Forest damage

This interaction between airborne acid components and the tree-soil system may alter the ability of the trees to tolerate other environmental stressors such as drought, insects, and other air pollutants like ozone. In Germany, considerable attention is focused the role of ozone and acid deposition as a cause of forest damage. Forest damage is a complex problem involving the interaction of acid deposition, other air pollutants, forestry practices, and naturally occurring soil conditions. 

Global climate change, air-quality degradation (coal, oil), lake acidification and forest damage (coal, oil), land disturbance and others, if hydrogen is produced by fossil fuels ... 

That Al3+ is the main toxic agent in many acidified lakes is supported by observations of improved fish survival rates when the silica content of the water is increased, as dissolved silica can form either soluble or insoluble aluminosilicates (see Section 7.6). Mobilized aluminum has also been linked to forest damage, since, in sufficient concentration, it is directly toxic to roots of spruce trees and many other plants. 

Beneficial and Harmful Effects. At low levels, sulfur dioxide in the atmosphere is not harmful to crops, but damage can occur at excessive levels (305—309). Crops differ gready in their sensitivity. Forest damage attributed to acid rain is often cited but the observed symptoms seem to have multiple causes and the contribution of sulfur acids is unspecified. The sulfur in precipitation is, up to a point, beneficial to plant growth because sulfur is an essential nutrient. Lessening the sulfur content of the atmosphere requires that supplementary sulfur be provided in fertilizer to some crops some crops already require supplementary sulfur. Sulfur dioxide itself has been found useful in drip irrigation systems (310,311) and in calcareous soils (308). Small field generators have been developed for this purpose. 

For Further Reading W. Jackson, Altars of Unhewn Stone Science and the Earth San Francisco, North Point Press (1987). J. Raloff, Pollution helps weeds take over prairies, Science News 150, 356 (1996). S. E. Schwartz, Acid deposition unraveling a regional phenomenon, Science, 243, 753 (1989). W. H. Smith, Air pollution and forest damage, Chemical and Engineering News, November 11,1991, p. 30. 

Historically, the combustion of fossil fuels has directly or indirectly been the source of air contaminants at three levels local, regional, and global. Pollutants of importance at the local level have included sulfur dioxide and trace metals. Local forest damage is confined to a zone of a few km immediately surrounding a facility and for a distance of several to tens of km downwind. 

Scholz (1984) has reported on the present extent of forest damage due to air pollution in Europe and North-America for the UN Economic Commission for Europe (ECE). This report is based on official sources of the affected countries. This official estimate of damaged area is listed in table 7. 

The wide-spread forest decline in Europe and North-America is regarded from scientists of different schools as caused predominantly by the impact of air pollution. Without anthropogenic air pollution there would not be forest damages to the present extent (Scholz, 1984). 

Table 7 - Statistical data on forest damages in ECE cotintries (Adapted from Landerbeiichte der EFC/FAO, ausgewertet vom Bundesamt fiir Ernahrung und Forstwirtschaft, 1983 , Federal Republic of Germany) - Scholz, 1984. 

Country Land area 1979 1000 ha Total forested 1979 1000 ha area % of land area Area of forest damages % of forested 1000 ha area Forest damages Regional centres Main tree species ... 

Table 8 - Increase of forest damage in the Federal Republic of Germany from 1982 to 1984 (Adapted from Bundesminister fiir Ernahrung, Landwirtschaft und Forsten, 1984).

Forest damage was also discovered soon after (if we exclude the first observations of Guderian in Germany in 1962) in many other places in continental Europe. The similarity of effects lead some scientists to infer a similarity in causes but the lack of proof is evident forest damage in Europe was thus attributed successively to SO2 pollution, NO2, NO2-SO2 combination, heavy metals and acidity pollution, dryness, frost, disease, lead present in exhaust gases, etc. I would also suggest the intermediate compounds resulting from the photochemistry of naturally... 

Rock, B.N., Hoshizaki, T. and Miller, J.R., 1988. Comparison of in situ and airborne spectral measurements of the blue shift associated with forest damage. Rem. Sens. Env., 24 109-127. 

Considering the rapid expansion of the regional air pollution problems in Europe during the later years, as examplified by the forest damage, the appearance of "red tide" in the North Sea, and the increasing mercury content of the freshwater fish, the development of EMEP has been slow. It is interesting to note that when the OECD project started in 1972, Canada participated as an observer, while the US EPA did not believe that acid precipitation would become a problem in North America as well. Similarly, the European countries did not think that photochemical oxidants would become a problem in Europe. There was not enough sunshine, they reasoned. 

Initially forest damage was believed to be another effect of acid precipitation toxic aluminium ions released from the soil minerals were poisoning the root system of the trees. But the forest damage also occurred in areas with soils rich in carbonates, and in valleys it often appeared at certain height levels where fog was frequently observed. This pointed to air pollution as a direct main cause for the damage. 

Results of the 1989 European forest damage survey according to defoliation of sample trees are presented (Figure 1.1) for illustration of air pollution impact on plants. 

Figure 1.1 Results of the 1989 European forest damage survey expressed as a percentage distribution of sample trees according to defoliation [d]...

UN-ECE/UNEP-GEMS 1990 Forest Damage and Air Pollution Report of the 1989 Forest Damage Survey in Europe, prepared by the Programme Coordinating Centres with the assistance of the United Nations Environment Programme, Nairobi, and the Secretariat of the UN-Economic Commission fa Europe, Geneva. 

Beginning in the 1970s, acid rain was identified as a serious issue in Europe, most prominently in Scandinavia and in the Black Triangle, a large swath of Poland, the Czech Republic, and southeastern Germany that suffered from acute forest damage induced by acid rain. Acid rain is a rapidly... 

Crop and forest damage by direct acidification and biotoxicity due to solubilized metals... 

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