Preliminary estimates of fallen dead wood and standing dead trees in managed and unmanaged forests in Britain.
Abstract
The amount of dead wood, particularly as fallen dead wood and standing dead trees, in British forests is attracting attention from forest managers as part of their interest in increasing biodiversity within forests managed for timber. Existing levels of dead wood in managed and unmanaged forests were assessed to provide a basis for what might be considered high or low amounts of dead wood under present conditions. Estimates of fallen dead wood, derived from line-intersect sampling, were collated for 63 sites (87 stands) in Britain. The values obtained ranged from virtually zero in recently cut coppice to 60-140 m3/ha in stands largely undisturbed over at least the last 80 years. The highest values (from unmanaged stands) overlap with estimates for the volumes of fallen logs in old-growth broadleaved forests in North America and continental Europe. Forests currently managed for timber had less than 20 m3/ha of fallen logs. In unmanaged stands, localized accumulation of fallen material was often associated with exceptional events such as the 1976 drought or the 1987 great storm. Following the 1987 storm the amounts of fallen dead wood in unmanaged forests in eastern England appears to have doubled from about 10 to 23 m3/ha. Large standing dead trees (snags), >40 cm diameter, were rarely recorded in the forests surveyed because most forests in Britain have been cut over at least once this century and any large timber removed. The following, based on the range of values found in this survey, are proposed as provisional benchmarks for amounts of dead wood in British broadleaved forests: low <20 m3/ha fallen dead wood, 0-10 snags/ha (all below 10 cm diameter); medium 20-40 m3/ha fallen dead wood, 11-50 snags/ha (of which some are more than 10 cm diameter); high >40 m3/ha fallen dead wood, more than 50 snags/ha (of which some are more than 40 cm diameter). Further work on assessing the dead wood resource in British forests is needed.