At the start of the 20th century, northern elephant seals were on the brink of being wiped out by hunting. ‘Genetic analyses suggest that the population was likely reduced to fewer than 25 animals at that time,’ explains Professor Dr Joseph Hoffman, lead author of the study and head of the Evolutionary Population Genetics group at Bielefeld University. Such drastic population declines can squeeze out a species’ genetic diversity, increasing the risk of inbreeding and threatening its survival. The population of northern elephant seals has since recovered to around 225,000 individuals. The study published in the journal ‘Nature Ecology and Evolution’ examines how this near-extinction event impacted the species’ genetic diversity and health.

Adaptability at risk

For their analyses, the researchers combined genetic data, health records, modelling of population sizes and genetic simulations. Their findings suggest that the severe population decline led to the loss of many beneficial and harmful genes from the northern elephant seal’s gene pool. This pattern was not observed in the closely related southern elephant seal, which did not experience such a drastic decline.

‘The highly reduced genetic diversity, including the loss of beneficial gene copies, may impair the ability of northern elephant seals to cope with future environmental changes, including those caused by anthropogenic climate change, changes to the species’ habitat, or even natural threats such as disease outbreaks,’ warns Professor Dr Kanchon K. Dasmahapatra from the University of York, UK, who is the senior author of the study.

Surprising results on inbreeding

All individuals of a species carry some harmful mutations, though their effects are usually hidden. However, inbred individuals may face health issues as these mutations become exposed. ‘We looked at several key health traits in these seals, including body weight, blubber thickness and disease susceptibility. To our surprise, we found no signs of health problems related to inbreeding,’ Joseph Hoffman says. ‘We believe the severe population decline may have eliminated many harmful mutations.’

Significance for species conservation

‘Our study illustrates how a species’ unique population history shapes its genetic diversity,’ says Dasmahapatra. The findings offer important insights for species conservation and ecosystem management. Hoffman adds: ‘Our research underscores the importance of understanding a species’ history when planning conservation strategies. Each species responds differently to threats, so individualized approaches are essential.’

A team of researchers led by University of Maryland Atmospheric and Oceanic Science Professor Ning Zeng analyzed a 3,775-year-old log and the soil it was excavated from. Their analysis, published on September 27, 2024, revealed that the log had lost less than 5% carbon dioxide from its original state thanks to the low-permeability clay soil that covered it.

“The wood is nice and solid — you could probably make a piece of furniture out of it,” Zeng noted.

Understanding the unique environmental factors that kept that ancient log in mint condition could help researchers perfect an emerging climate solution known as “wood vaulting,” which involves taking wood that is not commercially viable — such as trees destroyed by disease or wildfires, old furniture or unused construction materials — and burying it to stop its decomposition.

Trees naturally sequester carbon dioxide — a potent planet-warming gas — for as long as they live, making tree-planting projects a popular method of mitigating climate change. But on the flip side, when trees die and decompose, that greenhouse gas is released back into the atmosphere, contributing to global warming.

“People tend to think, ‘Who doesn’t know how to dig a hole and bury some wood?'” Zeng said. “But think about how many wooden coffins were buried in human history. How many of them survived? For a timescale of hundreds or thousands of years, we need the right conditions.”

In 2013, while conducting a wood vaulting pilot project in Quebec, Canada, Zeng discovered the 3,775-year-old log that became the focus of the Science study — a chance encounter that for Zeng felt “kind of miraculous.” While digging a trench to bury fresh wood, Zeng and other researchers spotted the log about 6.5 feet below the surface.

“When the excavator pulled a log out of the ground and threw it over to us, the three ecologists that I had invited from McGill University immediately identified it as Eastern red cedar,” Zeng recalled. “You could tell how well it was preserved. I remember standing there thinking, ‘Wow, here’s the evidence that we need!'”

While past studies have analyzed old samples of preserved wood, they tended to overlook the surrounding soil conditions, according to Zeng.

“There is a lot of geological and archeological evidence of preserved wood from hundreds to millions of years ago, but the focus of those studies was not ‘How we can engineer a wood vault to preserve that wood?'” Zeng said. “And the problem with designing a new experiment is that we can’t wait 100 years for the results.”

Shortly after the Quebec dig, UMD’s collaborators at MAPAQ, a government ministry in Montreal, conducted carbon dating to determine the log’s age. Then, in 2021, Distinguished University Professor Liangbing Hu in UMD’s Department of Materials Science and Engineering helped Zeng analyze the 3,775-year-old sample’s microscopic structure, chemical composition, mechanical strength and density. They then compared those results to that of a freshly cut Eastern red cedar log, which revealed that the older sample had lost very little carbon dioxide.

The type of soil covering the log was the key reason for its remarkable preservation. The clay soil in that part of Quebec had an especially low permeability, meaning that it prevented or drastically slowed oxygen from reaching the log while also keeping out fungi and insects, the decomposers typically found in soil.

Because clay soil is common, wood vaulting could become a viable and low-cost option in many parts of the world. As a climate solution, Zeng noted that wood vaulting is best paired with other tactics to slow global warming, including reducing greenhouse gas emissions.

As he and his colleagues continue to optimize wood vaulting, he looks forward to putting what they’ve learned into practice to help curb climate change.

“It’s quite an exciting discovery,” Zeng said of this latest study. “The urgency of climate change has become such a prominent issue, so there was even more motivation to get this analysis going.”