Vegetation mapping as an aid in detecting temporal vegetation changes in the Demer valley (Belgium)

Attempts to get an insight in the major physical processes which lie at the basis of the recent plant species diversity decline in Flanders are mostly based on a black-box analysis of species Lists. We argue that plant divers ity monitoring programs should be based on a geographically explicit vegeta tion description approach. In this paper we present a phytosociological ana lysis and subsequent vegetation mapping of the Demer valley between Diest a nd Werchter. We used G.I.S. analysis tools to compare the derived vegetatio n map with a vegetation map of the same area made in the 50's. Land use cha nged dramatically and a clear dichotomy could be noticed between land use c hanges on dry versus wet sites. Most ecologically valuable grasslands serio usly declined or disappeared as a result of urbanization, poplar plantation and intensive drainage and fertilization. Besides the total area of these grasslands, also the mean patch area decreased leading to smaller, spatiall y isolated communities. This development threatens the long term species su rvival within these remnants.