In Search of Undiscovered Giants


In the northern corner of Borneo lies the Maliau Basin, a huge crater-shaped landform surrounded by a steep mountain rim and covered by a dense tropical rainforest. The basin remains one of the world’s last true wildernesses. It has never been permanently settled by humans and only became known to the outside world in 1947, when a British pilot nearly crashed his plane into the cliffs of the basin’s northern rim. Here, deep in the rainforests in the basin, stands an 89.5m tall Yellow Meranti tree. For five months in 2016 it held the title of the tallest tree in the tropical latitudes. This is the story of how I helped measure it.

THE ROOTS: Music at Maliau

In August 2015, I travelled to the Malaysian state of Sabah, located in northern Borneo and home to the Maliau Basin. The state is also home to Tawau Hills Park, a rainforest reserve east of the basin containing an 88m Shorea tree. At the time, this tree was thought to be the tallest tree in the tropics, towering over the much shorter rainforest canopies of South America and Africa. I had come to Sabah to work as a research assistant (RA) for a PhD student, in order to collect data for my undergraduate dissertation on tropical forest plant communities. I was helping Matheus Henrique Nunes, a Brazilian PhD student from the Cambridge Plant Sciences Department with his research on the structure and chemical traits of tropical forests.

I spent my first two weeks in Sabah helping Matheus survey areas of logged forest in the midst of the region’s extensive palm oil plantations. These weeks served as an introduction to the patchwork of agricultural landscapes that stretched across much of Sabah’s lowlands. Since 1990, the extent of palm oil agriculture has increased fivefold, to the point where palm oil plantations now cover 19% of the Sabah’s total area, and are the main driver of tropical deforestation in the state.

In the logged forest sites, I saw first-hand the expanses of oil palm plantations that now sweep across Sabah, surrounding the leftover patches of tropical rainforest that we had come to survey. These cultivated palm-tree landscapes act as barriers to the migration and survival of the unique species that live in Sabah’s forests. However, agriculture and logging operations also produce nearly 40% of the state’s GDP, presenting a major challenge for Malaysia, a country tasked with balancing vital conservation measures with economic development. After two weeks of fieldwork in logged forests we journeyed to the Maliau Basin Conservation Area to continue Matheus’s research, this time in the Basin’s federally-protected rainforests.

We spent a week in Maliau following a routine schedule for fieldwork. Every morning we set off from our accommodation in the Maliau Basin Field Centre at the edge of the Basin, and trekked into the surrounding forest, accompanied by one or two local research assistants to help us find research plots. At each plot, Matheus, the RAs and I measured forest plants and deadwood to collect more data for our projects. At the same time, Matheus used our time in the forest to practice measuring trees with a device called a Trupulse lazer hypsometer. The Trupulse works by aiming a laser at the base of the tree and then to the top to compute two vertical angles (taking the second angle is not easy when the tree top ascends high into the overgrown canopy). By using those angles and the distance from the tree, the Trupulse calculates and displays the tree height, which in Maliau would often pass 40m (taller than the Rio de Janeiro’s statue of Christ the Redeemer statue in Matheus’s native Brazil).

After lunch under the forest canopy, we would trek back through the forest to the Field Centre, where we would write up our new data. We spent our downtime swimming in the nearby Maliau River or chatting to the other researchers we were living with. Amoung our newfound friends were Hannah, a British Post-Doc studying forest insects, and Unding, a Malay tree climber who was helping organise the wider BALI (Biodiversity and Land-use Impacts) research project we were attached to.

Malay Bearded Pig in the Maliau Basin

Bornean Bearded Pig in the Maliau Basin

The evenings at Maliau were rarely a quiet affair. Each night the fringes of the forest would croak and cackle away as hundreds of frogs made their presence heard. Matheus meanwhile, upon discovering that I was not a morning person, would spend every morning singing Nina Simone’s ‘Feeling Good’ in order to get me ready and alert for the day of fieldwork. This musical training continued in the evenings when he’d show me his favourite Bossa Nova music from his native Brazil, usually while dancing around the annex as the music played from his laptop. This may have hindered our efforts to finish writing up data each evening but, one week into our time at Maliau, a healthy mix of Miss Nina and the musical stylings of Mina Gerais had become our way of maintaining energy when fieldwork days starting at 6am began to drag.

Our research routine lasted for most of the week we spent at Maliau. I became accustomed to the quirks of rainforest life over that time. I grew used to the geckos that crawled all over the annex walls. Likewise with the bearded pigs that would waddle past the building with their young in the afternoons and then dive into the surrounding forest. Then, towards the end of the week, when Matheus and I were sitting round a table in the middle of the annex writing fieldwork results, he peered over from his laptop and said:

“So Alex, I’ve been given a bunch of GPS coordinates for the tallest trees in the Maliau research sites and one of them could be the tallest tree in the tropics.  Wanna go find it?”

THE TRUNK: Two hundred thousand lasers

It’s worth explaining how we ended up with the coordinates for one of the tallest trees in the tropics. The year before Matheus and I came to Sabah, Matheus’s supervisor, Professor David Coomes from the Cambridge Plant Sciences Department commissioned an airborne survey of the Maliau Basin and surrounding rainforest areas. The survey sent a research plane to fly over the Basin with a machine attached to its undercarriage known as a LiDAR scanner. The LiDAR scanner works by firing 200,000 laser pulses per second at the forest below and calculating the distances in 3D from each reflected pulse as it bounces off the tree tops.

After the research plane was flown across the southern end of the Basin, David and his research team used the laser pulse data to build up a 3D map of the rainforest. That map recorded the shape and height of every tree in the area covered by the survey.

This LiDAR data, recording the structure of the forest canopy at Maliau in great detail, was the backbone of mine and Matheus’s research projects. However it had captured much more than I had realised. Before heading out to Sabah, David had given Matheus a set of GPS coordinates for the tallest trees recorded in the survey area, one of which measured taller than had ever been recorded in the tropics.

Lidar rendering of the Maliau tree by Michele Dalpont, (Plant Sciences, Cambridge)

Lidar rendering of the giant Maliau tree by Michele Dalpont, (Plant Sciences, Cambridge)

“We’ll need to use your GPS”, Matheus told me after explaining  that the coordinates for what might be the tallest tree in the tropics was in fact just a few kilometres from the Field Centre. I had borrowed a handheld GPS from my University Department before travelling to Sabah. I’d been using it to mark the location of each forest plot we surveyed, but what Matheus was suggesting was a lot more exciting. We would upload the coordinates for the tallest trees in the data set to the GPS and I would use it to track our location as we trekked through the rainforest towards them. I didn’t need much persuading to go on this adventure, and Matheus could hype a science project like the best of them:

“These trees could be over ninety metres tall. Think about that! That’s a new world record!”

The following day we headed into the forest in search of this arboreal giant. According to David’s data, the tallest trees recorded by the LiDAR survey were a few kilometres from some of the forest plots we had already surveyed. The route seemed simple enough but this time we would be trekking without RAs.


They had all left Maliau that day before with Unding to begin a new phase of the BALI project in a protected rainforest area east of the Basin called Danum Valley. Considering the amount of times I had already fallen over or become entangled in spikey vines during our fast-paced treks through the forest with RAs, (one of the first words I learnt in Malay was ‘duri’, the word for thorn), I couldn’t help but wonder how we’d do without them.

To get to the tree coordinates our first task was to hike to the forest on the other side of the Maliau River from the Field Centre. This meant crossing a rope bridge that stretched across the river. As the bridge swayed side to side with each of our steps, I looked down below to the swirling tea-brown waters of the river; the result of the water leaching tannins from the decaying leaves on the forest floor as it flowed through the heart of the basin. Ahead of the bridge on the far bank of the river, a steep hillside awaited us, covered in an undulating blanket of trees of seemingly every height.  Somewhere in that vast stretch of green was our destination.

Our plan was to head to the furthest plot we had surveyed on this side of the river, and then improvise as we headed towards the GPS point from there. Fortunately I began to realise just how much of the trail I could remember from our previous treks with the RAs. I even recognised certain trees and hillsides in what seemed at first like an identical landscape of tree trunks and saplings sprouting out of brown earth. Armed with these recollections and my GPS, Matheus and I began to work our way across the rolling terrain of the basin.

As we trudged up a slope, I heard the sound of wings flapping somewhere above the forest canopy. The noise had become familiar to me after several weeks in Sabah. It was the sound of a hornbill flying over the forest, beating its great black and white wings as it passed over us. As we trekked through the morning I heard other sounds I had learnt to identify. The howls of gibbons calling their mates from the tree tops. The far-away bark from a sambar deer. The constant clicking of insects in the background. All reminders that Matheus and I were not alone in a place that humans have yet to fully explore.

Rhinoceros Horbill (Buceros rhinoceros) flying over the Maliau Basin, Sabah, Malaysia

Rhinoceros Horbill (Buceros rhinoceros) flying over the Maliau Basin, Sabah, Malaysia

At the top of the slope I suddenly felt the full heat of the midday sun. We had found a forest gap where fallen trees had broken the near continuous canopy cover, allowing the sun to finally light up the forest floor. Without the cover of tree crowns above the sun was blinding, too much for the saplings that typically covered the forest floor in the shade to survive. The gap had been made naturally and was littered with deadwood from the fallen trees. Over time new plants that could tolerate direct sunlight would colonise it, providing shelter for tree saplings and eventually allowing the forest to regenerate, as it had done in Maliau for millennia.

In the logged forests that Matheus and I had surveyed before Maliau however, the story was different. As the forests were harvested for timber, or cleared for palm oil plantations, larger gaps would be made and the forests would become fragmented. New plant species would creep in to these gaps and create a thick undergrowth of vines, shrubs and grasses. Done on such a large scale, it would impede the re-establishment of tree species, altering the course of forest recovery and forcing any animals that relied on the forest fragments for habitat to migrate, and face a perilous future elsewhere. There are now less than 700 km2 of primary (undisturbed) rainforest currently remaining across the whole of Sabah, making up less than 10% of the state’s total land area.

I had seen the tangled grasslands being created across Sabah by logging and palm oil plantation agriculture. I had met researchers who would point out vine-covered gaps and tell me it had once been a forest stand where they had seen an orangutan, or a rare Bornean elephant. They were sobering sights that seemed a polar opposite to the protected green wilderness of the Maliau Basin. However they were the reality waiting outside it. The giant we were searching for was a rarity in a place undergoing dramatic environmental change.

Logged Forest and Oil Palm Plantations, Sabah, Malaysia

Logged Forest and Oil Palm Plantations, Sabah, Malaysia

We clambered across the deadwood floor of the forest gap and made it back into the dense canopy cover. I scanned the screen of my GPS. We had almost reached the coordinates.

THE BRANCHES: Measuring a giant

Away from the forest gap, the ground sloped downwards towards a wide ditch.
On the side of the slope, buttress roots splayed out in all directions, anchoring a tree trunk that twisted up in an L-shape from the ground to the sky.

The giant on the forest hillside. A 90m tall Yellow Meranti (Shorea faguetiana) in the Maliau Basin

The giant on the forest hillside. A 90m tall Yellow Meranti (Shorea faguetiana) in the Maliau Basin

At the top of the tree, the pointed leaves of an epiphyte, a type of plant that grows on tropical trees, surrounded the trunk, and above it the branches of the crown sprawled out like a compass star. The GPS confirmed it. We had found the tallest tree of the dataset.

Now was the time to measure it and see if it was the new world record Matheus had promised. This was no simple task. The tree was rooted halfway up a slope and its exact top was obscured in the canopy, making it hard to measure with the Trupulse. We looked to the near surroundings for somewhere where both the tree top and base were visible. 

The ditch next to the slope was littered with rocks and roots, and a large vine-covered boulder perched at the top. Matheus climbed to the top of it whilst I stood on a rock downslope to the side of him and the tree.

Matheus atop a boulder using a Trupulse to measure the tree

Matheus atop a boulder using a Trupulse to measure the tree.

Over the following hour we worked together on a set of measurements for the tree’s height. Matheus used his viewpoint from the boulder-top to aim the Trupulse laser at the base and at top of the tree, bending back to try and find the second point high up in the canopy. After each measurement, he shouted out the results for me to record in my notebook.

After several rounds of measurements, we had recorded a list of height estimates ranging from 88.5m to as high as 90m. These measurements placed the tree as a contender for the new world record.

“I think it’s a Shorea” Matheus said to me as he stared up at the tree “the same genus as the Tawau Hills tree. You can’t really tell exactly what species a tree is just by looking at it, but they’re the only ones that are known to grow anywhere close to this tall”.

Matheus grabbed a tape measure and headed to the base of the tree, hoping to get an idea of the width of its trunk. While he stepped over the tree’s great buttress roots I heard the faint sound of rain from above. I looked to the edge of the slope and saw in the sun beams breaking through the trees, streams of raindrops were falling through the forest canopy. Where I was standing though, I couldn’t feel any of it. The tree crowns above had blocked the coming downpour from reaching us. I smiled and thought “it’s raining and I’m being sheltered from it by one of the tallest trees in the tropics”

Rain breaking through the canopy around the tree.

Rain breaking through the canopy around the tree.

We packed up and after taking plenty of photos of the site around us, we headed back home. We trekked back through the basin, out of the forest, and across the rope bridge of the Maliau River, returning to the Field Centre after a day spent uncovering the secrets of the Basin.

THE CROWN: the forgotten and the future

After our week in Maliau, Matheus and I travelled to Danum Valley, another protected rainforest area, where we met up with Unding, and Matheus’s other research colleagues from the wider BALI Project. I spent my final week in Sabah at Danum before I returned home to start my final year of university, parting ways with Matheus as he continued his research at Danum.  Before we left Maliau he sent off our measurements of the tree to David, who responded saying that he was working on an article to announce its discovery. However months passed with no news, until June 2016 at the very end of my degree, when the Cambridge Plant Sciences Department released a press article announcing a new discovery to the world.

Unding, an experienced tropical tree climber, had ascended right to the top of the tree we had attempted to measure, tape measure in hand and aided by David’s research team.  The height wasn’t even the most perilous aspect of his climb. As he reached the top he sent a text message to the researchers waiting at the bottom:

“I don’t have time to take photos using a good camera because there’s an eagle around that keeps trying to attack me and also lots of bees flying around.”

Despite this tree–top battle with the birds and the bees, Unding and the researchers managed to finally record the tree’s full height at 89.5m and its species as a Yellow Meranti. The Cambridge Plant Sciences Department duly announced that the tallest tree in the tropics had been discovered in June 2016 – an enticing piece of news as I was finishing my degree. However the discoveries in Sabah did not finish there.

In November 2016, Greg Asner, an ecologist from the Carnegie Aerial Observatory of Stanford University, announced the results of the Observatory’s own Lidar survey across Sabah, discovering 50 trees in the state that surpassed the height of the Maliau tree. One of these newly-discovered trees, growing in Danum Valley to a height of 94.1 metres, has now been awarded the title of the tallest tree in the tropics. The title is well deserved. At over 94 metres tall, this particular tree almost reaches the same height as London’s Big Ben Tower. Asner’s survey also concluded that the Maliau tree found in David’s survey is actually over 90 metres tall, making it at least one of the tallest tropical trees, despite being dwarfed by the Danum discovery.

There’s a point where my own experience with Sabah’s forest giants can feel insignificant in comparison to the increasingly bigger discoveries and cutting edge remote-sensing research happening alongside it.  In the space of just five months, the forests in the small state of Sabah have been the source of two world records, and one of our preconceptions about the natural world, that tropical trees aren’t capable of growing taller than 90 metres, has been dismantled. The discoveries of the past year in this small part of the world show that there is still much to learn about tropical rainforests, and it will take the efforts of many dedicated researchers across the world to unearth them. This is a scientific field of inquiry that will generate many more stories and experiences than the one you are reading right now.

At the same time, it remains true that I got to be there, staring up at one of the tallest trees in the tropics before it had been announced to the world as such. It’s a memory that myself, Matheus, Unding and all the researchers involved in measuring these giant trees get to keep for the rest of our lives. I just hope the tallest trees in the tropics and their forest habitat last just as long.

Extensive logging by the palm oil industry has heavily depleted Yellow Meranti numbers in Sabah, and the species, along with the Orangutan and many of Borneo’s unique animal species, is now classified as endangered by the International Union for Conservation of Nature. However the Sabah government recently announced that it would act to restore a heavily logged area just to the east of the Maliau tree, as part of an initiative to preserve the region’s biodiversity. If we can hold onto landscapes like the Maliau Basin, if we can protect them for future researchers to explore and study, then there may be many more stories and discoveries around the corner. Who knows what we’ll find next in the realm of giants.

Standing under a 90m tall Yellow Meranti in the Maliau Basin, Sabah


Want more science and less travel writing? Here you go:

Romnell et al. (2009) Forest Floor light conditions in a secondary tropical rainforest after artificial
gap creation in Northern Borneo. Agricultural and Forest Meteorology 149. 929-937

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