Forest decline

Plants may be affected by indirect modifications of the environment. Soil acidification, for example, can cause the leaching of nutrients, and the release of toxic aluminum. These effects may operate together to produce nutrient deficiencies or imbalances to plants. High soil concentrations of aluminum may prevent uptake and utilization of nutrients by plants.Increased availability of aluminum in soils has been implicated as a cause of forest declines in both Europe and the United States, possibly through the toxic effects on small feeder roots 14),... 

Forests in particular must endure the combined stresses imposed by climatic extremes/changes, invasion of insects and diseases, and forest management practices in addition to the added stress of acidic pollutants. All of these stresses modify forest health and productivity. Under this complex situation, it has not been possible to establish the exact role that acidification has had on forest decline nor to develop critical deposition levels at which damages are believed to become important 14), However, the geographical coincidence of forest decline and elevated levels of acidic pollutants offer strong evidence that a linkages exists. 

Cowling, E. Krahl-Urban, B. Schimansky, C. In Forest Decline] Krahl-Urban, B. Brandt, C.J. Schimansky, C.S. Peters, K. Eds. Assessment Group of Biology, Ecology and Energy of the Jiilich Nuclear Research Center Jiilich, FRG, 1988 pp 120-125. 

Forest Decline Program, Botany Department, University of Vermont, Burlington, VT 05405... 

Contemporary forest declines were initiated about 1950-1960, virtually simultaneously throughout the industrial world at the same time as damage to aquatic systems and structures became apparent. A broad array of natural and anthropogenic stresses have been identified as components of a complex web of primary causal factors that vary in time and space, interact among each other, affect various plant growth and development systems and may result in the death of trees in mountainous ecosystems. As these ecosystems decline, the alterations in forest ecology, independent of the initial causal complex, become themselves additional stress factor complexes leading to further alterations. 

Obviously, one looks for causes. That declines in one or another species have natural factor etiologies is unequivocal. The demise of American elms and of the chestnut were due to natural factors. Insect infestations, bacterial and fungal diseases, hurricanes, floods, freezes, droughts and many other stresses can cause extensive tree death (5). But in such declines typically only a single species is affected or climatic events caused decline in a delimited area. In almost all declines caused by natural events, the causal factors can be identified we know their precise etiologies. Natural events are always part of the natural environment and must be factored in when evaluating forest declines (Table I). 

The initial causes of forest decline - natural and anthropogenic - have resulted in a forest decline syndrome that is, per se, a new series of causal factors whose consequences are themselves new causes for ecosystem alteration. 

Acknowledgments. Research and preparation of this manuscript supported by the R. K. Mellon Foundation and the Vermont Agricultural q)eriment Station. Data obtained from research of Forest Decline Project participants, including Gregory Adams, Mark Easter, Maureen Jennings, Mark Hemmerlein and Heiko liedeker. 

Forest Decline and Air Polhitioru A Study of Spruce (Picea abies) on Acid Soils. Schulze, E.D. Lange, O.L. Oren, R, Eds., Springer-Verlag Berlin. 1989. 

Backhaus, B. and R. Backhaus. 1986. Is atmospheric lead contributing to mid-European forest decline Sci. Total Environ. 50 223-225. 

Durka W, Schulze ED, Gebauer G, VoerkeUus S (1994) Effects of forest decline on uptake and leaching of deposited nitrate determined from N and 0 measurements. Nature 372 765-767... 

Rippen G, Zietz E, Frank R, et al. 1987. Do airborne nitrophenols contribute to forest decline Environ Technol Lett 8 475-482. 

Cape JN, Freersmith PH, Paterson IS, Parkinson JA, Wolfenden J. 1990. The nutritional status of Picea abies (L) Karst across Europe, and implications for forest decline. Trees Struct Funct 4 211-224. 

Nitrate and nitrite photochemistry might also play a role in atmospheric hydrometeors. Nitrite photolysis has been shown to account for the majority of hydroxyl photoformation in irradiated fog water from a polluted site [ 14]. In addition, the generation of mutagenic and carcinogenic compounds from amino acids and amines dissolved in fog water [147] is a process that can be linked with nitrite photochemistry [20,141]. Furthermore, the formation of atmospheric nitrophenols partially takes place in aqueous solution. Reactions in the aqueous phase can account for about 30% of the atmospheric sources of mononitrophenols and for the vast majority of the dinitrophenol ones [ 148], and irradiation of nitrate and nitrite can possibly play a role in the process (see Sect. 3.2). Mono- and dinitrophenols are toxic compounds, and their occurrence in rainwater is thought to be a contributory factor in forest decline [149-151]. 

Most of the photo-initiated processes in the atmosphere are radical reactions. However, the hydroxyl radical ( OH) is of special significance for the chemistry of the atmosphere (Ehhalt, 1999). This reactive species is mainly responsible for the photooxidation of trace organic chemicals in the troposphere and hence for the oxidative cleansing of the atmosphere (Fabian, 1989). It is nature s atmospheric detergent (Comes, 1994, Ravishankara, et al. 1998). Furthermore, several years ago it was well established that the interaction of UV/VIS radiation and environmental pollution seems to be responsible for the dramatic forest decline that has been observed, for example in the higher areas of the Black Forest or the Ore Mountains in Germany (Schenck, 1985). 

ScHENCK GO (1985) is the New Forest Decline a Photodynamic Disease Caused by light and Peroxyacetylnitrate, Ozone, Ha-locarbons and Others , Europ. Photochem. Assoc. Nemslett., No. 23/24 15-41. 

From fume damage to forest decline Affected Species... 

There was a steady development from localized but very severe cases of mortality and growth loss due to oxides of sulfur or to fluoride, first to regional destruction as in the Ruhr district or the Erzgebirge , later to a statewide and finally continental dimension of forest decline. 

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). 

Prinz et al. (1982) see ozone as main cause for the forest decline in Germany, however they admit the need for further clarification. 

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