RUOLO DELLE POPOLAZIONI FORESTALI MARGINALI NEL FAVORIRE L'ADATTAMENTO AL CAMBIAMENTO CLIMATICO

Marginal forest populations are located at the edges of the species distribution and usually grow under non optimal ecological conditions. They are small and grow with difficulty, moreover the genetic flow among them and populations present within the main diffusion area is reduced. Marginal populations are usually characterized by low internal genetic diversity, because of isolation and genetic drift phenomena. However, they show adaptability to particular ecological conditions, namely high temperature and reduce water availability. As a consequence, marginal populations can be considered as a source of genetic traits that, in the near future, could acquire great importance even in the species main diffusion area. Phylogeographic surveys show that rangewide patterns of population genetic diversity are usually shaped by past climate-driven range dynamics rather than by demo-genetic stochasticity. As a consequence, marginal populations commonly harbour peculiar genetic aspects. They are also older because they survived in ¿refugia¿ areas in the south of the species distributions to glaciations. The report analyses the status of marginal populations in three forest species widespread in Italy. In case of Scots pine, marginal populations growing in the Apennine chain show high genetic differentiation but low genetic variability, probably due to isolation and genetic drift. Southern populations of silver fir still show consistent genetic differentiation, but also internal genetic variability is comparable with that of alpine populations: this is probably due to the fact that Apennines are considered a refuge area for the species, where the latter survived during last glacial period. Lastly, in wild cherry it was possible to observe that southern marginal populations are not genetically differentiated and show an amount of genetic biodiversity comparable with that of northern populations. This dissertation also analyzes the potentiality of assisted migration, that consists of transferring seeds from marginal populations to locations where climate changes are expected. The actual yield loss is expected to decrease to zero as a result of the progressive climate change. Lastly, an European Project (COST Action) involving the study of forest marginal populations from all Europe and aimed at defining effective strategies for their preservation is shortly presented.