Vegetation succession on the dunes near Oostvoorne,The Netherlands; a comparison of the vegetation in 1959 and 1980

The vegetation of a 150 ha coastal dune area in the SW Netherlands was carefully analyzed and mapped at a scale of 1:2500 in 1959 and 1980. About 600 relevés were treated numerically. 127 vegetation types were distinguished, the overlap in community composition between the two years was very small. An intermediate level between this community level and the level of the structural-physiognomic formation was adopted. 56 so-called subformations, in which floristic and structural characters are combined, have been recognized and the overlap was then considerably larger, at least in number of types. Ordination results suggest that in each subset: grasslands, dune slacks, woodlands + scrubs, the first axis reflects floristic differentiation along with progression. The ordination of the entire material shows moisture as the main factor underlying the first axis, zonation as the second and nutrient status as the third factor. Change in vegetation was detected through a network overlay with 2 300 points for each of which the transition between 1959 and 1980 was scored. The pattern of change between 1959 and 1980 is apparently multiple pathway in type. This would be one of the few examples of such a pattern to be established on the medium term level of change, which is considered as succession sensu strictu. On an areal basis the change in vegetation is extremely large; even on the subformation level only 15% of the area was found to be unchanged, and on the community level only 4%. The overall trend is progression with a strong increase in the area of tall scrubs and woodlands. Retrogression also occurs, partly as a result of disturbances such as fire, partly due to local death of a dominant woody species. This latter phenomenon is interpreted against the background of the starting point of the succession; a sudden release of the inner dune area from overgrazing by cattle and a subsequent rapid dune development (outer dunes) on the beach in front of the inner dunes. Both species and community diversity increased, which is related to both differentiation under progression and to retrogression.