The ability of the forests to absorb carbon dioxide is related to a number of factors: the age of the trees, how the forests are managed, the local climate, the nutrient content of the soil and the level of precipitation.
The forests in southern Sweden absorb more carbon dioxide in a shorter time than the forests in the northern parts of the country. Conversely, more carbon dioxide is released from forest land in southern Sweden than in northern Sweden. This is because the rate of decomposition is faster in the south owing to the higher annual mean temperature.
- Seedling and young stands (1 to 20 years old) - forest land releases carbon dioxide after harvesting due to increased penetration of sunlight, which speeds up the rotting process in the soil layer. The trees are still too small to make up for the release of carbon dioxide.
- Younger and middle-aged stands - the trees grow fastest during this period and absorb far more carbon dioxide than the soil releases.
- Older forests (80 years and older) - the trees' growth and ability to absorb carbon dioxide decline as they become older. At the same time the forces of decomposition start to act. Branches fall to the ground and some trees die, which increases the release of carbon dioxide.
Why a managed forest is better for the climate than an unmanaged one
A managed forest is planted, cleaned, thinned and harvested at regular intervals over 300 years. A stock of wood is built up over a period of 70 years which is then mostly harvested. Wood and biofuel are used to replace other materials and sources of energy with an impact on the climate.
An unmanaged forest is allowed to develop freely over 300 years. The stock of wood is built up once – and then changes insignificantly over time. The trees act as a carbon sink, but in the unmanaged forest the substitution effect goes completely unused.