Tree Rings
Tree rings are climate archives.
This spruce is approximately 61 years old. A spruce tree the same age, or older, growing near Old Crow might have a trunk 10 cm (4 inches) wide and be less than a metre (3 feet) tall. Where the growing season is extremely short, cold and dry, trees put most of their limited resources into the leaves that feed them and the roots that store their food. Very little new wood is added to the trunk each year.
Tree rings in a young spruce.
New wood creates rings in tree trunks that are a living record of the local climate. In the spring, when moisture is plentiful, trees produce large cells that are generally lighter in colour. The smaller cells that grow in the late summer are darker. The number of rings tells you the tree's age. Variation in the rings year to year is due to changing environmental conditions. Wide rings indicate good growing conditions. Narrow rings indicate a harsh climate.
125,000-year-old tree rings tell us Beringia was warm.
The rings of 125,000 year-old spruce tree stumps found buried in the permafrost near Fairbanks, Alaska, are amazingly similar to the rings found in spruce in the same area today. This tells us that the climate of central Eastern Beringia at that time was similar to, or even warmer than, today's climate.
Left: Spruce tree trunk cut from a log preserved in permafrost in the Eva Forest
Bed near Fairbanks, Alaska. It grew approximately 125,000 years ago. Photo:
D. H. Ball, Arizona State University
Right: Cross section of a white spruce tree that was cut in 1990 near Fairbanks,
Alaska at the same elevation as the 125,000-year-old tree. Note how similar
the trunk and ring sizes are to those of the older tree. Photo:
D. H. Ball, Arizona State University
If we didn't have seasons, would there be tree rings?