In this volume the conifer forests are treated in a context of ecosystems and biomes. The ecosystem integrates the interaction of the biotic and abiotic environment. The producers - the green plants - are interacting with consumers and decomposers. They give the structure to the ecosystem. The ecosystem is then characterized by its function expressed as cycles of carbon, mineral elements and water as well as the unidirectional flow of energy. Ecosystems are subject to perturbations - natural or man-made. The effects of the disturbances may be buffered or lead to a change into a new state. Successions occur. Biomes designate groups of ecosystems occurring over larger regions having similarities in vegetation, climate, and soils. We refer here mainly to boreal, temperate, Mediterranean and tropical regions or biomes and their forest ecosystems. Coniferous forests also occur in mountainous zonations. Treating a life form such as conifers, which occurs worldwide, means that there will be connections to other volumes describing other ecosystems or biomes in the Ecosystems of the World series. The present volume has two chapters on boreal forests - Chapter 2 Eurasian and Chapter 3 North-American, respectively. References to the boreal conifer forests are also to be found in Volume 7 on Temperate Deciduous Forests (Barnes, 1991, pp. 314-317, and Jahn, 1991, pp. 451-454, on North America and Europe, respectively). In the same way chs. 2 and 3 also contain some references to deciduous forests - for instance, the area of south of the taiga bordering the steppe region with deciduous elements. As some of the trees occurring there are also elements in the boreal environment, it has been considered important to describe not only the conifers, but also other characteristic elements of the boreal areas. Similarly, Chapter 5, "Coniferous forests of the temperate zone of Asia" and Chapter 6, "Non-boreal coniferous forests of North America" deal with some elements also occurring in the boreal chapters 2 and 3. Conifer species are frequently used as artificial tree crops and ornamentals. This topic has also been treated in another volume of this series - Volume 19, Tree Crop Ecosystems. Chapter 4 (Lines and Freer-Smith, 2001), 5 (Burdon, 2001), and 6 (Barnes, et al., 2001) of that volume discuss the use of conifers in plantations is discussed. Conifers have been planted for a long time in all the continents. These planted forests are often a dominating feature in many regions, which has led us to treat them also in this volume.
