Different Routes


Why does deadwood last almost forever? Only now is this being studied properly.


Different Routes


Why does deadwood last almost forever? Only now is this being studied properly.

Deadwood brings us tidings from the past – sometimes from as long as a couple of thousand years ago. But when and why do some pine trees produce almost decay-proof wood? Journalist Sampsa Oinaala headed out into the autumnal forest to collect samples with Associate Professor Tuomas Aakala.

No dry pine snags – or in Finnish, kelo trees – in sight. The car hurtles northwards down the highway from Joensuu. The landscape is one of commercial forest that carries a heavy human handprint. Although pine trees can live for hundreds of years, around here it’s rare to see a tree that’s more than 80 years old. Even a hundred-year-old pine will turn heads.

The journey takes a couple of hours – that’s how rare these grey-trunked pines have become. We eventually find a few hectares of forest reserve near the eastern border – like finding a pine needle in a haystack of intensive forestry. This reserve is named after the forest researcher A. K. Cajander, who also served as Finland’s Prime Minister in the 1920s and 30s.

And here they finally are: pines that bring us tidings from the distant past. We park the car in a ditch, grab the research equipment, and head out into the forest!

Not all pines dry out

We should probably begin by defining the word ‘kelo’. In the vernacular, it can mean almost any dead pine – or even a spruce or aspen – that has died in an upright position, lost its bark, and turned grey. But there are many types of dead tree. Some will come crashing down in only a few years or decades, and will decay soon afterwards.

Even scientists have not reached a precise definition of what a kelo is. But in any case, the entire lifecycle of deadwood from a tiny sapling to its eventual decay can be quite incomprehensible in comparison to human lifespans.

“The oldest living pine tree in Finland is about 800 years old. In Lapland, there are kelo trees that have remained upright for up to a thousand years after the tree’s death. How long will fallen deadwood remain on the ground? That we don’t really know yet,” says Associate Professor Tuomas Aakala from the University of Eastern Finland.

And there’s plenty more we don’t know about deadwood. Why does one pine become a kelo and not another? What will the loss of kelo trees mean for the species living in our forests?

There has been little research into kelo trees. Which is why doctoral researchers Mariina “Tilla” Günther and Pemelyn Santos (in the photo) are now in the autumnal forest on the border of North Karelia and Kainuu.

Samples show how a tree died

After a short walk, we find a place marked with a blue ribbon. A woodpecker greets us loudly, and continues to tap away at some distance. The only other sound is the murmur of the wind.

This is one of the 150 kelo research plots that can be found in North Karelia, Kuusamo and the Salamanperä Nature Reserve in Kivijärvi, Central Finland. The study was launched in summer 2022 by setting up the research plots and measuring 3,000 dead pines. Sampling will now begin, and will continue next summer.

“The samples will reveal the tree’s growth history: how the tree died and how any disturbances during its lifetime may have influenced its development into a kelo,” says Aakala.

Aakala teaches his students how to take samples. It’s a meticulous task. The tree must be marked at the place where the sample was taken. The sample must be taken from a place where the wood is hard. If the sample comes out in pieces, they must be stored in the correct order.

Studying a tree’s chemical composition requires a great deal of precision, and the equipment must be extremely clean.

“I compare the chemical composition of wood from kelo trees and other dead pines. Kelos contain chemicals that inhibit the activity of decomposing agents,” says Günther.

Could we facilitate the creation of kelo trees?

The increment borer squeals as it bites into the wood. Although the deadwood lying on the ground appears decayed and is covered with moss, dry rock-hard wood can be found right below the surface. The annual rings in the sample are so dense that it’s difficult to count them with the naked eye. The wood has a pitchy scent. I feel the urge to light a campfire, but we’re in a conservation area. And besides, it seems such a waste to throw a deadwood log on the fire after all we’ve talked about.

By studying a tree’s chemical composition and growth history, we can determine what causes trees to produce chemicals that protect them against decay. Old wood always contains durable heartwood, but is that enough or is some disturbance required to slow the tree’s growth or change its chemical composition in some way?

It’s biologically interesting how the pine itself derives no benefit from being decay-proof after its death.

“It’s just a side effect of what happens during a tree’s life,” says Aakala.

Making kelo trees artificially is very difficult. This was attempted during the 1980s deadwood construction boom.

Traces of the most likely kelo-creating disturbance can be seen on all of the kelo trees in this research plot: catfaces, that is, the scars of wildfires on their trunks. In this forest, the most recent scars date back to the 1800s. The effect of wildfires can still be seen in the structure of the stand.

If the study reveals that fire is required for kelo creation, it also indicates that practically no new kelo trees are being created these days.

At least we know that making kelo trees artificially is very difficult. Metsähallitus attempted to do so commercially during the 1980s deadwood construction boom, by killing no less than ten thousand old pine trees and leaving them standing in the forest. Only a tiny fraction of them became kelo trees. The trees apparently died too quickly, and began to decay immediately.

In spite of this, the final phase of the deadwood study will launch long-term field trials to determine whether kelo creation could be promoted on the basis of the data collected during the study.

As long as I don’t have to sit indoors all day

Tuomas Aakala was originally destined to become a forester.

“On the way to a moose hunt, my father sometimes mused that if he could start over, he’d choose to be a forester. So he’d get to do work that wouldn’t just be sitting around indoors all day….”

However, when Aakala was a student, it soon became apparent that modern forestry mostly involves sitting around indoors all day. Today’s foresters rarely spend their time wandering amongst the trees.

It was then that Tuomas began to be drawn to research, and turned his gaze from commercial forests to natural forests.

“I was on an exchange at an agricultural university in Austria, where I took a really interesting course on the dynamics of natural forests.”

After that, Timo Kuuluvainen, an associate professor in forest ecology, invited Tuomas to do his master’s thesis in Canada. When Aakala continued with a doctoral thesis on the dynamics of dead trees, his choice of career was firmly set.

He brainstormed ideas for a deadwood study with another well-known veteran researcher, Harri Vasander. This idea spent several years on the back burner until Kone Foundation granted funding for the project in 2020.

Aakala has also studied natural forests in Lapland and Russia. The original idea had been to search for kelo trees on the other side of Finland’s eastern border. Research plots had been planned in the Kalevalsky National Park in the Russian Republic of Karelia.

But along came the pandemic, which postponed the study’s launch by a year. And then came the war. The changed state of the world meant they had to abandon the idea of fieldwork in Russia and cooperation with Russian scientists. Which is why we’re now in a small conservation area in Lieksa.

Tuomas Aakala drills a sample from a kelo. Photo: Mariina Günther

Deadwood researcher also studies belfry timber

And suddenly “damn it!” echoes around the forest. The research team uses English, as Pemelyn Santos is originally from the Philippines. She got interested in Finnish forest management after coming here as an exchange student in 2018.

But now things are so bad that Aakala soon switches to Finnish: “Perkele!” The increment borer is stuck in the wood and won’t budge. Well, it’s happened before. After half an hour of swearing, the borer finally detaches itself with the aid of a contraption that has been rigged up using bits of rope tied to nearby trees.

When taking samples, Aakala has also experimented with a cordless drill equipped with a special hollow bit. He’s also used this drill to take samples from timbers in the belfry of Kustavi Church. These samples will help determine the year in which the bell tower was built. “I’m interested not only in ecology, but also in the history of forest usage,” says Aakala

Strong language is likewise not uncommon in discussions about Finnish forests. The debate on forest usage has been polarised and contentious for decades. The commercial exploitation of forests is at odds with conservation efforts. There’s also dispute over management methods within the forestry sector itself, and particularly between homogeneous and heterogeneous forest management practices (that is, between clear cutting and continuous-cover forestry).

Aakala thinks that this heated debate stems from the fact that the fate of forests is Finland’s most important conservation issue, and yet the country also has considerable economic interests in forests. Finland has 570,000 forest owners, so issues related to forest usage also affect a significant proportion of the population on a personal level.

“A lot of this debate is pretty useless, because it’s so polarised,” says Aakala.

As a member of a younger generation of researchers, he tries not to pick camps, but that’s not always enough to avoid being labelled.

“As I see it, my role is to provide information that is as factual as possible.”

This is vital, as public debate contains persistent myths about carbon sequestration in forests.

Where can we find carbon sinks and stocks?

One common claim is that young and ‘well-managed’ forest is the best carbon sink. However, research data doesn’t back this up.

In reality, the clearings created by logging are sources of carbon emissions, and sapling stands sequester less carbon than natural forest. Commercial forest only beats natural forest as a carbon sink towards the end of the felling cycle – when it’s cut down again.

Commercial forests also have smaller stocks of carbon.

“In old-growth forests, more carbon is stored in the soil in particular, even though the carbon sink formed by living trees and decaying wood is approaching zero.”

In Northern Finland, climate change has spurred even thousand-year-old primeval forests into vigorous growth and carbon sequestration. These forests are naturally few in number, but as growing conditions become more favourable, they can support more trees.

“Old-growth forest is not withering away, as has been claimed.”

In a natural forest, a pine can live to be over 800 years old, then stand as a kelo for the same period, and remain on the ground as deadwood for another few centuries.

‘Good management’ – that is the clearance and thinning of sapling stands – does not increase the overall growth of the forest either. Although it does increase the growth of those trees that are left to grow, it may even reduce the per-hectare cubic growth of the forest as a whole.

This can also be seen with the naked eye by comparing the nature reserve we’re currently exploring with the surrounding commercial forest. There is very little wood in the surrounding forests. Yet natural forest constitutes a huge carbon stock in which carbon remains for hundreds of years in both standing dead and fallen wood on the forest floor. That is, in the deadwood.

The carbon contained in trees that are felled from commercial forests will be back in the atmosphere within a few years. A maximum of twenty per cent of it will end up in long-lasting stocks, such as buildings and furniture.

Aakala points out that the study of natural forests and the development of forest management are not in opposition to each other.

“Natural forests can provide information on which forest management can be based. The same laws govern trees in both natural and commercial forests.”

Biodiversity loss, for example, has been the subject of much recent debate; and solutions are currently being sought by comparing commercial and natural forests, and then modifying management recommendations for commercial forests.

Eternal wood from the dawn of history

It’s time for a break. A sturdy piece of fallen deadwood naturally makes for a sturdy seat. And sparks a train of thought. In homogenous forest management, the rotation time may be only a few decades at its shortest. (That is, the time from the establishment of the sapling stand to clear felling.)

In a natural forest, a pine can live to be over 800 years old, then stand as a kelo for the same period, and remain on the ground as deadwood for another few centuries. In other words, there is deadwood in Finland that dates back to the time when a certain Jesus of Nazareth first opened his eyes.

We’re sitting on top of eternity as we munch on our sandwiches and sip our coffee. A log truck speeds along a nearby road, probably towards the mills in Uimaharju. Then silence descends once more.

Although kelo trees are part of Finland’s iconic national imagery, there has been very little research into them. But now they’re finally being studied properly. This is a four-year research project, and the knowledge it produces may also lead to further studies.

Data obtained in Finland may also have broader significance. Pines are the most widely dispersed evergreens in the world. They are found everywhere from the tropics to the taiga, and from the Far East to Alaska, and these other pine species also become kelo trees.

“The results of our research can also tell us how other pine species become kelo trees,” says Aakala.

Although the sampling trio are focusing on ecology during this trip, the team also has expertise in ecosystems, flora and fauna – in everything from insects to fungi and birds to lichens.

The team includes researchers from the Universities of Eastern Finland, Jyväskylä and Helsinki, the Finnish Environment Institute, the ELY Centre, the Finnish Museum of Natural History, and Metsähallitus. Both kelo trees and their study are also being documented by photographic artists Sanni Seppo and Ritva Kovalainen, who have been photographing Finnish forests for decades.

The research plots will be bustling next year, as samples are collected and observations of trees, wood fungus and hole-nesting species are made. The remainder of the four-year project will be spent analysing the samples and observations, and writing the research reports.

Kelo trees have dramatically declined in number as a result of the commercial exploitation of forests. The assumption is that the insects that live in kelo trees have also experienced the same fate.

New data about the inhabitants of kelo trees

In the spring, insect researcher Juho Paukkunen and his colleague Gergely Várkonyi attach artificial nests and window traps to kelo trees. They are used to catch hymenoptera, such as bees, bumblebees, wasps and ants.

Hymenoptera play a major role in the forest ecosystem. Many of them are important pollinators. Parasitic and predatory hymenoptera regulate the populations of other insects. Some of these are also pests, such as the pine sawfly, which devours pine needles during its larval stage.

Kelo trees are also fairly unresearched when it comes to hymenoptera.

“The hymenoptera that live in kelo trees have not been studied to any great extent. This study will provide us with new information about the species that live in kelo trees,” says Paukkunen during our telephone interview.

Research will also be carried out from the perspective of potentially endangered species. Kelo trees have dramatically declined in number as a result of the commercial exploitation of forests, and are now mostly found in little islands created by nature reserves. The assumption is that the insects that live in kelo trees have also experienced the same fate.

“We’re particularly interested in whether we can find species that live only in kelos.”

“This is the best!”

The late autumn days are short. When the sky is covered by a thick curtain of clouds, twilight begins to descend in the afternoon.

But this doesn’t discourage the research team, who move another couple of hundred metres along to the next plot. They dig out their headlamps, so as to find the trees that were marked with inconspicuous numbers during the summer.

Surprisingly, they also find some small numbered tags that were attached to the trees by someone else years ago.  The old plot of some unknown researcher partially overlaps with that of today’s deadwood researchers.

“This shows how few old-growth forests still remain. Others have been here to take measurements too,” says Aakala, laughing.

The chatter dries up as everyone concentrates on their work. The borers spin in the almost dark forest. It starts to drizzle.

Although Tuomas Aakala woke up at five am, he seems more lively than ever.

“This is the best – this is what I love! It’s a pity that you rarely get to do much fieldwork these days.”

Tuomas Aakala is an associate professor of forest sciences at the University of Eastern Finland, and is coordinating the deadwood research project.

Mariina Günther is writing her doctoral thesis in biology on the topic of deadwood.

Pemelyn Santos is writing a doctoral thesis on deadwood in the field of agriculture and forestry.

Juho Paukkunen is a senior museum technician at the Finnish Museum of Natural History, and Gergely Várkonyi is a senior researcher at the Finnish Environment Institute. In the deadwood project, they are focusing on the study of hymenoptera.