A three year fertilization experiment was conducted in which nitrogen (N series: 20 g N m -2 yr 1), phosphorus (P series: 4 g P m -2 yr 1) and potassium (K series: 20 g K m -2 yr -1) were added to a mixed vegetation of Erica tetralix and Molinia caerulea. At the end of each growing season the percentage cover of each species was determined. At the end of the experiment percentage cover of each species was found to be positively correlated with the harvested biomass. In the unfertilized control series the cover of Erica and Molinia did not change significantly during the experiment. In all fertilized series however, especially in the P series, cover of Erica decreased significantly. The cover of Molinia increased significantly in the P series only.
In the fertilized series the biomass of Erica and total biomass per plot did not change significantly compared with the control series. In the P series the biomass of Molinia increased significantly.
It is suggested that with increasing phosphorus or nitrogen availability Molinia outcompetes Erica because the former invests more biomass in leaves which in turn permits more carbon to be allocated to the root system, which thereupon leads to a higher nutrient uptake.
Nomenclature." follows Heukels & van der Ivleijden (1983). Flora van Nederland. Wolters-Noordhoff, Groningen.