EXPERIMENTAL MANIPULATION OF SUCCESSION IN HEATHLAND ECOSYSTEMS

An experiment was carried out in two heathland ecosystems, one dominat ed by Calluna vulgaris and the other by Molinia caerulea, to analyse t he effects of soil organic matter accumulation and nutrient mineraliza tion on plant species dynamics during succession. The experiment inclu ded one treatment that received nutrient solution and two treatments w here the rate of soil organic matter accumulation was reduced by remov ing litter or accelerated by adding litter. In a fourth treatment the C. vulgaris litter produced in the C. vulgaris-dominated plots was rep laced by litter of M. caerulea and vice versa. Treatments were applied over 8 years. Addition of nutrient solution caused C. vulgaris to dec line, and grass species to increase sharply, compared to the control p lots. Addition of litter enhanced both N mineralization and the biomas s of M. caerulea and Deschampsia flexuosa but reduced the biomass of C . vulgaris. The effects of replacing C. vulgaris litter by M. caerulea litter, or vice versa, on N mineralization and species dynamics could not be attributed to differences between the decomposability of the d ifferent litter materials that were transferred. The results confirm t he hypothesis that increased litter inputs accelerate the rate of spec ies replacement during succession.