Based on the research of Dr. Shannon LaDeau and colleagues
Exotic pests and pathogens are one of the most serious threats facing our forests. Moved around the globe intentionally and accidentally, these invaders can dramatically alter the structure and function of our forestland, to the detriment of native plants and animals.
Take the case of chestnut blight. In the early 1900s, this fungal disease entered the U.S. on imported lumber. Once established, it wiped out chestnut trees across eastern North America.
Impacts of non-native insects
Plant-insect interactions are commonplace in forests, where they have evolved slowly over time. Because of this, native plants and insects have natural constraints that allow them to coexist. Many invaders lack these constraints, so their impact can be devastating.
The hemlock woolly adelgid is just one example. Spotted in Virginia some 50 years ago, this tiny insect is now present throughout the Northeast, where it is ushering in the demise of eastern hemlocks, a keystone species that plays an important role in the ecology and hydrology of our forests.
Signs and effects of woolly adelgid infestation
Infested trees have cotton-like balls at the base of their needles. Underneath this protective covering, insects use a feeding tube to tap into the tree’s starch reserves. Heavy infestations result in needle loss and diminished vigor, with many impacted trees dying within 4 to 10 years.
The hemlock woolly adelgid’s complex lifecycle may explain why northern hemlocks have fared better than their southern counterparts. The insects have two generations each year and cold winter temperatures limit their success and establishment.