EFFECTS OF VEGETATION MANAGEMENT AND RAISING THE WATER-TABLE ON NUTRIENT DYNAMICS AND VEGETATION CHANGE IN A WET GRASSLAND

1. The results of a restoration experiment carried out on a permanent grassland on peaty, heavy clay in the Netherlands are described. The e xperiment started in 1985, 7 years after fertilizer application had ce ased, and was designed to provide insight into ecologically significan t processes accompanying restoration. An analysis was made of the effe ct of management regime and of raising the water table on nutrient ava ilability, dry mailer production, tissue nutrient concentration, dynam ics of species numbers and plant species replacement. Three management practices were compared: cutting and removal (RR), cutting and mulchi ng (M M), sod removal in 1985, and thereafter cutting and removal of t he hay (RS). Data are presented on changes during a 5-year period. 2. No trend was discernible in soil pH, total C, N and P in the RR treatm ent; extractable P and K decreased sharply in the field with the raise d groundwater level. 3. Nine years after fertilizer application ceased , dry matter production had fallen from 10-11 to 6-7 t ha(-1) year(-1) . In the subsequent 5 years of the experiment it declined to 5-6 t ha( -1) year(-1) when all cut biomass was removed. and to about 4 t ha(-1) year(-1) after sod removal. Mulching caused an increase to 11 t ha(-1 ) year(-1). No effect was seen of the raised water level. 4. The dry m atter yield of the first June cut in the RR treatment decreased. The t issue It concentration also decreased, but no increase of the tissue P concentration was detected. II was concluded that the availability of K and to some extent of P was more important than N availability in e xplaining the decrease in dry matter production. The tissue nutrient c oncentrations were not influenced by the water table. 5. Sod removal t o a depth of 5 cm resulted in the lowest productivity and the lowest t issue concentrations of P, while tissue concentrations of N and It wer e not affected. 6. Raising the water level resulted in a more rapid es tablishment of species indicative of wet conditions, some of which inv aded from nearby ditches. 7. The trends of dominant species are descri bed with a set of response models. The species were ranked from disapp earing to colonizing species. The relationship between rank order of r eplacement and indicator values of species was investigated. Raising t he water table resulted in species indicative of wet conditions becomi ng dominant, independently of vegetation management. The removal of nu trients resulted in the appearance of species with a lower maximal hei ght, indicative of lower P and K availability.