From The University of Connecticut: “Palms at the Poles- Fossil Plants Reveal Lush Southern Hemisphere Forests in Ancient Hothouse Climate”

From The University of Connecticut

May 31, 2022
Elaina Hancock

Ancient plants provide clues about life on earth in a warmer and wetter climate.

Arid today, Australia was once covered by lush forests, according to new research (Adobe Stock).

For decades, paleobotanist David Greenwood has collected fossil plants from Australia – some so well preserved it’s hard to believe they’re millions of years old. These fossils hold details about the ancient world in which they thrived, and Greenwood and a team of researchers including climate modeler and research David Hutchinson, from the University of New South Wales, and UConn Department of Geosciences paleobotanist Tammo Reichgelt, have begun the process of piecing together the evidence to see what more they could learn from the collection. Their findings are published in Paleoceanography & Paleoclimatology.

The fossils date back 55 to 40 million years ago, during the Eocene epoch. At that time, the world was much warmer and wetter, and these hothouse conditions meant there were palms at the North [Global and Planetary Change] and South Pole [Nature] and predominantly arid landmasses like Australia were lush and green. Reichgelt and co-authors looked for evidence of differences in precipitation and plant productivity between then and now.

Since different plants thrive under specific conditions, plant fossils can indicate what kinds of environments those plants lived in.

By focusing on the morphology and taxonomic features of 12 different floras, the researchers developed a more detailed view of what the climate and productivity was like in the ancient hothouse world of the Eocene epoch.

Reichgelt explains the morphological method relies on the fact that the leaves of angiosperms — flowering plants — in general have a strategy for responding to climate.

“For example, if a plant has large leaves and it is left out in the sun and doesn’t get enough water, it starts to shrivel up and die because of excess evaporation,” Reichgelt says. “Plants with large leaves also lose heat to its surroundings. Finding a large fossil leaf therefore means that most likely this plant was not growing in an environment that was too dry or too cold for excess evaporation or sensible heat loss to happen. These and other morphological features can be linked to the environment that we can quantify. We can compare fossils to modern floras around the world and find the closest analogy.”

The second approach was taxonomic. “If you travel up a mountain, the taxonomic composition of the flora changes. Low on the mountain, there may be a deciduous forest that is dominated by maples and beeches and as you go further up the mountain, you see more spruce and fir forest,” says Reichgelt. “Finding fossils of beech and maple therefore likely means a warmer climate then if we find fossils of spruce and fir.” Such climatic preferences of plant groups can be used to quantitatively reconstruct the ancient climate in which a group of plants in a fossil assemblage was growing.

The results show that the Eocene climate would have been very different to Australia’s modern climate. To sustain a lush green landscape, the continent required a steady supply of precipitation. Warmth means more evaporation, and more rainfall was available to move into Australia’s continental interior. Higher levels of carbon dioxide in the atmosphere at the time, 1500 to 2000 parts per million, also contributed to the lushness via a process called carbon fertilization. Reichgelt explains that with the sheer abundance of CO2, plants were basically stuffing their faces.

“Southern Australia seems to have been largely forested, with primary productivity similar to seasonal forests, not unlike those here in New England today,” Reichgelt says. “In the Northern Hemisphere summer today, there is a big change in the carbon cycle, because lots of carbon dioxide gets drawn down due to primary productivity in the enormous expanse of forests that exists in a large belt around 40 to 60 degrees north. In the Southern Hemisphere, no such landmass exists at those same latitudes today. But Australia during the Eocene occupied 40 degrees to 60 degrees south. And as a result, there would be a highly productive large landmass during the Southern Hemisphere summer, drawing down carbon, more so than what Australia is doing today since it is largely arid.”

Hutchinson says the geological evidence suggests the climate is highly sensitive to CO2 and that this effect may be larger than what our climate models predict, “The data also suggests that polar amplification of warming was very strong, and our climate models also tend to under-represent this effect. So, if we can improve our models of the high-CO2 Eocene world, we might improve our predictions of the future.”

See the full article here.

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The University of Connecticut is a public land-grant research university in Storrs, Connecticut. It was founded in 1881.

The primary 4,400-acre (17.8 km2) campus is in Storrs, Connecticut, approximately a half hour’s drive from Hartford and 90 minutes from Boston. It is a flagship university that is ranked as the best public national university in New England and is tied for 23rd in “top public schools” and tied for 63rd best national university in the 2021 U.S. News & World Report rankings. University of Connecticut has been ranked by Money Magazine and Princeton Review top 18th in value. The university is classified among “R1: Doctoral Universities – Very high research activity”. The university has been recognized as a “Public Ivy”, defined as a select group of publicly funded universities considered to provide a quality of education comparable to those of the Ivy League.

University of Connecticut is one of the founding institutions of the Hartford, Connecticut/Springfield, Massachusetts regional economic and cultural partnership alliance known as “New England’s Knowledge Corridor”. University of Connecticut was the second U.S. university invited into Universitas 21, an elite international network of 24 research-intensive universities, who work together to foster global citizenship. University of Connecticut is accredited by the New England Association of Schools and Colleges (US). University of Connecticut was founded in 1881 as the Storrs Agricultural School, named after two brothers who donated the land for the school. In 1893, the school became a land grant college. In 1939, the name was changed to the University of Connecticut. Over the next decade, social work, nursing and graduate programs were established, while the schools of law and pharmacy were also absorbed into the university. During the 1960s, University of Connecticut Health was established for new medical and dental schools. John Dempsey Hospital opened in Farmington in 1975.

Competing in the Big East Conference as the Huskies, University of Connecticut has been particularly successful in their men’s and women’s basketball programs. The Huskies have won 21 NCAA championships. The University of Connecticut Huskies are the most successful women’s basketball program in the nation, having won a record 11 NCAA Division I National Championships (tied with the UCLA Bruins men’s basketball team) and a women’s record four in a row (2013–2016), plus over 40 conference regular season and tournament championships. University of Connecticut also owns the two longest winning streaks of any gender in college basketball history.