The cool and humid climate of the boreal zone has created conditions suitable for accumulation of a large reservoir of carbon in the soils. About 40% of the estimated 1150 Pg reservoir of global forest carbon is stored in the soils of the high-latitude region. Global warming could lower the climate humidity. There is potential for a positive feedback into the climate system: CO2 emissions from fossil fuels => climatic warming => additional CO2 from boreal soils => additional warming. The carbon reservoir is 1.21.5 times larger in the boreal soils than in the atmosphere. The feedback mechanism can be very significant.
Carbon occurs in three large sub-reservoirs: peat formations, the humus layer, and mixed in the mineral soil. Measurements from Finland are presented which quantify the different sub-reservoirs. There is evidence that each sub-reservoir responds differently to changes in temperature and humidity.
Although many soils in Scandinavia are managed, boreal soils globally are mostly unmanaged. Natural processes control the development of the reservoirs: photosynthesis and increment, and the various respiration and decay processes (plant and soil respiration, decomposition, and fire). The concept NetEcosystem Productivity is used in ecology to describe the net impact of all these processes.
The processes affecting soil carbon are sensitive to climatic warming. Both fast and slow responses are involved. Many studies suggest that, in fact, the carbon reservoir in boreal soils would grow larger in response to an eventual climatic warming. Boreal soils would hence provide a negative feedback to climate warming. The premises of this conclusion are discussed.
Key words: climatic change, soil carbon reservoir, boreal forests.
Correspondence: Maximilian Posch, RIVM, P.O. Box 1, 3720 BA Bilthoven, The Netherlands
Telefax: +31-30-742971
E-mail: Max.Posch@rivm.nl