A model-based assessment of the potential impact of climate change on Italian forest systems

The future dynamics of forest species and ecosystems depends on the effects of climate change and their resilience and adaptive potential are highly related to forest management strategies. The main expected impacts of climate change are linked to forest growth and productivity. An increase in the length of the growing season and greater productivity are likely as well as shifts in average climatic values and more variable frequency, intensity and duration of extreme events. The purpose of this doctoral thesis is to provide information to support forest management strategies potentially useful to mitigate the effects of climate change to Italian forests. Among all the forest tree species occurring across the Italian peninsula, 19 were considered as the most important for their economic, ecological and aesthetic value. The ecological niche of species was firstly described on the bases of climate requirements and compared with existing scientific literature and expert knowledge in Italy. Then the described niches were projected into the future by means of a species distribution modelling approach to derive insight of the forecasted impact of climate change on Italian forests and to derive implication for future forest management strategies. To model the climatic requirements, interpolated climate data of average annual temperatures and precipitation (1km) were used and 6 different Global Circulation Models (GCMs) were employed to describe future climate condition and in addition to a local Regional Climate Model (RCM). Future climate data were referred to unique emission scenario (the intermediate RCP 4.5) for 2050s. Results showed a substantial shift in knowledge with only 46% of the observations falling within the potential joint temperature and precipitation limits as defined by expert knowledge. Moreover, the similarity between current observed and potential limits differ from species to species with broad leaves, in general, more frequently distributed within their potential climatic limits than conifers. Paying attention to future climate conditions the analysis showed strong differences between the different climate models; the RCM demonstrated to be a more variable scenario than GCMs. The Apennines strip will probably be affected by strong and important changes as well as the sub-alpine zone. However, no sensible variations in the extension of the forest area have been predicted. The analyses also indicated that forest suitability is going to remain almost unchanged in mountain areas, while in valleys or flood and plains areas is likely to decrease. Moreover, the model establishes a possible strong negative impact of climate change at the level of pure woods compared to mixed woods, characterized by greater species richness and therefore a higher level of biodiversity. Finally, pure softwood stands (e.g. Pinus, Abies) may be more affected by the impacts of global warming than hardwoods (e.g. Fagus, Quercus). According to the provided results and scenarios, specific silvicultural practises should be applied to increase the species richness and favouring hardwoods currently growing as dominates species under conifers canopy. Increased thinning frequency and intensity and a reduced rotation period may contribute to increasing the natural regeneration, gene flow and (eventually) support species migration.