From a climate perspective, what matters is not the growth rate of a tree, but the amount of carbon sequestered at maturity, and the length of time this sequestered carbon "spends" in the ecosystem. As a forest grows and matures, it reaches a "steady state", as ecologists call it. What is that? A situation where the amount of carbon absorbed by trees each year is perfectly balanced by the amount of CO₂ released through respiration by the plants themselves, as well as by the microorganisms living in the soil.