World’s Oldest Forest Reveals Modern Trees Emerged Earlier Than Thought

(CN) – A research team of faculty from Binghamton University in New York revealed surprising evidence Thursday that the transition to the everyday forests we know today began much earlier than previously thought.

This collection of figures shows the fossilized root system of Archaeopteris, the earliest known plants to have formed leaves, from the Devonian period some 385 million years ago. (Stein et al / Current Biology)

Researchers have uncovered an extensive root system while sifting through fossil soils in the Catskill region near Cairo, New York. The roots belonged to 385-million-year old trees that existed during the Devonian Period, an interval of the Paleozoic era. These incredibly well-preserved root systems show evidence of the presence of trees with leaves and wood at the peak of their growth – a fascinating feat considering both features are common in modern seed plants, which did not exist until roughly 10 million years later.

The findings, which will be published this week in the journal Current Biology, is the first piece of evidence discovered to hold evidence that the transition toward modern forests began earlier than previously thought.

“The Devonian Period represents a time in which the first forest appeared on planet Earth,” said lead author William Stein, emeritus professor of biological sciences at Binghamton University. “The effects were of first order magnitude, in terms of changes in ecosystems, what happens on Earth’s surface and oceans, CO2 concentration in the atmosphere, and global climate. So many dramatic changes occurred at that time as a result of those original forests that basically, the world has never been the same since.”

For years, Stein and his team have been studying this underground phenomenon in the Catskills. In 2012, they described what they called “footprint evidence” of the Gilboa Fossil Forest, known for many years to be Earth’s oldest forest – until now. The team’s remarkable discovery in Cairo, a mere 40-minute drive from the original site, presents scientists with an even older forest dramatically different in composition.

The newly discovered Cairo site presents three unique root systems, which Stein and his team hypothesize is similar to why trees of today exhibit the same pattern: the forests of the Devonian Period must have been heterogeneous, meaning different types of trees will occupy different places depending on the local climate conditions.

The first rooting system Stein and his team identified is what they believe belonged to a palm-tree like tree called Eospermatopteris. This plant was first discovered at the Gilboa Fossil Forest site and had rudimentary roots with a relatively limited range. Because of this, the tree most likely only lived a year or two before dying and their roots were replaced by other trees that would then occupy the space.

In life, they grew up to 26 feet tall with slender trunks topped with forked branches that spread out like fingers. Similar to weeds, Eospermatopteris is thought to have occupied many different environments, which explains its presence at both sites.

Aerial view of a fossil of Archaeopteris, a 385-million-year-old tree with surprisingly modern-looking roots. (Image credit: William Stein and Christopher Berry)

The second system of roots Stein and the team discovered was from a tree known as Archaeopteris, which actually shares several similarities with modern seed plants. This tree behaved more closely to ferns in terms of reproduction, releasing spores into the air rather than forming and spreading seeds. It did, however, exhibit early hints at what would one day become seed plants.

Archaeopteris are the earliest plants known to have formed leaves, and resembled large, woody plants formed from secondary tissues. Thanks to new evidence found at the Cairo site, this tree was discovered to have a surprisingly modern underground system. This allowed for the continuous expansion of roots, able to accommodate continuous growth of a long-lived larger type of tree, which presents the probability that this tree could potentially dominate the local forest ecosystem.

“Archaeopteris seems to reveal the beginning of the future of what forests will ultimately become,” said Stein. “Based on what we know from the body fossil evidence of Archaeopteris prior to this, and now from the rooting evidence that we’ve added at Cairo, these plants are very modern compared to other Devonian plants. Although still dramatically different than modern trees, Archaeopteris nevertheless seems to point the way toward the future of forests.”

Stein and his team were also pleasantly surprised to find a third root system within the fossilized soil at the Cairo site that belonged to an elusive tree, thought to only have existed during the Carboniferous Period and beyond: “scale trees” belonging to the class Lycopsida.

“What we have at Cairo is a rooting structure that appears identical to great trees of the Carboniferous coal swamps with fascinating elongate roots. But no one has yet found body fossil evidence of this group this early in the Devonian,” Stein said. “Our findings are perhaps suggestive that these plants were already in the forest, but perhaps in a different environment and earlier than generally believed. Yet we only have a footprint, and we await additional fossil evidence for confirmation.”

Looking to the future, Stein and his team are eager to continue investigating the Catskills and compare their findings with other fossil forests from around the world.

“It seems to me, worldwide, many of these kinds of environments are preserved in fossil soils. And I’d like to know what happened historically, not just in the Catskills, but everywhere,” said Stein. “Understanding evolutionary and ecological history – that’s what I find most satisfying.”

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