Research co-led by a James Cook University professor suggests the Amazon rainforest is changing fast—but not fast enough to keep up with climate change.
JCU Professor Bill Laurance showed in 2004 that forests in the central Amazon had mysteriously changed over the previous two decades.
Among other changes, Laurance found the biggest trees had grown larger and many small tree species had declined in number.
Now research by more than 100 scientists has shown that comparable changes are happening in forests all across the Amazon Basin.
“Bill Laurance’s research was an inspiration for this work,” said lead author Dr Adriane Esquivel-Muelbert from the University of Leeds in the UK. “The fact that we are seeing broadly similar trends over vast areas is scientifically reassuring but scary—because it suggests that climatic changes must be driving these alterations,” she said.
The team led by Dr Esquivel-Muelbert found that since the 1980s, stronger droughts, rising temperatures and higher levels of carbon dioxide in the atmosphere have slowly altered the growth and mortality of different tree species.
“There are clear winners and losers,” said Professor Laurance. “In particular, moisture-loving tree species are dying out, but species suited to drier climates have been unable to replace them.”
“Because Amazon droughts are occurring more frequently now than in the past, this suggests the rainforest is unable to keep up with the demands of climate change,” said Dr Esquivel-Muelbert.
Like Professor Laurance, the researchers also found that large tree species are also growing faster and overwhelming smaller plants.
This finding confirms one of Professor Laurance’s key suspicions: that big trees benefit greatly from rising concentrations of carbon dioxide in the atmosphere, which is a direct result of human greenhouse gas emissions.
“Big, tall trees are winners because they get lots of sunlight up at the top of the forest canopy. They can exploit increasing carbon dioxide to photosynthesise, and thereby grow, more rapidly,” said Professor Laurance.
And small tree species, which have to survive in the low light of the forest undergrowth, just can’t keep up,” said Professor Laurance.
“Collectively, these findings suggest that climatic change is having wide-ranging impacts on Amazonian trees,” said Dr Esquivel-Muelbert.
“And because animals specialised for pollinating and feeding on different tree species will be affected also, we can expect the entire Amazon ecosystem to be altered,” said Professor Laurance.
Images available for download: https://drive.google.com/open?id=1wSZrOfPyWdINxdswdNqFinbW44AMWloj
The paper “Compositional response of Amazon forests to climate change” will be published in Global Change Biology on 8 November 2018 (DOI: 10.1111/gcb.14413)