Veranderingen in de flora van het laagveen natuurreservaat De Wieden

In 1994 and 1995 a remapping of 80 plant species of interest has been carried out in the marsh and fen nature reserve De Wieden (province of Overijssel). Species were mapped in a grid of 100m by 100m squares. Their occurrence and distribution were compared to those of the preceding mapping, which took place in 1982 and 1983. A number of marsh species ( Calla palustris, Hottonia palustris, Myriophyllum verticillatum, Ranunculus lingua and Stratiotes aloides) have increased, possibly due to a different management of the ditches. The Berne-Convention species Liparis loeselii was found in 104 (against 41) plots, probably a real increase. Within quagfens, Carex pulicaris, Cladium mariscus, Dactylorhiza incarnata and Scorpidium scorpioides have decreased. Hammarbya paludosa and Linum catharticum, which were observed in very low numbers in the first mapping, have not been found again. Other species have increased, probably because they profit by special management measures such as removing off the top-layer of acidified reed-lands and digging of ditches: Carex buxbaumii, Parnassia palustris, Pedicularis palustris, Sparganium natans, and Utricularia intermedia. In the hayfields Carex echinata and Juncus filiformis have increased due to acidification, while Cirsium dissectum has decreased.