A team of 90 researchers has discovered that the uptake of carbon in the Amazon rainforest is decreasing over the long term. This is due to a recent decline in the growth rate of trees, while tree mortality has increased. As a result, carbon is stored in the rainforest for a shorter period. A possible cause of the shorter lifespan of trees could be greater variation in climate. This was one of the findings of the study, which was published in Nature. The participants included researchers from the Naturalis Biodiversity Center, Wageningen UR and Tropenbos International.
Data on CO2 in the atmosphere show that large amounts of carbon have been stored during the last century on the land area worldwide. The storage of carbon in a reservoir (such as forests) is also known as a sink. The largest carbon sink on the Earth is located in the Amazon region. “It is unclear what happens if the climate keeps changing the composition of the atmosphere and tree growth," says Hans ter Steege, researcher at Naturalis Biodiversity Center. “The observed decline in the Amazon sink is very different from the recent increase in uptake of terrestrial carbon on a global scale, and also goes against our expectations.”
The researchers, led by Roel Brienen of the RAINFOR network (Leeds University) confirm that the Amazon, as described in previous studies, has long been an important sink for carbon. In contrast to these studies, they have also shown that less and less carbon is accumulating over the long term. “The previous studies made predictions on carbon storage in the Amazon,” says Lourens Poorter of Wageningen University, “but there remains significant uncertainty about what exactly is happening, because both the future climate and its effects on the vegetation are unclear.” Therefore, in this study the researchers did not make predictions, but looked at the long-term effects on individual trees in the tropical forests of South America. Boot (Tropenbos International): “We used unique data collected over many years from a very large region. There are no other studies about longer periods and larger areas than the Amazon.” This study also shows that long-term monitoring on location is very important to elucidate changes in the largest carbon sink on earth.
- Long-term decline of the Amazon carbon sink
Nature 519, 344–348 (19 March 2015) doi:10.1038/nature14283