It is believed that trees exhibit morphology and functions that are appropriate to the local environment. Therefore, by studying morphological characteristics, we can predict the optimal environment for tree growth, which will lead to predictions of the optimal planting environment and how its distribution will change with climate change.

Tropical forests are known to be a hotspot of tree diversity on the planet, with the number of species found varying greatly depending on soil, elevation and other factors. On the other hand, the morphology and function of tree species that would appear in which environment has not been well understood, especially in the tropical forests of Southeast Asia. A study conducted at Mount Kinabalu (4,095 m above sea level) on the island of Borneo, the highest mountain in Southeast Asia, in collaboration with the University of Sabah, Malaysia (Kawai et al. 2020), showed that tree species with thick, robust leaves are distributed at higher altitudes and wider altitudinal range. In addition to low temperatures, high humidity, and strong winds, the high altitude areas of Southeast Asia are subject to multiple environmental stresses, suggesting that trees maximize the duration of photosynthesis by having robust leaves. The morphological characteristics of leaves and wood, which are related to water use, were not related to distribution elevation, indicating that water use by trees is not a major factor in environmental adaptation at sites where precipitation is high and wet throughout the year. On the other hand, the characteristics that determine the lowest elevation at which a species appears could not be clarified in this study, and further research is necessary.

Subsequently, a collaborative study with the Thailand Institute of Science and Technological Research (TISTER) and Kasetsart University confirmed that the leaf characteristics that were found to be important in predicting altitudinal distribution were also related to species distribution along the soil moisture gradient of the soil in Northeast Thailand, which has a dry season (Kawai et al. 2021 ). The leaf characteristics examined in this study can be measured without expensive equipment or special analytical environments. Therefore, by establishing the generality of the above findings in a variety of environments and species, we believe that they can be used to evaluate the optimal planting environment for forestry species and to predict the effects of climate change after planting, using easily measurable morphological characteristics as indicators. These results are expected to contribute to the realization of a highly productive forestry industry that is robust to climate change in Southeast Asia and other tropical regions.

Dr. Kawai received the 25th Kira Award (Outstanding Young Researcher Award) from the Japan Society of Tropical Ecology for his research on Mount Kinabalu in Borneo.
 
This research was supported by a Grant-in-Aid for the Promotion of Science Research Fellows (DC2) and Grant-in-Aid for Young Scientists (start-up) from the Japan Society for the Promotion of Science (JSPS).

References
Kawai K, Ahmad B, Palle I, Okada N (2020) Variations of leaf and stem traits in relation to altitudinal distributions of 12 Fagaceae species of Mount Kinabalu, Borneo. Tropics 29:57–66 . https://www.jstage.jst.go.jp/article/tropics/29/2/29_MS19-14/_article

Kawai K, Waengsothorn S, Leksungnoen N, Okada N (2021) Functional differentiation among 12 dipterocarp species under contrasting water availabilities in Northeast Thailand. Botany 99:321–335 . https://cdnsciencepub.com/doi/abs/10.1139/cjb-2020-0155?journalCode=cjb

Contributor: KAWAI Kiyosada (Forestry Division))