Forest decay

Thank you very much, Dr. Knabe. It is very interesting and this is quite clear evidence of the impact of the chemical events in the atmosphere on the biosphere. I would like to ask Dr. Knabe if he has seen a recent report in Environmental Science and Technology saying that it is not always possible to correlate air pollution in general with forest decay. 

The third combination to be mentioned is that of fog and air pollution. These areas with high frequency of fog again lie in those mountains where we have the strongest forest decay. So climate has to be taken into account, and I agree with you also that special climatic events in the last years may have affected the trees. But this research requires more time and man-power, I can only show the importance of the problem and hope that some other group will start to work on it. 

I cannot agree with this proposal. There are a number of links between the source or cause and the effect, a whole range of stages as emission, transportation, immission, deposition and dose, and they are influenced by climate, site, genetic resistance, which can alter the picture. In summary, the effect is very far apart from the source. If you measure the dose within the plant, the amount of pollutants which the plant has taken up, or the state of the soil as it has changed by air pollution, then you have a much closer relation to the effect than just by an emission survey. We have now the forest decay just in those areas which are maybe 100 kilometers away from the industrial areas and not in the industrial areas themselves. So this proposal would not work. It is, however, very useful to find out the main sources and to start measures to reduce emissions in general or for certain pollutants. 

The low fertility of the soils of the fir stands is not the only factor able to explain forest decay. Other parameters must also be taken into account. 

Atmospheric pollution can be considered as the main predisposing factor in forest decay phenomena, which can increase cation depletion and worsen nutritional imbalance. Climatic characteristics (rainfall deficits) can also be considered as a"weakening factor" in forest decay. 

The places from which pollutants emanate are called sources. There are natural as well as anthropogenic sources of the permanent gases considered to be pollutants. These include plant and animal respiration and the decay of what was once living matter. Volcanoes and naturally caused forest fires are other natural sources. The places to which pollutants disappear from the air are called sinks. Sinks include the soil, vegetation, structures, and water bodies, particularly the oceans. The mechanisms whereby pollutants... 

Forest systems also act as sources of CO2 when controlled or uncontrolled burning and decay of litter occur. In addition, release of ethylene occurs during the flowering of various species. One additional form of emission to the atmosphere is the release of pollen grains. Pollen is essential to the reproductive cycle of most forest systems but becomes a human health hazard for individuals susceptible to hay fever. The contribution of sulfur from forests in the form of dimethyl sulfide is considered to be about 10-25% of the total amount released by soils and vegetation (12). 

Savory, J. G. and Packman, D. F., DSIR Forest Products Bulletin No. 31 entitled Prevention of Decay of Wood in Boats, H.M.S.O (1954)... 

The land biota reservoir (3) represents the phosphorus contained within all living terrestrial organisms. The dominant contributors are forest ecosystems with aquatic systems contributing only a minor amount. Phosphorus contained in dead and decaying organic materials is not included in this reservoir. It is important to note that although society most directly influences and interacts with the P in lakes and rivers, these reservoirs contain little P relative to soil and land biota and are not included in this representation of the global cycle. 

Highley TL, Dashek WV. Biotechnology in the study of white-rot and brown-rot decay, in Forest Products Biotechnology (Bruce A, Palfreyman JW, eds.), Taylor and Francis, London, UK. 1998, pp. 15-36. 

The rate of growth of the trees slows as the forest reaches maturity and canopy closure occurs. In addition, the forest eventually establishes equilibrium with the environment, where the rate of carbon sequestration is exactly balanced by the loss of carbon dioxide to the atmosphere due to decay of dead trees and other biomass. 

The use of wood in long-life products, such as buildings, ensures that this sequestered carbon is held in a materials pool for a longer time. If the use of renewables is encouraged, then more carbon is stored in this manner. Eventually, of course, such systems will establish equilibrium with the environment, as the materials flow into the pool equals the materials flow out into the environment. The use of wood in this way intervenes in a natural cycle, so that wood use and ultimate disposal replaces the natural cycle of wood decay in the forest (Figure 1.5). 

Stamm, A.J. and Baechler, R.H. (1960). Decay resistance and dimensional stabihty of five modified woods. Forest Products Journal, 10(1), 22-26. 

Sulfur dioxide is produced by both natural and anthropogenic sources. The most important of the natural sources are volcanic eruptions, which account for about 40 percent of all natural emissions of the gas. Since volcanic eruptions are episodic events, the amount of sulfur dioxide attributable to this source in any one year varies widely. Other natural sources of the gas are forest fires and other natural burns, biological decay, and certain metabolic processes carried out by living organisms, especially marine plankton and bacteria. Natural sources release about 27.5 million short tons (25 million metric tons) of sulfur dioxide per year. 

Field studies suggest that the nitrate radical reaction can also be a major contributor to isoprene decay at night, as well as contributing to the formation of organic nitrates in air. For example, Starn et al. (1998b) found that when the product of N02 and 03 (which form N03) was high in a forested region in the southeastern United States, isoprene often decayed rapidly at dusk. This reaction of N03 with isoprene was estimated to be the major sink for N03 under some conditions in this area. 

---