The causal factors of reed decllne In Lake Constance-Untersee (West-Germany). Reed decline phenomena attected the reed belts (Phragmitetum typicum) of Lake Constance-Untersee between 1954 and c. 1983: about 88 ha (= 23% of the total area of reedswamp in 1954) were lost. The temporal an spatial patterns of the regression were investigated by a quantitative evaluation of aerophotos. Nine hypotheses were tested whether they could explain these patterns. As a result it was confirmed that the "pelagic eutrophication", the "nutrient enrichment of the reedbed sediments" and the "existence of detrimental redox conditions in the upper sediment layers" are no convincing concepts. Damage of the lakeside reedbelts by a f100d disaster, two heavy storms and a hailstorm in June 1965, have been found to be the only factors which coincide with the patterns of the regression. As a consequence, the concept of reedbelt management and maintenance should be modified, giving more protection against mechanical damage and bank erosion. Autor Dr. WOLFGANG OSTENDORP, limnologisches Institut, Universitat Konstanz, Postfach 5560,0-7750 Konstanz.
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