Hard to believe: The long-standing notion that old forests are carbon neutral – that is, that from a certain age forests cease to absorb and accumulate carbon – has its origin from a mere decade worth of data from one single site.
Although timidly questioned every so often, this apparently wrong postulate has prevailed for more than 30 years, leaving its mark in the Kyoto Protocol which excludes old-growth forests from national carbon budgets.
The finding, reported in this week’s Nature, that old forests do accumulate carbon, and apparently in vast amounts, is therefore anything but marginal. Tropical forests were excluded from the study, because there are too few monitoring sites. But primary forests in the boreal and temporary regions of the Northern Hemisphere alone capture some 1.3 gigatonnes of carbon a year, the meta-analysis of data from 519 plots of forests between 15 and 800 years of age has revealed. An editor’s summary of the paper is here.
“Hence, 15 % of the global forest surface, which is currently not being considered for offsetting increasing atmospheric CO2 concentrations, is responsible for at least 10% of the global net ecosystem production,” the authors write.
Obviously, the carbon sequestered in old forest was previously accounted for elsewhere. Disturbingly, given that some offset profiteers praise tree planting as a panacea of sorts for climate change, young forests may actually be sources, rather than sinks, of CO2, if decomposition of soils and older vegetation preceded their creation.
Leaving intact and protecting old forests seems a far better option. This insight comes rather late, but better late than never. Oh, and it will really give climate negotiators something to think about.
My colleague Emma Marris has more in her news story here.