Effects of the age class distributions of the temperate and boreal forests on the global CO sub(2) source-sink function

• Published in: Tellus. Series B, Chemical and physical meteorology Vol. 47B; no. 1-2; pp. 212 - 231
• Main Authors: Kohlmaier, G H, Haeger, Ch, Wuerth, G, Luedeke, MKB, Ramge, P, Badeck, F-W, Kindermann, J, Lang, T
• Format: Journal Article
• Language: English
• Published: 01.01.1995
• ISSN: 0280-6509

The role of the temperate and boreal forests as a global CO sub(2) source or sink is examined, both, for the present time and for the next hundred years. The results of the Forest Resource Assessment for 1990 of the Economic Comission for Europe and the Food and Agricultural Organisation of the United Nations (1992) serve as the main database in this study. Out of the estimated total area of approximately 20[small solid circle] 10 super(6) km super(2) of forests and wooded lands in the temperate and boreal zone only approximately fifty percent is documented within the category of exploitable forests, which are examined in detail here. In this study, a general formalism of the time evolution of an ensemble of forests within an ecological province is developed using the formalism of the Leslie matrix. This matrix can be formulated if the age class dependent mortalities which arise from the disturbances are known. A distinction is made between the natural disturbances by fire, wind throw and insect infestations and disturbances introduced through harvesting of timber. Through the use of Richards growth function each age class of a given biome is related to the corresponding biomass and annual increment. The data reported on the mean net annual increment and on the mean biomass serve to calibrate the model. The difference of the reported net annual increment and annual fellings of approximately 550[small solid circle] 10 super(6) m super(3) roundwood correspond to a sink of 210-330 Mt of carbon per year excluding any changes in the soil balance. It could be shown that the present distribution of forest age classes for the United States, Canada, Europe, or the former Soviet Union does not correspond to a quasi-stationary state, in which biomass is accumulated only due to a stimulated growth under enhanced atmospheric CO sub(2) levels. The present CO sub(2) sink function will not persist in the next century, if harvesting rates increase with 0.5% annually or even less. The future state will also be influenced by the effect of the greenhouse climate, the impact of which may range from a stimulating effect on growth, which is calculated by the Frankfurt biosphere model, up to a transitional negative effect through a shift in vegetation zones.