This study evaluates three important parameters of biodiversity in first generation Scots pine forests on sandy soils: herbal layer, natural regeneration and stand structure. The research was undertaken in the Belgian Campine Region, where the original oak-birch forest had been destroyed in the course of time and finally been replaced by monocultures of Scots pine. These pine forests are characterised by a low biodiversity. In maturing stands of this type, however, a spontaneous increase of biodiversity is noticed. Herbal species diversity is very limited in all age classes. Spontaneous establishment of Scots pine seedlings is presently a widespread phenomenon in aging stands. Different regeneration patterns are found. Mainly due to the lengthening of the rotation in combination with the ingrowth of several hardwood species, the homogeneous Scots pine stands are gradually and spontaneously transformed into heterogeneous mixed stands, featuring a noticeable increase of biodiversity. Nevertheless, selected human interventions may further increase biodiversity. The fundamental management principles are discussed: avoidance of big disturbances, lengthening of the rotation period, use of native tree species, utilization of natural regeneration, protection of small valuable biotopes and permanent monitoring.