In a towering forest of centuries-old eastern hemlocks, the tiny hemlock woolly adelgid spends its life sucking sap and eventually killing the tree. The bug is one example of an expanding horde of insects draining the life out of forests from New England to the West Coast. Aided by global trade, a warming climate and drought-weakened terrain, this invasion represents one of the greatest threats to biodiversity in the U.S. Scientists say they are already driving some tree species toward extinction and causing billions of dollars a year in damage, with the situation expected to worsen.

Today’s connected world enables foreign invaders to cross oceans in packing materials or on garden plants, and then reach American forests to rapidly expand their ranges. According to a new study in Ecological Applications, scientists say several species of hemlock and 20 species of ash could become nearly extinct in coming decades. Such destruction would eliminate a critical sponge to capture greenhouse gas emissions, a natural shelter for birds and native insects and a reliable food supply for bears and other animals. Dead forests also increase the danger of wildfires.

This article appears in the April 2017 issue of Natural Awakenings.