Scientists discover hidden ancient forest on treeless island

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No trees have grown on the windswept Falkland Islands in the South Atlantic Ocean for tens of thousands of years — just shrubs and other low-lying vegetation. That’s why a recent arboreal discovery nearly 20 feet (6 meters) beneath the ground caught researchers’ attention.

Dr. Zoë Thomas, a lecturer in physical geography at the UK’s University of Southampton, was doing fieldwork on the island in 2020 when she got word from a friend that tree trunks had been unearthed from a layer of peat at a building site near the capital of Stanley.

“We thought that’s really weird, because one of the things about the Falklands that everyone knows about is that no trees grow,” said Thomas, lead study author of recent research on the Falklands. “It’s very sort of windswept and barren.”

The Falkland Islands are a British-ruled overseas territory over which Great Britain and Argentina fought a brief war in 1982. Britain won the war, but Argentina continues to claim the islands.

Thomas and colleagues went to the site and began “picking up these big chunks of wood.” The tree remains were so pristinely preserved they looked like driftwood, Thomas said. But knowing the history of the Falklands, the researchers knew the remnants couldn’t be modern.

“The idea that they’d found tree trunks and branches made us think how old can this stuff be? We were pretty sure that no trees had grown there in a long time,” she added.

The presence of the tree fossils suggests the island was once home to a temperate rainforest — a dramatically different ecosystem from the islands’ current environment, Thomas and her collaborators reported earlier this month in the journal Antarctic Science. But the story of this hidden forest goes back even further in time than the researchers initially thought.

The tree remains proved too old for radiocarbon dating, which can determine the age of organic matter up to 50,000 years old. The international team of scientists turned to microscopic pollen and spores found in the peat for answers. Fossilized pollen is indicative of a particular span of geologic time, so its presence can help determine the age of a fossil site, said Michael Donovan, paleobotany collections manager at Chicago’s Field Museum. He wasn’t involved in the study.

The researchers transported the wood remains and samples of the peat layers for lab testing at Australia’s University of New South Wales to make use of an electron microscope that could produce highly detailed images of the wood and its cellular makeup.

There, they also analyzed a variety of spores compacted and sealed in the same layers of peat as the wood. Pollen records led them to conclude the tree trunks and branches date to between 15 million and 30 million years old. “The age limits for the study site were estimated based on age-ranges of pollen species from Patagonian rocks and comparisons with similarly aged floras from southern Patagonia and Antarctica,” Donovan said in an email.

Through their analysis, the study authors were also able to identify what species the trees were.

The specimens would have belonged to a rainforest similar to what’s found in modern Patagonia, suggesting that the climate in the Falkland Islands millions of years ago must have been wetter and warmer than it is today.

However, it would have been cooler than tropical rainforests such as the Amazon — but still able to support a rich, diverse ecosystem of plant and animal life, Thomas said.

“A lot of tree species that are growing (in Patagonia) now hadn’t evolved yet, but we found close relatives (in the Falkland Islands samples),” including species of beech and conifer, she said.

“The Falkland Islands are currently covered by grasslands and lack native trees,” Donovan added. “The fossil pollen, spores, and wood presented in this study paint a much different picture of the ancient environment, providing direct evidence of the presence of cool, wet forests.”

Exactly why trees don’t still grow on the Falkland archipelago, also known as the Islas Malvinas, is unclear because they do flourish at the same latitude in South America, according to the study.

Thomas and Donovan both said the strong winds that the islands experience and the acidic peat-rich soil found there could be factors.

Those distinctive traits also highlight why the Falkland Islands are an important location for studying climate change in the Southern Hemisphere, added Thomas, whose original research goal was to understand environmental changes on the archipelago over the last 20,000 years.

Prevailing westerly winds may affect Antarctic ice, atmospheric circulation and precipitation patterns, and the islands are one of only a few landmasses in their path, she added. Understanding how these winds strengthened or weakened in the past, given the islands’ location near Antarctica, could help predict future changes in climate.

However, the islands are unlikely to see a return to a forest landscape anytime soon, Thomas said.

“Current projections suggest the region will get warmer but also drier — leading to concerns about the risk of erosion to the peatlands, which are sensitive to climate change,” she said.