This is the conclusion reached by researchers at the University of Oxford, after a long-term study of which the results were published on Wednesday in the scientific journal Nature†
The scientists investigated the causes of death of 81 tree species at 24 sites in ‘primary forests’ in the northern Australian state of Queensland. The accelerated mortality they observed occurred in all tree species and at all sites studied. The researchers, who say they were ‘shocked’ by their findings, fear that the trend will also be visible for other (tropical) rainforests on the earth.
Tropical rainforests inhibit global warming by absorbing about 12 percent of human-caused carbon dioxide (CO2) emissions. Doubling the rate at which trees die in those forests would mean that the carbon stored in trees would return to the atmosphere just as quickly. If that is the case, tropical forests could soon become sources of carbon and the challenge of keeping global warming well below 2 degrees will become not only more urgent, but also more difficult,” said one of the researchers.
The fact that accelerated tree deaths can be attributed to climate change is innovative
Pieter Zuidema, professor of Forest Ecology and Forest Management at the University of Wageningen (WUR), calls the research of high quality. He calls it ‘unique’ that the researchers had datasets that cover a period of about fifty years. ‘Data on tree mortality are very scarce, especially in tropical forests’, says Zuidema. According to him, developments in tree mortality over time are even more difficult to record, because there are years with a lot of mortality and years with average mortality. Zuidema therefore calls the statistic from this study, which clearly shows the increasing mortality.
According to Zuidema, the conclusion that the accelerated death of trees can be attributed to climate change is also innovative. ‘There is a lot of interest in climate science to explain extremes in weather due to climate change, but that is not happening much in ecology yet,’ says Zuidema.
The new study is in line with research that Zuidema and colleagues published a month ago in the journal Nature Geoscience† This showed that the trunk growth of tropical trees decreases in years with a warmer and drier dry season than usual. The effect of drier and hotter years is greater in drier or warmer regions, they concluded. This could indicate that tropical trees are becoming more sensitive to climatic fluctuations due to climate change.