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Researchers are inducing a drought in an Australian rainforest to study its effects

  • The drought experiment allows the team to study a wide range of plant life, from trees and vines to shrubs and epiphytes, in order to determine which are most vulnerable.
  • Thanks to a “canopy crane,” the researchers can look at plant and animal responses to the drought at all vertical levels of the forest canopy, from the ground to the tops of the trees.
  • We’re already seeing the impacts of El Niño-exacerbated drought across the globe.

Susan Laurance and colleagues at James Cook University in Australia wanted to study how different groups of plants in tropical forests are affected by drought.

So a few months ago, the researchers used 3,000 clear plastic panels to create what they call a “raincoat for a rainforest,” artificially inducing a drought in several thousand square meters of the Daintree Rainforest on the northeast coast of Queensland.

The drought experiment allows the team to study a wide range of plant life, from trees and vines to shrubs and epiphytes, in order to determine which are most vulnerable, Laurance says.

“This just cannot be achieved with greenhouse experiments because they can only focus on small or young plants in a very artificial environment,” Laurance told Mongabay in an email, “and studying drought events in nature in existing plots is very difficult because these events are either too rare or inconsistent.”

Not only can Laurance and team examine a variety of plant life at different stages of their life cycles, but, thanks to a “canopy crane,” they can also look at plant and animal responses to the drought at all vertical levels of the forest canopy, from the ground to the tops of the trees.

A canopy crane allows the team to study drought responses at all vertical levels of the forest. Photo by Bill Laurance.

Prior to embarking on the drought study, the researchers spent two years monitoring the growth and survival rate of 700 large trees and 1,000 lianas, a climbing plant that grows on trees, in a 1-hectare (about 2.5 acres) area that is fully accessible to the canopy crane. They also measured the movement of carbon dioxide and soil water through the rainforest, as well as sap flow in trees.

Now, they hope to study how the rainforest responds when they create “El Nino drought” conditions, where the typical 4-month dry season is 6 months in length.

One of the key questions the team wants to answer is whether or not larger tree species are especially vulnerable to droughts, as has been suggested by recent studies. If so, the implications could be huge, Laurance said, since big trees store a lot of carbon and provide food and shelter for numerous animal species.

But it’s not only big trees that have an important role to play in regulating Earth’s climate by sequestering carbon. Tropical forest ecosystems as a whole play a crucial role in cycling carbon and water in the Earth’s atmosphere.

“By determining how vulnerable forests are to droughts (by breaking it down into the individual responses of trees, vines and shrubs) we will have a better understanding of what that means for the survival of biodiversity at a local scale and climate function at the larger scale,” Laurance said.

A wide-angle view beneath the plastic panels. Photo by Yoav Daniel Bar-Ness.

There is a wealth of research showing that droughts cause the release of massive amounts of carbon from tropical forests.

Researchers found that a 2010 drought in the Amazon, for instance, triggered the release of nearly 500 million tons of carbon (1.8 billion tons of carbon dioxide) into Earth’s atmosphere — and that figure only accounts for the lower CO2 uptake by vegetation caused by drought stress. If you were to include emissions from the wildfires that increased in size and frequency thanks to the drought, that tally would likely be much higher.

Climate models project that most of the Amazon will see increases in the frequency and area of drought over the coming decades, mostly due to rising global temperatures and the El Niño event currently warming surface waters in the Pacific Ocean.

The Daintree experiment only began in May, but the rainforest is already visibly wilting, Susan and fellow James Cook University professor Bill Laurance, who is also a part of the drought study, wrote in a piece for the Conversation. They say this is “just a taste” of what could be in store for forests around the globe, writing, “Climatologists are telling us to buckle our seatbelts because the ride could get scary.”

Susan Laurance points out features of the study to a field assistant. Photo by Bill Laurance.

The current El Niño event is expected to be one of the strongest ever witnessed and to create torrential downpours and floods in some regions while producing heatwaves and droughts in others. Global warming will only reinforce its effects.

Susan Laurance notes that we’re already seeing the impacts of El Niño-exacerbated drought across the globe: forest fires creating a noxious haze that blanketed much of Southeast Asia, unprecedented droughts and wildfires in western North America, massive crop failures in New Guinea.

There’s ample evidence that future droughts will be worse than what we’ve already seen, making it vital we develop a better understanding of how droughts will affect rainforests, Laurance says. She’s hopeful that the Daintree experiment will help.

“This study has not been easy — in truth it’s been a logistical nightmare to steal the rain from a rainforest,” she writes. “But the study is now fully set up, and in the end we think it will be worth all the sweat and hard work.”

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