Amur corktree

Invasive Plants in Southeastern Wisconsin

Phellodendron amurense

The Amur cork tree (Phellodendron amurense) is a deciduous tree native to East Asia, particularly in China, Korea, and Japan. It has become an invasive species in North America and parts of Europe, posing a significant threat to native ecosystems and biodiversity. Recognized by its distinct cork-like bark and compound leaves, the Amur cork tree is part of the Rutaceae family, which includes citrus plants. While it has been historically valued for its medicinal properties and ornamental appeal, its spread beyond its native range has caused ecological concerns.

Identification

Common Name: Amur Cork Tree
Scientific Name: Phellodendron amurense
Family: Rutaceae (Citrus family)
Native Range: China, Korea, Japan, and the Russian Far East

Physical Characteristics:

Height: Can grow up to 40-50 feet tall
Leaves: Opposite, compound, and pinnate with 5-11 leaflets, often giving off a citrus smell when crushed
Bark: Thick, corky texture with a gray-brown color and deep ridges
Flowers: Small, greenish-yellow, and inconspicuous, appearing in late spring or early summer
Fruits: Small, black drupes that attract wildlife, but their spread contributes to the tree's invasiveness.

Ecological Impact

The Amur cork tree disrupts native ecosystems primarily through competition with native plants, forming dense stands that outcompete understory and ground vegetation. Key ecological impacts include:

Resource Competition: Amur cork trees establish deep root systems that deplete soil nutrients and water, leaving less available for native plants.
Biodiversity Loss: By forming monocultures, these trees reduce plant diversity, leading to a cascading effect on local wildlife that depends on native flora.
Allelopathic Properties: Some studies suggest that Amur cork trees may release chemicals inhibiting the growth of nearby plants, further enhancing their competitive edge.
Habitat Alteration: Dense stands of cork trees modify the forest structure, impacting light availability and microhabitats for various species.
Suppresses regeneration of native tree species and displaces native shrub and herbaceous layers.
Research shows decreases in acorn and hickory nut production as well as overall tree populations where Amur cork tree is present.
Adaptable to different soil types (clays to sands), acidic to alkaline, but prefers moist, well-drained soils.
Grows in both full sun and under dense shade.
Reproduces by both seeds and by resprouting from stumps. A female tree can produce thousands of seeds.
Grown throughout the United States; tolerant of urban areas (pollution, parking lots, golf courses, highway medians).

Distribution in North America

Introduced to North America as an ornamental and medicinal plant, the Amur cork tree has spread across the northeastern and midwestern United States and parts of Canada. It thrives in various soil types, from floodplains to drier uplands, making it highly adaptable and challenging to control once established.

Control and Management

Effective management of Amur cork tree infestations includes both mechanical and chemical methods:

Mechanical Control:
- Manual Removal: Young saplings can be pulled out by hand, while larger trees may require cutting. However, cutting alone may stimulate regrowth, so follow-up treatments are often necessary.
- Girdling: Removing a ring of bark around the tree can prevent the tree from transporting nutrients, eventually leading to its death. This is often more effective than cutting alone.
Chemical Control:
- Herbicide Application: Applying herbicides like glyphosate to cut stumps or girdled areas can effectively kill the tree and prevent regrowth. Care must be taken to avoid harming nearby native plants.
- Timing: Applying herbicides in late summer or early fall, when trees actively transport nutrients to roots, is generally most effective.
Monitoring and Follow-Up:
- Regular Monitoring: Consistent monitoring of treated areas is essential, as the Amur cork tree has a high potential for regrowth from seeds and root sprouts.
- Preventative Measures: Educating the public on avoiding the planting of Amur cork trees and promoting the use of native species can help prevent further spread.