Policy brief: Nitrogen budgets and the link to carbon sequestration in the Nordic forests

We have quantified annual changes of N stocks in forests in Sweden, Finland, Norway and in Denmark in two independent ways. First, we quantified major inflows (atmospheric deposition and biological N fixation) and outflows (leaching of N to runoff and tree harvest). The N outflows were between 70% and 130% of the N inflows, not indicating major loss or build-up of organic matter in any of the four countries. Then we calculated N stock change in forests based on annual C stock changes reported to UNFCCC and known C/N ratios. All four countries report annual increase of forest C stocks. The sources of N to make the C stock increase possible have not been identified in the N budgets based on inflows and outflows. The discrepancy between forest N and C budgets raises the question of the consistency between reported N and C flows and stock changes.