Looking for the tallest tree
How does one know or describe how tall a tree is? For instance, Taiwania (Taiwania cryptomerioides) is the tallest tree species in East Asia, and Taiwan’s indigenous Rukai people describe it as the tree that “knocks the moon.” Rebecca C.C. Hsu of the Taiwan Forestry Research Institute takes a different approach, measuring the height of these trees by climbing them.
Hsu is a forest ecology researcher with a special interest in the epiphytic plants that grow in the forest canopy, so getting up into trees is essential for her work. At first, she adopted her predecessors’ methods of collecting plants and seeds, driving L-shaped spikes into trees to ascend them. Later she adapted rock-climbing techniques to climbing trees.
Apart from her work on epiphytes, Hsu also has an interest in finding giant trees. Since she was always hanging out in treetops, she began to wonder how tall the trees could grow, and what factors influenced their growth.
Early in her quest to find Taiwan’s tallest trees, she mostly worked on word of mouth from forestry professionals or used a clinometer and trigonometric calculations to make estimates. Nowadays she is using more advanced devices and techniques. She works with Wang Chi-kuei, a professor in the Department of Geomatics at National Cheng Kung University, and his team, applying an algorithm to data gathered by an islandwide airborne LiDAR (light detection and ranging) survey program commissioned by the Ministry of the Interior following Typhoon Morakot in 2009. The technique takes advantage of the ability of laser beams to penetrate the forest canopy to chart out a model of the height of the treetops and the topography of the ground beneath. After using the LiDAR data to pinpoint areas with old trees, Hsu then goes with an exploration team to check out the sites in person. In 2019, they discovered the tallest Taiwania tree yet found in Taiwan. Measuring 72.9 meters, the tree is located on the upper reaches of Nankeng Creek on Mt. Daxue.
Hsu and her team also successfully scaled a 46.4-meter giant camphor (Cinnamomum camphora) in Nantou County’s Shenmu Village, and got it listed on the Monumental Trees website as the world’s tallest known camphor tree.
Once you’ve measured the tallest trees, then what? “Actually, a lot of scientific research emerges from researchers’ curiosity,” says Hsu. But curiosity can elicit great resonance. In 2017 she launched a project to make isometric photos of Taiwania specimens. She invited a photographic team from Tasmania-based The Tree Projects to come to Taiwan and take isometric photos of three large trees known as the “Three Sisters,” located along Forest Route 170 in the Mt. Qilan Forest Area. The Three Sisters are at least 800 years old. One of them rises to 69.5 meters, about the height of a 23-story building. Seeing the trees fully revealed in photographs, many observers remarked on how few people even know that Taiwan has trees this beautiful, recalls Hsu. “It fosters a sense of pride and identity.” The project is spotlighting the beauty of Taiwan’s forests and raising awareness of forest conservation. It’s one more fruit of the search for big trees.
The epiphytic orchid Dendrobium sanseiense. (courtesy of Rebecca Hsu)