Vegetation of ant-hills in a mountain grassland: effects of mound history and of dominant ant species

Vegetation in grasslands with well-developed long-lasting ant-hills in the Slovenske Rudohorie Mts., Slovakia, was studied in relation to (i) position on the mound, (ii) ant species forming the mound, and (iii) history of the mound. Permanent plot recordings of mound size and dominant ant species started fifteen years prior the study began provided information on the history of individual mounds. The mound vegetation bears a striking similarity to vegetation in similar habitats across a large part of Europe due to presence of species such as Agrostis capillaris, Dianthus deltoides, Polytrichum commune agg., Thymus pulegioides, and Veronica officinalis. Out of the three major ant species-groups present at the site (Lasius flavus, Tetramorium caespitum and Formica spp.), L. flavus had the most pronounced and the most lasting effect on the mound vegetation. The dominance of the plant species listed above increased with the time span over which the mound was inhabited by L. flavus. The effects of other species on vegetation composition, though discernible from short-term observation, disappeared over several years. The mounds proper did not differ from the undisturbed grassland in the proportion of myrmecochorous plants or plants with specific seed size or dormancy type. However, there was a highly significant concentration of myrmecochorous plants in the grassland patches immediately neighbouring the mounds; this is likely to be due to seeds deposited there by the workers from the nest after the elaiosomes had been consumed. The mound vegetation was composed mainly of species with long stolons or rhizomes; however, there was no significant difference in formation type or length of stolons/rhizomes between mounds and the rest of the grassland or among mounds formed by different ant species.