OBJECTIVES OF THE THESISHeathlands in The Netherlands are vanishing due to the invasion of trees. The transition from heathland to woodland in Dutch heathlands may either proceed directly or is preceded by the development of an intermediate grass heath. These changes are due to natural succession in the absence of management. In addition to the absence of management atmospheric pollution i.e. increased inputs of nitrogen has accelerated the replacement of heather heath by grass heath.The main hypothesis in this thesis is that the encroachment of grasses in heathlands as well as the response of the vegetation to management and environmental change depend on soil type, climatic conditions, and previous management. This thesis deals in particular with the performance of heather (Calluna vulgaris) and grasses (Molinia caerulea, Deschampsia flexuosa) on dry lowland heath as a function of environmental conditions in a site, with the purpose of matching management options with site conditions (Chapter 1).CHANGES IN DUTCH HEATHLANDSEvidence for replacement of heather by grasses in The Netherlands was obtained from sequential air photographs of heathlands. It is shown that apart from the transition of heathland to woodland, even before atmospheric pollution started in the seventies, heather was already being replaced by grasses in sites where there was no periodic management. However, in most sites the increase of grasses has been accelerated appreciably during the last decade (Chapter 2).RESTORATION OF HEATHThe results of long term field experiments (since 1976) show that a heathland taken over by grasses can be restored by turf cutting. Other treatments i.e. burning, ploughing or mowing treatments had no result, or in the case of mowing (including removal of the biomass), the result was short lived (Chapter 3).The good result of turf cutting may be due to physical environmental changes or changes in nutrients. It is shown that the establishment of heather after turf cutting has partly a physical explanation i.e. can be ...