Yield and species density of grasslands during restoration management

Abstract. The relation between the dry matter production and species density of 27 grasslands with different fertilization histories in the Netherlands was studied. The range in species density was 12–28 species on 150 m², the average annual dry matter production in 1983–1985 varied between 3.3 and 12.8 ton /ha. The results show an optimum curve and confirm the hump-backed model proposed by other researchers for a great variety of vegetation types. It is concluded that a high species density can be expected when the annual dry matter production above a stubble height of 5 cm, is between 4 and 6 ton/ha (ca. 4.6 - 6.0 ton seasonal maximum standing biomass). Species density can be expected to decrease when the dry matter production exceeds values of 6 - 7 ton ha^-1yr^-1 (ca. 6.0 - 6.7 ton seasonal maximum standing biomass). The implications of this relation for grassland restoration, aimed at an increase in species density, are discussed. The results agree with other grassland data based on the seasonal maximum standing biomass. The difference between annual production estimated by harvesting the biomass after mowing at 5 cm above the soil surface (mostly in two cuts), and the maximum seasonal standing biomass must be taken into account. It is proposed to compare data on the basis of the estimation that 62 ± 5% of the annual yield is harvested at the first cut, and that there is a linear relation between the total standing biomass, y (g/m²), and the biomass harvested above a stubble height of 5 cm, x (g/m²) that could be described by the regression line y = 1.10 x + 189.6 (r = 0.89, p < 0.01, n = 34).