There are two invasive trees and seven invasive shrubs that Michigan officials want residents to be aware of.
The black locust tree was planted throughout the Midwest for erosion control, fence posts and fixing nitrogen in the soil but its leaves, stems, bark and seeds are toxic to horses.
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Most of the shrubs are a concern because they will outcompete native plants for resources. Below I’ll go over the trees and shrubs that Michigan has listed online, how to identify them and what threat they pose to you or the ecosystem.
- If you believe you have found one of these invasive trees or shrubs, you can report it through the Midwest Invasive Species Information Network. Just click here and search for the tree or shrub.
Invasive Trees
Black Locust
This fast-growing tree has been planted throughout the Midwest for erosion control, fence posts, and fixing nitrogen in the soil. It forms dense colonies that can harm native vegetation. It’s also toxic to horses.
How to identify it:
- Fast-growing tree that grows 40-100 feet high.
- Compound leaves have 7 to 21 oval leaflets that are dark green on top and light green beneath.
- Fragrant, white flowers hang in elongated clusters, blooming in May and June.
- Black locust seed pods are flat, brown and 3 to 4 inches in length.
- Twigs have ½ inch, paired thorns.
Where is it found?
It is established in Michigan and prefers sun and well-drained soils but will grow in poor soils and disturbed areas including roadsides, open fields and forest openings. It has been planted throughout the Midwest, West Coast and Texas for erosoin control, fence posts and fixing nitrogen in the soil.
Why is it a concern?
Black locust spreads by root suckering and stump sprouting, forming dense colonies that shade prairies and forest openings, harming native vegetation. Black locust leaves, stems, bark and seeds are toxic to horses.
Tree of Heaven
This fast-growing tree can reach up to 70 feet. It has been detected in Michigan. Its roots can damage sewers and structures, they also produce chemicals that inhibit the growth of other plants.
How to identify it:
- Fast growing deciduous tree reaches up to 70 feet.
- Bark is smooth, spotted and pale gray to brown.
- Leaves are 1-3 feet long, comprised of 11-25 long, narrow leaflets resembling native sumac.
- Leaflets have one or more rounded teeth near the base.
- Small, yellowish-green flowers form large, upright clusters in June.
- Fruits are flat, twisted, winged seeds.
- Flowers and leaves have an unpleasant, rotten peanut butter odor.
Where is it found?
It has been detected in Michigan and can tolerate poor soils and drought but requires some sun. It can be found in old fields, forest edges and openings, and in urban environments where it was used in landscaping. It is widespread throughout most of the United States.
Why is it a concern?
Root shoots can develop into dense thickets. Roots can damage sewers and structures. Roots also produce chemicals that inhibit the growth of other plants.
Read: Let’s talk about Michigan’s invasive herbs: How to identify them and the threat they pose
Invasive Shrubs
Autumn Olive
This shrub can grow to 20 feet high and is established in Michigan.
How to identify it:
- Deciduous shrub that can grow to 20 feet high.
- Leaves are bright green on top and distinctively silver underneath.
- Spring-blooming cream or yellow flowers have a strong fragrance.
- Abundant red berries are lightly speckled and easily seen in the fall.
- Flowers arranged in spikes near the end of the stem are small, numerous and creamy white in color.
- Flowers bloom in August and September in Michigan.
Where is it found?
It is moderately shade tolerant and occurs on a variety of soil types. It spreads rapidly in old fields and is also found in open woods, along forest edges, roadsides, sand dunes, and other disturbed areas.
Why is it a concern?
It was originally planted for wildlife food and habitat but it is highly aggressive. Its seeds are widely dispersed by birds and mammals. It can shade out native plants and fixes nitrogen in the soil, which can degrade native plant communities that thrive on low-nutrient soils. It is difficult to control because cut stumps and roots will resprout.
Common Buckthorn
This small tree or shrub can reach 25 feet tall and is established in Michigan.
How to identify it:
- Deciduous small tree or shrub – can reach 25 feet tall.
- Leaves are dark- green, oval and slightly toothed.
- In spring, small, yellow-green, 4-petaled flowers grow in clusters of 2-6 at the base of leaves.
- Small, purple to black fruits ripen in the fall.
- Twigs often have a single, sharp thorn at their tip.
- Distinctive orange inner bark.
Where is it found?
It can be found in disturbed and undisturbed areas like roadsides, pastures, old fields and woodlots.
Why is it a concern?
It spreads quickly and crowds out native shrubs and understory plants. It is a host for alfalfa mosaic virus and crown fungus, and may be a possible host for the soybean aphid.
Giant Knotweed
This perennial and herbacious shrub can grow over 12 feet high and has been detected in Michigan.
How to identify it:
- Perennial, herbaceous shrub that can grow over 12 feet high.
- Hollow stalks are light green, smooth and swollen at the nodes, resembling bamboo.
- Similar to Japanese knotweed, and the two plants may hybridize.
- Flowers are arranged in spikes near the end of the stem are small, numerous and greenish-white in color.
- Flowers do not extend past the length of the leaves.
- Flowers bloom in August and September in Michigan.
- Giant knotweed leaves are 6-14 inches long, heart-shaped at the base and have fine hairs on the underside.
Where is it found?
It likes moist soils in sunny areas along roadsides, disturbed fields or vacant lots and along streams or river banks.
Why is it a concern?
Giant knotweed spreads aggressively by roots (rhizomes) and cut or broken stems. It can form dense thickets along streambanks, actually increasing erosion potential and decreasing habitat value.
Glossy Buckthorn
This small tree or shrub can reach 18 feet tall and is established in Michigan.
How to identify it:
- Small tree or shrub – can reach 18 feet tall.
- Leaves are simple, alternate, shiny and un-toothed.
- Flowers are tiny, contain 5 greenish-white petals and are clustered at the base of leaves (late May-September bloom).
- The plant does not have thorns.
- Pea-sized fruits ripen from green to red to dark purple (June-September).
- Distinctive orange inner bark.
Where is it found?
It prefers sunlight in moist soils but can tolerate shade. It’s often found in wetlands, along fence rows, roadsides, open woods and in pastures.
Why is it a concern?
This invasive shrub is a threat to native plants in prairie fens and other ecologically important wetland communities. It is a host for alfalfa mosaic virus and crown fungus and may be a possible host for the soybean aphid.
Japanese Barberry
This shrub is usually 1-2 feet tall, but can grow up to 6 feet in height. It’s established in Michigan.
How to identify it:
- Spiny, deciduous shrub usually 1-2 feet, but can grow up to 6 feet in height.
- Small, oval-shaped green leaves with smooth edges turn red in the fall.
- Brown to reddish stems with thorns at each node.
- Small, pale yellow flowers with six petals hang from stems, blooming in spring.
- Fruits are small, bright red, egg-shaped berries that persist into winter.
- Can be confused with the native American barberry, which has toothed leaves.
Where is it found?
It thrives in the sun or shade. It is often found in forests, pastures, and old fields. It can be found along woodland edges, roadsides, and disturbed areas.
Why is it a concern?
Japanese barberry is a common ornamental plant that can easily escape cultivation. Its seeds are dispersed by birds and wildlife. Plants are not browsed by livestock or wildlife due to thorns, giving it a competitive advantage over native plants. Shrubs form dense stands that displace native species. Japanese barberry can raise pH levels in soil.
Japanese Knotweed
This shrub can grow from 3 to 10 feet tall and is established in Michigan.
How to identify it:
- Perennial, herbaceous shrub that can grow from 3-10 feet high.
- Hollow stalks are persistent through winter, looks similar to bamboo.
- Stems have a fine white coating that rubs off easily.
- Flowers arranged in spikes near the end of the stem are small, numerous, and creamy white in color.
- Flowers bloom in August and September in Michigan.
Where is it found?
It can be found along roadsides, wetlands, wet depressions, woodland edges, and streams or river banks. It prefers full sun, but can tolerate some shade and a wide range fo soil and moisture conditions.
Why is it a concern?
Japanese knotweed grows very aggressively in disturbed areas. It excludes native plants by light limitation, nutrient cycling alterations and allelopathy (releasing toxic or inhibiting chemicals to suppress the growth of potential competitor plant species).
Multiflora Rose
This shrub can grow up to 15 feet and is established in Michigan.
How to identify it:
- Multi-stemmed shrub that grows to 15 feet.
- Leaves divided into 5 to 11 sharply-toothed leaflets.
- Stems are green to red and arching, with recurved thorns.
- Clusters of small, 5-petaled, white to pink flowers have a strong fragrance.
- Fruits are small, bright-red rose hips that persist into winter.
Where is it found?
It is found in pastures, old fields, roadsides, forests, streambanks, and wetlands. It tolerates a broad range of soils and moisture conditions and can live in sun or shade.
Why is it a concern?
Multiflora rose spreads aggressively, both by rooting canes (ends of branches) and by seed dispersed by birds and wildlife. Dense thickets of this shrub crowd out beneficial shrubs and plants and may deter native birds from nesting.
You can visit Michigan’s invasive species website to learn more about these invasive trees, shrubs and other invasive species.