Oak and Prairie Habitats

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Meet the Oregon White oak

Oak and prairie ecosystems support an abundance of wildlife.

Oregon white oak, Quercus garryana, is associated with a range of habitat types.

From low-lying, wet prairie to upland woodland, these unique ecosystems are used by roughly 200 species of birds, mammals, amphibians, and reptiles – some of which rely solely on Oregon white oak to survive.

Wildlife make use of acorns for food, tree cavities for nesting, and prefer the lack of shrubs and sparse tree density associated with prairies and oak savannas.

Once common throughout the region, these important ecosystems are increasingly rare today.

Meet the mighty Oregon white oak:

It's the only oak tree native to Washington County.

Mature Oregon white oaks can become enormous trees, ranging from 50 to 90 feet tall and 2 to 4 feet around. We know some have lived for 500 years!

Thick grey/brown bark, lichen covered branches, and harmless growths called galls are characteristics of this tree. Rounded leaf lobes set it apart from other oak trees that tend to have pointy lobes.

Acorns are produced in the fall and grow about 1 inch long. The number of acorns produced varies year by year.

Four illustrations are shown: a mature Oregon white oak in spring, a single oak leaf, a pair of acorns, and a lichen covered branch with an oak gall attached.

Three closely related habitats.

Oak and prairie refers to several, closely related ecosystems. These habitats are not always clearly separated but rather, they form a spectrum of change between environmental conditions. These are prairies, oak savannas, and oak woodlandsOak Woodlands A mix of oak trees and shrubs..

Prairies are typically low-lying grassland that is prone to wetness. They contain diverse flowering plants but oaks are not present here.
Savannas are grasslands that contain many of the same species found in prairies and also contain some shrubs and oak trees scattered about. With lots of space to grow, the oak trees here have large, mushroom-shaped canopies with wide-reaching limbs.
Woodlands refer to groves of oak trees growing closer together. More shrubs are present and sometimes other tree species too. In this environment, oaks grow tall and narrow as they compete for sunlight.

This simple illustration shows the transition from prairie on the left side to oak savanna in the center, to oak woodland on the right. The further right the illustration goes, the more trees are present.

This graphic illustrates the habitat transition from prairie to oak savanna to oak woodland. It's rare today to see this spectrum in tact. More commonly, you will see fragments of either prairie, savanna, or woodland.

Oak and the original people of the valley.

For thousands of years, people and wildlife lived alongside Oregon white oak.

Because of this, many important lifeways and plant communities depend on the habitat associated with oak trees. Learn about our area's original people, the Kalapuya:

Visit the Confederated Tribes of Grand Ronde Chachula Museum and Cultural Center.
Explore the digital exhibit This IS Kalapuyan Land hosted by the Five Oaks Museum.

Since before human memory, Native Americans intentionally burned prairies and oak woodlands.

Burning helps maintain the open habitat for hunting and also produced acorns and camas bulbs – important staples in their diet [1]. The low-intensity fires kept other tree species from competing with the more fire-resistant oaks and allowed the prairie and savanna species to flourish.

Threats to oak and prairie:

Oak woodlands and prairies are among the most endangeredEndangered A species or group at serious risk of no longer existing. It is also a legal term under the U.S. Endangered Species Act. habitat types in the Pacific Northwest.

Prior to European settlement, there were about 400,000 acres of oak-dominated habitat in the Willamette Valley [2]. Agriculture, urban development, wildfire suppression, and the introduction of non-native species have disrupted and replaced most of this historic ecosystem.

Oak trees need disturbance to thrive.

A common threat to existing oak woodlands comes from competition by Douglas fir, grand fir, cherry, and big leaf maple trees.

Oak has only a moderate tolerance to shade, and once crowded out by taller trees, it will eventually die. The burning by Indigenous people prevented this type of competition as oak is more tolerant to disturbance than its conifer neighbors.

A single oak tree is surrounded by conifers at the edge of a field.

Photo by Francis Eatherington.

Conservation efforts:

Protecting oak and prairie requires help from private landowners and residents.

Over 80% of the remaining oak habitat in the Pacific Northwest is on private lands. These offer some of the best opportunities for oak conservation.

Residents can help restore Oregon white oak habitat by protecting mature oak trees and planting new oaks today.

Our Habitat Conservation program can help you maintain the oak habitat on your property.

Learn more:

No matter if you're a large property manager or an urban apartment renter, everyone can be involved with oak and prairie conservation. Click the squares below to access tutorials, guides, and other media.