You and a Ginkgo Tree Can Help Scientists Study Climate Change

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ginkgo tree leaves in Yonghe Lamasery, Beijing, China
Ginkgo trees have distinctive fan-shaped leaves, which are green all summer before turning a vivid yellow in autumn. V.apl/Shutterstock
ginkgo biloba tree with green leaves
A ginkgo tree in Tokyo shows off its green summer foliage. Blew_s/Shutterstock

Most of us can't do much to stop climate change, but doing a little is still better than nothing. And along with the many lifestyle changes that can shrink our carbon footprints, one undervalued way to help is by serving as a citizen scientist. This August, if you have some free time and legal access to a ginkgo tree, there's an easy way to help researchers study this increasingly hot mess.

Ginkgo biloba trees are living fossils, like time travelers from the Triassic Period. The oldest traces of their species date back more than 200 million years, including iconic fan-shaped leaves from the early days of dinosaurs. The species has endured three mass extinctions, but it's now the lone survivor in an entire taxonomic class, and might be the most ancient tree species alive today.

Because ginkgo trees haven't changed much in all that time, they're in a unique position to help us learn what Earth was like many millions of years ago — and what it might be like in the coming centuries. The long continuity of ginkgos makes it easier for scientists to compare modern specimens with prehistoric remains, which can reveal how Earth's atmosphere has changed naturally over time, and how today's sped-up climate change might affect plant life (and, by extension, us) in the near future.

That's the idea behind the Smithsonian Institution's Fossil Atmospheres project, which is using modern and ancient ginkgo leaves to build a clearer record of atmospheric changes through time. In one part of the project, researchers are growing ginkgo trees in greenhouses with varying levels of carbon dioxide, then studying how different CO2 levels affect cells in the leaves. With this data, they explain, "we should be able to pick up a fossil ginkgo leaf and know the composition of the air in which it grew."

For the other part of the project, researchers are relying on help from citizen scientists. This is a multiphase initiative, as Meilan Solly reports for Smithsonian Magazine, including a long-term component as well as one that only runs through August.

Reading leaves

ginkgo tree leaves in Yonghe Lamasery, Beijing, China
Ginkgo trees have distinctive fan-shaped leaves, which are green all summer before turning a vivid yellow in autumn. V.apl/Shutterstock

This project's main goal is to clarify the relationship between atmospheric CO2 levels and two kinds of cells — stomatal and epidermal — in ginkgo leaves. Once that's fully understood, fossilized ginkgo leaves should provide more reliable climate proxies, the researchers explain, a term for data sources that can reveal details about climates of the distant past.

One climate proxy found in plants is the stomatal index, or the number of tiny gas-exchange holes (stomata) on a leaf compared with the number of other cells. Stomata are key to photosynthesis, since they let plants take in CO2 and water while releasing oxygen. Plants regulate their gas exchange by opening and closing their stomata, and their optimal number of stomata depends on several environmental factors. Atmospheric CO2 levels are the dominant factor, the researchers explain, but other variables like temperature and humidity also play a role, and we still don't fully understand how this blend of influences works.

In the greenhouse experiment, the researchers are growing 15 ginkgo trees at various CO2 levels. As they monitor those leaves, though, they're also seeking a much wider dataset beyond one group of just 15 trees. And that's where citizen science comes in.

yellow ginkgo tree in Geneva
After turning yellow, ginkgo leaves typically fall abruptly, often all dropping in a single autumn day. Fabrice Coffrini/AFP/Getty Images

As noted above, there are a couple ways to participate. The newest option, available only this month, seeks to crowd-source ginkgo leaves from a variety of habitats. According to paleobiologist Laura Soul, an education specialist with Fossil Atmospheres, this gives researchers far more data than they could gather on their own. "We can't go out and get leaves from every state in North America, but the public can," Soul tells Solly, "and that's why citizen science performs [such] a vital role in what we're doing."

If you'd like to help perform that role, there are a few things to know before getting started. You'll need to join the project on iNaturalist (which is free), either via its website or mobile app, and you'll need a smartphone or a computer plus a camera. Your ginkgo tree must be at least 10 feet tall, and should either be located on public property or private property that you have permission to use for this purpose. Identify whether the tree is male or female (the project site offers tips to help), then take a photo of the entire tree and one of its base, which you'll post to iNaturalist. You'll also need to gently collect at least six leaves from a single short cluster, secure them in a "cardboard ginkgo sandwich" and then mail them off to the researchers.

For the full protocol on collecting, packaging and sending your samples (including the project's mailing address), see this detailed PDF of instructions from the Fossil Atmospheres team. All samples must be mailed before the end of August, so don't dawdle. By providing specific instructions and limiting the time window to one month, the researchers are trying to limit the number of variables that can affect stomatal count. With fairly standardized samples all collected in the same month, they hope to focus on just a few factors like geographic range, temperature, rainfall, elevation and latitude.

closeup of leaves on a ginkgo biloba tree
A closeup of leaves on a ginkgo tree, whose iconic fan-shaped foliage might be even older than the dinosaurs. Istvan Balogh/Shutterstock

Another option is an online tool for stomatal counting, letting anyone with an internet connection help researchers by counting stomata in photos of both modern and fossilized ginkgo leaves. This can be tricky, but the tool offers tips and tutorials, and also features an an "easier count" mode to help you hone your skills before trying the more advanced stomatal count. According to the site, more than 3,300 volunteers have completed nearly 25,000 classifications since the project launched in 2017.

This kind of research is becoming "vital" for climate science, Soul tells Solly, since it lets us collect more data in less time about an increasingly urgent issue. While that's generally good for anyone on the planet, projects like this can also help more people get interested and involved with science. And of all possible scientific topics, this one needs all the enthusiasm it can get.

"The real benefit [for volunteers] is to participate in a project that's actually answering useful questions about our changing climate," Soul says, "which is one of the most pressing issues that we're facing at the moment."