Lessons from the ice age: How climate change reshapes plant life

Global warming has already contributed to an alarming decline in plant species. By some estimates, around 600 plant species have vanished since 1750, which is twice the number of animal species lost in the same period. 

Yet, questions persist: which plant species are most vulnerable to climate change, and how does changing biodiversity influence interactions between plants? 

A research team from the Alfred Wegener Institute (AWI) tackled these issues by analyzing centuries of plant genetic material preserved in lake sediments.

By focusing on the dramatic warming at the end of the last ice age – approximately 15,000 to 11,000 years ago – the experts gained novel insights into how flora reorganized during what they consider the last major mass extinction event prior to today.

The findings, published in the journal Nature Communications, may help us gauge what could lie ahead in our current era of rapid climate change.

Climate clues from ancient plant DNA

“Everyone knows that the woolly mammoth went extinct, but virtually no-one mentions the plants that were lost at the end of the last ice age,” said Ulrike Herzschuh, a scientist at AWI. “Until recently, we lacked suitable methods for investigating the extinction of plant species in detail.”

Traditionally, scientists studied fossil pollen to learn about past vegetation, but pollen cannot reliably reveal extinct species or pinpoint which ones died out.

The AWI team employed advanced methods to scrutinize old DNA fragments deposited in lake sediments taken from Alaska and Siberia. 

“Using cutting-edge methods, we analysed old DNA from sediment cores taken from lakes in Alaska and Siberia, which allowed us to reconstruct the changes in vegetation in these regions,” Herzschuh explained. 

Those cores, containing up to 30,000-year-old plant DNA, were enriched, sequenced, and matched with existing genetic databases in specialized labs.

Plant interactions changed with the climate

The scientists used their data to chart where and when plant species emerged or disappeared across Siberia and Alaska, unlocking details about how plant communities evolved toward the end of the last ice age. 

“We’ve now been able to determine in detail when and where species appeared and disappeared in Alaska and Siberia,” said Herzschuh.

“Our research shows that the composition of plant species changed substantially at the end of the last ice age, and that this was accompanied by fundamental changes in the ecological conditions.”

Crucially, they found a link between temperature shifts and plant-to-plant interactions. During colder periods, plant species often supported one another, while in warmer periods, they primarily competed. 

“In the DNA from the lake sediments, we found e.g. many cushion plants, which most likely supported the expansion of other species by forming sheltered habitats,” Herzschuh noted. 

In the modern Arctic, however, this helpful role might speed the cushion plants’ own decline. 

“Since the warming of the Arctic has already progressed quite far, woody plants can survive even in the high latitudes. The cushion plants could facilitate their spreading, hastening their own extinction in the process,” explained Herzschuh.

The disappearance of entire vegetation types

The end of the last ice age triggered the loss of key types of vegetation, as the researchers confirmed using their new method. For instance, the mammoth steppe – a vast, grassy biome widespread during the ice age – vanished during the Earth’s transition to the current warm phase. 

Identifying which species ceased to exist posed a particular challenge since modern DNA databases only catalog living plants.

“To identify the species that no longer existed, we had to use a trick,” Herzschuh said. They sifted through all DNA fragments in the sediment cores and systematically ruled out those resembling any species still alive. What remained were sequences likely belonging to extinct plants. 

From this analysis, the experts concluded that grasses and shrubs are among those most at risk in a warming climate, while woody plants typically expand under warmer conditions. A surprising discovery was the time lag. 

“That means the full impacts of today’s human activities might not become apparent until the distant future,” Herzschuh added.

Implications for today’s Arctic

The researchers emphasize that their findings offer essential reference data for assessing ongoing Arctic shifts, where the climate is changing more rapidly than almost anywhere else on Earth. 

Their two new studies illustrate how warming influences not only individual species but also their ecological interactions – and how these changes may lead to permanent shifts in biodiversity.

“Our studies show how important it is to understand biodiversity and ecological interactions, also in the long term, in order to better predict the impacts of climate change,” Herzschuh said. “Using the information locked in old DNA from sediments, we can gain the fundamental knowledge needed to do so.”

By establishing extinction rates for ancient plants and examining how temperature-induced stressors remolded their communities, the research provides a valuable lens through which to view future risks. 

The team hopes that comparing past extinctions with current conditions can guide policymakers and conservationists in predicting – and possibly mitigating – the fate of today’s Arctic and global ecosystems, which face many of the same pressures that once toppled the woolly mammoth and its lesser-known plant neighbors.

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