Large forest area, ancient woodland of beech forests, just south of Brussels. In this forest, numerous research activities covering silviculture, forest history, biodiversity inventories, geomorphology, recreation etc... have taken place. Therefore, the complete forest is proposed as an LTSER-platform. Within the forest, two active long-term ecological monitoring programmes are present: - one ICP Forests Level II intensive forest monitoring plot (permanent sampling since 1987) - strict forest reserve monitoring programme on an area of 100 ha (periodic sampling of 15 ha since 1986, extended to 100 ha in 2000) On July 7th 2017, the strict forest reserve 'Joseph Zwaenepoel', together with 4 other unmanaged reserves in the forest, was added to the UNESCO Natural Heritage Site ' Primeval Beech Forests of the Carpathians and Other Regions of Europe' (http://whc.unesco.org/en/list/1133). Besides these, a large number of former research projects, PhD research and a detailed management follow-up make the Sonian Forest one of the best mapped and documented forests in Belgium / Europe.