## 4 Discussion
Temperature is therefore an important factor, but our results often do not show a significant relationship between this parameter and SOS and POS (Table 5). This can be explained by the fact that, in addition to temperature, there are other factors that may influence phenological dates, such as CO\({}_{2}\) concentration, the presence of nitrogen in soil, solar radiation, wind speed, atmospheric pressure, snow cover or precipitation [67; 68]. Snow cover for instance, as reported in [PERSON] et al. [77], can act through temperature accumulation but also independently as a driver of plant phenology. Regarding precipitation, [PERSON] et al. [78] observed an earlier onset of the grassland growing season due to higher temperatures only when water was not a limiting factor, with a non-linear response. In contrast, [PERSON] et al. [68] pointed out that high precipitation can have a delaying effect on the peak season (POS) as a result of the high correlation between this phenological stage and rainfall. Our study highlighted the influence of altitudinal and latitudinal conditions on the phenological stages of grassland with significant changes (F \(\leq\) 0.1) in SOS and POS during 2001-2021. Correlations between the magnitude of change in SOS and altitude and latitude indicated higher absolute values than the respective correlations with POS. The sites that showed higher changes in the dates of SOS and, to a lesser extent, POS were those located at higher latitudes and lower altitudes (e.g., DEN, 56.1995\({}^{\circ}\)N, 40 m a.s.l. ), while at low latitudes and high altitudes (e.g., TUR, 41.2610\({}^{\circ}\)N, 2524 m a.s.l.) showed smaller phenological changes. The contrasting behaviour of changes (i.e., advances and/or postponent) in SOS and POS dates can also be explained by the variability in botanical composition as a result of the different environments in which the study sites are located. This is confirmed by several studies [55; 79; 80; 81; 82] that highlight the importance of species or functional types on the phenological stages of plants. In addition, as observed by [PERSON] et al. [67], diverse plant functional types have different phenological changes in response to multiple environmental factors (e.g., CO\({}_{2}\) concentration or soil resources). Moreover, the changes in temperatures recorded over the last few decades, beyond having a direct effect on the early or late season, may have influenced the change in the composition of functional groups [83], which in turn may alter the grassland phenological stages. Nevertheless, the main aim of our work was to highlight general trends in phenology, without a particular focus on the species present in the test areas. Given the spatial-temporal extent of the trend analysis, reliable and timely information on the specific botanical composition at the 31 study sites over the years of investigation was, moreover, difficult to obtain. Indications regarding phenological responses of different species can, however, also be gathered indirectly from observing the results in Figure 6, which analyses the phenological changes observed at different altitudinal and latitudinal gradients, conditions that reflect the type of vegetation that may be present in those environments. Although investigating the phenology of different species was not our main objective, knowing the type of species or functional groups present would have provided useful information to increase understanding of the results. In fact, as explained above, this information may clarify the contrasting results obtained for some study sites. Nevertheless, the results showed a clear general tendency of grassland phenology to advance, especially the SOS date. Overall, our results confirmed what was already observed in a sparse and limited number of EU countries [36] and under a different time span in Europe [38], while remaining in line with other studies in other areas of the world [61; 68].