East Asia’s tallest tree

 "The Heaven Sword" new tallest tree with whopping 81 meters

Determined researchers have found East Asia’s tallest known tree in a secluded valley near one of Taiwan’s longest rivers. The team named the massive fir tree “Heaven Sword of the Da’an River”, a nod to the legendary weapon from Jin Yong’s martial arts novels. Researchers estimate the Heaven Sword,  towering 84.1 meters (276 feet) tall, is about 1,000 years old. The quest to identify the Taiwania fir spanned a decade. The Indigenous Rukai people who inhabit the island’s southern mountains refer to the evergreen species, formally known as Taiwania cryptomerioides, as “the tree that hits the moon.” After nearly 10 years of forest treks and scientific sleuthing, researchers have finally pinpointed East Asia’s tallest tree: “The Heaven Sword.” Measuring 84.1 meters (nearly 276 feet), you might expect it to be relatively easy to find such a huge object, but the task was anything but simple. “When we confirmed the tallest tree, we were so relieved because it was really a long journey to achieve that result,” Dr Rebecca Chia-Chun Hsu, study author from the Taiwan Forestry Research Institute, said.

Researchers used LiDAR and field surveys to confirm an 84.1-meter Taiwania fir after a decade-long search and a map of 941 giant trees. Researchers identified East Asia's tallest tree, 'The Heaven Sword,' in a secluded valley in Taiwan, according to a study published in the journal Frontiers in Forests and Global Change. A group nicknamed the Taiwan Tree Seekers spent nearly 10 years surveying vegetation, using LiDAR technology and crowdsourced volunteers to analyze 57,065 candidate images to find the tallest specimen. It was discovered in Taiwan, an island that’s known to harbor exceptionally tall trees amid its rugged mountain terrain. Chief among them is a species known as the Taiwania fir (Taiwania cryptomerioides), a giant that the local Indigenous Rukai people would call “The tree that hits the moon.” The team managed to track them down, with the tallest measuring 69.3 meters (227 feet) and a trunk diameter of nearly 3 meters (nearly 10 feet), certainly impressive, but the researchers suspected even bigger firs were out there. “Taiwan is an island across the Tropic of Cancer. So the island holds many tree species from both temperate and tropical regions. Thanks to the massive area of steep mountains, many old-growth forests remain untouched by past logging,” added Chia-Chun Hsu. The search was launched in August 2014, when researchers from the Taiwan Forestry Research Institute set out in pursuit of a legendary grove known as the "Chilan Three Sisters." 

Located in the Chilan conservation area, rumors about this giant trio had circulated for years, yet they had never been scientifically documented. For reference, the world’s tallest known living tree is Hyperion, a coast redwood in California’s Redwood National Park, which currently measures 116 meters (381.3 feet) tall. Dramatically mountainous, Taiwan is home to a rich diversity of plant life. Forests cover about 60% of the island, which has an estimated 950 million trees, according to an earlier study. The colossal trees which grow in many of Taiwan’s forests made searching for the Heaven Sword a formidable task. Undaunted, a group of Taiwan tree seekers, including professional tree climbers, ecologists, geologists and remote-sensing specialists, has been working since 2014 to document the island’s tallest trees, including Taiwania firs such as the Heaven Sword. They next turned their attention to a more remote region near Mount Benya and Great Ghost Lake, where locals suggested the largest population of Taiwania firs might be found. The expedition was grueling, requiring four days of heavy hiking through dense forest. They managed to climb a 71.7-meter (235-foot) tree during the trip, but still suspected that more scientific methods might reveal something taller. Lead study author Dr. Rebecca Chia-Chun Hsu from the Taiwan Forestry Research Institute scaled the massive tree, using tape-drop measurement which confirmed the record height of 84.1 meters. Taiwan's steep, mountainous terrain and stable oceanic climate create a rare environment sustaining giant trees, though the Heaven Sword remains shorter than the 116-meter Hyperion coast redwood in California. 

To become more rigorous with their approach, the team used LiDAR (Light Detection and Ranging), a technology that sweeps across vast swaths of landscape by firing laser pulses from an aircraft. But there was a small hiccup. Taiwan's unique geography can be deceiving to these airborne, technological methods. On rugged, uneven terrain, trees perched beside steep cliffs can appear far taller than they actually are, for instance. To overcome this hurdle, they simply used hundreds of people to double-check the LiDAR findings, as human eyes are much better at recognizing these subtleties. It turned out that the algorithm had misjudged the height of around 93% of the trees in the survey. “Taiwan’s giant forests [are] some of the most carbon-dense environments in the entire world, comparable to the most famous old-growth forests on Earth. These ‘trees that hit the moon’ are not just natural wonders; they are essential guardians of the environment,” they added. The group undertook years of aerial scanning surveys, created the Taiwan Giant Tree Map and sought input from citizen scientists. Ultimately, the team identified the Heaven Sword the old-fashioned way, by scaling the massive tree and dropping a tape measure from the top, according to a study. The careful and creative mixture of methods employed by the team could be used to identify large trees on broader scales, a crucial task for conserving Earth’s biodiversity and safeguarding against the climate crisis, experts say. 

As a result, the team published the "Taiwan Giant Tree Map" by the end of 2022, flaunting 941 individual trees which stood over 65 meters (213 feet) in height. In January 2023, during the Lunar New Year holiday, they launched a fresh expedition to find the tallest tree on the map. When they believed they had found it, climbers scaled the trunk and dropped a measuring tape from the very top to confirm it. It was official: the “Heaven Sword of the Da’an River” was recorded as the tallest specimen in Taiwan and East Asia, measuring 84.1 meters (nearly 276 feet). The tree atlas also led the scientists to an extraordinary "temple of giants" near Mount Benya, featuring a grove of 11 trees each exceeding 65 meters (213 feet). They also discovered a new "pure forest" of around 30 giant Taiwania firs near Great Ghost Lake, growing in a dense, ancient cluster. These pockets of gigantic Taiwania firs are vital not only to the species' health, but to the health of the planet itself. As immense stores of living wood, these trees draw down huge quantities of carbon from the atmosphere, locking it away in their trunks and root systems. Without them, Earth would be in an even sadder state. “These trees are vital for the planet’s health,” the researchers said after their discoveries. “Taiwan’s giant forests [are] some of the most carbon-dense environments in the entire world, comparable to the most famous old-growth forests on Earth. These ‘trees that hit the moon’ are not just natural wonders; they are essential guardians of the environment,” they added. Abundant yearly rainfall and a steady climate have made Taiwan one of the rare environments on Earth capable of sustaining for hundreds and thousands of years the continuous growth of old, giant trees, said lead study author Dr. Rebecca Chia-Chun Hsu. Industrial logging between 1912 and 1991 depleted some of Taiwan’s ancient forests, but the island’s incredibly steep terrain kept old trees out of the reach of loggers, she added. Now, many of the trees grow in protected areas.

The Taiwan tree seekers first came together 12 years ago to measure and document “The Three Sisters,” a trio of giant Taiwania firs long known to locals in the expansive Cilan conservation area across northern and northwestern Taiwan. The group galvanized into action when Hsu encountered experts in lidar, or light detection and ranging, at a conference. They described the difficulties in searching for giant trees while relying solely on raw remote-sensing data. Professional tree climbers and members of Indigenous communities joined the group as it embarked on increasingly challenging expeditions, sometimes involving days of hiking to reach one site. The team realized that identifying the tallest trees from the ground was a nearly impossible task. The group had climbers who could scale towering trees, but the members needed a bird’s-eye view of the multitiered canopy to gain a broader perspective of Taiwan’s dense forests. Partnering with remote-sensing experts from Taiwan’s National Cheng Kung University, the team used lidar to transmit pulses of light from aircraft, measuring how long it took for the light to bounce back to them. The technique enabled the team to create a detailed 3D map which highlighted the height of the trees. Human eyes and thought processing also played vital roles. 

Taiwan’s uneven terrain can trick remote sensing, which will measure trees as taller than they are depending on nearby features, such as steep cliffs. Reaching the Heaven Sword involved over 20 km's (12 miles) of swimming and rock climbing upstream, followed by two days of an arduous, uphill hike. Then, it was time to ascend the tree. “On-site, we use drones to investigate the target tree before climbing,” Hsu wrote in an email. “However, the most accurate way to determine a giant tree’s height is tape-drop measurement.” When the tape measure read 84.1 meters, Hsu recalled feeling immense relief. The grueling hike in the middle of nowhere had been worth it. Forester Michael Taylor, codiscoverer of the Hyperion tree and lidar specialist for the Columbia Land Trust in California, applauded the efforts of the team for putting in the hard work of manual measurements for confirmation. Taylor was not involved in the study. “Very few other groups actually do that, instead over-relying on these inflated figures using automated height generation software alone without consideration of hillside leaners,” Taylor said. Hillside-leaning trees often grow in a way in which they are trying to seek additional sunlight or compensate for shifting soil. Hsu believes every expedition has been worth the effort, even when navigating unpredictable weather and unfavorable conditions, because the group has had to forge their own paths through stunningly beautiful but isolated locales that they might not otherwise see.

Giant trees play an ecologically important role in forests, absorbing CO2 and acting like protective guardians of their ecosystems. Taiwan’s forests of giant trees may be some of the most carbon-dense environments in the world. “Beyond their carbon value, large trees contribute to the structural complexity and functional diversity of forests and provide critical habitat for other organisms,” said Lalasia Bialic-Murphy, head of the forest diversity and biodemography group at the Swiss Federal Research Institute WSL. “At the same time, forests are increasingly threatened, with recent estimates suggesting that over 30% of the world’s tree species face elevated extinction risk.”. Tall trees are some of the most vulnerable to climate change, according to the new study. They face greater sensitivity to drought and extreme weather events, such as the strong typhoons and heavy rainfall-driven landslides which plague Taiwan.