Investigating the Blessings of Tropical Rainforest at the Top of Treesる 〜Photosynthesis at 50 Meters Above Ground〜

Today's Pick up is a translation of an article in Japanese published in JIRCAS Koho (Public Relations) magazine, and introduces research to learn about and protect the power of tropical rainforests from the perspective of a young researcher at JIRCAS.

What is a tropical rainforest?

What kind of forest comes to mind when you hear the word "tropical rainforest"? You probably have an image of a forest that is hot and humid, overgrown with grasses and trees, and teeming with wild beasts and poisonous snakes.

I had the same image until I went to Borneo when I was a university student.

Indeed, based on my first experience, I found a tropical rainforest to be dark and damp. But it never gets as hot as midsummer in Japan, and the mornings and evenings are cool and comfortable. Of course there are mosquitoes and leeches, but large animals are often hidden and rarely encountered. The rainforest is also home to many kinds of creatures, including colorful and strangely shaped insects. Plants are also abundant. For example, about 1,200 species of trees grow in a 1040 m x 500 m research area on Borneo Island. This is equivalent to the number of tree species growing all over Japan, and shows that tropical rainforests are a treasure trove of living creatures.

The many blessings provided by forests

Although the tropical rainforests are a bit far from Japan, the products of the rainforests are found all around us. For example, if you see "lauan" wood on a piece of furniture or flooring, it means that the wood comes from the tropical rainforest. In addition, there are also fruits and resins that are used as raw materials for chocolate, oils for cosmetics, incense sticks, and medicines. Of course, food, medicine, and drinking water obtained from the forests are  indispensable for the local people as well. Without these blessings from the rainforests, human life would not be possible.

Research to understand and protect the power of tropical rainforests

One of the major functions of tropical rainforests is to mitigate global warming. This is because rainforest trees carry out photosynthesis year-round and store large amounts of carbon dioxide in their trunks and other parts. However, there is much we do not know about the capacity of tropical rainforests to absorb carbon dioxide. Therefore, I decided to study leaf photosynthesis in detail. To do this, I needed to directly measure photosynthesis in the leaves of trees growing at various heights in the forest. It is extremely difficult to climb up to the leaves more than 50 meters above the ground with heavy batteries and measuring materials. We even tried to climb up the trees with ladders, but after climbing several trees a day, we reached the limit of our physical strength, and furthermore, when a strong wind blows, the trees sway and make us feel like we are not alive. This problem was solved by using a 90-meter-high crane built on the island of Borneo, and we now know that the majority of photosynthesis takes place in the upper layers of the forest and that there are differences among tree species.

On the other hand, rich tropical rainforests are also deteriorating due to the depletion of resources such as timber caused by excessive logging. There is an urgent need to restore degraded forests and to conduct sustainable forestry. However, even if seedlings are blindly planted in degraded forests, they will not adapt well to the environment and will soon die. Therefore, in cooperation with local researchers and forestry officials, we are conducting repeated planting trials of various tree species and monitoring them over a number of years to determine which tree species and varieties are suitable for forestry and how to plant them.

Photo: Riding a crane in the tropical rainforest in Malaysia to observe the forest canopy and examine leaf photosynthesis in the treetops more than 50 meters above the ground.

Note: This is a translation (with some modifications) of an article in Japanese published in JIRCAS Koho (Public Relations) magazine. https://www.jircas.go.jp/ja/publication/jircas/11

Contributor: TANAKA Kenzo (Forestry Division)