Carbon budgets in fertile grey alder (Alnus incana (L.) Moench.) stands of different ages

Leaf litter accounted for the largest (44-61%) annual organic C input to soil, the fine roots contributed with 12-32% and the herbaceous understorey (aboveground + belowground), with 14-26% to it. Annual cumulative soil heterotrophic respiration (Rh) in the studied stands ranged between 2.6 and 5.8 t C ha−1 yr−1; C leaching was negligible, being 10-30 kg C ha−1 yr−1. The C sequestration to soil depended on previous land use; in the first forest generation, i.e. a stand growing on previous agricultural land, the annual Corg input into soil exceeded Rh, which indicated C accumulation in soil. Although grey alder stands are generally C accumulating ecosystems, the annual biomass production of the studied stands was highly variable; thus annual NEP depended on the effect of the year rather than on stand age. The current study demonstrates that use of repeated time-series measurements applied for stands of different development stages can provide more detailed estimation of C accumulation in forest ecosystems.