Small-scale landforms influence plant species richness, but their mechanisms and effects
in semi-natural dry grasslands have been poorly investigated. In this study we compared
vascular plant richness, species composition, plant traits, soil properties and biomass
nutrient content of convex (hillocks) and concave (hollows) karst landforms in a mountain
pasture of the Central Apennines (Italy), at a small spatial scale (1 m(2) plots).
We found hillocks had significantly higher species richness than hol-lows. On hillocks,
smaller Specific Leaf Area and Lateral Width, together with greater allocation of
resources to Below-Ground Organs, indicated lower water availability, whereas hollows
had deeper (thus moister), more acidic and more fertile soils, with aboveground plant
biomass displaying higher nutrient levels. Partial correlation and regression tree
models suggested that fine scale richness patterns were not directly determined by
abiotic properties, but were rather the result of competition levels associated with
the cover of Agrostis capillaris (=A. tenuis) a calcifuge and drought-sensitive grass
able to achieve dominance only in hollows. The higher functional convergence exhibited
by hollows suggests that A. capillaris is a strong competitor both aboveand below-ground,
mediating the effects of topography by imposing a biotic filter. On hillocks, competition
is released by lower levels of available soil water in summer and higher soil pH,
resulting in higher species richness and a more function-ally divergent assemblage.
(C) 2020 Gesellschaft fur okologie. Published by Elsevier GmbH. All rights reserved.