– A recent study explored how Western Siberia’s climate has shifted over the past 7,000 years, thanks to dendrochronology. How old are the trees involved?
– The researchers determine the year a growth ring forms, not the tree’s total age. Age is counted by the number of rings. Trees of the same species in a region respond similarly to environmental changes. For instance, warm years produce wider rings, while cold years yield narrower ones. If segments covering 50–100 years are analyzed, the yearly ring variability forms a unique pattern. This has been demonstrated through empirical study.
First, a small drill makes holes in living trees. A 5 mm wooden core is extracted to reveal all the rings. In a living tree, every year’s ring is known. If a seed from 2022 is used, the latest ring is 2022, and the count starts from that year.
When a dead tree stump is found, a saw cut is taken, all rings measured, and the living tree’s pattern is compared with the log. If their lifespans overlap, the numbers align. This cross-dating method extends the chronology beyond the life of a single tree.
There can be hollow rings or false rings—during very cold years, growth may occur only near the top of the stem sample, making lower sections unavailable. Sometimes several rings are missing over the years, which is common in the north. Cross-dating helps reveal these missing rings. If ten trees show a ring while one or two do not, it likely means those rings fell out, especially when the ten trees have narrow rings.
False rings are a second layer formed within a year when growth halts due to deteriorating conditions and resumes later, creating two rings in one calendar year. This is rarer in northern regions.
The dating can extend quite far into the past, especially in Yamal where permafrost preserves wood exceptionally well. The chronology now stretches back 8,768 years, surpassing a recently published paper, and there is confidence that it could reach 9,100 years next year.
But there are questions about whether this would hold in the distant future. Some scientists suspect a decline in tree numbers in Yamal by then.
– How long can dendrochronology reveal climate history beyond Yamal?
– The longest continuous chronology today runs about 12,460 years in Central Europe. Our method has an edge because northern trees are highly climate-sensitive and ring width closely tracks temperature, whereas similar precision is hard to achieve in Europe due to different regional dynamics.
The comparison between living trees and semi-fossil logs raises questions about how their environments affect data accuracy and interpretation.
– A more precise way is to describe them as semi-fossil rather than fossil. While a tree may be decayed, some specimens retain bark, branches, and cones in place.
What are the oldest trees known?
– Annual rings appear in trees dating back roughly 350–250 million years, though exact timing remains uncertain. It is likely that rings began with coniferous trees. A South American study reported some ancient trees more than 50,000 years old.
– In Russia, what are the oldest living examples?
– Among living trees, Yakutia researchers found a 945-year-old larch. They also identified a tree that died more than a millennium ago at the same site, aged 1,216 years at death. In Altai, larch can live to about 1,300 years. The oldest woody plant in the Urals is a juniper with 840 rings. Beyond that, the longest-lived trees are spiny pines, common in the United States, reaching near 5,000 years.
– Besides climate study, what other purposes do these data serve?
– About 80–90% of applications relate to climate, including temperature, precipitation, and drought indices. Dendrochronology is a traditional method for dating events. For example, archaeologists in Salekhard linked a wooden nail in a mummy to a death year of 1282.
Trees offer clues to extreme weather, such as mid-summer frosts that drop temperatures below freezing in July. Frost rings reveal these events with remarkable precision, down to a week, such as identifying a severe cold in 1627 BC on July 10. Volcanic eruptions also influence ring patterns; the Tambora eruption in 1815 and the Huyanaputina eruption in 1600 contributed to Northern Hemisphere cooling and famines, including in Russia during the Time of Troubles, leaving marks in growth rings.
Natural events like avalanches and pest outbreaks also show up in the rings. Reconstructing insect cycles helps understand epidemic frequencies, and fires can create abnormal rings as well.
– How could an explosion have such lasting effects?
— Products reaching the stratosphere from an explosion create sulfate aerosols that reflect sunlight, driving a sudden temperature drop.
– Are there notable discoveries from dendrochronology?
– About a decade ago, a scientist from Nagoya studied Japanese cedar rings and found a huge radiocarbon increase in 775, suggesting a large cosmic-ray flux. This was later linked to a solar flare, a watershed moment for understanding Miyake events. Researchers later confirmed similar radiocarbon spikes in 775 across four dozen global locations. This year, a study co-authored by the same team discussed strong solar flares in 7176 BC and 5259 BC.
– Is dendrochronology used in forensics?
– Two lab members frequently apply it to forensic cases. One notable instance involved identifying the year a branch-laden corpse in Sverdlovsk was cut, helping establish a time of death. More often, it helps verify whether a log felled illegally matches patterns on suspect property, aiding illegal logging prosecutions.
– Could warming in Siberia harm biodiversity?
– The climate is changing, and the tundra is shifting. Some northern species migrate faster than trees, especially insects and birds, altering the ecosystem balance.
– A University of Washington projection suggests life in the tropics could become untenable by 2100 due to extreme heat. The researchers cited by that study may be right; climate extremes are likely to rise, and regional patterns will vary, but the trend is clear.
What current research is underway?
– The immediate goal is to extend the chronology to 7100 BC and reconstruct long-term climatic changes using dendroclimatic analysis, cellular structures, and oxygen-18 isotope data. Another focus is analyzing radiocarbon in annual rings to describe past intense solar flares and overall solar activity. A supplementary direction examines changes at the northern forest boundary over the past century, through dating both living trees and preserved remains.