Oak Woodlands

Photo by Tracy Robillard, NRCS (available from Flickr).

In a landscape dominated by conifers, oak ecosystems of the Pacific Northwest are unique and support a rich array of plants and animals. They are often associated with dry, low-elevation sites and sites that experienced regular fires in the past. Oak woodlands are generally characterized by a relatively open understory of shrubs, grasses, and herbaceous plants and a tree canopy that obscures 25-75% of the sky. They may grade into oak savannas, mixed woodlands, riparian areas, forests, or other habitat types.

Oak trees are a defining feature of oak woodlands. They provide essential food, shelter, and breeding sites for native wildlife, from the Acorn Woodpecker to the western gray squirrel. Large, mature oaks produce abundant acorns and host a multitude of insects and other invertebrates on their foliage, dead wood, and associated epiphytes such as mosses and lichens. The oaks also offer nesting cavities, dens, roosts, and cover from weather or predators. All in all, they are a haven for biodiversity.

Changes to oak ecosystems over the last 150 years have been dramatic. Prior to European settlement, Native peoples played an integral role in the maintenance of prairie-oak communities, using fire as a tool to retain an open landscape and support the big game and plant resources they depended on. Without periodic fires to remove conifer seedlings, or without other active management, most oak ecosystems will gradually succeed into conifer forests.

Today, most oak habitats have been lost to fire suppression, urban and rural development, and conversion to agriculture. Even in protected sites, oak woodlands face additional threats such as invasive vegetation, pests, and pathogens. For example, the goldspotted oak borer, an invasive wood-boring beetle, is contributing to oak tree mortality in southern California, and sudden oak death, a serious plant disease, has killed tanoaks and other susceptible oak species in much of California and in Curry County, Oregon. Most oak woodlands now persist in small, fragmented patches on private lands, underscoring the importance of collaborative conservation strategies.

Acorn Woodpeckers are well-known for their habit of caching acorns and other nuts in individually drilled holes in storage trees. They excavate larger tree cavities for nesting and roosting. Photos by Keith Kohl, ODFW.

Explore interactive Acorn Woodpecker data from eBird. Map from eBird, Cornell Lab of Ornithology.

While there are many approaches to wildlife conservation, the Oregon-Washington Partners in Flight Conservation Strategy for Landbirds in Lowlands and Valleys of Western Oregon and Washington emphasizes “focal species” and draws attention to habitat attributes most important in a functioning oak ecosystem. Focal species are highly associated with particular habitat features or conditions. By managing for these focal species, other species with similar habitat needs may also be conserved.

Oak woodlands support more than birds!

Check out this companion article featuring the western gray squirrel, a Species of Greatest Conservation Need in Oregon and Washington. Photo by Keith Kohl, ODFW.

Read more about conservation and management issues affecting oak woodlands in Oregon and Washington:

Citizen science at oak restoration sites! If you’re a landowner undertaking oak restoration activities on your property, consider monitoring birds pre- and post-restoration to document changes in the avian community; oak restoration and bird monitoring tips available here:

eBird Northwest articles on oak woodlands and associated focal species:

Interested in another habitat? Find all of eBird Northwest’s habitat pages here.