The Oregon Ash is the only ash tree native to the Northwest. The Oregon Ash are the dominant tree along the Tualatin River. The Oregon Ash can be identified by each complete leaf having 5 to 7 oval leaflets. Ash trees are susceptible to Emerald Ash Borer, an invasive pest first sighted in Oregon in June 2022. The insect was introduced to Michigan in about 2002 and has spread rapidly, causing extensive mortality of all native ash species. It is anticipated the Emerald Ash Borer will eventually kill most of the Tualatin River valley ash trees.
