Meetings of the Botanical Society of the Netherlands

In a North Drenthe heath vegetation boundaries and gradients were studied. Relations between vegetation boundaries and the abiotic environment were detected. Three methods of quantifying the “amount of boundary” along a transect were compared. 1. A method of van der Maarel (1968) and Bellamy, c.s. (1969). The affinity (Jaccard’s coefficient) between each pair of adjacent quadrats is calculated (Grq). 2. Each species in a quadrat gets a score g=l when it is not present in both adjacent quadrats, else g—0. The sum of g’s within each quadrat is expressed as a percentage of the total number of species in the quadrat (Go)- 3. Of each transect as a whole the correlation coefficients between all species pairs are calculated and assembled in a matrix. In each quadrat the mean correlation between species expresses the amount of boundary (Grs). The third coefficient Grs turned out to be least oscillating and so presenting the most usable curves. An investigation of the relation between species and their presence within a boundary zone yielded information about the species of the Nardo-Galion. Factor analyses of the variables in each transect showed that sometimes relations between vegetation and environment cannot be analysed indirectly. A simple simulation was carried out. A number of variables between which all interrelations were known were representing the participants of a biocoenosis within an area. A comparison of factor analysis of random chosen stands and transect gradient analysis showed that the indirect method yields information about the conduct along a gradient of the vegetation as a whole, but that the study of relations between species populations and environment needs direct analysis.