Forests in the Temperate–boreal Transition—Natural and Man-made Features

Abstract

To fit nature into categories is always difficult, especially with complex vegetation. In the northern hemisphere forest vegetation in the temperate zone usually consists of deciduous forests and in the boreal zone often of coniferous forests. In the transition zone there are forests with deciduous trees, coniferous trees and also very often deciduous and coniferous trees mixed (later in this chapter referred to as mixed forests). In the Nordic countries this transition is termed the ‘hemiboreal’ zone (Ahti et al., 1968; see map in chapter 7). In Sweden this zone is about 600 km wide and in the western Soviet Union even wider. Thus, the hemiboreal zone covers large areas. In spite of this its main ecological features are less well understood than those of more southern and northern zones. This is due to intensive exploitation in historic times and the complex dynamics between deciduous and coniferous trees. The separation of natural and man–made factors affecting vegetation dynamics has been especially difficult. In this short presentation of the hemiboreal zone in Sweden the description of some important features and processes must be very brief due to space limitation. I present major landscape changes and their main causes over the last 1000 years. Keystone species, i.e. species whose presence affects the distribution and/or abundance of several other species or whose absence would cause cascading effects throughout a community, are sometimes treated in more detail. Examples of such species are major forest trees and shrubs, common vertebrate predators and herbivores, pollinators and seed dispensers.