The boreal element

The boreal element in Europe is a northeastern element centred on the great conifer formation, the taiga, of northern Russia and Siberia. Boreal species form a series of equiformal progressive areas in the sense of Hultán (1937), from species with a very restricted distribution in northern Russia and perhaps penetrating into northern Finland to species with a much wider distribution, reaching the northern parts of the British Isles and the higher mountains of the Iberian Peninsula and the Balkans. It is typically a forest element. Only a few species extend north of the arctic forest-limit or much above the altitudinal timber-line. The distribution patterns show that boreal species tend to be absent from areas with mild winters along the southwestern lowlands of Europe. Such species were called ‘southwest coast avoiders ’ by Conolly & Dahl (1970) (see also Dahl 1951). They are able to tolerate high summer temperatures as shown by their occurrence in the lowlands of eastern and Central Europe. In this respect they differ from the true arcticalpine plants. However, in the southwest they are restricted to higher elevations. Climatic correlations Many of the boreal species have distribution patterns that are the inverse of the atlantic species. For example, the horizontal distributions of Picea abie and Ilex aquifolium overlap only in the former Yugoslavia, but there Picea grows in the mountains whereas Ilex is restricted to lower elevations. Another example from Norway, pointed out by Blytt (1869), is that only in a restricted area along the Sognefjord does the atlantic species Digitalis purpurea occur in the same area as the boreal Aconitum septentrionale .