SUMMARY

The results of a study on the composition, the ecology and the structure of grass communities developed close around six mineral CO2-springs in central-western Italy are reported. The phytosociological sampling of the grasslands surrounding the gas vents has led to the circumscription of an azonal endemic association, the Agrostidetum caninae subsp. monteluccii, which was characterized by a strong species poorness and a high ecological specialization. The typical monospecific stands were developed on peatlike soils with pH ranging between 2.4 and 3.7 and a content of soluble aluminium well above the toxicity thresholds known within the Al-tolerant gen. Agrostis. On the basis of published data and preliminary measurements of atmospheric CO2 concentration, it is known that this association is developed in areas with elevated levels of atmospheric CO2, a factor which could contribute to enhancing the competitive capacity of its dominant species within the natural vegetation. Indeed, above-ground biomass, canopy height and other structural parameters of A. canina revealed its outstanding vegetative vigour in the monospecific grassland close around the vents. On the contrary, in the peripheral areas of the CO2 springs a decreased vigour in A. canina accounted for the different structure and density observed in the grass community and probably also for its different species composition. The syntaxonomical placing of the Agrostidetum is not immediate because of the absence in the European literature of other works on geothermal acidophilic vegetation. Therefore, despite some ecological affinities with oligotrophic species-poor communities of European acidic fens and mires of the Scheuchzerio-Caricetea fuscae, the syntaxonomical placing requires further coenological investigation of geothermal sites on a broader geographical scale.