 A plant pathologist for the U.S. Forest Service who works in Durham, New Hampshire, said this, One of the biggest threats, if not the biggest threat to our forests in this part of the world, are invasives, like pathogens and insects. If the researchers noticed a tree struggling, they could investigate which pathogens or pests we're likely to blame. Foreign invasives can hitch a ride into the U.S. with wood products, packing materials, or live plants imported by nurseries, for example.