Finding and saving the world's biggest trees before they disappear

Found on the island of Taiwan, The Heaven Sword is the tallest tree in East Asia.

Measured at a whopping 84.1 metres tall, the 1,000-year-old tree is five times the height of Queensland's Big Pineapple, and belongs to an ancient cypress species.

Despite its seemingly unmissable height, it was only found a few years ago through a decade-long project to map Taiwan's tallest trees.

The tall tree, and the methods used to find it, are described in a new study published in Frontiers.

Large trees create their own mini-ecosystems, according to lead author Rebecca Hsu, a forest ecologist at the Taiwan Forestry Research Institute. 

"These [tallest] trees provide unique habitats for many creatures," Dr Hsu said.

"Many orchids are growing on these trees like a thick carpet … and you can see the flying squirrels … they sleep and play there."

Big trees are also important because they can often store as much carbon as a whole stand of mid-sized trees in forest ecosystems.

The Heaven Sword is a Taiwania cryptomerioides, the last remaining species from a genus of cypress that has been around for 100 million years, and was once found across the northern hemisphere from North America to Europe and Asia.

Now they are predominantly found in mountainous regions of Taiwan with a few small pockets in China, Vietnam and Myanmar.

Using lasers to find tall trees

In order to find the tallest tree in Taiwan, Dr Hsu first needed a technique that could measure many trees at once. 

Utilising airplanes, the team used light detection and ranging (LIDAR) — which measures distances with lasers — to capture a 3D map of Taiwan over six years, with flights between 2010 and 2016.

Of the more than 950 million trees on the island, there were just over 50,000 trees that were estimated to be above 60m tall.

The researchers then needed to verify the height of each tall tree to make sure they were not just short trees on the sides of cliffs.

Luckily, they were processing data during the COVID-19 lockdowns and enlisted about 400 volunteers stuck at home to help. 

"We planned to finish the project within a year … but surprisingly, we finished within one month," Dr Hsu said.

After narrowing it down to a small number of potential tallest trees, Dr Hsu and the team set out to accurately measure them by climbing them.

Looking up into the clouds

It took the team about three days to reach The Heaven Sword.

Australian photographer Steven Pearce, who takes portraits of giant trees and was on the trek, said they had to cross a river in the middle of winter to get there. 

"It wasn't an easy hike, that's for sure … walking through a thick forest with no track, on this 30-degree slope, and having to carry a 27 kilo bag," he said.

Before climbing any tree, the Taiwanese team members would pay their respects.

"We Taiwanese believe old trees have their own spirits, so we would like to have permission to climb them," Dr Hsu said.

As they climbed higher, they found different species inhabiting the tree. The more they climbed, the more they discovered.

Dr Hsu said there were some species that only existed at the top of the trees, and orchids that were only observed in the oldest trees.

"The giant older trees have evolved with those plants for more than a thousand years," she said.

Threatened titans

The researchers found that the giant trees were at risk of climate change-related pressures, including a decrease in low cloud coverage and water, and extreme weather events such as typhoons.

While even typhoon winds might not knock down the trees, flooding from high rainfall can bring erosion and landslides.

Dr Hsu said there was an abnormally high amount of deaths among Taiwan's tall trees.

Dr Hsu hypothesised that the high death rate may be because of reduced cloud coverage, which means less moisture for mountain tree species.

Previous analyses also suggest typhoons that have hit Taiwan in the past four decades have increased in strength by 35 per cent.

Illegal felling of Taiwan's tall trees also still occurs, despite 95 per cent of them falling within protected areas.

More needs to be done to protect tall trees

Australian National University ecologist David Lindenmayer, who was not involved in the study, believes more needs to be done to protect trees around the world. 

He said that often the tallest trees in the world grew in temperate and tropical regions, which meant they got lots of rainfall but were also more sensitive to climate change.  

"In temperate regions, there are more fires, in tropical regions, more droughts," Professor Lindenmayer said.

"It won't just be climate change. It will be climate and insects or climate and something else.

"The best way to protect trees is to create more reserves and limit things that damage them, like logging and building roads."

Australia is home to several species that can reach heights of 80m or more.

Some are in danger of extinction, with alpine ash forests recently added to Australia's list of endangered ecosystems.

The future of tall trees globally is uncertain as it becomes harder for new generations to reach the same lofty heights. 

But we would not even know what we are losing if not for the scientists, photographers and tree-loving volunteers stepping out to find them.