CARBON IN DUTCH FOREST ECOSYSTEMS

The present stock of carbon in living biomass, litter and stable humus and the annual accumulation of carbon in the stems of fifteen forest types has been quantified from inventory data on growth and standing v olume, and forest soil information in combination with literature data on forest biomass. The study was carried out within the framework of the Dutch National Research Programme on Global Air Pollution and Clim ate Change. The forest area in the Netherlands equals about 330 000 ha . It mainly consists of young plantations of conifers such as Scots pi ne, Douglas-fir and larch on poor, dry sandy soils. The average age is approximately 50 years. The present average standing volume is 170 m3 ha-1 and the average volume increment was 9.0 m3 ha-1 yr-1 over the p eriod 1984-1989. At present, approximately 63.7 Mt C is stored in the entire forest, including dead organic matter in the forest soil. Almos t 60% of this is stored in the stable humus in the soil compartment. T he average carbon stock in the stable humus is 113 Mg C ha-1, whereas only 59 Mg C ha-1 is contained in the living biomass and 19 Mg C ha-1 is contained in the litter layer. The average stock in the living biom ass is largest for beech stands with 124 Mg C ha-1. Annually, about 0. 66 Mt C of atmospheric carbon is stored by means of stem volume increm ent when harvesting is not considered. On average, for the entire fore sted area, at present about half of the annual storage is harvested ea ch year, which means that the forest at present acts as a net carbon s ink to the amount of approximately 0.33 Mt C yr-1. At present, the lar gest net accumulation is attained in beech stands, and amounts to 1.8 Mg C ha-1 yr-1. The average net accumulation for the entire forested a rea amounts at present to some 0.97 Mg C ha-1 yr-1. Long rotations wit h species like oak, beech and Douglas-fir which may build-up a large s tanding biomass and which produce durable wood products, are most suit able for a long-term storage of carbon.