A survey of the health of Fagus sylvatica in southern Britain.
This survey examined health of beech (Fagus sylvatica) trees at 72 survey sites in southern Britain. Tree health was assessed using crown thinness, crown architecture and leaf chlorosis as criteria. Diverse variables including soil and stand characteristics were recorded. Relations were sought between tree health and local site conditions, regional climate and pollution levels. Approximately 25% of all beech trees surveyed were in poor health as assessed by crown thinness and architecture. Incidence of chlorosis was generally low at 5%. Different assessment techniques showed markedly different geographical distributions, suggesting that they are not measuring responses to the same environmental variables. Sites of high nature conservation interest for beech showed substantially poorer tree health than other sites. Differences in local environmental conditions could explain much of the variation in levels of beech health. Disturbance, tree age, openness of the stand and soil characteristics, especially pH and drainage properties, were closely linked to tree health as assessed by crown thinness and architecture. Incidence of chlorosis was most closely associated with amount of free calcium in top soil. Crown thinness was positively related to SO2 concentration, whereas crown architecture was better in areas with a high concentration of NH3. Trees had thinner and more chlorotic crowns where they had experienced intense drought in 1976. For all cases where significant relations were found between pollutant levels and tree health on acidic soils, health was worse on sites receiving high levels of the pollutant concerned. In contrast, on calcareous soils tree health was better with higher levels of pollutants. The relation between air pollution and tree health on acidic soils is consistent with the soil acidification hypothesis that has been proposed to explain forest decline.