La Betulla dell’Etna: uno studio multidisciplinare sui fattori di deperimento della specie

Etna birch (Betula aetnensis Rafin) is one of the tree species that during the last glaciations has moved southward,where currently it establishes populations that can be considered relicts because they are present exclusively onthe summit of Etna Mount. Etna birch stands are present on the eastern and western slopes of Etna, at an altitudebetween 1,400 and 2,000 m a.s.l.. These are pioneer populations that colonize unaltered and/or poorly developedvolcanic substrates where they establishes small, pure or mixed stands together with Pinus nigra subsp. calabrica(Loud.) A.E. Murray. In the past, such woods were subject to coppice management, but only until 1987, followingthe establishment of the Etna Regional Park. In recent years, a progressive decline in Etna birch natural populationshas been observed, resulting evident from the limited occurrence of natural regeneration and from the increasein decay processes of adult plants. Many natural populations are attacked by fungal pathogens (for example ofthe genus Heterobasidion and Armillaria) that are causing their disappearance. Due to the remarkable scientific and biogeographical interest of Betula aetnensis, and considering the growing threats that characterize it, a multidisciplinary investigation has been launched to study various aspects of the ecology of the species, including the extent and role of mycorrhizal symbioses, and taking into account also the risks for the conservation of the species, among which also climatic change. In fact, it is well known that mycorrhizal fungi can have multiple positive effects on the growth of endangered species, on their productivity, as well as on plant health. However, up to now the mycorrhizal status of Etna birch, and that of most of threatened species, has not yet been evaluated. The aim of the present work is to evaluate the degree of decay of Betula aetnensis, its interactions with symbiotic fungi (endomycorrhizae and ectomycorrhizae), and to verify whether or not climatic change actually affects the plant growth and survival. The study areas in which pure birch or mixed stands with Calabrian pine are in good conditions have been compared to areas with clear effects of decay. The survey of the regeneration in each study area showed the total lack of regeneration in the most altered substrates, confirming the strong pioneer role of the species. The dendrochronological sampling provided information on plant age, growth dynamics and the sensitivity of birches to climate factors such as rainfall and temperatures.