*4.2. Current Potential Habitat and Future Projection*

The results obtained confirm the hypothesis that the predicted climate change affects the probability of occurrence only for *Eucalyptus dunnii* since the occurrence of *E. grandis* remains unchanged in the long term. The areas with the greatest probability of occurrence of both species are associated with the deepest A horizon, with low amounts of clay and silt, corresponding to soils of the North of the country (Figure 4A,B). This kind of soil structure favors the availability of water (even when the rate of evapotranspiration is high, as in the summer), drainage, and a large exploration volume for the roots. The high probability of occurrence is also related to the high average temperatures of the area, which decrease from NW to SE by 4 to 5 ◦C. This favors growth during periods with greater potential water availability, such as fall [60]. Conditions that promote the growth of *E. grandis* combine deep, well drained, loamy to slightly sandy soil and an annual precipitation of 1000–1800 mm, in a temperature range from 8 to 36 ◦C, the optimum being 26 ◦C (Table S1 Supplementary Materials) [69,70]. This species has low tolerance of frosts and may grow at altitudes close to 900 m.a.s.l., although it has been cultivated successfully at higher levels. The natural distribution of the species (Australia) occupies a large area, with a latitude from 17◦ to 36◦ south, and covers different growing conditions. The areas with a greater probability of occurrence in Uruguay, according to our work, are similar to the ones described for *E. dunnii* (Figure 4B). Soils with the required characteristics are also present, although over a smaller extension, in some central and western areas, and in some reduced areas in the north-west. The soils of south-western Uruguay show less potential because they are shallower-and therefore have lower water holding capacity and nutrients availability and have higher silt and clay contents. The relative heterogeneity of the probability of occurrence of this species that is depicted in the map (at a national level) is explained by the high heterogeneity of soils, resulting from the variety of geological parent materials. On the other hand, temperature increases are foreseen for this region, towards ranges more favorable for the growth of this species. The cardinal temperatures of *E. grandis* are reported to be 8, 25, and 36 ◦C (minimum, optimum, and maximum, respectively), while the average values in Uruguay are 12.9, 17.7, and 22.6 ◦C, respectively. Therefore, an increase in temperature could have a negative effect on growth by influencing the availability of water, but it is not expected that it will negatively influence the physiology of the species.

The stability of the area occupied by *E. grandis* can be explained by the fact that its presence is closely related to soil characteristics and the topography, and less so to climatic variables, such as the temperature (Figure 6). For this reason, the average increase in temperatures projected for this region of 1 to 1.8 ◦C [9] would not imply changes in the species' area, although effects on its productivity may occur. The expected temperature increase (particularly in the north) would be accompanied by an increment in precipitation of 2.5% to 7%, which would have a positive effect on tree growth [17]. For these authors, the response of forest crops to pests and diseases would change in a climate change scenario [71], as well as for extreme climatic events [72] or an increase in the CO2 level in the atmosphere [73].

The reduction in the area of occurrence of *E. dunnii* is predicted for the period 2000–2050 (Figure 5); afterwards, the area would stay relatively unchanged for all the temperature increase scenarios (Table 4). Although one of the most important variables explaining the occurrence of this species is the thickness of the A horizon, the future presence seems to be heavily influenced by the temperature change. Despite the forecasted increases in temperature and average annual precipitation, increased variation between periods within years is also forecasted [9]. Such studies predict temperature increases during summer (1.2 to 1.8 ◦C) that will be greater in the period 2020–2050. This increment may explain the decrease in

the presence of this species, given the negative effect of this variable on the probability of occurrence (Figure 2). Temperature increases in summer could cause plant water deficiency, given the negative balance between evapotranspiration and precipitation. Despite these predictions, some authors have determined some capacity of eucalypt to adapt to situations of lower water availability through changes in the architecture of the root system [74]. These changes have been detected even in species considered as "less specialized" which could be a strategy of adaptation to future climate change. To this must be added the important genetic diversity of these species which determines a response potential that is observed in a wide geographical distribution [75].
