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Fossil Trees Reveal the Oldest Known Forest in Asia

The grove of lycopsid trees is 365 million years old and covers 2.7 million square feet

(Deming Wang)
smithsonian.com

Paleontologists are generally thrilled to find pieces of an ancient tree or a few well-preserved fossil leaves, but researchers in China recently hit the mother lode, uncovering an entire fossilized forest covering about 2.7 million square feet. The trees are the oldest found in Asia, providing insights into how the root systems of modern forests developed. The research appears in the journal Current Biology.

Hannah Osborne at Newsweek reports that the forest was discovered in 2016 in the Jianchuan and Yongchuan clay mines near the village of Xinhang, in the east central part of the country. The ancient trees are visible in the walls of the quarry, including the trunks and structures resembling pinecones.

The lycopsid trees date back to the Devonian period 365 million years, making them the oldest known forest discovered in Asia. But this forest was no towering cathedral of trees. Maya Wei-Haas at National Geographic reports that it’s difficult to gauge the height of the lycopsid trees because many of the tops were broken off during fossilization. But researchers estimate that, based on the size of the trunks, the trees maxed out at about 10 feet with most in the five- to six-foot range.

The ancient lycopsids didn’t look like modern trees either. Jan Zalasiewicz, a University of Leicester paleobiologist not involved in the study, writes for The Conversation that the species of tree, part of the new genus Guangdedendron, had no flowers or seeds. The short trees had trunks fringed with leaves and four short drooping branches at the top with bottle-shaped structures on their tips that spread spores. He describes the trees as “[a] little like a green, living version of an art deco streetlamp.”

A modern visitor might not recognize the lycopsid grove as a forest at all. “The large density as well as the small size of the trees could make Xinhang forest very similar to a sugarcane field, although the plants in Xinhang forest are distributed in patches,” lead author Deming Wang of Peking University says in a press release. “It might also be that the Xinhang lycopsid forest was much like the mangroves along the coast, since they occur in a similar environment and play comparable ecologic roles.”

It’s likely the forest was once part of a coastal swamp that periodically flooded. Those floods, it’s believed, buried trees in sediment, allowing them to fossilize.

The most striking part of the trees, at least for those interested in their evolution, are the roots, which are much more advanced than researchers believed they would be during the Devonian period. Wei-Haas reports that the Xinhang trees have stigmarian roots, or branching roots covered in rootlets. These same types of roots allowed trees in the swampy Carboniferous period that followed to grow much taller. Those swamps full of decaying trees eventually formed the coal seams that humans discovered hundreds of millions of years later.

“This is what fired the Industrial Revolution,” Cardiff University paleobotanist Christopher Berry, not involved in the study, tells Wei-Haas. “This is the basis of our present civilization; this little [root] structure, which we see for the first time in this forest.”

These early forests and their roots had other major impacts as well. Zalasiewicz writes that as these early forms of land vegetation proliferated, they stabilized river banks, creating new habitats where early animals including amphibians and millipedes could move onto land. And the tall, rooted trees also began sucking up and locking away so much carbon dioxide that it changed the atmosphere, plunging the world into 50 million years of glaciation.

There are so many trees in the clay pits that Wang says there’s still much more to learn about the stumpy little forest. “The continuous finding of new in-situ tree fossils is fantastic,” he says in the press release. “As an old saying goes: the best one is always the next one.”

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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