Are Fe and P availabilities involved in determining the occurrence and distribution of Calluna vulgaris (L.) Hull in semi-arid grasslands on calcareous soils?

Calluna vulgaris (L.) Hull is primarily found on acid soils and is generally classified as a calcifuge species. Therefore, its occasional growth in semi-arid grassland on shallow calcareous soils gave rise to the question as to whether special soil conditions, deviating from the typical conditions in calcareous soils, enable this unusual occurrence. In an attempt to answer this question, we analysed selected soil factors, comparing plots where C. vulgaris was growing besides calcicole species (=CF plots) with neighbouring plots where only calcicole species were present (=CC plots). Main emphasis was placed on Fe and P availability because results from growth experiments indicate that the availability of either Fe or P to calcifuges causes calcifuge species to fail on calcareous soils. The results of our investigations do not support the hypothesis that the occurrence of C. vulgaris in semi-arid calcareous grasslands depends on higher Fe and/or P availability. Rather, its growth on carbonate-buffered soils shows that this species is not really calcifuge. Since the CF plots differ from the CC plots either by a lower inclination or by a more northerly exposition, we assume that the primary establishment and this species’ distribution pattern in the investigated semi-arid grassland are not dependent on soil chemical factors, but are governed by topography and its consequences for soil humidity and drought stress.