Large ancient white oaks (Quercus garryana) with their broad, rounded canopies are one of the Willamette Valley’s most profound residents. Their deep incised bark, lustrous green-colored lobed leaves and stout gnarled limbs make for a beautiful and majestic tree. Thin strands of lichen drape from their branches, their upper canopies are often filled with bunches of mistletoe, and thick vines of poison oak cover their lower trunks which adds to the image of an organism that is primal and deeply rooted in the history of the Valley. On fertile soils, the trunks of some legacy oaks may be 5 feet in diameter. Occasionally when a large oak is toppled by a winter wind storm and after the huge trunks are cut for removal, I try to count the rings but soon lose patience because they are too numerous and tightly grained. They were old trees when Lewis and Clark paddled down the Columbia River and David Douglas rode under their huge limbs traveling south on his way to the Umpqua Valley.
Savannas characterized by scattered large oaks in upland prairies covered a good part of the Willamette Valley prior to the arrival of Euro-American fur trappers and settlers. Native Americans burned the prairies in the valley to create vast fields of camas and lush grass forage for deer and elk in the springtime. White oaks are fire-resistant so the burning kept conifers from encroaching on oak savannas and open oak woodlands, and created unique understories filled with a wonderful variety of native grasses and forbs.
Most of these large white oaks are gone. Farmers cut them down so they could work their fields or harvested the trees for lumber. Conifers regenerated in many of the oak dominated stands after fire was excluded and overtopped the slower growing oaks. Understories were invaded by exotic grasses and forbs that outcompeted most of the native species. However, there is an emerging and widespread awareness that we are in danger of losing the remnants of this unique part of Oregon’s natural resource legacy. A movement to save this legacy is gaining steam. Lands filled with white oak forests are being protected and restored, and many communities are developing plans that place a high value on oak habitats.
This summer has been very hot. I noticed the leaves on the tips of branches on a number of the white oak trees on Bald Hill Farm were turning brown. My first thought was that the trees were suffering from the effects of our current drought, but learned that the condition was caused by a wasp (Basettia) that lays its eggs under the bark of the oak branches. Eventually the larva (grubs) produce oak galls; those pale-colored, balled shaped ornaments that you often see hanging from oak branches. The grubs may girdle the branches or squirrels may strip the bark to eat the grubs, thus girdling the tip. Apparently this event is common and does not harm the tree.
Greenbelt has initiated some bold oak work on Bald Hill Farm this summer. We are removing a number of conifers that threaten to overtop large oaks on the southeastern slope of Mulkey Ridge. We are also thinning some of the smaller oaks in denser woodlands to create more savanna-like conditions so that the larger oaks can grow in more open grasslands. Over the next few years we will be reseeding the understories with native grasses and some forbs, and initiating a more concerted effort to control invasive plants.
Blog Post: Michael Pope
