Do the distribution patterns of vascular plant species correspond to biogeographical classifications based on environmental data? A case study from northern Belgium.

摘要

Belgium has a long tradition of so-called 'biogeographical' classifications that are actually based on environmental (mainly geological, hydrological and climatic) variables. Ironically, no serious attempts have been made to examine their correspondence to distribution patterns of major species assemblages. We here analysed the distribution of vascular plant species in northern Belgium. The distribution data were derived from a grid based mapping scheme during the period 1972-2008 of all vascular plant species in 6495 grid units of 1 km2. We first used the K-means clustering method to group grid squares on the basis of similarity in plant species composition. Subsequently, we regrouped the resulting clusters into a smaller number of geographically coherent distribution groups. This yielded classification of the grid units into nine major phytogeographic square groups that are spatially well separated. The distribution of these groups is largely determined by soil type, as evidenced by analyses of Ellenberg indicator values and by the correspondence with soil types distribution. Three of the phytogeographic square groups coincide with geobotanical districts and/or ecoregions that were formerly defined using environmental factors. However, a large number of other 'biogeographic' entities appear ill-supported by our analyses and two of our phytogeographic groups are not recognized within the existing 'biogeographic' classifications. Our results provide a well-founded botanical basis for the delimitation of phytogeographical regions in Flanders that is based on the actual distribution patterns of a large number of plant species, rather than of a pre-defined small selection of indicative species or environmental factors.