Ancient woodlands: modern threats.

This review discusses the following adverse influences on long-established forests, wood-pastures, and savannas in Europe and other continents: destruction and fragmentation; depletion; pollution and eutrophication; fire and lack of fire; excessive shade; excessive numbers of deer; invasive species and cultivars; infilling of savanna; climate change; and globalization of plant diseases. Human influences on the world's mainland forests and savannas have been pervasive throughout the Holocene, to the extent that recovering 'virgin forest' becomes a somewhat nebulous conservation objective. Present and future threats arise both from increasing human activities and from withdrawal of the human activities that have shaped forests in the past. The severity of different threats depends on so many factors, especially the properties of different plants and animals, that generalization is impossible; however, in the long term, spread of pathogens is probably the most serious threat.