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 that 'grass-encroachment', the dominance of a few tall grass species in formerly open, species-rich dune grasslands in the Netherlands, results in a loss of species, notably therophytes, bryophytes and lichens, as well as a strong reduction of the availability of daylight at the ground floor. Grazing with cattle and ponies as a control against 'grass-encroachment' has been studied in two coastal dune areas. Grazing with shetland ponies in 'de Zepeduinen' began in 1983. Aerial photographs of 1978, 1988 and 1993 were compared. After an initial increase in tall 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. Comparison of vegetation maps of 1986 and 1992 revealed that tall grass cover 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-grazed area, open communities declined dramatically (from 77% to 17%) and tall grass cover increased accordingly (from 3% to 53%). These preliminary 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 structure.