World's Tallest Tropical Trees Discovered

Laser scanning in Borneo has revealed 50 trees that break previous records. The giants are about as tall as five sperm whales stacked end to end.

The tallest tropical tree in the world is right where we thought it was—in a protected forest reserve in the state of Sabah, Malaysian Borneo. But it’s not the one we thought.

Greg Asner of the Carnegie Airborne Observatory (CAO) revealed the new record holder this week in his keynote speech at the 2016 International Heart of Borneo Conference.

Earlier this year a team of researchers led by David Coomes of Cambridge University made headlines with their announcement of the tallest tropical tree measuring 89.5 meters (293.6 feet) in Maliau Basin, a protected reserve managed by the Sabah Forestry Department. However, concurrent laser scanning in May 2016 across a broad swath of Sabah’s forests conducted by Asner shows that one behemoth tree on a hillside in Danum Valley, another protected reserve, measures 94.1 meters (308.7 feet), surpassing the Maliau specimen for the honor of the world’s tallest tropical tree.

The tallest known trees anywhere are California redwoods, which live in the temperate zone. They have been measured up to nearly 116 meters.

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The large-scale census in Borneo covered many of Sabah’s protected forests, and actually pinpointed 50 trees that broke the previous record scattered across the state—33 in Danum Valley, 10 in Tabin Wildlife Reserve, and 10 within the United Nations Development Program’s biodiversity conservation project area. He also found that the Maliau Basin tree was in fact just over 90 meters tall, adding that “either that tree grew half a meter or one of us is wrong”—a collegial nod to Coomes, who worked closely with Asner on his work in Sabah.

For reference, Asner noted in his talk that the height of the Danum Valley tree was about equal to five sperm whales stacked snout-to-fluke, an image enjoyed by the audience of scientists, government officials, and public and private stakeholders working in the Heart of Borneo—an area in the interior of the island of Borneo that includes parts of Malaysia, Indonesia, and Brunei.

Since the tree was measured remotely, scientists aren't sure which species it is, although it is likely in the genus Shorea, they say. That group includes nearly 200 species of mostly rainforest trees native to Southeast Asia. The trees can live for hundreds of years but many are endangered. Borneo has more than 130 of the species, including 91 found nowhere else. A number of the species are prized for their lumber.

The tree was measured with laser scanning, using technology called Light Detection and Ranging (LiDAR), which is essentially the laser version of RADAR. But instead of radio waves, light pulses are emitted from an airplane, bounce off the forest below, and the rate of these bounces allows for three-dimensional mapping of forests across entire landscapes in incredible detail.

LiDAR is rapidly becoming one of the most useful tools in forest research, management, and conservation. Recent applications of the technology have allowed researchers and policymakers to assess carbon stocks, track deforestation, and even uncover archeological sites.

Asner summarized the utility of the technology: “Our ability to measure forests at large scales, yet with actionable detail, is key to managing and conserving them.”

Despite the exciting discovery, Asner stressed that his analysis of the data is far from over. He showed preliminary figures of the carbon storage provided by the various forest types and land use histories across Sabah, all of which will be publicly available, a move that he hopes will help policymakers create informed conservation plans in the future.

Asner himself admits that he had at one time been skeptical of the conservation potential in Sabah. Imagery from the Landsat program, the longest-running satellite imagery operation, seemed to indicate that Sabah’s forests had all but vanished. Cynthia Ong, executive director of Forever Sabah, a local organization committed to supporting the state’s “transition to a diversified, equitable, green economy,” convinced Asner to think otherwise. After an initial scouting trip to visit some of Sabah’s protected forests, Asner and Ong sought support from the Sabah Forestry Department and other local and international organizations to fly the scanning technology over Sabah.

The research was funded by James Cameron's Avatar Alliance Foundation, the UN Development Programme, Rainforest Alliance, and WWF-Malaysia.

“Tallest tree aside, this work really highlights the value of protecting primary forests,” said Glen Reynolds, referring to forests that have had little or no human impact with intact ecological processes. Reynolds was also involved with the project as program manager for the Royal Society’s South East Asia Rainforest Research Program (SEARRP) and senior scientist at Danum Valley Field Centre, where the giant tree was located.

He added, “These ancient trees are really only found in primary forests, many of which are not properly protected. A detailed map like this will be useful for establishing conservation priorities.”

Orangutan on the Edge

The International Heart of Borneo Conference is held annually in Kota Kinabalu, Malaysia, bringing together environmental leaders to present and discuss findings and needs in the region. This year the discussions were focused on conservation finance, the science-policy interface, and community engagement. The day’s presentation was met with enthusiastic applause from the audience, who will undoubtedly be awaiting further results at next year’s conference or sooner.

Kevin McLean is an ecologist and a Fulbright-National Geographic Digital Storytelling Fellow, who is using camera traps to study the rainforest canopy in Borneo and the Amazon. Follow his work here.

Full disclosure: McLean has published unrelated work with Greg Asner and has received assistance on his project from Glen Reynolds and Cynthia Ong, unrelated to the tree study.

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