Fine-Scale Species Interactions of Clonal Plants in a Mountain Grassland: A Removal Experiment

Abstract

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 competition effects and (3) determine the overall structure of competitive network within a community. Observation of the species response at the fine spatial scale was done using the grid of 3.3 x 3.3 cm cells. The competitive effects at the level of cells were measured by the correlation 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 procedure. At the level of the whole 25 x 25 cm plot, there was no clear tendency in the response to removal of any species except for Nardus stricta, which increased significantly in treatments with Deschampsia flexuosa and Anthoxanthum alpinum removed. Anthoxanthum alpinum increased its biomass per shoot in the treatments with other species removed. At the fine scale level of 3.3 x 3.3 cm cells, some species began to occupy the empty space made by the removal of their neighbours, indicating release from competition following removal. The most pronounced change was the increase of Deschampsia flexuosa following removal of Nardus stricta. Some responses were species-pair specific. Two species pairs (Deschampsia-Anthoxanthum, Deschampsia-Fesiuca) showed reciprocal response at the fine scale; each species increased if the other one was removed. In two species (Nardus stricta, Deschampsia flexuosa) the effects 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 rather short range and appears already at the scale of the cell) and (2) different plasticity in their clonal growth architecture.