Dramatic development in the dying of German spruce-fir forests: In search of possible cause-effect relationships

ABSTRACT Kohlmaier, G.H., Sire, E.O., Brohl, H., Kilian, W., Fischbach, U., Plochl, M., Muller, T. and Jiang, Y., 1984. Dramatic development in the dying of German spruce-fir forests: in search of possible cause-effect relationships. Ecol. Modelling, 22: 45–65. Tree diseases caused by air pollution have been observed for the last 100 years in the near neighbourhood of industrial facilities. In the middle of the 70's, for the first time tree injury and death in fir species were recognized in extended areas remote from pollution sources in the southern parts of the Federal Republic of Germany. Since the beginning of the 80's at an ever accelerating rate dieback of other tree species, especially within the very common Picea abies stands, has been observed affecting practically all forest areas in Western Germany. This paper focuses on the dynamics of the dieback of forest stands in a formal kinetic description. After a short review of the time development of spruce dieback in Western Germany, the emission and immission data of the main air pollutants in Europe are summarized and observed pollution effects are discussed. Rather than concentrating on the effect of a specific pollutant to specific parts of the forest ecosystems we are interested here in what type of dynamics will lead to an abrupt change in the variables of state following a nearly constant input of fume gases or an increasing input of NO x and heavy metals. A threshold model with continous accumulation of pollutants up to a certain critical level and following collapse is discussed and applied to the changes in soil chemistry, especially pH-changes following acid input. Second, a model of canopy photosynthesis as affected by pollution is presented and possible transitions from healthy to injured states following a change in pollution parameters are discussed.