VEGETATION TRANSITIONS OF FLOATING WETLANDS IN A COMPLEX OF TURBARIESBETWEEN 1937 AND 1989 AS DETERMINED FROM AERIAL PHOTOGRAPHS WITH GIS

The transition from open water to a swamp forest of a complex of ponds in the 'Polder Westbroek' (The Netherlands) in the period 1937-1989 i s studied. Changes between structurally different vegetation types are determined using remote-sensing data and a Geographical Information S ystem. The transition follows a clear pathway from open water through Phargmites/Typha-dominated community and Carex-dominated vegetation, t o Alnus-dominated vegetation. The rate of this transition shows strong correspondence to changes in local management, demonstrating the larg e human impacts on ecosystems in this area.