These Bizarre Blue Tree Rings Are Unveiling Details About Cold Summers From A Century Ago
In order to grow properly, trees need an adequate period of warmth during their growing seasons; otherwise, the cell walls of new growth won’t develop correctly and create blue rings that appear when samples of wood are dyed.
These blue rings help scientists look into the past and pinpoint any cold summers that took place. Scientists examined pine trees and juniper shrubs from northern Norway to identify two cold summers in 1902 and 1877. They were possibly caused by eruptions of Mount Pelée on the island of Martinique and Cotopaxi in Ecuador.
“Blue rings look like unfinished growth rings and are associated with cold conditions during the growing season,” said Dr. Agata Buchwal, the lead author of the study from Adam Mickiewicz University in Poland.
“In general, we found more blue rings in trees than in shrubs. Shrubs seem to be more adapted to cooling events than trees, which is probably why shrubs are found further north.”
The researchers sampled cores from 25 Scots pine trees and stem-base disks from 54 common juniper shrubs located on Mount Iškoras in northern Norway.
Then, they stained these samples and photographed them under a microscope so that the growth ring widths could be measured and any blue rings identified.
Only 2.1 percent of the pine trees’ rings and 1.3 percent of the juniper shrubs’ rings were blue. In 1902, blue rings occurred in 96 percent of pine trees and 68 percent of juniper shrubs.
And, in 1877, they occurred in 84 percent of pine trees and 36 percent of juniper shrubs. It appeared that pine trees were more susceptible to forming blue rings than juniper shrubs.
Blue rings can weaken pine trees in boreal regions, increasing their vulnerability to damage and disease. If the blue rings persist over several years, the trees will be unable to recover too well in later years.
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When the researchers compared the blue ring data with local weather records, they found that the summers of 1902 and 1877 had very low temperatures.
The coldest June ever recorded was in 1902, which delayed the growing season. The 1877 cooling event happened in August.
The cold June of 1902 could be linked to the eruption of Mount Pelée the month before. The eruption of Cotopaxi in June 1877 aligns with that year’s cold August as well.
So, it’s possible that cooling after large volcanic eruptions was one of the factors that gave rise to the blue rings.
“We hope to inspire other research groups to look for the blue rings in their material,” said Buchwal.
“It would be great to establish a blue ring network based on trees and shrubs to reconstruct cooling events at the northern treeline over long timescales.”
The study was published in Frontiers in Plant Science.
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