DENVER — Some of the USA's most treasured tree species, from ash and aspen to white pine and Hawaii's native wiliwili, are under attack by insects and diseases in a growing assault coast to coast.
Some of the killers are foreign pests brought here in cargo or by travelers. Others are homegrown insects at epidemic levels because of drought and unusual warmth. This year has been the warmest on record.
The Agriculture Department's Animal and Plant Health Inspection Service finished adopting new rules this summer barring cargo from abroad unless crates and pallets are treated with chemicals or heat to kill any bugs in the wood.
"We're at one of those points in time where it's all happening at once," says Wayne Shepperd of the U.S. Forest Service.
The mountain pine beetle, a native, has ravaged millions of acres of Western forests. Trees were weakened by drought or subjected to worse infestations because warmer temperatures allowed the bugs to multiply faster. The emerald ash borer from Asia is killing species that have no natural defenses.
Ash borers can spread in diseased trees cut up for firewood. The Agriculture Department airs radio ads in eight states and has billboards that warn: "Pack marshmallows, not firewood."
California's Big Sur region and Sonoma and Humboldt counties have "tons of new mortality this year" from sudden oak death, another disease, says Katie Palmieri of the California Oak Mortality Task Force. "Entire hillsides are just gone."
A nursery shipment is blamed for spreading the hemlock woolly adelgid into Great Smoky Mountains National Park in Tennessee and North Carolina. The park hopes to save older hemlocks by using insecticides and beetles that eat the aphid-like bugs.
Scientists don't yet know what is killing aspens across much of the West. "This die-back just occurs, boom, and we're not seeing new sprouting" of trees, Shepperd says. He says drought is a possible cause, but "we see (aspen) dying in wet areas, too, so I'm not convinced it's drought alone."
A study this year in BioScience said exotic bugs and diseases "pose the most serious current threat to the forests of eastern North America."