## 3 Results
### Review of Thematic Foci on Extreme Weather Events and Climate Change
#### 3.6.6 Trend Change
Five studies looked at the impact of climate change on the productivity of Asian forests [107; 197; 198; 199; 200]. [PERSON] et al. [199] and [PERSON] et al. [107] used NDVI timeseries to investigate the impact of climate change on net primary productivity. [PERSON] et al. [107] found that, in general, the Net Primary Production (NPP) of Chinese forests is increasing steadily, although there are spatial patterns. [PERSON] et al. [199] mainly mentioned the variability of precipitation as a conditional variable. In contrast, [PERSON] et al. [197] and [PERSON] et al. [198] used only mono-temporal multispectral data to investigate the influence of different climatic conditions on productivity. [PERSON] et al. [198] were able to prove that temperature and soil moisture have the greatest influence on productivity. They are the only two studies that fall into the \"trend change\" category and only use mono-temporal data. Their assignment to this category was based on the authors' assumption that the various climatic conditions studied in the study areas will change in the future, and that the trend can therefore be studied in advance by using sites that are already drier. The influence of trend changes on productivity has also been investigated for European forests. The two studies by the first author [PERSON] et al. [201; 202] modelled net primary productivity in Romania using the Landsat archive and machine learning methods. Both studies were able to show that above-ground biomass (AGB) in Romania has increased since 1987, and that Romanian forests have recently experienced a large-scale improvement in carbon fluxes and stocks. [PERSON] et al. [203] took a different approach by incorporating phenological shifts due to changing climatic conditions into a process-based ecosystem simulation model. The results showed that, in European forests, phenological variation reduces net ecosystem exchange. As a possible reason, the authors pointed to the opposite effect of increased heterotrophic respiration directly induced by the extension of the growing season. This result is in contrast to other studies. Only four studies, all located in Asia, focused on forest and tree mortality as a result of changing climate conditions using only multispectral timeseries [108; 174; 204; 205]. For example, it has been shown that forest cover in northeastern China is more dependent on active disturbance (e.g., logging) than on climate trends [108], and that NDVI and Normalized Difference Infrared Index (NDII) are negatively correlated with mortality in birch forests in northern China [205]. Several trend studies did not include a precise description of the effects at the forest level (phenological changes, mortality, or productivity changes). However, these studies commonly described changes in vegetation indices and associated changes in vegetation as a result of changing climatic conditions [101; 109; 206; 207; 208; 209; 210; 211; 212; 213; 214]. In summary, the studies dealing with trend changes focus mainly on changes in phenology. Here, the results are mostly in agreement in saying that higher spring temperatures in particular lead to an earlier start of the season, regardless of the location of the study site. It has been shown that, in most cases, forest productivity increased in the long-term, and that forest decline was usually caused by active disturbances such as logging.