A thousand years old and 20 storeys high: tracking down Taiwan’s tallest trees

A thousand years old and 20 storeys high: tracking down Taiwan’s tallest trees

The Lush Canopy of Life

A thousand years old and 20 storeys - As one ascends the towering, ancient trees of Taiwan’s dense forests, a hidden world unfolds with each step. Beneath the dense foliage, ferns flourish in the cool, shaded undergrowth, while flying squirrels and owls find shelter in the hollowed trunks of the colossal giants. Higher up, the lower canopy is a vibrant tapestry of yellow rhododendron blooms, their bell-shaped flowers catching the faintest light. Above, the air grows colder, and dense lichen cling to the bark, creating a natural mosaic. At the very top, nestled in cloud-drenched branches, the rare Bulbophyllum ciliisepalum orchid thrives—a testament to the tree’s ability to sustain life in even the most extreme conditions.

“In one tree, every species has their preferred location,” says Dr Rebecca Hsu, an assistant researcher at the Taiwan Forestry Research Institute. “Every metre the temperature, the wind, the sun, the light is different.”

These ecosystems are not merely layers of vegetation but interconnected habitats that support a vast array of biodiversity. The vertical complexity of such trees allows for unique microclimates, fostering species that might otherwise struggle to survive. Hsu and her team have spent over a decade meticulously mapping these towering structures, combining aerial surveys with ground-based expeditions through Taiwan’s rugged terrain. Their findings, recently published in *Frontiers in Forests and Global Change*, highlight the ecological significance of these giants, with one specimen standing as a record-breaker: a 20-storey-high Taiwania cryptomerioides, named “Heaven Sword of the Da’an River,” reaching an astonishing 84.1 metres. This conifer, likely over a millennium old, towers above the average building, making it a natural landmark in its own right.

Global Giants and Their Challenges

While the Heaven Sword is a marvel of Taiwan’s forests, it is part of a broader global phenomenon. The tallest known living tree, a coast redwood (*Sequoia sempervirens*), stands at 116 metres in Redwood National Park, California. For context, this height surpasses that of London’s Elizabeth Tower (Big Ben), which measures 96 metres. Chris Swanston, director of science for Save the Redwoods League, emphasizes the ecological value of such towering trees. “Height is an engine for biodiversity,” he explains, noting that in a single 2,000-year-old redwood, dozens of species can coexist within its canopy. “When you’re thinking about massive trees like old-growth redwoods, their branches aren’t just branches like normal trees, they’re neighbourhoods.”

Yet, these ancient sentinels face mounting threats from the climate crisis. Rising temperatures, prolonged droughts, and more frequent extreme weather events are pushing these giants to the brink. In California, for instance, it is estimated that 17.6% of large giant sequoias have been burned since 1984, with a significant portion perishing during the severe wildfires of 2020 and 2021. Similarly, in Tasmania, the 2019 fires claimed at least 17 of the state’s largest trees. Such losses underscore the urgency of conservation efforts.

Technology and the Hidden Forests

Researchers like Hsu are leveraging cutting-edge technology to uncover the secrets of these towering trees. LiDAR, the same system that aids driverless cars, has revolutionized the way scientists analyze forest canopies. By emitting laser pulses and measuring the time it takes for light to return, LiDAR creates detailed 3D maps of terrain. However, its accuracy can vary depending on deployment methods. In Hsu’s study, 93% of LiDAR-measured trees reviewed by citizen scientists were found to be inaccurate, highlighting the technology’s limitations in uneven landscapes such as Taiwan’s steep slopes.

Despite these challenges, LiDAR remains a powerful tool for identifying potential candidates. For example, a 2019 airborne survey in the Amazon revealed an 88-metre tree, but the study covered only 282 square kilometres. This suggests that many tall trees may still be undiscovered in remote areas. “There are probably more unrecorded giants hidden deep within forests,” notes Matheus Henrique Nunes, an assistant research professor at the University of Maryland studying tropical forests. He adds that deploying LiDAR from aircraft or drones offers a broad overview, though backpack-mounted systems provide greater precision. “The further [away] you go, you decrease resolution,” he says, illustrating how technology must adapt to the terrain.

The findings from Taiwan’s forests are alarming. Over the past decade, the death rate among tall trees has averaged 4% to 5%, a statistic that Hsu calls “beyond our imagination.” This decline is attributed to a combination of factors, including increased fire frequency, pests like bark beetles, and shifts in climate patterns. As global heating intensifies, the clouds that these trees rely on for moisture are being lifted higher, reducing their access to vital water sources. These changes are not only endangering individual trees but also disrupting the delicate balance of the ecosystems they support.

Conservation and the Road Ahead

Conservationists are now exploring innovative strategies to protect these ancient giants. In some regions, thinning forests has been proposed as a way to mitigate the risk of uncontrolled wildfires. Others are investigating the impact of pests, such as the bark beetle, which can weaken trees and make them more susceptible to damage. Yet, the challenge remains significant, especially in areas where tall trees are yet to be cataloged.

For Hsu, the discovery of the Heaven Sword underscores the importance of continued research. “It’s not just about measuring height; it’s about understanding the tree’s role in sustaining life,” she says. The study’s results highlight how climate change is reshaping the natural world, even in the most remote corners. As researchers work to document these towering trees, the question remains: how many more are waiting to be found? The answer may lie in the combination of traditional fieldwork and modern technology, ensuring that these ancient giants are not lost to the relentless march of environmental change.

While the climate crisis threatens these ecosystems, the resilience of tall trees offers hope. Their ability to absorb carbon dioxide makes them vital allies in the fight against global warming. However, their survival depends on our capacity to protect them from the growing array of challenges. As Hsu’s team continues their work, the data they gather could shape future conservation policies, preserving not just individual trees but the entire ecological web they support. In a world where forests are shrinking, these ancient giants serve as a reminder of nature’s capacity to thrive—and the urgent need to safeguard it.