An invasive green beetle called the emerald ash borer arrived in the Midwest from Asia, and it’s killed over 100 million ash trees across the country since it was discovered in 2002. Now it’s killing ash trees in Oregon, which don’t have any defenses against this invader. “There’s nothing that can stop emerald ash borer from coming through. We can only slow it down,” said Wyatt Williams, an invasive species specialist for the Oregon Department of Forestry. So far, infestations have been found in Washington, Marion, Yamhill and Clackamas counties. …But experts say the beetle will eventually kill the vast majority of ash trees in Oregon, including native Oregon ash, which provides valuable shady streamside habitat for salmon and steelhead. …Gathering seeds from healthy ash trees is one thing people are doing in the face of this invasion — just in case any of those trees prove to have natural resistance to the emerald ash borer.