## 5 Results  
Figure 3 shows the monthly average temperature and total precipitation of the areas covered by deciduous oaks (FT 8), which is the most widespread and uniformly distributed forest type in Italy (Table 1); the data are reported both for the present and the future scenarios. The present annual mean temperature is about 11.9 \({}^{\circ}\)C, with a minimum in January of about 4 \({}^{\circ}\)C and a maximum in August of about 21 \({}^{\circ}\)C. The present annual rainfall total is about 1,178 mm. The distribution of rainfall is bimodal, with a primary peak in autumn and a secondary peak in spring. The summer dry period lasts about one month. The expected future scenario implies an average temperature increase of almost 2 \({}^{\circ}\)C (from about 11.9 \({}^{\circ}\)C to 13.6 \({}^{\circ}\)C), mostly effective during late summer and winter. Total annual rainfall is almost stable, but its seasonal distribution is irregularly reduced during some months and increased in others. Figure 4 shows the correlation coefficients computed between the seasonal GPP averages estimated by Modified C-Fix and the corresponding temperature (A) and rainfall (B) averages of the four seasons. These statistics highlight the importance of the different driving variables in relation to the esophagiological characteristics of each species. In general, the positive influence of temperature is stronger for the forest types which are spread on the high altitudinal belt (especially for FT 1), while forest types that cover the warmest and driest areas (_i.e._, FT 7 and FT 8) are more sensitive to rainfall. As expected, autumn temperature and rainfall variations have generally marginal correlations with annual GPP. Figure 3: Thermo-pluviometric diagram descriptive of the present and future climate scenarios for the areas covered by deciduous oaks forests (FT 8), which are the most widespread forest type over the Italian territory. The other four forest types are spatially spread, following a gradient from temperate-humid to Mediterranean-arid climates (Table 2). FT 1 and FT 4 characterize the high Italian altitudinal belt and show the lowest average temperature (respectively of 6.0 \({}^{\circ}\)C and 7.6 \({}^{\circ}\)C) and the highest precipitation. FT 7 shows the highest annual temperature and the lowest total rainfall. These spatial distributions are obviously reflected in the autoecological characteristics of these species, which are differently adapted to the typical Mediterranean summer dryness. The multivariate regression models derived from the same data-set are summarized in Table 3. The models account for 52% to 88% of the total GPP variations. In general, the regression coefficients are positive for spring temperatures, mixed for winter temperatures and negative for summer temperatures. This reflects the relevance of the thermal factor in controlling the beginning of the growing season and the negative effect of high summer temperatures, which usually coincide with drought occurrence [24]. The patterns are more complex and variable for rainfall, whose regression coefficients are positive in winter and mixed in spring and summer. This indicates that winter water recharge is important for all forest types, while spring and summer rainfall exerts a positive effect on FT 7 and FT 8 due to the relevance of water availability in these arid Mediterranean environments. As regards to the expected climate changes (Figure 3 and Table 2), all future scenarios show rather uniform monthly temperature increases (from 1.7 to 2.1 \({}^{\circ}\)C) and more variable rainfall variations (from 3% up to 9%). The highest temperature increase is simulated for FT 1 (2.1 \({}^{\circ}\)C), which is placed in the coldest, most humid areas. The GPP responses of the five forest types to these expected scenarios are summarized in Figure 5. The effects of the simulated climate changes are generally negative except for FT 1 (fir/spruce), which covers the highest altitudinal belt.