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Summary Deadwood is an integral and often substantial component of natural forests. It provides wildlife habitat, maintains ecosystem health and influences geomorphological processes. In managed forests, however, potential deadwood volumes are reduced by felling and extraction of timber to a small fraction of the volume found in natural forests. This impairs biodiversity and can affect some aspects of ecosystem health and geomorphological processes. Recent international conventions and national policy commitments aimed at sustaining biodiversity and ecosystem functions imply that British forests should contain more deadwood. This review identifies priorities and outlines a strategy whereby quantities of deadwood, and the benefits that it offers, may be usefully increased without disproportionate reductions in the output of timber and wood.

Summary Forty-six unmanaged urban and ex-industrial sites in the county of Avon, South Staffordshire and the West Midlands were visited in 1992/93 during a survey which aimed to relate site factors with natural colonization by trees and shrubs. The factors observed included: type and texture of substrate; the predominant type of vegetation; aspect; the presence of parents in the near vicinity of the site and the numbers and species of colonizing woody plants. The extent of woody colonization was very variable and despite an average stocking density of 1500 stems ha"1, only 19 per cent of the land surveyed was colonized to an acceptable woodland standard. Woodland produced by natural colonization was species poor with an average of three per site; the most abundant species were ash, birch, goat willow and hawthorn, which made up 85 per cent of the colonization recorded. Although there was variation between species, the presence of the parent was usually the most important factor associated with colonization; when potential parent trees were visible from the site there was, on average, a 58 per cent probability of finding colonization of the corresponding species. In general, colonizing plants were positively associated with subsoil, small stony substrates such as gravel and ballast, and a weak grass sward. Conversely colonization was negatively associated with loam soils, sand, unfractured rock/concrete substrates, and sites with grazed sward or no vegetation.