COMPETITION IN HEATHLAND ALONG AN EXPERIMENTAL GRADIENT OF NUTRIENT AVAILABILITY

Competition between Erica tetralix and Molinia caerulea and between Calluna vulgaris and Molinia was studied at 4 levels of NPK availability. In monocultures of the unfertilized control productivity of both Erica and Calluna exceeded that of Molinia by a factor of 2. At the highest fertilisation level the rank order of productivity was Erica<Calluna<Molinia. Relative yield was used as a measure of competitive ability and was positively correlated with the Light Interception Coefficient. In the 3 lowest nutrient treatments Erica was the superior competitor and Molinia was outcompeted. In all nutrient treatments Calluna was the superior competitor and Molinia was outcompeted by Calluna, despite its higher potential growth rate and its greater maximum foliage height. The high competitive ability for light interception of Erica and Calluna with respect to Molinia can be attributed to their evergreen habit, which permits canopy closure early in the growing season. -from Authors