The fossil forests, with tree stumps preserved in place, were found in Svalbard, a Norwegian archipelago situated in the Arctic Ocean. They were identified and described by Dr Chris Berry of Cardiff University’s School of Earth and Ocean Science.
Prof John Marshall, of Southampton University, has accurately dated the forests to 380 million years.
The forests grew near the equator during the late Devonian period, and could provide an insight into the cause of a 15-fold reduction in levels of carbon dioxide (CO2) in the atmosphere around that time.
Current theories suggest that during the Devonian period (420-360 million years ago) there was a huge drop in the level of CO2 in the atmosphere, thought to be largely caused by a change in vegetation from diminutive plants to the first large forest trees.
Forests pulled CO2 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 CO2.
Because of the high temperatures and large amount of rainfall on the equator, it is likely that equatorial forests contributed most to the drawdown of CO2. Svalbard was located on the equator around this time, before the tectonic plate drifted north by around 80° to its current position in the Arctic Ocean.
“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 on the Earth,” said Dr Berry.
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 – around 20cm – between each of the trees, which probably reached about 4m high.
Dr Berry had 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,” Dr Berry continued.
“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 most northernmost inhabited areas in the world with a population of around 2,500.
Svalbard now plays host to the ‘Global Seed Vault’ – a secure, underground frozen seed bank in which a large variety of plant seeds are preserved. The vault functions to provide a safety net against a loss of diversity in a global crisis.
“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,” continued Dr Berry.
The new findings have been published today in the journal Geology.
“It’s been suggested before and I think it’s a very reasonable hypothesis, that wild species of pumpkin and squash weren’t used for food early in the domestication process,” said Logan Kistler, NERC Independent Research Fellow, University of Warwick, U.K. and recent Penn State postdoctoral fellow. “Rather, they might have been useful for a variety of other purposes like the bottle gourd, as containers, tools, fishnet floats, etc. At some point, as a symbiotic relationship developed, palatability evolved, but the details of that process aren’t known at the present.”
Researchers believe that initially humans did not eat wild pumpkin and squash — members of the cucurbita family — because the wild fruit is not only bitter but also toxic to humans and smaller animals. However, clear evidence exists that very large animals — megafauna — that lived 12,000 years ago did eat these fruit.
“Lee Newsom (associate professor of anthropology, Penn State and study co-author) has recovered many wild gourd/squash seeds from ancient Mastodon dung, suggesting that large herbivores may have been an important feature in the natural history of these wild plants,” said Kistler.
The researchers looked at varieties of modern domestic cucurbits, modern wild cucurbits and archaeological specimens. They believe that changes in distribution of the wild plants are directly related to the disappearance of the large animals.
“We performed an ancient DNA study of cucurbita including modern wild plants, domesticated plants and archaeological samples from multiple locations,” said George Perry, assistant professor of anthropology and biology. “The results suggest, or confirm, that some lineages domesticated by humans are now extinct in the wild.”
Without elephant-sized animals to distribute seeds, wild plants will grow only where the fruit drops — as far as the pumpkin rolls. At the same time, the disappearance of megafauna altered the landscape from one of a patchwork of environments to something more uniform. Cucurbita are weedy plants that liked the disturbed landscape created by the megafauna, but faired less well in the new landscape of the Holocene.
The researchers also looked at bitter taste receptors in animals and found that smaller animals with more diverse dietary patterns posses many more bitter taste receptors than large animals that ete only a few things.
“We compared bitter taste receptor genes in about 40 living mammals and found that body sizes and dietary breadth were important,” said Perry. “The greater the size, the fewer receptors. The greater the dietary depth, the more receptors.”
If humans initially used cucurbita for nonfood applications, they somehow eventually managed to find those plants that mutated and lost their toxicity. According to Kistler, cucurbita may have been domesticated at least six different times in six different places.
“There is a huge amount of diversity in some of the domestic species and between them as well,” said Kistler. “Cucurbita pepo is probably the most variable, with jack-o-lantern pumpkins, acorn squash, zucchinis and others. Cucurbita moschata contains the butternut squashes and the kind of pumpkin that goes into the cans that a lot of folks will be baking into pies in a few weeks.”
Today, we sit down and talk with Professor Ian Haynes of Newcastle University.
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