Biogeographical study of West Siberian hemiboreal forest associations with species range overlay methods

The geographical distributions of plant communities are usually inferred from mapping relevés. Here, we study another approach to map the ranges of associations and higher syntaxa: the joint distribution of the constant species of the associations, i.e. those species most frequently found in the relevés. We ask whether the joint distribution of the species reflects the distribution of the associations and higher syntaxa. Because of limited availability of plant distribution maps we consider species occurring in more than 40% of the relevés of four associations belonging to Western and Central Siberian hemiboreal forests of the class Brachypodio pinnati–Betuletea pendulae. Those species are the most informative for syntaxonomic considerations. The joint distribution is established by overlaying the distribution maps of the species and numerically compared with the mapped distribution of the vegetation communities using Cohen's Kappa. Most species occurring in the associations have a small to mid-sized range. The range size distribution of the contributing species approaches a normal distribution after logarithmic transformation of the range sizes. The geographical extents of the associations are well reflected by the overlays of all constant species. Removing sequentially the species beginning with those having the smallest distribution ranges from the overlay leads to progressive loss of similarity between mapped and modelled range of the associations. For the higher syntaxa (order and class) the similarity between mapped and modelled range increases first but drops at the end of the removal procedure. The less widespread species are particularly important for the recognition of a local plant community, i.e. the association. In contrast, more widespread species allow the definition of the ranges of higher syntaxa and reveal more large-scale geographic relationships of the vegetation. From our quantitative assessment of mapped and modelled maps of the distribution of plant communities, we conclude that the overlay method is useful to infer the geographical extent of plant communities.