*4.2. SDM as a Tool for Forest Management Options in the Italian Framework*

According to the provided evidence, the altitudinal gradient will play a very important role in Italy determining different patterns of species distributions in future climate conditions. This parameter already influences the shape, structure, and specific composition of forests worldwide with a direct effect on a series of important processes, such as water availability, temperature, and soil properties [51,86,87]. The tendency in altitudinal shift of different organisms, both animal and plant, is often confirmed by many research papers [8,12,88,89] with the altitudinal shift generally occurring at much lower speed than latitudinal [83]. If the velocity of colonization of new areas is too low when compared to expected climate change scenarios, then AM might be planned. In this case most of the studies are focused on the upper elevational limit, sometimes also called the leading edge, while the lower elevational limit or rear edges is less investigated even if it is fundamental to plan adequate conservation scenarios for threatened species [28,89,90]. According to Lenoir et al. [8] an average trend shift of 29 m in upward sense for a decade seems to be a reliable value for forest tree species in southern France considering the variation in optimum climate of species in two different periods, that is 1905–1985 and 1986–2005. A confirmation of this process regarding Italian mountains can be found in Rogora et al. [91], where a progressive thermophilization process of climate and a progressive natural introduction of typical species of lower altitudinal strip both for Alps and Apennine has been detected. According to our results, the altitudinal movement of the forested areas with the worst scenario (COSMO) seemed to be lower and around 18 m per decade, demonstrating a possibility of Italian forest tree species to colonize new lands. In this sense, the higher sensitivity to climate change of pure broadleaf stands is one of the main results of our modelling efforts. This result confirms the recent literature where a general contraction of broadleaf species, especially those species that are adapted to cold and wet conditions, was studied [92,93].

According to the provided results, forest management will play a fundamental role in a changing climate. Silvicultural practices in Italy should be aimed at increasing the species richness and favoring hardwoods currently growing as dominated species under conifer canopy, stimulating the natural regeneration, gene flow, and supporting (spatial) migration processes. The spatial variation we found in our models confirms the results of previous studies that establish for Mediterranean areas a general tendency to a loss in habitat suitability as consequence of decreasing precipitation amount and increase in temperature and in frequency and severity of drought period [53,74,94,95]. The possible consequence of climate change may also be accompanied by an increased wildfire and safety risk. This issue has also been acknowledged in many other research studies and mainly connected to extreme climatic events [96,97]. However, uncertainty assessment has also been detected as fundamental in this case too when predictive models are generated [98].

Our results highlight that only three species seem to be favored by climate change phenomenon: Arolla pine, Douglas fir, and laricio pine. The scientific literature confirms these results. As example, Casalegno et al. [99] indicated an increment of spatial distribution of Arolla pine as consequence of the progressive abandonment of pastures in the Alps. Instead, Douglas fir is indicated as a tolerant species versus drought events [100,101] and its habitat suitability is indicated in increment in Europe in future time periods by Dyderski et al. [102]. In the end, laricio pine is indicated as tolerant to heat and drought events [103]. Considering broadleaf species and the oaks group, our outcome is partially in agreement with the existing knowledge. A negative variation in habitat suitability was also predicted in Perkins et al. [104] while a negative decrease in habitat suitability can be read in Kim et al. [105] for cork oak in

the Mediterranean area. Finally, a decrease in habitat suitability during the future period was predicted for holm and turkey oak by Vitale et al. [106] in the same environment we studied. Conversely a contrasting result with existing literature was found for downy oak. In this sense, our outcome highlights a possible decrease in habitat suitability while a potential increment was calculated by Vacchiano and Motta [88]. However, the difference might be attributed to the spatial extent they studied, a small region of Northern Italy where our model predicted an increase too. With attention to other broadleaf species, a possible negative variation in suitability values is expected for European beech that confirms the hypothesis by Noce et al. [53] and especially in the center and south of Apennine. With attention to conifer species such as European larch and Norway spruce, a reduction of habitat suitability is a possible event. A negative variation in habitat suitability of Norway spruce represents a focal point for the high economic value of timber and it reported by different previous works [92,107]. A negative variation in habitat suitability for European larch is also confirmed by Dyderski et al. [102] and Mamet et al. [108]. Additionally, silver fir loss in habitat suitability values is in agreement with Vitasse et al. [109]. Given the economic relevance of this group of species, SFM in Italy should take particular care in their management and supporting local enterprises and avoiding species substitution, maybe using different provenances and genotypes [110,111]. Finally, despite being considered as typical Mediterranean species, a possible decrease in suitability was predicted for species such as Italian cypress and stone pine. This possibility was confirmed in Klein et al. [112] with attention to Italian cypress and in Freire et al. [113] if stone pine is considered. A decrease in suitability values is also a possibility for Aleppo and Maritime pine and finally for black pine as previously reported by Silvério et al. [114] and by Buras and Menzel for black pine [74]. All the cited literature reports as main causes of the decrease in habitat suitability a high sensitivity towards drought events, an increase of wildfire events, and in the end an increase of pests and pathogens. Even if probably in agreement with literature, the low occurrence across INFC2005 might be the main shortcoming of our model for these tree species, owing to a possible underestimation of their potential ecological niche which will be the real niche responding to climate. In this framework, only monitoring efforts and provenance trials will support the solution of the issue in the next decades and allowing models to consider phenotypic plasticity [9].
