FINE-SCALE SPECIES INTERACTIONS OF CLONAL PLANTS IN A MOUNTAIN GRASSLAND - A REMOVAL EXPERIMENT

A removal experiment (one species removed per treatment) in a species poor mountain grassland community was established to (1) determine the horizontal competitive effect at the fine scale, and distinguish them from the effects at the plot level, (2) identify species specific com petition effects and (3) determine the overall structure of competitiv e network within a community. Observation of the species response at t he fine spatial scale was done using the grid of 3.3 x 3.3 cm cells. T he competitive effects at the level of cells were measured by the corr elation between the presence of the removed species in the cell before the removal and the density change of the target species in the cell. Significance of the correlation was estimated by a permutation proced ure. At the level of the whole 25 x 25 cm plot, there was no clear ten dency in the response to removal of any species except for Nardus stri cta, which increased significantly in treatments with Deschampsia flex uosa and Anthoxanthum alpinum removed. Anthox-anthum alpinum increased its biomass per shoot in the treatments with other species removed. A t the fine scale level of 3.3 x 3.3 cm cells, some species began to oc cupy the empty space made by the removal of their neighbours, indicati ng release from competition following removal. The most pronounced cha nge was the increase of Deschampsia flexuosa following removal of Nard us stricta. Some responses were species-pair specific. Two species pai rs (Deschampsia-Anthoxanthum, Deschampsia-Festuca) showed reciprocal r esponse at the fine scale; each species increased if the other one was removed. In two species (Nardus stricta, Deschampsia flexuosa) the ef fects observed at the level of the whole plot and at the level of the individual cells differed. This is attributed to (1) different role of belowground competition (which has wider horizontal range and appears at the scale of the plot) and aboveground competition (which is rathe r short range and appears already at the scale of the cell) and (2) di fferent plasticity in their clonal growth architecture.