If you have one or more Oregon white oak (Quercus garryana) trees on your property, consider yourself lucky. They are part of a “rare and declining” habitat type – either oak woodland or oak savannah, which is grassland with scattered oak trees (one or two per acre). For every 100 acres of oak habitat that previously existed in the Willamette Valley, only 7 acres of woodland and 1 acre of grassland or prairie, remain. Fortunately for us, some of that precious oak habitat is found within west Multnomah County, including much of Sauvie Island. There are also scattered Oregon white oaks in the rural West Hills and even within city limits. If you have Oregon oaks on your land, please let us know.
To ensure the longevity of your Oregon oak, which live several hundred years, maintain habitat the species likes. Avoid compacting the lateral roots and soil under the tree canopy’s “drip zone” with vehicle traffic, livestock or heavy equipment. There is no need to irrigate established Oregon oak trees since they send a tap root deep into the soil to find moisture; they are adapted to low moisture conditions, including talus (rocky) slopes with little top soil. This special tree also loves sun, which means it does best if you limit shade from other trees. Tall Douglas firs are particularly troublesome when growing on the south side of an Oregon white oak.
Lastly, to enhance the habitat value of your Oregon oak, control nearby invasive plants in favor of native species. Be sure to control particularly aggressive competitors such as English ivy and Himalayan (aka “Armenian”) blackberry. English ivy seeds have made their way onto Sauvie Island and have begun creeping up Oregon oak and other desirable trees.
