Portland Landscape Design and Arborist Tree Service

Estimating age, and increment borer ring sample

Historic Catalpa at Beekman House in Jacksonville, Oregon

Copyright M. D. Vaden: 2010

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How is the age of a tree determined without knowing the germination or planting date?

One way is by taking wood samples with an increment tool that extracts a small core.

This page covers just one Catalpa that I was asked about by someone from the Southern Oregon Historical Society. The Catalpa was at the Historic Beekman House property in Jacksonville.

A couple of local tree people suggested removal because it was leaning.

It's true that the trunk has some lean, and roots were damaged once, but the new growth of the past 20 years or so showed vertical growth. Indicating that it was not leaning anymore.

The main bit of information I used to figure out the age was the core sample from the boring tool.

It did not reach half way through entirely, and the center ring positions could not be known for sure anyway. The original center of a trunk does not always remain as the center indefinitely. Some trunks eventually become oval or irregular shaped.

Since the ring sizes from the core did not vary much, I used a formula where every so many inches of trunk would be equal to a certain number of rings. What I came up with, was about 106 years.

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And that sample was taken at 4.5 feet up from the ground, which could be about 5 years worth of growth also, to reach that point. Adding 5 years to the 106 years means roughly 111 years of age.

This project was August, 2007.

That means this hardwood was probably planted on the site around 1896 based on those numbers.

There was one other way to estimate age for this old historic Catalpa. There is a large limb extending toward the power lines, and that limb was cut or stubbed about 15 feet east of the trunk, above the white fence shown in the image.

The end of that stub cut showed close to 94 growth rings that I recall. The SOHS has a document that I gave them in 2007 with the exact numbers, but what I'm writing here is very close.

The tree likely needed 8 years for the main trunk to grow up several feet and initiate that limb in the first place. Then if we allow 1 foot of growth for each year, the limb would have needed 15 years to extend out to where the stub cut was made. Adding 94 years + 15 years + 8 years = 116 years.

In that case, 116 years of age, dating back to 1891 is as far back in time as I can place the age.