Afforestation of agricultural land is a current interest in Flanders and in Europe. Fertilization of agricultural land has caused an accumulation of nutrients in the top soil layer, of which phosphorus (P) is particulary persistent. P concentrations are still elevated hunderd to thousand years after abandonment of agricultural practices. This persistently elevated bioavailable P is a paradox for ecosystem fulfillment of new forests on agricultural land: a higher bioavailability of P can on one hand stimulate stand productivity and tree growth, but on the other hand limit the development of typical forest plant communities and other associated organisms. Limitation of bioavailable P is a necessity for ecological recovery of species-rich target communities and the preservation of endangered species. The main objective of this project is to study the tree-species dependent long-term changes in P fractions as a consequence of afforestation of agricultural land. The study aims to deliver a statistical model that predicts relationships between the bioavailability of P and the proportion between different soil P fractions as a function of forest age and tree species.