SOIL AND VEGETATION IN 2 DANISH FENS FOLLOWING CHANGES IN WATER REGIME

Over a six year period, lowering of the water table throughout the year in two Danish eutrophic fens led to an increase in bulk density and a decrease in pH, exchangeable base cations, total P, available P, and available Mn. The vascular plant flora and ecological characteristics of the vegetation (weighted Moisture-value, Drainage Index, Nitrogen-value and Reaction-value, and proportion of fen species, of different growth forms, and of different seed dispersal types) changed in accordance with changes in water regime towards more dry conditions, changes of edaphic variables towards more acid and oligotrophic conditions, and increased probability of establishment of plants on patches without vegetation. Additional two years with reestablishment of the original winter water table in one of the fens led to a further decrease in total P and available P. Most of the non-fen species, which had established in the period with low water table throughout the year, were significantly weakened. However, after a period of two years with reestablished winter water table the vegetation was still different from the original vegetation. Methods to state the statistical significance of changes in frequency of species and ecological characteristics of the vegetation have been worked out.