Acidic Precipitation Research in France

Abstract

Some cases of forest decline were known 10 or 20 years ago in certain regions of France, mainly in the vicinity of industrial cities, but also as a consequence of the severe drought of 1976. But, beginning in 1983, forest decline, with the same symptoms as observed in Germany, become visible in the Vosges and was noticed in the following years in the Jura, the Alps, and the Massif Central. At the end of 1986, 10% to 20% of the trees in these regions had lost more than 25% of their foliage.

A monitoring and research program, DEFORPA, was launched by the Ministry of Environment in the autumn of 1983 and today is administered by three ministeries: Environment, Agriculture, and Research. DEFORPA is divided into four main parts:

• 1. damage survey, symptomatic studies, and relationship with ecological conditions,

• 2. characterization of atmospheric pollution,

• 3. experiments on the direct action of atmospheric pollutants, and

• 4. study of the effects of air pollution through the soil.

The level of SO₀ in the Vosges is on the average rather low (15 μg m^-3) but there are several strong peaks in winter. The level of O₃ is more even, with peaks in summer and rather weak day-night variation.

The yellowing of Norway spruce and silver fir needles are related to nutrient deficiencies, mainly Mg and Ca, but sometimes K, according to the region.

Tree core analysis on silver fir in the Vosges and the first results of experiments in open-top chambers and in controlled conditions, as well as physiological characterization of declining trees in the forests, suggest that the current decline is the result of past drought periods, whose consequences might be worsened by acidic pollution and perhaps SO₂ peaks in winter.