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Interesting Things About Oak Trees

There are about 500 species of oak tree around the world. Just 60 of those are native to North America. When acorns and oaks came up on my random research article list, I wasn’t sure exactly what I would find. It turns out that oak trees are more fascinating than I thought, both scientifically and culturally. If you are a tree nerd who likes to annoy their friends with little bits of random trivia, then this is the article for you.



They were an important food source for Native Americans.


Acorns were a preferred food of Native Americans in pre-contact days, especially in California and the American Southwest. In California alone, three quarters of the population relied on this fruit of the oak tree. Acorns are storable, readily available most of the year, and have a good nutritional content for such a small nut. Some of the live oaks seen in California today were planted by Native Americans centuries ago, which is why they are growing in such random places.


Acorns are only edible if prepared properly.


Acorns contain large amounts of oak tannins that are toxic to humans and other animals, though the toxicity level depends on the species of oak and growing conditions. In order to be edible, the acorns must be soaked and leached in boiling water to remove the bitter tannins. Once this is done, they can be ground into flour and made into anything from bread to cookies to porridge. They can also be roasted and eaten whole like peanuts. Today this food source is not as popular as it was in the past, but you can still find acorn recipes on the internet.


They are used in traditional witchcraft.


Modern witches have all sorts of different uses for the oak. In the past, oak trees were the center of certain Druid rituals and religious idols were constructed from oak wood. Some witches say that acorns placed in windows guard against lightning entering a home. Burning oak wood in the home of a sick person is said to heal illnesses. Legend says that planting an acorn at the dark of the moon will bring you money. Oaks are also used for spells involving protection, luck, and fertility.


Oak worms are a disgusting common pest in California oak trees.


Oak moths are native to coastal California, especially near the San Francisco Bay Area. Though there are hatchings every year, oak worm (oak moth caterpillar) outbreaks occur every 8-10 years and last for about 2 years. During these outbreaks, thousands of oak moth caterpillars can infest an oak grove, leaving it severely defoliated in the process. The yellow-green caterpillars can grow up to an inch long and have a tendency to drop out of trees onto any unsuspecting person standing below. They are also known to get into houses in large numbers and congregate in huge mats on window panes and other surfaces. Though they are harmless to humans and animals, they are gross and annoying. My mother has told me horror stories of these caterpillars covering rooftops and clogging gutters.


Sudden Oak Death is threatening California redwoods.


This fungus-like invasive species from Europe, known as Phytophthora ramorum, was first recognized in the San Francisco Bay Area in the mid-1990s. Its introduction came through imported nursery products and soon spread across California. It first appeared in southwest Oregon in 2001 and continues to spread, though recent droughts have slowed its progress. The infestation has gotten into the tanoak population within the California redwoods and is creating increased fire danger due to the growing fuel load. This, along with climate change and increased fire frequency, could endanger our dwindling redwood population.


Oak tannins have many uses.


Plant tannins have been used as long ago as 5,000 BC in ancient Egypt. Ancient Greeks and Romans were some of the first to use oak tannins to convert animal hides to leather, and the chemical is still used for this purpose today. The tannins are sometimes used in medicinal teas. They are also used in the wine industry to stabilize the color of wines, and tannins in new oak barrels can add flavor to the wines as well. (This is the reason for this article's photo. Those are oak wine barrels, a common use of the wood.)


Oak trees are symbolic in many ways.


Because they are long-lived, oak trees are often associated with wisdom and longevity. They also symbolize nobility and honor. The oak was sacred to the Druids, and the ancient Greeks viewed it as a symbol of Zeus. Certain ancient cultures believed that gods inhabited oak trees and worshiped them for this reason. Today oaks are a common image used in jewelry designs and have appeared in the names of everything from ranches and cities.


Oak wood is used for many purposes.


The wood is rather expensive, both because of its quality and its slow growing nature. Oak wood is sought out for its strength and resistance to most fungus, which makes it a prime candidate for exterior siding, window frames, door fittings, and ship building. Oak wood is also used for hardwood flooring, furniture, and hardware. In California, the wood of some oak trees was once used for farming implements due to its strength and durability. According to an Oregon State University publication, an oak wood post in central Oregon lasted 100 years, which tells you just how durable this wood can be.


Oak galls are actually caused by an insect.


Oak galls, also called oak apples, form as the result of the tiny gall wasp. The wasp lays its eggs on oak leaves and a chemical injected into the leaf causes unusual growth in plant cells, which form a small, round, pearl-like object on the leaf to house the larvae. These wasps are harmless to humans and usually don’t hurt the tree in the long run. However, infestations can be so intense that oak groves can make clicking and rattling noises as new wasps hatch out of the galls.


The acorn woodpecker makes its home among oak trees.


Acorn woodpeckers are unusual in that they live in large groups and have a peculiar habit for storing their primary food source. The flocks gather large numbers of acorns, then store them away in “granary trees,” trees (and sometimes telephone poles and people's houses) that the birds have drilled full of holes to store the nuts. These trees can have over 50,000 holes apiece, and the acorns are packed so tightly that squirrels are unable to take off with the supply. Granary trees are often used by multiple generations of birds. Acorns make up to half of this woodpecker’s diet.


I have old memories of oak trees. When I was a little kid I used to visit my grandmother and help her collect acorns from the live oaks around her house. They were particularly large and colorful acorns that she liked to use in decorations and crafts. As an older child I moved to Florida, where my friends and I used to use the hard green acorns as ammunition or ground their orange hearts into powder if we got bored. Blue jays inhabited these trees and liked to throw acorns down on unsuspecting people walking below, as if they found it funny. These are kind of random stories, but so is this blog. Hope you enjoyed reading this little tidbit of nerd trivia.

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