being fixed, then it has to go somewhere and I think it is almost by the definition of an old growth forest that there is no more room for more carbon accumulation (competition among trees prevent it). So I would tend to think that calling the Amazonian forest the "lungs of Earth" is very misleading.
Some random WWF article
This WWF article seem to suggest that, contrary to my intuition, the answer to these two questions should be "yes".