The wild diversity of Sonoma County’s oak trees

Melanie Parker, THE PRESS DEMOCRAT

So why are oak forests important? Many would say they are a huge part of our county’s scenic landscape, but they also provide valuable habitat for more than 300 wildlife species and as many as 5,000 insect species. Oaks provide an abundant food source as well as cavities that house birds like the oak titmouse, and fallen logs and branches used by ants, beetles, salamanders and even frogs. Oak woodlands are simply teaming with life.

Where is your favorite spot to enjoy Sonoma County’s magnificent oak woodlands? Is it a stretch along your morning commute, a park you often visit, or perhaps the trees in your yard?

Oak trees are perhaps the single most iconic element of our landscape. So what do we know about them?

For starters, there are 10 different species in Sonoma County, and in many places the trees are blended together in an unusual way. While other counties boast high numbers of blue oak woodlands or Oregon oak woodlands, here scientists just scratch their heads and label many of our forest stands “mixed oak.” This diversity can be seen in the patchwork of greens in the forest canopy around places like Spring Lake.

Where they do carve out their own single-type stands, oaks can teach you something about the microclimate and soil type you are in.

The majestic valley oaks love the deep soils in our valley bottoms. Hike through the Laguna de Santa Rosa to get a good look at them. Their leaves are dull green, without sharp tips and deeply lobed. Blue oaks endure relatively hot and rocky locations. Look for them on inland ridges like those in Sonoma Valley above the town of Glen Ellen. Their leaves are blue-green, no sharp tips and shallowly lobed.

Black oaks are water lovers and enjoy shady canyons like those in Hood Mountain and Sugarloaf Ridge. Their leaves are large and sharply tipped, with deep lobes.

Oregon oaks take up where the valley oaks leave off on hillsides with fertile soils. They can be seen with the coast live oak rimming the meadows at places like Taylor Mountain. Leaves are bright green, lobed and not sharply tipped.

And finally there is our most ubiquitous oak, the coast live oak, which dominates the western portion of the county while holding its own in almost any setting. Its leaves are dark green, curved, with sharp little spines.

To make matters more interesting, many of Sonoma County’s oaks hybridize, creating another 12 versions of oak to inspire your appreciation for the wonders of nature. Annadel State Park is a good example of rampant hybridization between blue oak and Oregon oak.

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