Journal of Conference Abstracts

Restoration of Acidified and Nitrogen-Enriched
Terrestrial Vegetations

Maaike C. C. De Graaf (Maaikeg@sci.kun.nl), Jan G. M. Roelofs (Jroelofs@sci.kun.nl) & Roland Bobbink (Rolandb@sci.kun.nl)

Research Group Environmental Biology, Department of Ecology, University of Nijmegen,
Toernooiveld 1, 6525 ED Nijmegen, The Netherlands.

Heathlands and nutrient poor, moderately acidic grasslands are among the most endangered ecosystems of Western Europe. Although many of those heaths and grasslands are now situated in nature reserves, most have seriously declined as a result of changes in land use, soil acidification and nitrogen enrichment. Due to the fact that they are found on nutrient poor sandy soils, these ecosystems are very sensitive to the atmospheric input of acidifying and eutrophying pollutants as SO_x, NH_y and NO_z.

Many characteristic plant species of these ecosystems are very sensitive to high Al/Ca-ratios and to high NH₄⁺ concentrations, which is often the result of atmospheric input. Furthermore, the increase in N concentrations in the soil favors fast growing grasses, which eventually replace the characteristic vegetation of dwarf-shrubs and herbs.

Some management practices can be used for amelioration. Since the heaths and grasslands are semi-natural in The Netherlands, some management has always taken place in the past. Periodical removal of vegetation, litter and humus layers (sodcutting) in heathlands and mowing of grasslands was a regular agricultural practice until the 1950's. At present however, it is often necessary to increase the frequency of these management practices in order to reduce the negative effects of nitrogen enrichment.

However, mowing and sodcutting do not reverse the negative effects of soil acidification. To reverse the effects of acidification, new management measures have been applied. In dry ecosystems, the buffering capacity of the soil can be restored by liming. Although liming is often used in agriculture, lime has not been applied to species rich, low production grasslands and heaths so far. Since liming might enhance nitrogen mineralisation, lime has been applied after sodcutting in some experiments.

The combination of sodcutting and liming against both nitrogen-enrichment and soil acidification has been successful in restoring the original vegetation, provided that seed sources are still available. We shall now present the results of our field experiments on the effects of liming and sodcutting on soil and vegetation.