ATMOSPHERIC pollution is taking a heavy toll of European trees. The 1991 survey of trees conducted by the UN Economic Commission for Europe shows nearly a quarter of all trees are defoliated.The majority of critically affected forests are in Bulgeria, erstwhile Czechoslovakia, Germany, Poland and the UK. Overall conifires are in a worse state than the broadleaved trees.

Between 1987 and 1991, the rate of increase in damaged conifers was highest in Belgium (12.7 per cent), with Denmark and former West Germany close behind. Broadleaved trees have been worst affected in the UK (36.8 per cent increase), Poland and Belgium.Beech in Denmark, and birch in Sweden, show high levels of defoliation. In Portugal, adverse climatic conditions and forest fires appear to have affected oak.

High levels of sulphur dioxide, ammonia and nitrogen oxide (which get converted in the atmosphere to acids and ozone), in several areas of Europe, are now disturbing forest ecosystems.

Atmospheric pollution is seen as the cause of forest decline in Czechoslovakia, Germany, Lithuania and Poland. Mountain top forests, which are more than 60 years old, are more heavily defoliated than those at lower elevations in erstwhile Czechoslovakia, former West Germany and Poland.