Meet Swansea's Tropical Tree Ring Explorer

Dr Mary Gagen professor in the Department of Geography at Swansea University. A specialist in climate science, she describes herself as a ‘tree ring scientist’ focusing on the evidence that tree rings can provide about weather patterns.

By Jonathan Manning
Published 12 Oct 2018, 10:36 BST
Dr Mary Gagen on location. Analysing tree rings provides centuries of climate change data.
Dr Mary Gagen on location. Analysing tree rings provides centuries of climate change data.
Photograph by c Mary Gagen

What can we learn from tree rings?

Lots of people are very familiar with the rings inside tree trunks and the idea that they can tell us how old a tree is. But rings can also tell us what the weather was like. So if the rings are wide and the wood is very dense then it was a good year for trees to grow. And if the ring is narrow and the wood isn’t very dense then the climate in that year wasn’t very good.

Tree rings tell us how the climate was in the past, year-by-year. There are parts of the world where trees live for 4,000 or 5,000 years, so we can go way back before the time when we had instruments to measure the weather.

Can you spot certain years in every tree?

Yes. 1815, for example, is always a very narrow ring in Europe because it was the year the Tambora Volcano erupted and there was no summer. The sky was clouded by volcanic ash.

Dr Mary Gagen at work, drilling a core from a tree.
Photograph by Rex Adams

Is this the same all over the world?

No, the trees in the rainforest don’t make annual rings, so we use a different method to date them. What makes the annual ring is winter – it gets cool and dark and the ring closes. The tree makes a dark line of cells and stops growing, and that’s the end of that ring. The tree then makes a new one next spring, so the rings are the heartbeat of the tree.

But in the tropics there is no seasonality, so we have to use radio carbon dating instead.

So why do you concentrate on the rainforests of Borneo?

Borneo is about the hardest place on the planet to do tree ring science – the trees don’t make annual rings, the wood is very hard, the jungle is extremely hot and inaccessible. But to understand climate change, understanding what goes on in the tropics is really important, because it’s like the heat engine of our planet, yet we have such short climate records. We only have a picture of what has gone on over the last few decades.

Dr Mary Gagen in the primary rainforest of Danum Valley, Borneo.
Photograph by c Mary Gagen

Do you have to cut down the trees to count the rings?

No, but one of the reasons the work we do in the tropics is so challenging is because we take a core out of the side of the tree (like someone taking a core out of a big cheese).

How easy are they to drill?

The trees we work on are very hard Belian (also known as Borneo Ironwood), so the first thing we had to work on was a way to drill into them – you can’t just turn a core in by hand as you can with an oak tree or pine. We had to invent a new bit of kit – we burnt loads of drills in the process! This wood is so hard it even destroys chainsaws! We use tungsten carbide drill bits and put a long barrel on a house drill. It has to be battery-powered because we are in the jungle, but they don’t last long. These trees really fight back. They don’t like to be sampled!

What are ironwood trees like?

They are not the tallest trees. They are a single stem tree with a tall, straight trunk and a canopy way above you. If a child were to draw a jungle tree they would look like this. They have this beautiful red wood and very distinctive, slightly chemically smell. They stand out, even in a rainforest. The ironwood is such an incredible species with an amazing history. It’s endangered now and protected; because it’s so hard, the early people who used the forest as a resource realised how useful it was and used it to make railway sleepers and bridges. The wood does not rot.

Conditions are hot, humid and tough in Danum Valley, Borneo.
Photograph by c Mary Gagen

What form does your fieldwork take?

We will normally have identified an area where local research assistants and field guys know there are ironwoods. We’ll then hike into the area to take some samples. We spend a lot of time in the morning getting kit ready, charging batteries, and there’s a lot of kit to carry so we might be hiking for several hours. Drilling each tree can take up to an hour, with the bit getting stuck and the core breaking. You get this smell of the clutch burning inside the drill and know it’s time to take a break. In a day we would maybe only sample two or three trees. A lot of the preparation of the surface of the samples we do on site – along with lots of labelling, but all the chemical work takes place in hi-tech analytical chemistry labs.

What’s it like working in the jungle?

Hiking in the jungle takes a long time. It’s so uncomfortable and hot, and you move slowly. There’s a lot of sweating and picking off leeches. You get used to them eventually, but every branch there’s a leech wriggling out to get you. If we did not have the local guides with us we would be in trouble very quickly. I rarely set foot into the jungle at Danum without Jamil Hanapi, a research assistant at Danum Valley. He will just quietly say to you, ‘just step to your right’ and you haven’t even seen something that you were about to brush against or that might hurt you such as a vine with thorns or a snake. The snakes are amazingly camouflaged out there – I’ve never seen one.

How dangerous are the working conditions?

In Borneo, the most dangerous animals are tiny or huge, the little centipedes and the elephants, which are famously grumpy and really do take the doors off pick-up trucks if they don’t like the colour! There’s an amazing story at one of the camps where we stay, where they had to rebuild a bridge which had come down in a flood. They replaced it with a metal bridge, but the elephants didn’t like the metal and destroyed it again and again, until the bridge was made with wood again, when they left it alone.

Elephants repeatedly destroyed a replacement metal bridge in the Danum Valley until it was rebuilt in its original wood form!
Photograph by c Mary Gagen

What’s your camp like in Borneo?

We normally work out of the Danum Valley Research Centre, which the Royal Society set up in the 1980s, and it’s outrageously comfortable. It has power for many hours a day and cold running water. But some sites we go to are set up like long-term camps, with wood flooring and canvas roofs. We don’t camp out if we can avoid it because it’s quite dangerous camping in the rainforest. In a rainforest there’s usually something between you and something that is going to try to eat you. You need to be careful, there is malaria there, but I play down how rustic it is, because it’s such a privilege to work there. I mean, you see wild orangutans walking around.

What luxuries do you take with you?

Pretty much everything I take is useful, but I do take a digital reader and earplugs for the first couple of nights because the rainforest is so loud, especially for the first couple of nights. It’s frogs and insects largely - you can measure the noise in decibels. And then when I come home I can’t sleep because it’s too quiet!

How much time do you spend doing fieldwork?

I will probably be in Borneo for a month to six weeks this year. I spend about a month per year in the rainforest, and I have other fieldwork trips for a week here and there. That’s the strange thing in this job; you go from being sat at a desk for 10 hours a day to being expected to hike up a mountain.

"You get this smell of the clutch burning inside the drill and know it’s time to take a break." Dr Mary Gagen.
Photograph by c Mary Gagen

Do you train prior to an expedition?

I do. It’s very arduous at the high-altitude sites or in the rainforest. You really struggle if you don’t have walking fitness. 

How has National Geographic helped your research?

National Geographic funded the work to sample the ironwoods. I had been going out to Danum Valley to help other colleagues with their projects and I realised that there was the possibility of getting these long climate records from the old ironwoods. I approached National Geographic and they funded two expeditions out there to sample the trees and all of the work to invent the method of sampling. They absolutely started the whole thing really. What was great was the fact that it allowed us to build relationships with people who knew where these trees are.

I feel National Geographic were the dating agency between me and Borneo, they introduced us and it’s a very happy marriage! Now we take undergraduates from my university out there for field trips.

Where would you most like to be right now?

I really hate this question because I feel I have to choose between the arboreal forest of the high Arctic, where I have worked for a lot of my career, or the tropics. My head always starts asking, would you rather deal with malaria or polar bears? I think I am turning into a giant rainforest fan, although I feel as though I am cheating on the Arctic. You are plunged into biodiversity, with the birds and the insects, mammals, primates, trees. It’s the planet’s larder. As a geographer and natural scientist, being surrounded by life like that is incredible.

The other geographical love of Dr Mary Gagen's life - the Arctic. "I think I am turning into a giant rainforest fan, although I feel as though I am cheating on the Arctic," she says.
Photograph by c Mary Gagen

Where’s your favourite spot in the UK?

I live in South Wales, I’m a surfer and I’m about 10 minutes from the beach and just an hour from a couple of national parks, so I’m very happy here in South Wales.

What do you listen to on your expeditions?

Last time I was in Borneo I was listening to The XX’s album Coexist a lot, particularly travelling to get there. You’re flying, driving, running through airports or on a bus for most of 30 hours to get to Danum Valley – music is really important!

Which book has made an impact on you recently?

Don’t Even Think About It by George Marshall, which is about why we don’t understand climate change facts or respond to them. This book puts the people back into climate science. Because I work in climate science it’s such a scary time right now. People are stopping believing in climate change. They don’t believe that we need to do anything about it. As climate scientists we think this behaviour is really strange; if we show you a picture of how the temperature is changing on the planet and what happens when we deforest huge areas, why don’t you believe it? So I thought I needed to start reading some of these behavioural science books to understand why our approaches don’t work.

Who would you invite on your ideal expedition?

Michael Gove (Secretary of State for Environment, Food and Rural Affairs) because I think he’s starting to understand the evidence for environmental change and starting to make some really smart decisions, but I would want to solidify them. Sir David Attenborough – hearing nine decades of knowledge about the rainforest and conservation and what we need to do to keep these places safe would be amazing. It’s impossible to be in those places and not hear his voice anyway! And I’d like to take a school child from around here, so Michael Gove realises why this stuff is important. If the four of us were going to have a safe trip in to primary rainforest we would for sure need Jamil, or one of his team, with us, too!


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