The War-torn Woodlands of Britain: Reconstructing the ecological impacts of historical disturbance

In 1971 UKCEH surveyed a stratified sample of 103 broadleaved woodlands across GB. Understory and canopy species composition, stem diameters, soil and indicators of management were recorded in 16 random locations per wood. The survey was repeated in 2002 and the third survey is now underway in partnership with Woodland Trust. The sites include many SSSI and Ancient Woodlands. Analysis of change in canopy structure and understory between 1971 and 2002 showed a marked shift towards older, more-shaded woodlands and reduction in understory species richness. This pattern was widespread across and within sites indicating a common cause. The current hypothesis is that the age-class distribution of many woodlands in 1971 was a response to intensive timber extraction during/after WWII causing unusually high canopy openness. Subsequently, with declining traditional management, many woods recruited new tree cohorts so that, by 2002, sites had a closed canopy with few gaps, a paucity of natural regeneration and a simplified age structure. This hypothesis has not been tested, yet it is important because, if supported, it would suggest that for the past 75 years many British woodlands have followed a similar trajectory with a shared cause: an unusually intense pulse-disturbance followed by 75 years of succession, often in the absence of active management. We need to understand the role of disturbance history in the high species richness of understory plants recorded in 1971 and the dramatic reduction by 2002. We propose research that will, for the first time, test this hypothesis by combining population modelling, dendrochronology and historical ecology. Because the third survey is underway, the project provides an opportunity to research in selected woodlands, acquiring tree-cores to calibrate stem diameter data as input to a modelled reconstruction of canopy change. This project will have major implications for woodland biodiversity conservation, resilience and management.