A Winter Walk Among the Oaks

The clear fluting song of a western meadowlark rang out as I progressed slowly up the trail. It was a cold crisp winter evening and the sky was just beginning to darken as the sun slowly sank toward the horizon. The chill enlivened my cheeks and the heat radiating from my body turned my skin a rosy pink. 

However, it wasn’t the call of the meadowlark or the cold winter air that held my attention. Rather, it was the twisted trunks and limbs of the bare white oaks reaching toward the sinking sun that captivated my mind. These perhaps centuries old sentinels dotted the open grasslands and congregated in the woodlands where I walked. 

Natural History

Oak growth is often achingly slow, reaching heights of roughly 40 to 90 feet at maturity. 

Yet, these hardy hardwoods seem to withstand the test of time, capable of living for centuries in harsh conditions, including through windstorms, drought and fire. In fact, Oregon White Oak are considered a fire dependent species, as they rely on fire to keep competing plants at bay. 

Historically, natural wildfire and traditional burning practices of the indigenous Kalapuya maintained oak populations. However, with European colonization, fires were suppressed and the land was developed for other uses, like agriculture, eliminating as much as 99% of oak savanna in the Willamette Valley. 

Now, many of the oaks that remain are found nestled between concrete and farmland. Even in the refuge, where I rambled, restored oak habitats sit alongside several large tracts of agriculture, supplying seed and grain to wintering geese.

Habitat 

Rounding a bend, I entered denser woodland, the oak’s dry pinnately lobed leaves, long ago fallen, now crunched under feet. The trees grew straighter in the woods–their branches all reaching upwards toward the light. It was here that I noticed a small oak snag with a narrow open hollow. I wondered what occupied the space and drew in for a closer look. 

In general, Oregon oak ecosystems are incredibly important wildlife habitat. Oaks themselves provide abundant food. Many birds, like the acorn woodpecker, and native squirrels feed on their acorns. The oak’s minute flowers also provide nectar to many insect pollinators, while their leaves are food for a variety of native caterpillars. The oak genus is known as a keystone host plant for caterpillars. 

Then, of course, the cavities that form, especially in large trees that hollow out as they age, provide nesting habitat for birds, like the white breasted nuthatch, and bats. Though no one was home in my snag, it would not be surprising if at one point a northern pygmy owl or western gray squirrel had found refuge here. 

Supporting over 200 species, oak habitats are considered biodiversity hotspots. These habitats are home to many rare and unusual species, such as purple Kincaid’s lupine and endangered Fender’s blue butterfly. In spring, oak prairies are decorated with these species among others, like the lemon-yellow golden paintbrush and cat’s ear lily, to name a few. 

Sinking 

The sun was now much lower on the horizon as I neared the end of my walk. Through the branches of the oak and the dense horizon, the golden colors of sunset began to work their magic as I traveled onward toward fading light. Soon, I left the woods and walked toward the edge of an oak prairie hilltop. Arriving at a viewpoint, a few oaks silhouetted against the sky, I stopped and watched the sunset through the gnarled limbs of these magnificent trees. 

Then a few weeks ago, my heart sunk when I saw an article from OPB reporting a new threat to Oregon white oak trees. An invasive pest, the Mediterranean oak borer (MOB), has started wreaking havoc on the Willamette Valley’s Oregon white oak. Immediately, I thought about my experience walking among the oaks. Could the sun be setting on this important species permanently?

The MOB are reddish-brown beetles that are known to entomologists as ambrosia beetles–a type of beetle that bores into trees infecting them with a fungus that it uses as a food source. MOB are, in essence, farmers; however, the fungus being cultivated by the beetles ultimately kills the host tree. 

Summer trapping for MOB found that these beetles are present in the northern Willamette valley and that Oregon white oaks are being affected–though the extent of the problem still remains to be seen. Anecdotally, it seems that larger, already stressed trees are being killed by MOB. And so far there are no major die-offs of Oregon white oak reported. Good news for now. 

Heading Home

After the sun had dropped below the horizon, I walked down the hill and back to my car. As I descended, a flock of geese squawked a festive goodbye as they flew overhead. However, it was the silent farewell of the oak that I carried with me–a stoic silhouette against the ever darkening sky. 

Today, as I contemplate the fate of these ever significant trees, I choose to remain hopeful. Despite mounting threats, Oregon white oak still has a lot going for it as a climate adapted species, with the potential to thrive in our changing climate. Plus there are a lot of folks on their side, working to understand and protect oak. So for now, I will look forward to a new dawn and another winter walk among the oak.