Common Name: Amur corktree
Scientific name: Phellodendron amurense
Identification: Amur corktree is a deciduous tree that typically grows to 40’ tall with similar crown width at maturity. Mature trees often bear low branches that extend horizontally from the short, stout trunk. Older bark is deeply furrowed and corky. Younger growth is orange-yellow or yellow-grey. Inner bark is bright yellow. The leaves are opposite and compound, with each leaf being composed of 5-11 egg to lance shaped leaflets with smooth edges. The leaves are 10-15” long, while the leaflets are 2½-4½” long and half as wide. Foliage is shiny and dark green in summer, turning yellow in the fall. The species is mostly considered to be dioecious (male and female flowers grow on separate individuals), though some varieties may be polygamo-dioecious, bearing both single-sex and perfect flowers (Dirr and Warren 2019). Flowers of both sexes are about 1/8” across, green, and are borne in clusters in late spring. Female and perfect flowers give way to drooping clusters of fruit in mid-fall. Fruit are round, green in color, turning black when mature and about ½” in diameter. Fruit often persist on trees through the winter.
Look-alikes: Amur corktree is somewhat similar in appearance to a number of trees with compound leaves, including invasive tree-of-heaven (Ailanthus altissima), and the natives black walnut (Juglans nigra), yellowwood (Cladrastis kentukea), and Kentucky coffee tree (Gymnocladus dioicus). All of these species have alternately arranged leaves, while the leaves of Amur corktree are opposite. The yellow inner bark is also unique to Amur corktree among these species.
Amur corktree is reported infrequently in parts of the Great Lakes Basin. Isolated occurrences have been reported in northern Minnesota, northern Indiana, central Wisconsin, and central Michigan. It is has not been reported in northern Wisconsin, the Upper Peninsula of Michigan, or the Great Lakes portion of New York. It is also reported occasionally in the Mid-Atlantic and southern New England. It is generally considered hardy to Zone 3, so could potentially spread throughout the region.
Additional invasive species distribution data for specific Great Lakes jurisdictions is available via:
- Midwest Invasive Species Information Network (Michigan)
- iMapInvasives (New York and Pennsylvania)
- EDDMapS Ontario
The seeds of Amur corktree are dispersed by gravity and over long distances by birds, which eat the fruit.
Amur corktree typically invades disturbed woodland habitats, including roadsides, forest edges, woodlots, unmanaged areas of urban parks, and forest openings. However, its shade tolerance allows it to grow in mature upland and lowland forests if seed is introduced to these areas.
When a steady seed source is present, Amur corktree tends to establish dense populations of juvenile trees. While few of these juveniles will survive to maturity, they become large enough to cast significant shade, suppressing the growth of native understory herbs and shrubs and the regeneration of canopy trees (Glaeser and Kincaid 2005, Morgan 2012). Studies also show that Amur corktree is allelopathic, altering the soil bacterial community in ways that may suppress germination of other species seeds (Park et al. 2001). At maturity, female Amur corktrees produce thousands of seeds every year. Seed can stay viable in the soil for several years (Simons 2006).
Invasion by Amur corktree can be a problem in both natural areas and commercial woodlots because it reduces tree recruitment.
Amur corktree was introduced to North America as an ornamental tree in the mid-1800s (Yale University). Male cultivars are available in trade today. Its broad spreading crown, low hanging branches, and overall stately appearance have led to its use in parks, cemeteries, university campuses and similar spacious sites (Dirr 1998, Dirr and Warren 2019).
Most published literature maintains that Amur corktree is fully dioecious (male and female flowers occur on separate plants). Male varieties are fruitless and will not contribute directly to invasive populations, though they may pollinate any nearby female trees. Dirr and Warren note that at least one variety of Amur corktree believed to be male has produced fruit in “various locations,” indicating that some varieties may be polygamo-dioecious (2019). Further study is needed to confirm.
Please see our Landscape Alternatives landing page for more information about how the WIGL Collaborative selected alternatives.
| Alternatives for Amur Corktree
Common name (Latin name) |
Broad-crowned tree for large sites (>40’ spread) |
Low-hanging branches |
Attractive bark |
| American beech (Fagus grandifolia) | ✔ | ✔ | ✔ |
| Thornless honey locust (Gleditsia triacanthos f. inermis) ‘Skycole’ SKY LINE a |
✔ | ~ | |
| Kentucky coffeetree (Gymnocladus dioicus) ‘Espresso’ a |
✔ | ||
| Swamp white oak (Quercus bicolor) | ✔ | ✔ | ✔ |
| Chinkapin oak (Quercus muehlenbergii) | ✔ | ✔ | ✔ |
| Northern red oak (Quercus rubra) | ✔ | ~ | |
| Shumard’s oak (Quercus shumardii) | ✔ | ✔ | |
| Pecan (Carya illinoinensis) | ✔ | ✔ |
✔ = trait is present
~ = trait is somewhat present but not as pronounced as in check-marked examples
Green = native to part of the Great Lakes Basin
Yellow = native to the United States but not to the Basin
a Male cultivars of these species, including the ones listed, are often preferred because they don’t produce messy seed pods.
The WIGL Collaborative’s decision trees are designed to help site users, who are perhaps newly discovering that plants that are part of their home landscaping are invasive, prioritize which species should be removed first based on risk to the surrounding environment, economy, and occasionally, to human health. In a perfect world, everybody would remove all invasive plants from their landscaping right away, but in reality, removing mature woody plants involve a hefty investment of time and/or money. These diagrams can help people with multiple woody invasives in their landscaping prioritize to get the most benefit for their efforts.
To learn more about the methodology and information used to develop the decision trees and for helpful hints on how to answer the questions, please see the full report here (PDF).
The following is a brief overview of management techniques shown to be effective on Amur corktree. For more detailed information on how to use these techniques, visit our Management and Control page. For local assistance managing woody invasive species, please get in touch with a cooperative invasive species management group or a university extension program.
Timing and spread concerns: Amur corktree does not appear to be common in the Great Lakes region, so a good defense is the best offence. Natural areas close to college campuses, parks, public gardens and places where female trees are growing should be monitored closely for seedlings. Whenever possible, plants bearing female flowers should be controlled early, before fruiting. If control is undertaken when fruit is present, plant material should not be removed from the site to avoid spreading the seed.
Physical control: Small seedlings can be pulled easily from moist soil, and juvenile trees can be pulled using equipment. Girdling may be the most cost effective way to treat mature trees, and may be suitable where use of herbicide is not consistent with site goals. Amur corktrees should be girdled (a 3-4” strip of bark removed) in late spring to mid-summer. Top-killing methods such as mowing or felling can be used to prevent maturation but will not provide long-term control of juvenile plants.
Chemical control and combined approaches: Cut stump, basal bark, and application of herbicide to a girdle are effective on this species. Basal bark treatment can be used on juvenile trees less than 6” in diameter at breast height during most times of the year (avoiding early spring). For larger trees, cut stump treatment or application of herbicide to a girdle) are most effective. Girdle treatment should be done in late spring to mid-summer while cut stump can be done most times of the year, avoiding early spring. Staff at The Morton Arboretum found the cut stump method to be effective for controlling a large population of juvenile Amur corktrees (McKinney and Dreisilker, pers. com. 2019). In all cases, herbicide should be selected carefully based on site conditions, and label directions read and followed carefully.
With any treatment it will be necessary to monitor for and treat regrowth and new seedlings.
Resources on management of Amur corktree:
- Dirr, MA. 1998. Phellodendron amurense In: Manual of Woody Landscape Plants, Fifth Edition. Champlain, IL: Stipes Publishing. 703-705.
- Dirr, MA and KS Warren. 2019. Phellodendron amurense In: The Tree Book: Superior Selections for Landscapes, Streetscapes, and Gardens. Portland, OR: Timber Press. 565-566.
- Glaeser, CW and D Kincaid. 2005. The non-native invasive Phellodendron amurense in a New York City Woodland. Arboricultural Journal. 28(3): 151-164.
- McKinney, M and K Dreisilker. Personal communication on the control of Amur cork tree in natural areas at The Morton Arboretum, Lisle, IL. July 24 & 25, 2019.
- Morgan, EC. 2012. Stand dynamics of a 46-year invasion by Phellodendron amurense in an Eastern North American forest. Castanea. 77(1): 21-27.
- Park, YG, Choi, MS, Yang, JK, and JH Paik. 2001. Allelopathic potential and substances from cork tree (Phellodendron amurense). Journal of Korean Wood Science and Technology. 29(3): 92-98.
- Simons, D. 2006. Amur cork tree fact sheet. Plant Conservation Alliance. 7/25/2019.
- Yale University. Amur cork tree. In: Yale Nature Walk. 5/6/2020.
Header Photo: Leslie Mehrhoff, UConn, via bugwood.org
