Characteristics Of Phenology And Growth For Tropical Introduced Plants And Their Responses To Climate Change

Climate change is one of the focuses in the 21st century, especially the global warming. Due to such change, it is documented that the plants in the mid and high latitude regions has responded markedly, such as shifts in phenology, increases in vegetation activity. Corresponding to global climate change, it is found that climate change also accelerated in tropical regions. Compared with that in mid and high latitude, the magnitude of climate change in tropical regions is smaller. Thus, some researchers speculated that the evident phenological change would not happen in tropical regions. Lack of long-term plant growth data in tropical regions, however, there have been no studies being carried out tested the prediction.Xishuangbanna is located in southwest of China, and is one of the limited tropical regions in China. The tropical vegetation developed here is similar to the typical tropical rainforest in Asia, not only in forest structure and but also the flora composition. Xishuangbanna Tropical Botanical Garden (XTBG), in which there are 10,000 species growing, lies in Xishuangbanna. The phenology and growth of the species were recorded by the gardening staff. Some of the species have long t term phenological and growth records, which permit us to evaluate the responses of plants to climate change in tropical region. In addition, the differences in climate between source locations and introduced location also influenced the adaptability and phenology of plants. In this study, we have three aims, 1) climate change in Xishuangbanna Tropical Botanical Garden; 2) the adaptability of these plants in this Garden; 3) the relationship between phenological shift and temporal growth pattern and climate change. The results showed thatIn the nearly past 50 years, climate in Xishuangbanna demonstrated markedly shift, especially the mean annual temperature, the minimum annual temperature, the maximum annual temperature, and mean annual relative humidity, with shift rates of +0.17℃/10a,+0.10℃/10a,+0.14℃/10a, and -0.28/10a, respectively. Because the significant change of climatic variables happened at year or season level, the significant change in monthly climatic variable must occurred. It was found that the 1980~90s was the period with markedly climate shift.Except for fruit setting and fruit ripening, the leaf shedding, flushing, flower budding and flowering all showed evident seasonal rhythms, which was in accordance with climate rhythm in Xishuangbanna Tropical Botanical Garden. The frequencies of mean month for phenophases were strongly related to the month climatic variables in the preceding months. In addition, the influences of earlier months and later months from the mean phenophase month on the frequencies of mean month for phenophases were reverce. The relationship shifted with an interval of 6 months. Therefore, the climate in XTBG played an important role in phenology, but the affect was periodic.Although these plants came from different locations in the world, they showed good adaptability to Xishuangbanna Tropical Botanical Garden on overall. However, the plants from different regions showed a little difference in adaptability. The order of adaptability of the introduced plants is tropical Asian species, northern region of tropical Asian and subtropical region, tropical Africa, tropical Australia, and tropical America. Some family species showed better adaptability in Xishuangbanna Tropical Botanical Garden,such as Bignoniaceae, Myrtaceae and Mimosaceae, than others. We also found that the later the plants were planted, the better adaptability they demonstrated. At the same time, the temperature is increasing. The better adaptability at higher temperature meaned that climate change may be beneficial to plant introduction.Corresponding to climate change, phenology for about 14 percent of plants showed significant shift. Nevertheless, the phenophases shifts in these tropical introduced plants showed three characteristics different from that in mid and high latitudes. Firstly, the shift direction for the same phenophase was not in agreement, the direction was determined by species. Secondly, the phenological shift rates were greater than that in mid and high latitudes. Thirdly, the influence of climatic factors on phenological shift was complex. The influencing climatic factors on phenological shift for different species were not in common,and more than one climatic factors were related to phenological shift. Therefore, to predict phenological shift in tropical regions in respond to climate change with a single climatic factor would increase the risk of obtaining wrong results.The plant height deviation varied among years, and the different species showed same temporal pattern. The influencing climatic factors in the dry and hot season were closely related to plant height deviation. The influence of sunshine duration was negative, and the influence of relative humidity and wetness index and minimum temperature was positive. Such results were not consistent with the previous reports.The shift of shooting duration was not always positively related to plant height growth. Among 11 species, the relationship was positive for 6 species, and negative for 5 species. Although the shooting duration shift contributed to the relationship between climate and plant height growth, the contribution was smaller.Some species for different source locations showed different phenology in Xishuangbanna Tropical Botanical Garden. We also found that the same species living in different locations showed markedly different phenology, which was related to the different climate regimes.In conclusion, the introduced plants showed good adaptability to Xishuangbanna Tropical Botanical Garden on overall. In response to climate change, significant phenological shifts were found for about 14% of plants. The climate also greatly influenced the temporal plant height growth. In general, however, changes in shooting duration were not closely related to plant height growth. Because of the diverse responses to climate change, climate change did not improve adaptability of all plants. On the other hand, because of similar phenology pattern between introduced plants and indigenouse plants, the above results could be extrapolated to the native vegetation to some extent.