## 3 Results
### Review of Thematic Foci on Extreme Weather Events and Climate Change
#### 3.6.6 Trend Change  
With a total of 44 studies on the effects of trend changes due to climate change on temperate forests, this topic is the second largest. The distribution of the study areas is noteworthy. Overall, more than half of the study areas are in Asia (\(n=25\)), 20 of which are in China. There are clear trends in the breakdown of forest response categories. In contrast to the other drivers, the most common forest response in the trend change category is a shift in phenology. Studies from Asia are overrepresented in this category, and their approach is very similar. A longer timeseries of multispectral sensors were used to measure the changes caused by climate change and the influence of other variables on the start or end of the season or the length of the growing season [111; 112; 181; 182; 183; 184; 185; 186]. Common to all studies is that they show how changing climatic conditions affected the development of the seasons. Accordingly, the start of season (SOS) is shifting earlier in the year, and the end of season (EOS) is being delayed in the course of the year. This extends the length of the growing season. These studies also examined the influence of various independent climate variables on phenology. The results overlap. [PERSON] et al. [181] showed that minimum temperatures in particular control the dynamics of SOS and EOS in semi-arid mountainous regions of China, which was also confirmed by [PERSON] et al. [185], who emphasized night temperature as the most important driver of phenology changes. [PERSON] et al. [112] and [PERSON] et al. [184] showed how spring temperature evidently influences the start of the season. These studies demonstrate that precipitation has less influence on phenology in northern China. In addition, the influence of topography and exposure was proven [182; 186]. Also the study by [PERSON] et al. [187] on phenological changes in subalpine forests on Jeju Island, South Korea, confirmed that rising temperatures affect SOS. Similarly, the study by [PERSON] et al. [188] was on climate change-induced phenological changes in Turkish beech forests, in which chilling hours and growing degree days explicitly showed the highest correlations with SOS. Seven studies analyzed phenological changes as a result of climate change in North America. What they all have in common is the use of multispectral timeseries [106; 189; 190; 191; 192; 193; 194], while the time periods examined ranged from 10 [194] to well over 30 years [192]. These studies focused on the influence of hydrologic cycles on phenology, which is influenced by precipitation and temperature. For example, [PERSON] et al. [193] showed that earlier mean annual snowmelt was significantly correlated (Spearman rank correlation, \(p\) val = 0.046, \(p\) = 0.594) with earlier onset of green-up at the landscape scale. Similar results to the Asian studies were found in North America. [PERSON] et al. [189] identified thermal forcing as the main driver of spring phenology, while [PERSON] et al. [191] found that the phenology of deciduous forests in North America has shown an advanced SOS and delayed EOS over the last two decades, driven by climate variability. The proportion of studies with European study sites is below average. Only three studies address the effects of changing climatic conditions on phenology in Europe. [PERSON] et al. [195] focused on the development of a Bayesian hierarchical model for estimating spatial and temporal variation in vegetation phenology from the Landsat timeseries. [PERSON] et al. [196] investigated the effects of climate change on been phenology and found that the overstory SOS increased with higher mean April canopy temperature, although the understory was not affected by the temperature change. [PERSON] et al. [164] confirmed the already known phenomenon that beech forest types have a very high capacity to shift their phenology towards an earlier spring as a consequence of global warming. Changing climatic conditions also affect forest productivity.