GRAZING AS A CONTROL AGAINST GRASS-ENCROACHMENT IN DRY DUNE GRASSLANDS IN THE NETHERLANDS

A study in dune grasslands in two Dutch coastal dune areas suggests th at 'grass-encroachment', the dominance of a few tall grass species in formerly open, species-rich dune grasslands in the Netherlands, result s in a loss of species, notably therophytes, bryophytes and lichens, a s well as a strong reduction of the availability of daylight at the gr ound floor. Grazing with cattle and ponies as a control against 'grass -encroachment' has been studied in two coastal dune areas. Grazing wit h shetland ponies in 'de Zepeduinen' began in 1983. Aerial photographs of 1978, 1988 and 1993 were compared. After an initial increase in ta ll grass communities in both the valleys and the elevated dune ridges (8-20%) at the expense of more open vegetation, the photographs of 10 years of grazing revealed a decrease of tall grass cover (7-8%) and an increase of low grassland communities (4-5%). Grazing experiments in 'het Zwanenwater' started in parts of the area in 1984 and 1989. Compa rison of vegetation maps of 1986 and 1992 revealed that tall grass cov er increased over this period in the grazed areas (from 1-4% to 21-26% ), but open communities were still prevalent (38-53%). In the non-graz ed area, open communities declined dramatically (from 77% to 17%) and tall grass cover increased accordingly (from 3% to 53%). These prelimi nary results suggest that the present grazing regimes are perhaps not sufficient to stop grass-encroachment completely, but grazing seems a reasonably effective tool of management in terms of vegetation structu re.