The blue rings found on the stems of woody plants represent years in which the cells did not lignify properly because of very cold summers.
When the weather is cold, even trees struggle to grow. New research, carried out by Adam Mickiewicz University in Poland, has concluded that if they do not have a certain number of warm days in their growing seasons, the cell walls of these plants do not lignify properly, which causes them to appear. blue rings.
Since trees live for hundreds of years, identifying these rings allows scientists to identify the cooler summers of the past. That’s exactly what the Polish university team did, looking at pine and juniper bushes in northern Norway.
According to , experts identified two extremely cold summers in 1902 and 1877possibly caused by the eruptions of Mount Pelée, on the island of Martinique, and Cotopaxi, in Ecuador.
Detailed analysis of the samples allowed us to discover that the cells that have not lignified properly were found at the end of growth rings. Blue rings were most frequent in the 1902 samples – 96% of pine and 68% of juniper shrubs – followed by 1877 – 84% of pine and 36% of juniper shrubs.
Os pines appear to be more vulnerable to blue ring formation than shrubs, which could mean they are more sensitive to cool summers.
“Blue rings have the potential to weaken the tree, making it more susceptible to mechanical damage or disease,” explained Pawel Matulewski from Adam Mickiewicz University. “If this phenomenon persists for several years, it could prevent plant recovery in the following years.”
Other studies have already linked blue rings to global climate events, such as cooling after large volcanic eruptions.
The cold June of 1902 may be related to the eruption of Mount Pelée, which took place in May. The eruption of Cotopaxi, at the end of June, could be the reason that explains the cold in August 1877, even though there is no recorded evidence of cooling in northern Norway after this eruption.
This suggests that, in this case, the blue rings may have another cause behind it, which has not yet been identified.
The findings were published in Frontiers in Plant Science.
