Enclosed Rainforest In Arizona Goes Through Drought For Science

Dec 12, 2019

The world’s hottest rainforest isn’t the Amazon. It’s not even in the tropics. It’s kept under glass in the desert of Southern Arizona. Biosphere 2, operated by the University of Arizona,  was built 30 years ago as an experiment in space colonization, but now the ecosystems inside are perfect for climate change research. Unlike in the real world, scientists can control the elements—which is just what they did when they turned off the rain for two months. They’re tracking how carbon cycles through the enclosed rainforest during the drought. KNAU’s Melissa Sevigny reports, it’s a glimpse of what the world will look like in a hotter, drier future.


Christiane Werner of the University of Freiberg in Germany lines up a row of steel canisters on a table. She’s about to release twenty thousand dollars’ worth of carbon dioxide into the air.

"Why can you do it here? Because we are in an enclosed ecosystem," she says. 

In a real rainforest it’s impossible to track carbon cycles closely, but this forest is sealed inside a gymnasium-sized pyramid of steel and glass. Werner opens a valve and a puff of air escapes.  This is “heavy” carbon or carbon-13. It’s manufactured so instruments can detect it. Werner says, "We can really make the carbon flow through a system visible with this technique, and that’s why it’s so exciting."

Scientists know forests soak up about a third of carbon emissions from fossil fuels, but they don’t know exactly where that carbon goes—or how it’s affected by drought.

Laura Meredith, director of rainforest research at Biosphere 2, wants to find out if ecosystems will respond to droughts in a way that releases carbon and worsens climate change, "or in a way that actually helps mitigate it, helps slow down the process. Maybe they have some mechanisms that allow them to be very resilient and to absorb those changes."

It’s a massive experiment with more than 80 scientists from 13 institutions, funded by a 2 million dollar grant from the European Research Council.

Inside the Biosphere 2’s rainforest is a hollowed-out mountain buzzing with scientific instruments. A spiderweb of plastic tubes links about 20 gas analyzers to every part of the rainforest. "The plants look a little bit like they’re hospitalized with all of the sensors, too," Meredith says. "We have sap flow sensors, water storage sensors."

The team even had to hire climbers to scale the top of the glass dome and hook sensors onto individual leaves. Jana U’Ren, a biosystems engineer at the University of Arizona, says,  "We had to order 20 bags of—like turkey bags that you’d normally cook your Thanksgiving turkey in, and we made little enclosures for leaves." That’s to figure out how plants “spend” their carbon when they’re stressed: do they store it in roots and leaves, give it away to microbes, or breathe it back into the air as a kind of coping mechanism?

Joost van Haren is an earth scientist at the University of Arizona. "It’s this resilience that trees have which is so super cool," he says. "Because of many ways that trees are so different from us humans, we really don’t grasp that kind of resilience just yet."

The scientists will collect almost a petabyte of data, says cyber infrastructure expert Bonnie Hurwitz. That’s like a book with five hundred billion pages. She says, "Everything is wired and linked up, streaming to the cloud, and it gives us an opportunity unlike any other ecosystem where we have both the technology and science in place to really measure and monitor these global processes that are impossible to do in the field."

The idea is to build better models of how ecosystems work. The scientists say those predictions will be crucial as real rainforests begin to heat up. John Adams, deputy director of Biosphere 2, says it was built by people who dreamed of going to other planets, but now it’s about protecting our own.

"There is only one Earth," Adams says. "Everything had to come together to make it a suitable atmosphere and conditions for you and I to survive, and you just don’t find that anywhere else."

Today the team turns the rain back on and they’ll study the rainforest as it recovers.