Natural forests mainly exist as forest reserves in different European countries because the occurrence of original forest structures has decreased very rapidly during the last millennium. Especially the public awareness on the decline of natural forest ecosystems and the intention to practice a more nature oriented silviculture in forest management have set the focus on virgin- and semi-natural woodlands. The findings made in forest reserves in the recent past and in present research projects will allow to compare undisturbed and managed forests of all development phases, giving valuable information for practical forest management and the possibility of integrating biodiversity indicators into forest inventory. The main objective of the report was to summarize definitions on the state of forest ecosystems (e.g. virgin-, semi-natural-, or artificia forests) and to list categories of protected areas because their use, on an international level, is often not standardized and leads to misunderstandings. The selection criteria for establishing forest reserves also vary considerably in European countries. For these reasons it seemed appropriate to distinguish forest ecosystems and forest reserves by their origin of development and their history, management and protection status. The description of these terms can be regarded as a sound basis for the international discussion on the criteria and development of sustainable forest management regimes. The definitions can also be seen as a contribution to determine forest ecosystems and forest characteristics on an international scale. Depicting various parameters which describe biodiversity have to be based on the fact that forests occur in different climatic zones, resulting in a large number of vegetation types, each having its own typical characteristics. The development processes in temperate and boreal forest ecosystems are outlined in the report, giving an idea of the importance of changing ecological factors. As natural disturbances play a major role in the boreal forests (e.g. wildfires), unmanaged forests of the temperate zone mostly appear as a mosaic of various development stages. Therefore, biodiversity indicators will receive different weighing on a regional scale as well as at an individual stand level. Traditional pristine forest research has accomplished a great deal of work in the fields of structure and dynamics of undisturbed forests. The results from these studies and the fact that permanent plots have been observed for many decades are of high value for all examinations dealing with unmanaged woodlands. However,a gap in the traditional research is the absence of questions concerning biodiversity, due to the minor importance of this topic during the past decades. In comparison, ecosystem oriented research deals with very specific subjects of forest ecosystems making it difficult to integrate results into practical forest management. The methodology used in connection with these studies is very advanced and therefore of high interest for the formulation of questions on depicting biodiversity indicators in undisturbed forests. Trees and stand structure are in close interaction with other components fo the forest ecosystem such as ground cover vegetation, fauna and soil. For this reason stand structure, the dynamics and development of forest stands could play a key role in the description of biodiversity indicators in undisturbed and managed forests and woodlands in Europe.
