Influence of tree health on ground flora in the Chiltern Beechwoods, England

The aim of this study was to investigate whether changes in crown condition associated with decline in the health of beech ( Fagus sylvatica) stands are affecting the species composition of the woodland ground flora. Forty-three woods in the Chilterns region of south-east England were surveyed in the summer of 1989. In each wood, two sample plots (30 m × 30 m) were chosen on the basis of the relative health of their trees (i.e. one `healthy' plot and one `unhealthy' plot). The percentage cover of all species of ground flora was recorded for each plot. Stand, soil and site characteristics were also recorded. Data were analyzed using detrended correspondence analysis (DCA). The resulting axis scores were compared for healthy and unhealthy plots using paired t tests, and relationships between the axes and environmental variables were explored using correlation analysis. A significant difference was found in the ground flora under healthy and unhealthy trees on calcareous soils, using an axis which was determined by the light requirements of the plants. No other environmental or stand variable explained this difference. In plots with lower tree crown density, the ground flora comprised species more typical of clearings, rides and woodland margins, at the expense of more typical woodland species. This finding is important given evidence of declines in tree health in the Chilterns and elsewhere in Europe over the past decade.