What will the future forests look like? Comparison of performance between Mediterranean oak species in a common garden experiment

Forests are subjected to impacts of climate changes, including extreme drought phenomena, which can be very harmful for seedlings therefore compromising the regeneration. Phenotipic plasticity of tree species under environmental changes can be threatened and it is expected a decrease of tolerance to climate events (1). Modifications of forest structure and composition, including the substitution of mesophytic deciduous formations to xeric or evergreen forests and shrublands may occur. Such ecological changes will take place at landscape level, slowly and in uneven way, since the natural migration speed of trees, until reaching a new potential equilibrium with the modified conditions, may be too slow for an ordered successional process (2). Before planning any management and conservative actions to address the adaptability of forests to the changing environment, it is essential to know the physiology and ecology of tree species under current climate. The project ‘European Oaks under Climate Change’ (FUTUREOAKS) addresses this issue, simulating the assisted migration (i.e. replacement of existing forest species/genotypes by neighbouring species/genotypes filling the same ecological function) of tree species that could move from Mediterranean area to Central Europe. The performance (i.e. plant grow, photosynthesis, resource use efficiency, mortality) of Quercus ilex L., Quercus pubescens Willd., Quercus frainetto Ten., were tested, using two accessions (from Greece and Italy), grown in common gardens in Germany, Greece and Italy. The purpose was to assess the potential for the acclimation of species and provenances for planting as alternative forest species under the expected future drier and warm condition (3). This contribute refers to the field survey carried out in Italy, where a common garden has been established in Umbria (Santa Anatolia di Narco, Perugia). Results will be then compared with those obtained in the correspondent common gardens in Greece and Germany. The common garden was established in April 2017, by using seedling produced from acorns collected in selected forests in Italy and Greece and ripened in the autumn 2016. Our analyses started in September 2017, when the plants were one year-old. In September 2018 measures of plant growth (stem height), Specific Leaf Area, gas exchange (net carbon assimilation, stomatal conductance to water vapour, water use efficiency) and chlorophyll fluorescence were carried out on each species and provenance. Q. ilex and Q. pubescens resulted the best performing species, showing higher growth and photosynthetic efficiency respect to Q. frainetto. Seedlings of this last species exhibited greater mortality after one year than the other species, especially for the greek provenance. Differences between the provenances also resulted in the stem height, chlorophyll fluorescence and gas exchange parameters, with Q. ilex and Q. pubescens showing a better performance of the Italian seedlings compared to Greek ones. The xerophytic Q. ilex and Q. pubescens resulted the species more suitable for sustainable climate-adapted forests under the constrains of climate change. An increase of their distribution area in Central Europe is expected (4) and an ad hoc management strategy should be adopted to safe forest ecosystems and to adapt them to changing environment. 1) S. Noce, A. Collalti, M. Santini (2017) Ecology and Evolution doi 10.1002/ece3.3427 2) F. Bussotti, M. Pollastrini, V. Holland, W. Bruggemann (2015) Environmental and Experimental Botany 111, 91-113 (3) F. Bantis, J. Graap, E. Früchtenicht, F. Bussotti, K. Radoglou, W. Brüggemann (2019) Photosynthetica, submitted (4) T. Hickler, K. Vohland, J. Feehan, P.A. Miller, B. Smith et al. (2012) Global Ecology and Biogeography 21, 50-63