Do different competitive abilities of three fern species explain their different regional abundances?

Question: Do different competitive abilities of three fern species explain their different regional abundances? Location: Estonia, Europe. Methods: The factorial pot experiment, in which single individuals of three fern species were grown in natural soil with 0, 2,4, and 8 neighbouring individuals of Deschampsia flexuosa. Results: The response patterns of different biomass fractions and morphological parameters of fern species were similar to each other. The diploid D. expansa was the most vulnerable to competition, while tetraploid D. carthusiana and D. dilatata were more tolerant. D. carthusiana allocated relatively more to below-ground parts than the other two species and allocation to roots increased when neighbour density increased. For D. expansa and D. dilatata, allocation to below-ground parts decreased at high neighbour density, while in D. dilatata also the relative length of the stipe increased. Thus, the response of D. carthusiana corresponds to a 'persistence type' and that of D. dilatata to a 'foraging type'. Conclusions: Lower vulnerability of D. carthusiana to competition, compared to D. expansa, may explain the higher regional and local abundance of the former. The rarity of D. dilatata in Estonia, however, could rather be explained by the impact of climatic factors, since this species is near its northeastern distribution limit in Estonia.