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Understanding the role of dead trees in climate change

Published: 30 September 2024
Scientist in the forest squatting next to a collection of sticks with marks on them.

In forests, dead plants and animals are constantly decomposing, releasing carbon that had been stored in them. To better understand how climate and land use impact this process, a global study is currently underway, spanning 45 research sites across the world. The northernmost site is located just outside Umeå, Sweden, and is managed by researchers from the Swedish University of Agricultural Sciences (SLU).

Bearded lichen hangs in large clumps from the trees, while dead trunks, sporadically covered in moss and lichen, are scattered across the forest floor. Mushrooms sprout here and there in the damp soil, and woodpeckers hammer away on a long-dead pine that has long since shed its bark. In this nature reserve, located a few miles outside Umeå, Joakim Hjältén and his colleagues are conducting experiments on dead wood. 

"It’s crucial to understand the decomposition processes if we are to accurately calculate the Earth’s carbon flux and better grasp the forest’s role in the climate crisis," says Joakim Hjältén, professor emeritus at SLU in Umeå.

Large amounts of carbon in deadwood

Dead trees play a key role in biodiversity, serving both as habitats and as food for insects, fungi, and other organisms. Since large amounts of carbon are stored in dead wood, its decomposition plays a critical role in understanding the global carbon balance. 

"We have substantial knowledge about how trees grow and absorb carbon in different environments, largely because of the economic interest in this. However, our understanding of how quickly dead trees decompose and return carbon to the atmosphere is lacking. This is problematic, given that the carbon stored in dead wood globally amounts to almost a tenth of the carbon currently in the atmosphere. Every year, the carbon released from dead wood during decomposition is almost equivalent to the annual emissions from fossil fuels," Hjältén explains. 

In a forest clearing, numerous small cubes, covered in fine white fabric, are scattered around. Some cubes are completely sealed, others have openings in the roof, or lack walls, while a few are equipped with aluminium trays as floors. Each cube contains dead wood from four local tree species (Norway spruce, silver birch, grey alder, and rowan), as well as a reference sample of beech, which is used in all the global experiments. 

"We aim to understand the role different groups of organisms, such as insects and wood-decaying fungi, play in the decomposition processes. The experiments are designed to either exclude or include the effects of these groups, for example by preventing fungi from the soil or insects from the air from influencing the results," says Hjältén. 

Climate and active decomposers influence the process

The decomposition of dead wood is influenced by both climate and the fungi and insects that act as decomposers. In our northern forests, the process is slow—here, a dead tree can remain for many years before decomposing, whereas in tropical regions, the same process happens much more rapidly. 

This experiment will run for three years and is being conducted at 45 locations worldwide. At each site, the experiments are carried out in both natural forests and managed forests. Forestry practices can affect decomposition processes by altering the composition of the organisms involved. 

"This study will provide us with fundamental knowledge about the roles different groups of organisms play in decomposition and the rate at which it occurs in different parts of the world. It will also offer insights into how a warmer climate may affect these processes, as well as helping us understand the impact of forestry on decomposition, biodiversity, and improving our ability to assess the role of forests in the global carbon balance," Hjältén concludes.

Portrait of Joakim Hjältén.

Joakim Hjältén.
(Click for high resolution image).

Facts:

This global research study investigates how forestry and climate influence the decomposer communities in dead wood and the rate of carbon turnover, as well as the combined effect of these factors. 

The study spans 45 research sites across the world, applying a standardised experimental setup. Researchers compare the decomposition rate of dead wood from various tree species, the composition of decomposer communities, and the contribution of different species groups to decomposition in both natural and managed forests. 

The project (BIOCOMP) is led from Germany by Prof. Sebastian Seibold at the Technical University of Dresden and is funded by the EU (ERC Starting Grant). 

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