Resilient Forests: Managing Invasive Plants and Forest Pests in Eastern Parks

The threat

Eastern park forests are under pressure from invasive plants and pests. Tackling invasives strategically, to protect a park's highest-priority resources, and planning for pests and pathogens are core to keeping forests resilient.

Invasive plants

A recent study by the Park Service's Inventory and Monitoring (I&M) networks found invasive plants expanding in eastern parks. With help from Invasive Plant Management Teams, parks use three strategies:

Three strategies for managing invasive plants. NPS.

1. Early detection and rapid response: catching new invaders early, so they can be treated efficiently before they spread. Parks can enlist citizen scientists through iNaturalist, as in the Eastern Rivers and Mountains Network's early detection project.
2. Biological controls: for plants already widespread, biocontrols are often the only realistic option — usually host-specific insects or pathogens that feed on a single invasive plant, weakening it and curbing its spread. Their use is strictly regulated by federal and state law, an International Code of Best Practices and specific protocols. Japanese knotweed, for example, is being suppressed by an insect biocontrol in some parts of the country.
3. Managing special places: treating invasives where ecological or cultural value is highest. I&M's strategic management decision tool helps parks focus limited time and money where it counts — the key to a problem that can seem endless.

Managing invasive plants to release tree regeneration. NPS.

Forest pests

Exotic insects, diseases and pathogens can cause widespread tree damage and death. Among the most pressing:

• hemlock woolly adelgid (Adelges tsugae);
• emerald ash borer (Agrilus planipennis);
• gypsy moth (Lymantria dispar);
• beech scale insect (Cryptococcus fagisuga), which leads to beech bark disease.

When many trees die at once, invasive plants can move in — especially where regeneration is already weak. I&M monitoring tracks key pests' impacts, and parks can turn to the U.S. Forest Service's Forest Health Assessment Team in Morgantown, West Virginia, for evaluations, and to Forest Health Protection Grants to treat or suppress pests.

Replanting

Some parks may need to plant native trees to restart regeneration — where pests such as emerald ash borer or hemlock woolly adelgid have gutted stands, or invasives have been removed.

• Protect plantings where deer browse heavily.
• With enough light and protection, many small seedlings will regenerate a forest better than a few large saplings — though well-protected saplings can work in small, high-priority areas.
• Substitute species when a pest has wiped one out: in parts of Region 1, eastern white pine could stand in for eastern hemlock, and disease-tolerant elms for green ash in riverside forests. Weigh climate resilience too.
• Choose species using park vegetation maps, which describe each forest type's trees, shrubs and wildflowers, plus NatureServe and state natural heritage programs.

More in the series: Managing Resilient Forests: A Regional Initiative and Managing Deer Impacts.

Sources

Based on "Resilient Forests Initiative – Managing Invasive Plants & Pests," Managing Resilient Forests Initiative for Eastern National Parks, National Park Service; a work of the United States government in the public domain. A photograph of Japanese knotweed credited by name only is not reproduced.