"Long before it's in the papers"
November 19, 2015

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Fossil forest may shed light on the first big trees

Nov. 19, 2015
Courtesy of Cardiff University
and World Science staff

U.K. re­search­ers have found a fos­sil for­est—thickly packed with pe­cu­liar trees—from an era that gave Earth some of the first big trees, which in turn may have changed the cli­mate dras­tic­ally.

“These fos­sil for­ests shows us what the vegeta­t­ion and land­scape were like on the equa­tor 380 mil­lion years ago, as the first trees were be­gin­ning to ap­pear,” said re­search­er Chris Ber­ry of Car­diff Un­ivers­ity in the U.K.

Reconstructed draw­ing of Sva­lbard fos­sil for­est. (Cred­it: Chris Ber­ry, Car­diff U.)


The fos­sils, with stumps pre­served in place, turned up in Sval­bard, a Nor­we­gian archipela­go in the Arc­tic Ocean. 

By co­in­ci­dence, Sval­bard is al­so where peo­ple main­tain the Sval­bard Seed Vault, a re­pos­i­tory of seeds from around the world to be used in case of ec­o­log­i­cal dis­as­ter. 

“It’s amaz­ing that we’ve un­cov­ered one of the very first for­ests in the very place that is now be­ing used to pre­serve the Earth’s plant di­vers­ity,” said Ber­ry.

But Sval­bard it­self seems to have drifted, as it used to be near the Equa­tor at the time the trees lived, said Ber­ry, who iden­ti­fied the fos­sil for­est and de­scribed it Nov. 19 in a re­port in the jour­nal Ge­ol­o­gy. Today Sval­bard, pop­u­la­tion 2,500, is one of the world’s north­ern­most in­hab­it­ed ar­eas.

The for­ests grew dur­ing a pe­ri­od known as the late De­vo­ni­an, and could shed light on the cause of a plunge in lev­els of car­bon di­ox­ide in the at­mos­phere around that time, Ber­ry and col­leagues say. This change brought levels of the gas to an es­tim­ated one-fif­teenth of what they were be­fore.

Cur­rent the­o­ries sug­gest that dur­ing the De­vo­ni­an—420 mil­lion to 360 mil­lion years ago—there was a huge drop in car­bon di­ox­ide lev­els in the at­mos­phere, thought to be largely caused by a change in vegeta­t­ion from di­min­u­tive plants to the first large for­est trees. Forests pulled car­bon di­ox­ide out of the air through pho­to­syn­the­sis—the pro­cess by which plants cre­ate food and tis­sues—and the forma­t­ion of soils.

Al­though in­i­tially the ap­pear­ance of large trees ab­sorbed more of the sun’s radia­t­ion, even­tu­ally tempe­ratures on Earth al­so dropped dra­mat­ic­ally to lev­els very si­m­i­lar to those ex­pe­ri­enced to­day be­cause of the re­duc­tion in at­mos­pher­ic car­bon, the sci­en­tists ex­plain.

Be­cause of the high tempe­ratures and large amount of rain­fall on the equa­tor, equa­torial for­ests probably con­tri­but­ed most to the draw­down of car­bon di­ox­ide, they added.

The team found that the for­ests in Sval­bard were formed mainly of ly­co­pod trees, bet­ter known for grow­ing mil­lions of years lat­er in coal swamps that even­tu­ally turned in­to coal de­posits, such as those in South Wales. They al­so found that the for­ests were ex­tremely dense, with very small gaps, only around 20 cm or 8 inches, be­tween each of the trees, which probably reached about 4m or yards high.

Ber­ry pre­vi­ously worked with Amer­i­can col­leagues to de­scribe an­oth­er slightly old­er for­est, at Gilboa in up­state New York. The Gilboa for­est was at least 30 degrees south of the equa­tor at that time, and the tree stumps in place be­longed to dif­fer­ent types of plants.

“This demon­strates that there was al­ready geo­graph­i­cal di­vers­ity of for­est plant types and ecol­o­gy just as soon as they had evolved,” Ber­ry said.


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U.K. researchers have found a fossil forest—thickly packed with peculiar trees—from an era that gave Earth some of the first big trees, which in turn may have changed the climate drastically. “These fossil forests shows us what the vegetation and landscape were like on the equator 380 million years ago, as the first trees were beginning to appear,” said researcher Chris Berry of Cardiff University in the U.K. The fossils, with stumps preserved in place, turned up in Svalbard, a Norwegian archipelago in the Arctic Ocean. By coincidence, Svalbard is also where people maintain the Svalbard Seed Vault, a repository of seeds from around the world to be used in case of ecological disaster. “It’s amazing that we’ve uncovered one of the very first forests in the very place that is now being used to preserve the Earth’s plant diversity,” said Berry. But Svalbard itself seems to have drifted, as it used to be near the equator at the time the trees lived, said Berry, who identified the fossil forest and describes it Nov. 19 in a report the journal Geology. The forests grew during a period known as the late Devonian, and could shed light on the cause of a 15-fold reduction in levels of carbon dioxide in the atmosphere around that time, Berry and colleagues say. Current theories suggest that during the Devonian—420 million to 360 million years ago—there was a huge drop in carbon dioxide levels in the atmosphere, thought to be largely caused by a change in vegetation from diminutive plants to the first large forest trees. Forests pulled carbon dioxide out of the air through photosynthesis—the process by which plants create food and tissues—and the formation of soils. Although initially the appearance of large trees absorbed more of the sun’s radiation, eventually temperatures on Earth also dropped dramatically to levels very similar to those experienced today because of the reduction in atmospheric carbon, the scientists explain. Because of the high temperatures and large amount of rainfall on the equator, equatorial forests probably contributed most to the drawdown of carbon dioxide, they added. The team found that the forests in Svalbard were formed mainly of lycopod trees, better known for growing millions of years later in coal swamps that eventually turned into coal deposits, such as those in South Wales. They also found that the forests were extremely dense, with very small gaps, only around 20 cm or 8 inches, between each of the trees, which probably reached about 4m or yards high. Berry previously worked with American colleagues to describe another slightly older forest, at Gilboa in upstate New York. The Gilboa forest was located at least 30° south of the equator at that time, and the tree stumps in place belonged to different types of plants. “This demonstrates that there was already geographical diversity of forest plant types and ecology just as soon as they had evolved,” Berry said. “During the Devonian Period, it is widely believed that there was a huge drop in the level of carbon dioxide in the atmosphere, from 15 times the present amount to something approaching current levels. “The evolution of tree-sized vegetation is the most likely cause of this dramatic drop in carbon dioxide because the plants were absorbing carbon dioxide through photosynthesis to build their tissues, and also through the process of forming soils.” Svalbard is currently one of the world’s northernmost inhabited areas with a population of around 2,500.