Veränderungen der Grünlandvegetation im Holtumer Moor über vier Jahrzehnte

Abstract

Wittig, B.; Waldmann, T.; Diekmann, M.: Grassland vegetation change during four decades in the Holtumer Moor. – Hercynia N.F. 40 (2007): 285 -300.The vegetation of the Holtumer Moor, a grassland-dominated area in the lowlands of north-western Germany, was studied by Hartmut Dierschke already in 1963. After a first re-inventory in 1988 the area was again visited in 2006. In 1963 the grasslands of the area were mostly composed of meadows on moist to wet soil characterized by Senecio aquaticus and Bromus racemosus; only remnants of this community type were left in 1988, while in 2006 it had completely vanished except for one restricted site. The impoverishment of species in the grasslands already documented for 1988 has continued until today. Average species numbers have declined especially in those grasslands that have been used intensively since 1988 or in which the land use has been intensified after 1988 until today. However, even in the few permanently extensively used grasslands species numbers have decreased further. Only the grasslands that were intensively used in 1988 and that since the beginning of the 1990ies have been transformed to less intensively used meadows or pastures showed no clear differences in species number. The species with the strongest increase in abundance was Golden Foxtail (Alopecurus pratensis). The mean Ellenberg values reflected the changes in environmental conditions between the years. In general, the decrease in light availability and soil moisture and increase in soil pH and nitrogen already observed for the period 1963 to 1988 was also shown for the period 1988 to 2006, except for soil moisture for which only a negative trend was found. Only the grasslands that were taken out of the intensive use since 1988 did not show any changes in environmental conditions as reflected in the vegetation. The results demonstrate the difficulties to preserve remnants of species-rich, extensively used grasslands in an intensively used cultural landscape. Sufficiently large buffer zones are necessary to keep a high species richness. The regeneration of species-rich grasslands on not too nutrient-rich sites may be supported by a controlled introduction of species by means of diaspores with hay transfer.