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Monday - April 26, 2010

From: Oregon City, OR
Region: Northwest
Topic: Propagation
Title: 200 year old white oak with no acorns in Oregon City OR
Answered by: Barbara Medford

QUESTION:

We have a white oak tree in our yard that is about 200 yrs old. We have lived in the house for 30+ years, and have never seen an acorn. We have had it pruned by an arborist, who said it is in good health. Is this possible?

ANSWER:

There are 78 species of the genus Quercus (oak) native to North America but only 3 native to Oregon. Of those three, only one, Quercus garryana (Oregon white oak), is termed a "white oak,"and, according to this USDA Plant Profile, is native to Clackamus County in the northwest corner of Oregon. That doesn't necessarily mean that the Oregon white oak is what you have, but it's good for an example. We are surprised you didn't ask your question of your arborist, who would be more likely to know the answer than we are. We have a theory already formed on why no acorns, but we are first going to nose around, do some research, and see if we can find any other theories.  We learned that this tree can live to 500 years, but its population in Oregon has been decimated by cultural practices, urbanization and introduction of non-native species. 

We need to ask you some questions; we don't want answers back, this is just to help you figure out what is going on.You say you have lived with this tree more than 30 years, and it has never produced acorns? When did you first notice there were no acorns? The oak tree blooms in the Spring (like right now) and is a major allergen, so I'm sure you would notice if it was blooming. It produces acorns in the Fall, as they are the seeds for the tree resulting from the blooms.

From a previous answer to someone who had a lot of acorns being dropped all at once:

From this arcytech.org website Interesting Facts About Oak Trees, we excerpted this information:

"Oak trees can start producing acorns when they are 20 years old, but sometimes can go all the way to 50 years for the first production. By the time the tree is 70 to 80 years old it will produce thousands of acorns.

The oak trees produce acorns once a year during the fall. Acorn production varies year to year and normally alternates. Not even the healthiest and largest oak can accumulate enough food and energy to produce strong crops two years in succession. Real strong acorn productions might happen every four to ten years. In addition, a late spring frost can blight the flowers which prevents acorn development. Droughts and insect ravages can decimate crops.

Acorn production will increase year after year; following a similar pattern as the size of the tree's canopy. Production starts very slowly at around the 25th year, the number of acorns produced then accelerates, and when the tree reaches about 100 years of age, it starts slowing down until it reaches a yearly production of about 2,200 acorns per year."

So, to get back to my theory, which I found nothing to disprove. We once had a  Quercus stellata (post oak), also a white oak, that our arborist told us was about 250 years old. We lived with that oak 38 years and don't remember ever seeing an acorn from it, either. We had a younger live oak that we had planted when we moved into that property, and boy, did it have acorns! It had the seasonal fluctuations mentioned above, and some years when you walked across the area beneath it, it crunched with acorns. We had happy squirrels, but to us it was a nuisance. We had other post oaks on the property, not that old, but some of them had acorns, and some didn't. My theory? Even oaks get old. 100-year old women don't have babies any more, do they? A tree that large and that old has enough to do just staying alive. As mentioned above, it takes an enormous amount of energy to produce acorns. We think your tree has just retired.

Pictures of Quercus garryana (Oregon white oak)  from Google. 

 

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