A mature forest is a perfectly balanced carbon sink, with carbon released through death and decay, equal to the amount of carbon fixed by its growth – a climax ecosystem. Once it has reached this state it does not fix additional carbon. There it is, a giant store that would release a huge amount of carbon if burned, but while alive,it simply maintains itself. You can call the Amazon rain forest the lungs of the world if you like, because it does indeed respire. But don’t fool yourself that it is producing any net reduction in atmospheric CO2. For that you need young trees growing. Recent talk of achieving significant reductions in atmospheric CO2 by planting huge numbers of trees are not inherently unrealistic. They would give us a breathing space of perhaps 200 years before their growth starts to slow, 200 years to get in place a carbon neutral energy system, perhaps even harnessing something perfectly, metronomically reliable such as the tidal movement of water.