10 Fascinating Facts About Oak Trees for OAKtober

October marks Oak Awareness Month, affectionately known as OAKtober, in Illinois. It’s a special time to appreciate oak trees and the vital role they play in supporting wildlife and enriching our lives. To honor OAKtober, we’re sharing 10 fascinating facts about our native oak trees.

1

There are about 500 species of oaks in the world.
Around 90 species grow in the United States.

Map Credit - Reddit user: Brennejm; Data: US Tree Atlas

Some oak species commonly found in our area include:

quercus-alba

White Oak

Quercus alba

Bur Oak

Quercus macrocarpa

Swamp White Oak

Quercus bicolor

Chinquapin Oak

Quercus muhlenbergii

Black Oak

Quercus velutina

Pin Oak

Quercus palustris

Red Oak

Quercus rubra

Check out this field guide by the Field Museum to identify local oak trees!

2

Oak trees are part of our natural heritage in Illinois.

Oak trees have been present in Illinois for the past 10,000 years, around the time the glaciers receded. Playing a critical role in our local ecosystem for thousands of years, oak trees are an important piece of our nature heritage. Unfortunately, much of the original oak ecosystems have been lost.

Compared to pre-European settlement times, only 17% of oak ecosystems remain in our region.

3

Oak trees are long-lived trees.

Oak trees are mature at 75 years and have an average lifespan of 150-250 years. However, the oldest oak trees are over 1,000 years old!

This local oak tree in West Chicago was likely around during the signing of the Declaration of Independence. It makes you wonder what kind of scenes this oak has observed during its long life.

4

Want to start identifying different oak species? First start with learning the two main groups of oak trees: white oaks and red oaks.

White Oak Group

  • Have rounded lobes
  • Produce acorns every year
  • White oak species include white oak, bur oak, and chinquapin oak
bur-oak-rounded-lobes
Bur oak leaves with rounded lobes.

Red Oak Group

  • Have pointed lobes
  • Acorns take two years to develop
  • Red oak species include red oak, black oak, and pin oak
quercus-palustris-pointed-lobes
Pin oak leaves with pointed lobes.
5

Did you know…the oak leaf shape we know and love is not representative of the whole oak genus?

In fact, most oaks in the world do not have lobed leaves. For instance, lobing is rare among the 160 oak species in Mexico. Instead, the leaves have scalloped or spiked margins.

Oak Leaves with lobes

White oak leaves
White oak leaves with lobes.

Oak leaves without lobes

Quercus-virginiana-southern-live-oak
Southern live oak leaves without lobes.
6

Oak trees are ecosystem heroes.

Oaks have an essential role in the ecosystem, providing food and habitat for many animals. No other genus of plants comes close to supporting the number of species that oaks do! Because of their foundational role in local food webs, oak trees are called keystone species.

Oak Leaves provide food and shelter for wildlife

orangestriped-oakworm

Oak leaves are food for hundreds of species of caterpillars. For example, Doug Tallamy shares, “Over 900 species of Lepidoptera—and most of them are moths—use oaks and there’s no other genus that comes close to that.”

Kinglet

Most songbirds in North American are insectivores and especially depend on insects during their nesting period. Because oak trees support more species of caterpillars than any other plant, planting an oak tree is one of the best things you can do to help our local insectivorous birds.

Some caterpillar species overwinter on oak trees. These caterpillars are a critical food source for birds that overwinter in our area, such as kinglets, nuthatches, and chickadees.

Luna moth

Many critters use oak leaf litter for food or shelter as they overwinter. This includes moths, butterflies, katydids, earthworms, beetles, snails, slugs, centipedes, and many tiny organisms. This fall, leave the leaves where they fall in your yard (or collect them and place them in an unobtrusive place like a flowerbed) to help wildlife.

Acorns are the perfect nutrient package

squirrel-acorn-1

Many animals eat acorns for nourishment. Acorns are the perfect nutrient package, containing large amounts of protein, carbs, and fats as well as key minerals, so its no wonder many wildlife depend on them.

blue-jay

A few animals that eat acorns include…

  • Birds like blue jays, wild turkeys, and wood ducks
  • Mammals like squirrels, chipmunks, rabbits, deer, opossums, racoons, and voles
  • Acorn weevils, who spend their larval phase inside an acorn – and become a protein boost for acorn predators!
7

2023 is a mast year for acorns in the Chicago area.

You might notice an abundance of acorns this year—that’s because it’s a mast year for oak trees in the Chicago area. A “mast seeding event,” in which a species of oaks coordinate a high production of acorns, happens every few years. It’s still not fully understood how or why oaks have mast years.

Since acorn-eaters can’t always depend on a surplus of food, irregular acorn cycles help keep wildlife populations in balance. This year, however, the squirrels have an all-you-can-eat buffet of scrumptious acorns. 

The squirrels are having a BLAST.

8

Oak trees benefit people too!

Besides the many ways oak trees support local wildlife, oaks directly benefit us too.

Oaks improve our quality of life in a variety of ways, including:

  • Cleaning air and water
  • Stabilizing the soil
  • Locking up carbon, combating climate change
  • Infiltrating water, helping to reduce flooding
  • Providing shade, reducing electricity bills in the summer if an oak tree shades your home
9

Unfortunately, oak trees in Illinois are under stress.

There is concern that there are not enough young oak trees to replace the old oaks. A few reasons why our native oak trees are at risk include:

  • Removal and development of oak ecosystems
  • Competition from invasive plants
  • Diseases, such as oak wilt, root rot, and oak anthracnose
  • Herbicide drift
10

Celebrate OAKtober! Plant an oak tree.

Planting an oak tree at home is a fantastic way to celebrate OAKtober and support our local oak populations. In fact, the potential for enhancing the ecosystem through native plantings on residential properties is immense. That’s exactly what our Conservation@Home program is all about! So, let’s embrace the spirit of OAKtober by nurturing oak trees close to home, enriching our environment, and protecting our natural heritage for generations to come.

Find a nursery that sells native oak trees, shop seasonal native tree sales, or plant an acorn. Choosing a smaller tree will ensure it grows up into a healthy, mature oak. Large potted trees tend to be root bound and will spend their energy recovering instead of growing. Know that some oak species prefer different soil conditions. For example, pin oaks prefer acidic and moist soil.

Get Conservation@Home Certified!

If you’ve planted native trees, grasses, and flowers at home, your garden may be eligible for Conservation@Home certification!

Conservation@Home is a program for homeowners who are helping local nature by removing invasives, gardening with native plants, creating wildlife habitat, conserving water, and more. Homeowners who make these earth-friendly choices are certified as a Conservation@Home property and rewarded with a Conservation@Home sign to post in their yard.

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