Observations on north-west European limestone grassland communities. V, a. An experimental approach to the study of species diversity and above-ground biomass in chalk grassland

In 1971 a number of permanent plots were established in an abandoned Dutch calcareous grassland, then belonging to the association Arrhenatheretum elatioris with some elements of Mesobrometum erecti and Poo-Lolietum. A part of the plots was treated with fertilizer of varying N.P.K.-content. Another part was treated with farm yard manure, calcium carbonate, or left untreated. All plots were mown once a year. Each year, species composition, including bryophytes, as well as peak standing crop were determined. After seven years the plots treated with fertilizer are sharply distinct from the others ones, both in species composition and above-ground biomass. In the fertilized plots the number of species decreased considerably due to dominance of a few species, whilst the above-ground biomass varied from about 550 to 900 g/m2. In the course of the experiment the species number of the unfertilized plots increased; the above-ground biomass varied from 150 to 350 g/m2. Constancy of species composition was highest in the unfertilized plots, especially after a period of extreme drought in 1976. In 1978 the vegetation of the non-fertilized plots could be reckoned to the Mesobrometum erecti; the vegetation of the fertilized plots to an Arrhenatheretum elatioris variant poor in species. The influence of sod removal is discussed in detail. The study will be continued and expanded in the forthcoming years.