Learning from Tree Rings

Geoheritage Highlight!

What can a tree reveal about the heritage of the Earth? Every year, a tree forms a new growth ring. These rings can vary in size according to the weather during the years they formed. If you look at the rings in a modern tree that has been cut, you can see a record of changing weather during the past few decades. The fossil stumps at Florissant reveal what kind of climate existed here during the Eocene 34 million years ago, and how that climate varied between the seasons.

 

Within rings of humble stone lies the shadow of the past trapped in time!

NPS/SIP: Mariah Slovacek

Tree rings provide valuable information about the past environment and climate after they become petrified into stone. You will notice that the rings are still clearly visible in the photo below even after 34 million years.

 

A close up of the fossilized tree rings in one of the petrified stumps.

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Rings are formed during a tree's different growing seasons, and provide clues to the age of the tree, climatic conditions, fire, diseases, and more. Studies of these tree rings show that redwood trees at Florissant had more favorable growing conditions than the coastal redwoods of California today.

 

Fossil redwood foliage and cones compared to those of the modern redwood. Even after 34 million years they look very similar. (FLFO 6040)

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How do we know the stumps are from Redwoods?

Cone and leaf fossils of Sequoia affinis (ancient redwood), though smaller, are most similar to its descendant, Sequoia sempervirens (modern coastal redwood).

 

Microscope cross-sections of fossil redwood (left) and modern coastal redwood (right) demonstrating how they look nearly the same. The black brackets denote a single growth ring.

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The cellular detail preserved by permineralization reveals similarities in the wood of the two species as well. It is the combination of all these factors that has led scientists to describe the fossil trees as ancestors of the modern redwoods.

 

An illustration showing how the Big Stump might have once appeared when it was alive, towering over the ponderosa pines that grow around it today.

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How large and how old were the trees?

Thirty-four million years ago, huge redwood trees grew here in a warmer climate along the wet bottom of a stream valley. The trees may have been more than 230 feet (70 meters) tall and 500 to 1,000 years old when they were buried in volcanic mudflows.