ABSTRACT
With the exception of the important anomaly in western North America, the high latitude and high altitude coniferous forests of the northern hemisphere give way, in humid regions, to broad-leaved deciduous communities. Ultimately, in most cases, the coniferous life-form almost disappears. This change is usually achieved through a transition zone where the two life-forms exist side by side. The areas of competition are usually spoken of as zones of ecotone. The change in species-content as one passes through the ecotone is often imperceptible so that it is impossible to define its limits realistically and to show them on a map. In some areas, however, the ecotone is very wide and consists of coniferous and broadleaved species in almost equal quantities. Obviously such forests cannot be regarded as either coniferous or broad-leaved and it is customary to put them in a separate category known as 'mixed forest'. It seems likely that broad and distinct ecotones of this nature were the original vegetation in parts of north-central Europe, eastern Asia and north-eastern North America.
