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The invasion of the forest destroyers – And how science is fighting back

Joyce El Kouarti
Office of Communication

A picture looking up at a very tall ash tree.
This ash tree on the Allegheny National Forest is showing early symptoms of Emerald Ash Borer infestation, including crown thinning. (USDA Forest Service photo by Kathleen Knight.) 

Change is inherent in forests, but insects and pathogens that have been inadvertently introduced, known as invasive species, have brought about a novel kind of change that trees in both urban neighborhoods and ancient forests are struggling to survive.

Not only can invasive species damage the environment, they can also damage local and regional economies and human health. Many arrive from far-away places, as stowaways on imported freight, embedded in shipping pallets, in plants sold from  nursery stock, and young trees used to reforest the landscape.

When an invasive species first arrives to a new natural environment, it has no natural predators. This gives them a sort of super power to outcompete, kill, and replace native species. A forest weakened by invasive pests is more vulnerable to additional disturbances like wildfire, strong winds, hurricanes, drought and other extreme weather events.

USDA Forest Service scientists are exploring the impacts of invasive species in forests and rangelands of the United States and developing early intervention strategies that land managers can take as well as strategies for restoring impacted landscapes .

At the National Genomics Center, scientists are using environmental DNA to track invasive species. By detecting DNA remnants that organisms shed, this technology can reveal the presence of invasive species more efficiently and cost-effectively than traditional methods. Genetic analysis can also be used to identify the variations that help some tree species more successfully resist insect attacks.

Forest Service researchers are also using what are called electronic noses to detect invasive pests and pathogens early. These sensing devices are helping efforts to destroy the emerald ash borer, a nonnative insect that has killed millions of ash trees. Ash is prized for shading streets, homes, and parks in cities throughout North America and also used to build furniture, cabinets, baseball bats, and more.

From a practical perspective, agency scientists have developed guidelines to help city foresters manage these voracious insects.

A picture of a dense forest with a river flowing between.
Hemlock woolly adelgid are weakening hemlock forests that provide critical habitat for deer, bear, bobcat and other animals, leaving them vulnerable to wildfire, strong winds, and other disturbances. (USDA Forest Service photo by Steve Norman.) 

The Forest Service created a guide for land managers who want to preserve hemlock trees, which are under attack by the hard-to-see hemlock woolly adelgid. The insect native to East Asia latches onto the tree and, for the rest of its life, feeds on the tree’s starches while starving the tree into a slow death.

The health of a species of tree, like the hemlock, can have ripple effects across ecosystems. This iconic tree species provides food and shelter for deer, bear, bobcat and other animals as well as wood for framing and subflooring. Along streams, hemlock branches provide shade that keeps water temperatures cool enough to sustain native cold-water fish like brook and brown trout. 

While scientists study how to best combat invasive species, you are a powerful ally to native species.  The best way, of course, is to prevent invasive species from spreading

  • Avoid moving firewood, lumber, and wood packaging material across different regions. In other words, use it where you buy it.
  • Buy plants from a reputable source and know which species are native to your area. Don’t plant those that are not native species.
  • Clean your boots or sneakers between hikes and before leaving infested areas.
  • Report sightings of invasive pests to your state plant health director or USDA office.  

For more tips, visit the USDA National Invasive Species Information Center.