VARIATION IN SOME SALTMARSH AND DUNE VEGETATIONS IN THE NETHERLANDS WITH SPECIAL REFERENCE TO GRADIENT SITUATIONS

Abstract

Variation in vegetation as related to variation in some environmental factors was analysed in five quadrats, four of 32 sq. m and one of 64 sq.m, laid out in different coastal saltmarsh and dune vegetations including two distinct gradient situations. Vegetational variation was measured with five methods, viz. species diversity (number of species/area, α Williams, formulas of Margalef and Shannon applied to frequency data) and floristic fall between adjacent subquadrats (I = A + B − 2C). Environmental factors examined included detailed height measurements and analysis of soil samples for six factors, viz. moisture, pH, N, CaCO3, humus and e.c., taken in July and October-November. The results show how environmental variation is reflected in the vegetation, the total number of phanerogams in the quadrats ranging from 2 to 61. Highest species diversity was observed in the middle part of local environmental gradients, and frequency and distribution data revealed how four different types of species contribute to this high diversity, the most interesting being those species that are confined to the gradient. In one case a very high number of species (45 per sq. m.) was found in the gradient. The methods applied for measurement of vegetational variation are briefly discussed.