Since as early as the 1980s, scientists have studied the phenomena of many tropical trees of various species flowering at nearly the same time. Now, an international team of researchers, including Tomoaki Miura in the Dept. of Natural Resources and Environmental Management, have for the first time viewed this event from space using satellite technology.
The team consists of Tomoaki, along with scientists from the Japan Agency for Marine-Earth Science and Technology, Miyazaki University, University of Zurich, Yokohama City University, Sarawak Forestry Department, and Kochi University.
From its base in Lambir Hills National Park, located in the Malaysia part of Borneo, the team witnessed a mass flowering often called as “general flowering” of trees in tropical rainforests in Borneo and Southeast Asia. They were able to view the event from space using “PlanetScope” cubesat satellite technology, which revealed the spatial extent of this phenomenon by capturing individual flowering trees.
“Trees in tropical rainforests in Borneo and Southeast Asia region do not flower annually, and sometimes they do not flower for many years,” explains Tomoaki. “When they flower, a large number of various trees species flower all at once during a period of a few weeks to a few months, which is followed by mass fruiting.”
Borneo’s flora is among the most diverse in the world, with nearly 11,000 species of flowering plants, about a third of which are indigenous. Being near the equator, it rains abundantly and lacks a distinct annual dry season. Therefore, many researchers have been studying the seasonality of plant growth in the region, including flowering and fruiting, and what factors might trigger a general flowering event in these non-seasonal tropical rainforests.
Flowering is an important stage in a plant’s life cycle, and flowering and fruiting are very important for biodiversity conservation, as this gives researchers an opportunity to collect seeds of indigenous species only found in the area. They are also studying how climate change impacts the general flowering phenomenon.
In previous studies, researchers used traditional, in situ surveys or time-lapse cameras from a tower over experimental plots of various sizes (e.g., 4 ha - 8 ha) or along roads in order to study general flowering. The surveys have obtained flowering tree information on target individuals on a long-term basis, but for a limited area. Although satellite imaging is considered ideal for viewing large areas of land, the researchers found that previous satellite imaging could not view flowering trees in this cloud-prone tropical area.
PlanetScope is a commercial constellation of cubesats. The project began in 2014 and has gradually increased the number of available satellites. Today, there are more than 180 cubesats flying in formation in space and taking high-resolution digital images over land almost every day.
The UHM-led international team leveraged this new technology to obtain many cloud-free, high-quality images far above this national park. All of the international researchers have conducted field surveys regularly along with time-lapse imaging. The accumulation of knowledge from these field measurements and availability of in situ field observations allowed them to effectively analyze the cubesat imagery.
By analyzing the satellite imagery, the researchers found that the 2019 general flowering event occurred throughout the entire park. They noticed that flowering trees could only be seen in elevations ranging from 50 m to 300 m. They also found that most trees flowered in the month of May, but some flowered in April or June, which was directly linked to the species of tree.
“These findings should help improve our ability to monitor general flowering and our understanding of the functioning of the tropical forest ecosystem,” says Tomoaki. “Cubesat technology and the approach used in this study have the potential to monitor noxious weeds and invasive trees that bear distinctive flowers, such as fireweeds and African tulip trees, which should be a useful tool for management of these plants.”
The study, Utility of commercial high resolution satellite imagery for monitoring general flowering in Sarawak, Borneo, appears in the February 2023 edition of Ecological Research, DOI: 10.1111/1440-1703.12382. The study’s authors are Tomoaki Miura, Yuji Tokumoto, Nagai Shin, Kentaro K. Shimizu, Runi anak Sylvester Punnga, and Tomoaki Ichie.