If you grow a new forest in an area that was previously empty of biomass (not necessarily an easy thing to do), the trees don't all grow and then die and decomp

If you grow a new forest in an area that was previously empty of biomass (not necessarily an easy thing to do), the trees don't all grow and then die and decompose with nothing to replace them. Trees die, decompose, and others take their place. So long as the forest survives, the trees in that forest at any particular time are a net carbon sink.