I think it's best to look at this as mass preservation problem. Trees absorb CO2 from air and store in their bodies. Once they die, the CO2 gets released. Sinc

I think it's best to look at this as mass preservation problem. Trees absorb CO2 from air and store in their bodies. Once they die, the CO2 gets released. Since there's a limited tree mass per area unit that the ground can support, once you reach that mass the input and output need to zero out, since there's nowhere to store any additional CO2.