[diedyesterday]

A subtle point that is often missed is that only a growing plant population and ecosystem will have a positive oxygen balance and negative CO2 balance (trapping CO2 as tree biomass at ever increasing volume). Stable ecosystems reach an equilibrium and the carbon cycle stabilizes and net oxygen/CO2 production consumption becomes zero.

To increase net oxygen levels in the atmosphere and reduce CO2 levels we would also have to eliminate a lot of the microorganisms that help recycle dead trees and go back to the Paleozoic era and before when these organisms didn't exist and the Earth witnessed several glaciation events.

Adding more stable forests to the world does not reduce CO2 levels or increase oxygen levels (relative to after it becomes a stable forest). It just speeds up the carbon cycle.