Scientists are now using Arctic ice sheets to understand how forests have grown, retreated, and, most importantly, can recover over millenniums. The first-of-its-kind research has also demonstrated how rapid industrialisation has impacted global forests, providing crucial insights into the future management of forests.
Examining microscopic pollen grains and pieces of ash – trapped in the ice – they can, for the first time, study how forest cover changes in line with both human settlement and global warming.
Published in the journal Geophysical Research Letters, a group of scientists have worked with the Desert Research Lab – a global leader in applied environmental research, to understand how ice uncovered in Greenland can reveal critical insights into forests on Canada’s east coast.
It is the first time that the Desert Research Lab’s Ice Core Lab has been used to monitor forest pollen – with past research monitoring different types of materials trapped in Arctic ice.
Through detailed analysis of pollen grain found under a microscope, they recorded details of forest changes over 850 years, covering both the onset of the Little Ice Age around 1400 and the arrival of European settlers and subsequent intensive logging practices around 1650.
“Our results are exciting because pollen that travelled thousands of miles can illuminate changes that happened on a large scale in those forests,” according to Sandra Brugger, the lead researcher from the University of Basel.
According to Ms Brugger, pollen is much larger than other atmospheric particles, resulting in “fewer pollen grains travelling across oceans and (therefore) being preserved in Arctic ice sheets.”
As a result, the researchers developed a new method that made monitoring possible, involving carefully evaporating water from the ice core to collect the minuscule pollen grains.
“We also get a more precise chronology from the ice cores than from most lake sediments because we can date them almost to the year,” Ms Brugger said before adding, “This helps tie the information to, for example, European settlers coming to eastern North America, because we know from historical sources when they arrived and what they did to the landscape.”
Because Greenland is only sparsely covered by vegetation, at the margins of ice sheets and far from forested areas, “we don’t usually think about pollen in Greenland’s ice cores,” according to Dr Nathan Chellman, who helped co-author the study.
“It is pretty incredible to think that North American conifer forests can be told by measuring the few pollen grains that make it through the atmosphere to the ice sheet.”
The ice came from southern Greenland, with Dr Chellman revealing that the pollen was from conifer forests on the North Atlantic coast, “with smaller amounts from tundra vegetation and European forests.”
During the Medieval Warm Period – from 1160 to 1400, 60% of pollen records came from northern forest species, including pine, spruce and fir. After the onset of the Little Ice Age, from 1400, the species made up more than 80% of the pollen records, “demonstrating the expansion of forests as the climate cooled,” according to the researchers.
“Because there is no evidence that the northernmost tree line shifted over this timeframe, the forest spread likely came from changes in forest density, pollen productivity, and a southward expansion into more temperate regions,” they said.
The research also revealed that pollen from the same species halved to 40% as European settlers began to log the forests from 1650 to 1760 – with increased forest fires ruled out due to a decline in charcoal and black carbon in the ice core.
They also cross-referenced findings with historical records showing that white pine forests were harvested along the Miramichi, Saint John, and Ottawa rivers from 1850 onward.
From 1760, the ice reveals that “chemical signatures of fossil fuel pollution began to appear in the ice record,” which the researchers said marked the start of industrialisation in eastern North America.
This was when changes in human activities had a more significant impact on the pollen than climate influences, “suggesting the start of the human-driven ecosystem in the region.”
Conifer forests declined further at the beginning of the 20th century, with continued logging and clearing of forests for farmland throughout eastern Canada. At the same time, pollen records show increased ragweed, a shrub known to proliferate in disturbed landscapes. The pollen record indicates that pine forest recovery started around 1950 when a decline in logging coincided with rural farm abandonment and a shift in climate.
“This clarity of the signal showing pine forest expansion at the beginning of the Little Ice Age, and then this retraction once the Little Ice Age is over, and then human impact coming in — you see this on a large scale,” Brugger said. “I did not expect the story to be so clear in the ice.”
This study follows previous work by Ms Brugger on another ice core from central Greenland, where the pollen record was markedly different from this southern Greenland ice core. “This is because the two locations receive different atmospheric particles,” according to Ms Brugger, who said the central Greenland ice core recorded more changes in Arctic vegetation than distant locales.
The researchers worked to create computer models that could simulate pollen movement through the atmosphere to understand each location and their associated atmospheric circulation patterns.
“This southern ice core tracked the boreal forest,” Ms Brugger said, adding, “You get a completely different signal than with the previous study I did in central Greenland, where we tracked changes in the Arctic.”
“These two ice core sites track very different things, and it’s all confirmed by atmospheric models, which is beautiful.”
The research comes after Wood Central revealed in November that tree-ring research confirmed that the Vikings arrived in the Americas 500 years before Christopher Columbus landed in the New World – with evidence suggesting that they may have brought tree species back to Europe.
Archaeologists have been analysing wood from five Norse sites in western Greenland, concluding that tree species must have been imported from the Americas, “as the species did not exist in Northern Europe until well into the second millennium.”
Historical records suggest that the Vikings occupied Greenland between 985 and 1450 AD and relied on materials like iron and wood to establish farmsteads and villages.
They used the timber for infrastructure projects, shipbuilding, and creating artefacts for which local trees were unsuitable. In the case of driftwood, it is for fuel and domestic purposes.
