The strength of Marin County’s two dominant native oak species, which dot golden hills and shade streets and parks, has been tested mightily over the past decade. Coast live oaks, which thrive under the damp marine layer, have been decimated by sudden oak death. Now, valley oaks, native to West Marin’s dry valleys and popular in urban spaces, face a new threat from a pest barely 3 millimeters long.
The Mediterranean oak borer—referred to as…