Würzburg. How quickly dead wood is broken down in the forest depends on the climate as well as on fungi and insects. For the first time, a research team has determined the contribution of dead wood to the global carbon cycle. Living trees absorb a lot of carbon dioxide from the atmosphere and are therefore important climate protectors. Little is known about the role of dead trees in the global carbon cycle. The decomposition of wood and the return of the nutrients stored in it are among the most important processes in forests.
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How much carbon is rotting wood released worldwide? What role do insects play in this? This has now been examined for the first time in a global research project, established by the Bavarian Forest National Park and coordinated by the Julius Maximilians University of Würzburg (JMU) and TUM.
At 55 forest locations on six continents, researchers laid out pieces of wood from over 140 tree species in order to measure the influence of the climate on the rate of degradation. Half of the wood was in close-meshed cages. It was thus ruled out that insects were involved in the decomposition.
The data collected show that the rate of degradation and the contribution made by insects are very dependent on the climate and, above all, increase with increasing temperature. Higher rainfall accelerates degradation in warm regions and slows down degradation in regions with low temperatures. 50 research groups around the world carried out the experiment, sometimes under the most difficult conditions. Some areas had to be protected from elephants at great expense. One area was lost in a forest fire and was rebuilt, another area was flooded. “From the experiment we were able to model the extent to which deadwood is involved in the global carbon cycle,” says Rupert Seidl, Professor of Ecosystem Dynamics and Forest Management at the Technical University of Munich (TUM). “According to this, 10.9 gigatons of carbon are released from deadwood worldwide every year. Some of the carbon goes into the soil while another part is released into the atmosphere. The amount released from dead wood corresponds to around 115 percent of the emissions from fossil fuels, ”adds Dr. Werner Rammer, scientist at TUM who was in charge of the global calculations.
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“With 93 percent, the tropical forests make a disproportionate contribution to this result due to their high wood mass in combination with rapid degradation processes. Slow degradation in forests in northern and temperate latitudes means that carbon is stored in deadwood over long periods of time. Insects account for almost a third of the wood degradation, which is predominantly restricted to the tropics. In the forests of northern and temperate latitudes, however, the contributions made by insects are low, ”explains PD Dr. Sebastian Seibold, first author of the study. “The study underscores the role of dead wood in the global carbon cycle, as well as the functional importance of insects in breaking down wood. This closes another gap in the global modeling of carbon cycles, ”says Professor Jörg Müller, head of research in the Bavarian Forest National Park and the ecological station at JMU Würzburg.
“In the face of global change, we are seeing drastic declines in biodiversity and changes in the climate. The current study shows that both climate changes and the loss of insects have the potential to change wood degradation and thus the carbon and nutrient cycles worldwide, ”explains PD Dr. Seibold. From 2016 to 2020 he was a habilitation student at JMU; now he is doing research at TUM and in the Berchtesgaden National Park. uni
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