Photo: Adriane Esquivel Muelbert, University of Leeds

A 30-year analysis of Amazonian trees finds the world’s largest rainforest is already adapting to climate change, but probably not fast enough.

The study, published this week in Global Change Biology, paints what is perhaps our most comprehensive picture of how the Amazon rainforest’s trees are responding to climate change. While the authors found signs of adaptation to rising carbon dioxide and worsening drought, it doesn’t seem to be keeping pace with the environmental changes the region is seeing. That could spell bad news for the long-term health of the rainforest and its ability to buffer the planet against further climate change.

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Over the past 30 years, the Amazon’s climate has become more extreme, with the dry season growing longer and drier, especially in the south, and the wet season becoming wetter and possibly more flood-prone. The basin has recently seen three major droughts that have resulted in widespread forest die-offs, with hotter temperatures likely exacerbating regional thirst.

It’s super important to know how the Amazon is affected by these changes, because the rainforest itself plays a key role in regulating global climate. Its trees store an estimated 100 billion tons of carbon, roughly ten times humanity’s annual carbon emissions. Small changes in the Amazon’s capacity to inhale carbon dioxide could mean a lot more of it hanging around in the atmosphere.

A forest in the central Amazon in 2016
Photo: Adriane Esquivel Muelbert, University of Leeds

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The new study sought to investigate how the forest’s trees are faring and whether they have already begun to adapt. To do so, the researchers analyzed three decades of data from 106 monitoring plots, looking at how tree size, wood density, and the forest’s overall drought tolerance have changed over time.

The good news is that the forest already seems to be adapting: The authors found an increased abundance of drought-tolerant young trees over time. Coupled with greater mortality of big water-guzzlers, this suggests the next generation of woody giants will be more resilient to drought. The study also found an overall increase in the size of the biggest trees, which may have to do with rising carbon dioxide levels supercharging plant growth. Or it could be that big trees have deeper root systems, which helps them tap more water during droughts.

But the data also shows that drought-stress across the Amazon is increasing faster than the forest is changing in response.

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“Our results provide empirical evidence of the inertia within this system and clearly raise concerns about whether forests here will be able to track further climate change anticipated over coming decades,” the authors write.

Eric Davidson, a tropical forest ecologist at the University of Maryland who wasn’t involved in the study, said that the results make sense. “[I]t is a very novel analysis to show that what we suspect should be happening in terms of adaptation is happening, albeit apparently more slowly than needed given the pace of climate change,” he told Earther via email.

If the Amazon cannot keep pace, that could threaten the ability of the forest to provide crucial ecosystem services, from carbon sequestration to protection of the region’s immense biodiversity. But lead study author Adriane Esquivel Muelbert said humans still have an opportunity to help the Amazon face the hotter future by slowing down the tide of deforestation and creating more protected areas to help species to migrate out of harm’s way.

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The election of Brazil’s new far right president, who seems intent on carving up the Amazon for business, obviously makes that task harder. But Muelbert, a Brazilian, sees hope in the fact that most of our scientific knowledge about the value of the Amazon—and the myriad ways it’s threatened—is very new.

“As Western society we know the value of nature much more now” than we did a few decades ago, she told Earther. “I hope we use that information wisely.”