Deadwood in the global carbon cycle

Seibold, S., Rammer, W., Hothorn, T., Seidl, R., Ulyshen, M. D., Lorz, J., ..., Pavlíček, T. & Müller, J. 2021. The contribution of insects to global forest deadwood decomposition. Nature, 597(7874): 77-81

Dr Tomáš Pavlíček

Institute of Evolution

University of Haifa

Aba-Hushi Ave, Mount Carmel

IL-3478601 Haifa/Israel

Mob. +972 54 399 67 00

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Haifa, 02.09.2021

The importance of insects in the decomposition of wood

Deadwood in the global carbon cycle

The speed at which deadwood decomposes in forests depends on the climate as well as on the presence of fungi and insects. An international research team has now determined the annual contribution made by deadwood to the global carbon cycle and quantified, for the first time, the importance of insects in the decomposition of wood.

Living trees absorb a considerable amount of carbon dioxide from the atmosphere and therefore play an important role in the protection of our climate.

How much carbon is released from rotting wood worldwide? What role do insects play in this process? These questions have now been studied in a global research project conducted by the Bavarian Forest National Park and coordinated by the Julius Maximilians University of Würzburg (JMU) and the Technical University of Munich (TUM). RNDr Tomáš Pavlíček PhD, Institute of Evolution, University of Haifa, was the Israeli partner who conducted the local experiment in an open park forest with dominant evergreen Quercus calliprinos on Mt. Carmel (Fig. 1).

Fig. 1. A view of the Israeli experimental closed-canopy site near the Carmelite Order Muhraqa Monastery (abbreviated Muhraqa Monastery in the following text). (Photo: Patricia Cardet).

An experiment at 55 different locations provides the basis

At 55 forest locations on six continents, researchers laid out wood from more than 140 tree species to assess the influence of the climate on the rate of decomposition. The local experiment involved either caged (Fig. 2) and uncaged deadwood (Fig. 3). The deadwood was placed in mesh cages, either open or closed (Fig. 2).

Fig. 2. Experiment with deadwood cages near the Muhraqa Monastery: some of the wood is kept in closed cages to keep insects at bay and some in open cages to allow insects to enter the cage. (Photo: Patricia Cardet).

Fifty research groups worldwide completed the three-year-long experiment (Fig. 3), sometimes under exceptionally difficult conditions. For instance, it was necessary to take elaborate actions to protect some areas from elephants. One area was lost to a forest fire and reconstructed, while another area was flooded.

The collected data demonstrates that the rate of decomposition and the contribution of insects are highly dependent on the climate, and increase as the temperature rises. Higher levels of precipitation accelerate the decomposition in warmer regions and slow it down in regions where the temperatures are lower. The conclusion important for Israel is that at low levels of precipitation, temperature had only a minor influence on the effects of insects on the deadwood decomposition rate. Consequently, we can say that deadwood in temperate and boreal forests stores carbon over longer periods in comparison with deadwood in tropical and subtropical forests, explains RNDr Tomáš Pavlíček, PhD.

Fig. 3. Uncaged treatment of deadwood in an experimental site near the Muhraqa Monastery. Both, the insects and microorganisms had unrestricted access to the deadwood branches. (Photo: Patricia Cardet).

Global carbon cycling

“On the basis of the experiment, we were able to model the role that deadwood plays in the global carbon cycle,” explains Professor Rupert Seidl, Ecosystem Dynamics and Forest Management at the Technical University of Munich (TUM). “According to the report, some 10.9 gigatons of carbon are released from deadwood worldwide every year. In this context, part of the carbon is absorbed into the soil, while another part is released into the atmosphere. The amount of carbon released from deadwood is equivalent to roughly 115 percent of the emissions from fossil fuels,” adds Dr Werner Rammer, a scientist at TUM, who played the leading role in the global calculations. Decomposition in temperate forests, including the open park forests in Israel and in boreal forests is considerably slower than in tropical forests.

“At 93 percent, tropical forests contribute disproportionately to this result due to their high wood mass combined with their rapid decomposition processes. Insects account for almost one third of wood decomposition, although this is mostly confined to the tropics. In forests of northern and temperate latitudes, including forests in northern Israel, the contributions made by insects are small, though,” explains PD Dr Sebastian Seibold, leading author of the study.

The effects of global change

“The study highlights the role played by deadwood in the global carbon cycle and the functional importance of insects in the decomposition of wood. In this way, we are closing another gap in the global modelling of carbon cycles,” explains Professor Jörg Müller, Head of Research at the Bavarian Forest National Park and at the Ecological Station of the JMU Würzburg.

“At a time of global change, we can see some dramatic declines in biodiversity and changes in climate. This study has demonstrated that both climate change and the loss of insects have the potential to alter the decomposition of wood, and therefore, the carbon and nutrient cycles worldwide,” explains PD Dr. Seibold.

Publication:

Seibold et al (2021): The contribution of insects to global forest deadwood decomposition. Nature, 597(7874): 77-81.