Higher carbon storage in primary than secondary boreal forests in Sweden.

Boreal forests provide considerable global land carbon storage and uptake, but they are being rapidly transformed to managed secondary forests, with poorly quantified implications for ecosystem carbon storage. Here we present data from extensive mapping and field inventories of carbon storage in primary forests in Sweden and use multiple methods to show that primary forests store ~72% (70 to 74% across methods) more carbon than managed secondary forests in vegetation, deadwood, soils, and harvested wood products combined. Soils constitute both the largest carbon store and the largest difference between these forest types. The total carbon storage difference between primary and managed secondary forests is 2.7 to 8.0 times larger than previous estimates. Our results challenge estimated past and future contributions of boreal forest management to atmospheric carbon dioxide concentrations.