Predictable effects of intensified production and harvesting on the fertility of forest soils. II- the effects of silviculture

We defined the functioning of the ecosystem in our first article, devoted to the biological cycle (Ranger et Bonneau, 1984) and we now give an application of it to the management of mineral nutrient fertility in forest soils. Stress is laid on the relation between forest management and the export of nutrient elements out of the ecosystem, whether it relates to the choice of species, the length of the rotation, or the amount of the biomass produced that is harvested. By taking account of the average values of the inputs (atmospheric and weathering of reserves) it is possible to establish for each of the cases in question a balance sheet of inputs and outputs to describe the mineral nutrient balance of the rotation. Even if we overlook the qualitative changes which generally increase the 'output' term (changes in the organic matter, in the analytical properties of the minerals, etc...), it seems to be clear that a change-over to short rotations leads to a deficit budget (for all the major elements) in the great majority of forest soils. (authors)