But the picture is of course more complex than new trees versus old growth forests with regards CO2 absorption. While treelings cannot absorb so much CO2 yet, it appears as if middle-aged trees (50-140 years) absorb more CO2 than old trees (in which CO2 is already stored).

Sadly capital asset models like the Wicksell/Faustmann Rotation that tell how to manage timber to maximize profit are not being used to similarly maximize CO2 absorption (right?). If reforestation is most beneficial before 140 yr, there should be intelligent rotation schedules, as in timber industry