Tropical forests can handle the heat, up to a point

25. 5. 2020 -

Tropical forests face an uncertain future under climate change, but new research published in Science suggests they can continue to store large amounts of carbon in a warmer world, if countries limit greenhouse gas emissions. Three scientists from the Czech Republic also took part in the mentioned research.

The world’s tropical forests store a quarter-century worth of fossil fuel emissions in their trees alone. This is done with the help of photosynthesis, and tropical forests help maintain the stability of the Earth's climate. Carbon dioxide is one of the main greenhouse gases that contributes to the capture of heat from sunlight. However, the amount of carbon dioxide in the air is increasing sharply due to human activity and currently far exceeds not only pre-industrial values, but also concentrations over the last several hundred thousand years. This retains more and more heat in the atmosphere and shifts the climate balance, in other words, global climate change. There are fears that global heating can reduce this store if tree growth reduces or tree death increases, accelerating climate change.

A new study published in the international scientific journal Science shows that tropical forests are able to cope with global warming without significantly reducing their ability to sequester excess carbon dioxide from the atmosphere. This is the case if the amount of carbon bound by the growth of the trees is greater than the losses due to mortality and decomposition of the wood. And this only works under certain circumstances: the global temperature change must not be too fast, forests must remain untouched by human activity and the daily temperature must not exceed the critical limit of 32 degrees Celsius. For example, an increase in global average temperatures of 2 degrees Celsius compared to pre-industrial values will mean that about three-quarters of tropical forests will reach conditions exceeding this critical limit. Any further increase in temperature could then lead to increased tree mortality and the rapid release of carbon from forests.

Three authors from the Czech Republic also contributed to these results - Radim Hédl from the Institute of Botany of the Czech Academy of Sciences, Martin Dančák from Palacký University in Olomouc, and Martin Svátek from Mendel University in Brno. They contributed to the scope of the unprecedented study by long-term repeated measurements of the growth of several thousand trees and monitoring of their mortality on permanent areas in the Ulu Temburong National Park in Brunei, Borneo. They started operating in Brunei in 2007 and have been systematically researching Borneo's tropical forests ever since. In addition to joint research in the Brunei areas, Czech scientists are developing research on tropical forests in other related topics.

"The world's tropical forests contain so much carbon in trees alone that it offsets fossil fuel emissions in a quarter of a century. If we can mitigate climate change, these forests can continue to store large amounts of carbon. However, there are concerns that this repository is gradually ceasing to function, as excessive warming and droughts slow down the growth of trees or increase their mortality. The released carbon could then further accelerate climate change," adds Radim Hédl, who conducts long-term monitoring on permanent areas in Brunei, to the results of the current study.

Martin Dančák is a leading Czech expert on the biodiversity of tropical forests. It achieves one of the highest values in the world at the monitoring sites in Brunei. In this context, Dančák states: "It can be assumed that tropical forests are to some extent capable of long-term adaptation to climate change, partly due to their high biodiversity."

Martin Svátek coordinates research into the impacts of logging and fragmentation of tropical forests in Borneo. Regarding the new results, he says: "Current knowledge shows the admirable ability of untouched tropical forests to cope with high temperatures. However, most forests in the tropics are already affected to varying degrees by human activity, which can to extremes."

For the first time, a recent study used direct field measurements to examine the sensitivity of the world's tropical forests to climate change. In the long run, temperature appears to have a major effect on carbon storage through reduced tree growth, while the second key factor is drought, which leads to tree death. The insights into how the world's tropical forests respond to climate were only possible with decades of careful fieldwork, often in remote locations. The global team of 225 researchers combined forest observations across South America (RAINFOR), Africa (AfriTRON), and Asia (T-FORCES). In each monitoring plot, the diameter of each tree and its height was used to calculate how much carbon they stored. Plots were revisited every few years to see how much carbon was being taken in, and how long it was stored before trees died. To calculate changes in carbon storage required identifying nearly 10,000 tree species and over two million measurements of tree diameter, across 24 tropical countries.

 

More information on the article: Sullivan M. J. P. et al., 2020. Long-term thermal sensitivity of Earth's tropical forests. Science (DOI: 10.1126 / science.aaw7578)

Contact for more information: Ing. Martin Svátek, Ph.D., Faculty of Forestry and Wood Technology, Mendel University in Brno, martin.svatek@mendelu.cz

Illustration photo: Martin Svátek