Monitoring of changes in tree and shrub layers in Wytham Woods (Oxfordshire), 1974-1991

In 1974–76 164 permanent 10x10 m plots were recorded atalternate intersections of a 100x100 m grid in Wytham Woods,Oxfordshire. Tree and shrub data were collected from all theplots in 1974–76, from 27 in 1984–85 and from allbut one in 1991–92. Changes in the structure and composition of the wood were assessedin terms of canopy cover, mean tree diameter, basal area andspecies occurrence. The wood has become more open (reduced canopycover) partly through management, partly through natural processessuch as windthrow and disease. The shrub cover has also declinedgreatly, probably because of increased deer browsing. Most standsare predominantly young growth and for the wood as a whole meantree diameter, basal area and tree height have increased. Theoverall composition of the wood has changed little, but therehas been a significant decline in mean woody species numberper plot from 5.8 to 4.1, mainly through declines in understoreyspecies and young oak (Quercus spp.). Elm (Ulmus spp.) coverhas been reduced by disease and birch (Betula spp.) sufferedpreferentially from windthrow. The results are used to indicate gains and losses in natureconservation terms for the wood as a whole. The strengths andweaknesses of this system may hold lessons for future woodlandmonitoring exercises.