A decade ago, when the emerald ash borer first was discovered in the U.S., a confirmed outbreak was considered a death sentence for every ash tree for miles around. The insect that came to the U.S.

Its foliage, normally soft and green, is tough and brown or missing altogether. Nonetheless, the tree’s reddish bark, swooping branches and thick, conical base identify it as the Pacific Northwest’s ...

Dendrochronologists extract a small, pencil-shaped sample of wood from a tree with a tool called an increment borer. The tiny hole left in the tree's trunk quickly heals as the tree continues to grow.