Amazon trees could survive global warming

Posted by Kate Taylor

Some good news, for a change: a new genetic analysis indicates that many Amazon tree species are likely to survive global warming in the coming century, contrary to previous findings.

But things are never that easy, and University of Michigan evolutionary biologist Christopher Dick and his colleagues warn that extreme drought and forest fires will have an impact, and that over-exploitation of the region's resources continues to be a problem.

The evidence comes from the fact that some Amazonian tree species have already survived for more than eight million years - showing they're pretty resilient, and have already lived through the sort of temperatures forecast for 2100.

But this contradicts earlier papers, based on ecological niche-modeling scenarios, which found that even relatively small increases in global average air temperatures would cause extinctions.

"Our paper provides evidence that common Amazon tree species endured climates warmer than the present, implying that - in the absence of other major environmental changes - they could tolerate near-term future warming under climate change," says Dick.

The team used a molecular clock approach to determine the ages of 12 widespread Amazon tree species, including the kapok and the balsa, and looked at climatic events that have occurred since those tree species emerged.

The researchers determined that nine of the tree species have been around for at least 2.6 million years, seven for at least 5.6 million years, and three for an astonishing eight million years.

"These are surprisingly old ages," says Dick. "Previous studies have suggested that a majority of Amazon tree species may have originated during the Quaternary Period, from 2.6 million years ago to the present."

Air temperatures across Amazonia in the early Pliocene Epoch (3.6 million to five million years ago) were similar to IPCC projections for the region in 2100 using moderate carbon-emission scenarios. Air temperatures in the late Miocene Epoch (5.3 to 11.5 million years ago) were about the same as projections for 2100 using the highest carbon-emission scenarios.

But there are caveats.

"Because we've been in a cold period over the past two million years - basically the whole Quaternary Period - some of the trees' adaptations to warmth tolerance may have been lost," says Dick. "Additional research is needed to test whether this has occurred."

And study co-author Simon Lewis of University College London and the University of Leeds warns that the future may look different to the past.

"While tree species seem likely to tolerate higher air temperatures than today, the Amazon forest is being converted for agriculture and mining, and what remains is being degraded by logging and increasingly fragmented by fields and roads," he says.

"Species will not move as freely in today's Amazon as they did in previous warm periods, when there was no human influence. Similarly, today's climate change is extremely fast, making comparisons with the past difficult."