## 3 Results
### SOS and POS Trend Analysis (2001-2021)
Sites that display a significant POS-year correlation are marked with * (0.05 \(<\) F \(\leq\) 0.1), ** (0.01 \(<\) F \(\leq\) 0.05) and *** (F \(\leq\) 0.01). The results on the influence of winter and spring temperatures on SOS, showed a negative correlation between SOS and temperatures, significant in 7 sites (F < 0.1, AUS1, BOS, CZE, DEN, FRA2, LAT, SWI1) with winter temperature and in 6 (BOS, FRA1, LAT, POL, SWE, SWI1) with spring temperature as the main driver. Since POS always occurred several weeks after winter's end, in the analysis we considered only the effect of spring temperatures. Here, too, the relationship highlighted a negative correlation between phenological dates (i.e., POS) and temperature. In particular, 10 sites (AUS2, BOS, DEN, FRA3, ITA4, LAT, POL, RUS1, SCO, SPA1) showed a significance F in the POS-spring temperature relationship of less than 0.1. Taking into account the grasslands where the change was significant at both the SOS and POS dates (11 sites), we investigated the influence of two other potential phenological season variables: the latitude and altitude of the test sites. As can be seen in Figure 6, the change in advance during the period 2001-2021 is greater with increasing latitude for both SOS and POS, with the former showing a higher correlation (R = \(-\)0.81) than the latter (R = \(-\)0.55). Observing the correlations between changes in phenological dates and altitude, sites at higher altitudes show less advance in SOS and POS than those at lower altitudes. As in the case of the SOS and POS-latitude correlation, the absolute values of R are greater for the change in SOS dates (R = 0.69) than for POS (R = 0.36). \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Winter**} & \multicolumn{4}{c}{**Spring**} \\ \hline
**ID** & **T Mean** & **R Years** & **Sign.** & **R SOS** & **Sign.** & **T Mean** & **R Years** & **Sign.** & **R SOS** & **Sign.** & **R POS** & **Sign.** \\ \hline SCO & 1.22 & \(-\)0.37 & 0.12 & \(-\)0.18 & 0.47 & 6.71 & 0.24 & \(-\)0.31 & \(-\)0.14 & 0.56 & \(-\)0.47 & **0.05** \\ SLK b & - & - & - & - & - & - & - & - & - & - & - \\ SIV a & \(-\)0.25 & - & - & - & - & 11.69 & - & - & - & - & - & - \\ SPA1 & 7.08 & \(-\)0.11 & 0.66 & 0.08 & 0.74 & 15.48 & \(-\)0.87 & **<0.001** & - & - & \(-\)0.45 & **0.05** \\ SPA2 b & - & - & - & - & - & - & - & - & - & - & - & - \\ SWE & \(-\)8.69 & 0.03 & 0.89 & 0.24 & 0.34 & 1 & \(-\)0.34 & 0.17 & \(-\)0.69 & **<0.00** & \(-\)0.2 & 0.43 \\ SWI1 & \(-\)0.1 & 0.63 & **<0.001** & \(-\)0.56 & **0.02** & 9.37 & 0.17 & 0.51 & \(-\)0.46 & **0.06** & \(-\)0.15 & 0.55 \\ SWI2 & 0.15 & 0.52 & **0.02** & 0.01 & 0.97 & 10.51 & 0.03 & 0.92 & \(-\)0.16 & 0.51 & \(-\)0.02 & 0.92 \\ TUR a & \(-\)3.43 & - & - & - & - & 13.17 & - & - & - & - & - & - \\ \hline \hline \end{tabular}  
* Site names with a and b represent the sites with insufficient (c) or no (b) weather data to conduct the analysis. Results with significance <0.1 are shown in bold.  
\end{table} 
Table 5: _Cont._  
Figure 6: SOS and POS changes during the period 2001–2021 compared with the latitude and altitude of the sites where changes are significant in both SOS and POS. In addition to the analysis of the changes that occurred in SOS and POS over the reference period, changes in the duration of the timeframe between SOS and POS (i.e., SOS-POS duration) were also analysed (Figure 7). The data did not show any common trend within the framework of the European grasslands analysed. Indeed, within the dataset considered, some sites showed an increase in the SOS-POS duration (56.67%), while others showed a decrease (43.33%). The lengthening of the SOS-POS duration between 2001 and 2021 was determined by a less marked anticipation of the POS with respect to the SOS (e.g., DEN) or the postponement of the former (e.g., FRA1). The reduction in the SOS-POS duration, on the other hand, was generally caused by a higher advance in POS than in SOS (e.g., GER2).