Sustainability issues related to forest soils : Forest soil fertility: definition and management

Many forest ecosystems grow on acid and nutrient poor soils. In the context of decreasing atmospheric inputs and the intensification of silvicultural practices (changing tree species, increasing biomass exportation, forest mechanization), the sustainability of forest soil fertility is a major concern. Understanding how forest ecosystems will respond to increasing the external nutritional/silvicultural/climatic pressure is necessary to forest managers ensure the forest ecosystem sustainability. The main objective of this talk is to present the basic concepts of forest soil fertility and discuss the potential impact of silvicultural practices on it. TIn agronomy, soil chemical fertility is defined as the pool of plant-available nutrients in the soil at a given time and compared to nutrient requirements established for the different tree species. Forest ecosystems, however, grow over longer time spans (from several decades to centuries) and stores of plant-available nutrients mainly originate from the long term biological cycling of atmospheric and mineral weathering inputs. The limits of the “fertility = soil reservoir” concept and the basic principles of a new concept which takes into account the specificity of the chemical fertility of forest ecosystems will be discussed. The potential impact of silvicultural intensification on planted forest soil fertility will be presented through the following examples: tree species changes, increased biomass exportation and harvest mechanization