MONITORING OF CHANGES IN TREE AND SHRUB LAYERS IN WYTHAM WOODS (OXFORDSHIRE), 1974-1991

In 1974-76 164 permanent 10 x 10 m plots were recorded at alternate in tersections of a 100 x 100 m grid in Wytham Woods, Oxfordshire. Tree a nd shrub data were collected from all the plots in 1974-76, from 27 in 1984-85 and from all but one in 1991-92. Changes in the structure and composition of the wood were assessed in terms of canopy cover, mean tree diameter, basal area and species occurrence. The wood has become more open (reduced canopy cover) partly through management, partly thr ough natural processes such as windthrow and disease. The shrub cover has also declined greatly, probably because of increased deer browsing . Most stands are predominantly young growth and for the wood as a who le mean tree diameter, basal area and tree height have increased. The overall composition of the wood has changed little, but there has been a significant decline in mean woody species number per plot from 5.8 to 4.1, mainly through declines in understorey species and young oak ( Quercus spp.). Elm (Ulmus spp.) cover has been reduced by disease and birch (Betula spp.) suffered preferentially from windthrow. The result s are used to indicate gains and lasses in nature conservation terms f or the wood as a whole. The strengths and weaknesses of this system ma y hold lessons for future woodland monitoring exercises.