Een floristisch-oecologische waardebepaling nabij Utrecht ten behoeve van natuurbehoud en planologie

A floristic-ecological evaluation near Utrecht in behalf of nature conservancy and urban planning An alternative method to that of MENNEMA (1973) is proposed for the evaluation of data from floristic investigations, as there are practical and fundamental objections, particularly against the ‘vegetation value’ of Mennema. The main objection lies in the differences in size and homogenity of the sociological-ecological groups of VAN DER MAAREL (1971a), which are fundamental to Mennema’s method. The author introduces the ‘indication value for nature conservancy’ for every Dutch vascular plant. Some examples are given in table 2. Fundamentally these indication value is similar to the contribution of each species to the ‘vegetation value’ of Mennema. But it is now possible to take account of special factors, e.g. the origin of the species in the Netherlands (indigenous or neophyt), and for special environmental factors concerning the habitat of the species. The floristic-ecological value is the sum of the indication values of all species, recorded in the area. The results of a floristic investigation of 49 square kilometers in the vicinity of Utrecht (fig. I and 2) are expressed according to Mennema’s method (fig. 3, c), and to the floristic-ecological evaluation (fig. 3, e). It is the author’s opinion that the latter gives the best results in comparison with his field experiences with reference to the distribution of the botanical most important areas (fig. 7). Anyhow, it is clear that some parts of the valley of the rivulet Kromme Rijn have a great botanical significance, when considered nationally. Unfortunately the most important areas are now threatened by the construction of new roads and by the expansion of the town of Utrecht. Finally the author proves, that sociological-ecological groups can be useful to characterize phytogeographical districts (fig. 6).