Abstract
In recent decades dry heaths and nutrient-poor grasslands have been affected in the Netherlands by soil acidification and eutrophication as a result of atmospheric deposition. In dry heaths, atmospheric input of nitrogenous compounds has led to a transition from dwarf-shrub dominated to grass dominated communities. Besides this shift in dominance, a reduced species diversity has been observed in these ecosystems. Species of the acidic NARDO-GALION SAXATlLIS grasslands, and the related species-rich dry heathlands (GALLUNO-GENISTION PILOSAE), seem to be especially sensitive. Many herbaceous species (e.g. Arnica montana, Antennaria dioica, Dactylorhiza maculata, Genista pilosa, Genista anglica, Polygala serpyllifolia, Succisa pratensis and Thymus serpyllum) have declined and their occurrence is, at present, restricted to small patches on few sites. It has been suggested that atmospheric deposition of S and N has caused such drastic abiotic changes that these species are unable to survive. Dwarf shrubs, as well as grasses, are nowadays dominant in areas formerly occupied by these endangered herbaceous species. Sod cutting appeared to be an appropriate method to restore the acid-tolerant dwarf shrub vegetation but not for the intolerant herbaceous species. Liming after sod cutting improved the abiotic soil conditions a few years after sod cutting. In the year after sod cutting nitrogen mineralization is strongly enhanced, while nitrification rates are very low. This leads to an ammonium pulse after sod cutting and results in very poor seedling development of the nitrate-adapted herbaceous species. A second problem is that herbaceous species from these environments have a short living seed bank. In this project research will be conducted to investigate whether the nitrification rate after sod cutting can be improved. It will also be investigated whether a nitrate pulse after sod cutting (by adding nitrate) will improve the seedling development after sod cutting and liming.
Netherlands