Table 8 indicates that the absolute error between optimal hypotheses and the real experiments can range from 5 to 10 days in 2011; 0 to 4 days in 2012; 0 to 6 days in 2013. That is, the uncertainty of the simple and linear GDD model can be as small as 0, or as huge as 10 days, revealing some uncertainties of this model. On the other hand,
when the differences between hypothesis and reality transformed into relative standardized percentage divided by the parameter durations, the error of the OTHAIMs comparing to the real experiments can range from 0 to less than 15% (Table 9).
4 Discussion
With the GDD model and previous results from researchers in TRES (Lin et al., 2016), the results of the OTHAIMs are established, in analogy with Sakura Zensen, cherry blossom blooming frontline map, from Japan (Arakawa, 1955). Here are some issues brought to the surface and worth investigating after the construction of the visualized mapping.
The concept of Sakura Zensen, cherry blossom blooming forecast, from Japan is applied in this study. Although the development between different phases in physiology may be different in different varieties, the concept and process of heat accumulation remain the same. Therefore, despite the realm of tea in this study, the GDD model can also be applied to various species. Moreover, climate change causes an effect of not only daily average temperature elevation but also smaller diurnal temperature difference and larger interannual or seasonal temperature variation, resulting in a variance of the timing of tea growth.
Taken the High Mountain Tea, for example, its high-praised flavor and fragrance are said to be contributed by the fog surrounded the mountains annually. When climate change may cause the foggy weather patterns to transform or even disappear, the quality of High Mountain Tea is deemed to be impacted. Another example is the extreme weather events, e.g., there was a sleet fall event in Pinglin in 2016, an important town for Wenshan-Pouchong Tea (Figure 9). Although the sleet might happen when the tea trees are still within the phase of dormancy before the phase of budbreak at that time,
tea trees may be damaged if there is earlier budbreak under warming scenarios. Also, the original weather patterns suitable for many special kinds of tea in different local regions in Taiwan may be different under the ongoing changing climate, e.g., the Green Tea, Oolong Tea, and Pouchong Tea in Taipei region. The Oolong Tea in the northern region which needs the bites from an insect called Jacobiasca formosana, small tea green-leaf hopper, and the Pouchong Tea, Black Tea, and Oolong Tea in the central and eastern region in Figure 4 and Table 3. As a result, the accompanying issues of climate change should be investigated further in detail afterward.
Furthermore, the weather variable mainly considered in this study is temperature.
Nonetheless, there are several other parameters may be helpful if taken into consideration, e.g., precipitation, solar radiation, etc. Precipitation is said to be the most effective element within growing phase of plants or crops, while solar radiation contributes to the photosynthesis in the green leaves. Tea buds are said to break due to temperature; and that tea leaves are said to grow because of precipitation. The variation of precipitation in the future may affect the results of the timing in the mapping of OTHAIMs as well. Moreover, some remote yet large scale climate patterns may affect the weather of Taiwan, e.g., the El Niño Southern Oscillation (ENSO). There is a moderate La Niña happening during 2011-2012, which may result in variances from the ordinary patterns of temperature and precipitation (Figure 10) in Taiwan. On the other hand, the baselines chosen for the temperature datasets of the warming scenarios can also alter the results of mapping (Appendixes 2 to 19; Figures 7; Tables 6 and 7).
In addition, spring tea is the only target discussed in the OTHAIMs because the Pouchong Tea, light partly-fermented tea, manufactured in this season is the major
commodity produced in Taiwan, especially the Wenshan Pouchong Tea in the north and the High Mountain Tea all over Taiwan. Nevertheless, tea is produced also in the summer, autumn, or winter in Taiwan, while spring is the most profitable season in general. When tea can be manufactured in every season for many times, it can also be planted in plains, hills or mountains with different altitudes. Different locations of production may result in various kinds of tea with special features, i.e., Black Tea, Green Tea, or Oolong Tea. The Pouchong Tea mainly discussed in this study refers to the tea manufactured with light fermentation in Taiwan from the definition of the official institute TRES (Table 3; TRES, 1987). Although there are so many tea varieties cultivated by TRES or tea farmers alone, we only target the major two cultivars dominating the biggest percentage of plantation area harvested in Taiwan in this study.
Lastly, as warmer weathers deemed to happen in the upcoming future, it is still not sure if the conditions on tea growth will be better or worse. Due to the uncertainty on the extreme weathers, daily maximal or minimal temperatures are not yet to be predicted. Since then, we need more data on tea (Chen et al., 1991) or meteorology.
The report released in 1991 by Chen et al. recorded tea data from the experimental plantations all over Taiwan region. We do not use the data in this report due to the uncertainty whether these data match the methodology in this study or not. Although not utilized as the base of the OTHAIMs, successors can still investigate and examine this treasured and rare data source to the fullest. The bulletin released by TRES every season is a fine, stable, diversified, and compatible source on tea research from the official institute in Taiwan as well.
As mentioned above, the timing of tea harvest is to be affected while the
accompanied trends of quality and yield are actually unknown. The harvest timing of other tea kinds, Green Tea, Oolong Tea, and Black Tea, located all over Taiwan might be affected into an unexpected situation as well. When the tea farmers all over Taiwan region may manage their plantations with different methods or calendar, the results of OTHAIMs possess some limitations and shall be optimized with more future work for the enhancement of stability.