Carbon and nitrogen pools in an old-growth, Norway spruce mixed forest in eastern Finland and changes associated with clear-cutting

Abstract

The amount of carbon (C) and nitrogen (N) removed in stems after clear-cutting a forest in eastern Finland is compared with ecosystem pools (above- and below-ground tree and understorey vegetation biomass+ organic layer +0–60 cm mineral soil layer) and fluxes before clear-cutting. The tree stand was an old-growth mixed coniferous forest dominated by Norway spruce. The ecosystem pools of C and N before clear-cutting were 175 536 and 2848 kg ha −1, respectively. Most (62%) of the C was in living vegetation, mainly trees (60%), whereas most of the N pool was in the soil (80%). C and N pools in understorey vegetation were small (<2% of ecosystem pools) and those in dead tree compartments were somewhat greater (C: 8%; N: 4%). The annual net uptake (defined as net accumulation in tree biomass+aboveground litterfall) of C by trees was 2013 kg ha −1 and that of N was 16.1 kg ha −1. The annual return to the forest floor as aboveground litterfall was 958 kg ha −1 of C and 12 kg ha −1 of N, corresponding to 48 and 75% of annual net uptake, respectively. During clear-cutting, some 239 m 3 ha −1 of stemwood (overbark) were removed from the site, corresponding to 32% (C) and 3.0% (N) of the pre-harvest ecosystem pools; branches and foliage were left on site. The pool of C in living vegetation was reduced by 89% and that of N by 81% while the C pool in dead vegetation increased fourfold and that of N somewhat less. Our results indicate that clear-cutting will affect the C and N pools and fluxes of forest ecosystems significantly, even though some living trees are left on site.