Past anthropogenic influence on European forests and some possible genetic consequences

Present population structure and patterns of genetic diversity in forest trees have been influenced by past anthropogenic activities and the major aim of this review is to assess the scale and timing of this influence within Europe. Very little 'natural' forest (defined as areas that have not experienced a break in forest continuity because of cultural activities since conditions became suitable for tree growth) remains in Europe. Yet many contemporary European forests have developed by natural regeneration from local stock, so despite a massive anthropogenic impact, one can predict a survival of the 'natural' patterns of genetic diversity despite a general reduction in total diversity. Systematic interference with forests was closely associated with the spread of agriculture from south-east to north-west Europe during the last 10,000 years. It has been suggested that the spread of trees of early economic importance was linked to local agricultural development. However, closer analyses of spreading dynamics and comparisons with comparable spreading in the USA does not fully support this hypothesis. Indeed, modelling the present and past range limits (if forest trees has suggested that climate change is the major driving force for range changes, implying that genetic composition is primarily governed by natural processes. Anthropogenic activity did catalyse the spread of Fagus sylvatica through increasing the rates of forest disturbance. By the Roman period, there are documented cases of introduction of e.g. Aesculus hippocastanum and Castanea sativa to many parts of Europe. Countries with colonial histories have been importing undisputedly 'exotic' species for several centuries. Occasionally there is doubt over exotic status owing to lack of documentation or possible prehistoric introduction, e.g. Arbutus unedo in western Ireland. The translocation of native species with the aim of improving production potential is a relatively recent practice often documented in national histories of forestry. Thus despite considerable widespread and long-term intervention with European forest ecosystems, many of the observed patterns of genetic diversity observed in naturally regenerated forests primarily originate from natural processes. However, given the enormous recent increase in the long-distance translocation of seeds. this situation is rapidly changing in regions with intensive forest management. (C) 2004 Elsevier B.V. All rights reserved.