Common Name: Black alder, European alder
Scientific name: Alnus glutinosa
Identification: Black alder is a large deciduous tree. It can grow up to 50’ tall at maturity in favored growing conditions, with a crown that is 35’ wide and loosely pyramidal in shape. Leaves are alternately arranged on twigs. The leaves are oval to round in shape, often notched at the tip, and are typically 2 – 4” long and 3 – 4” wide. The leaf edges are coarsely double-toothed. Foliage is glossy and dark green with no color change in fall. Young leaves tend to be sticky with a gummy resin. Some horticultural varieties of this species have finely lobed leaves, and some have yellow or variegated (two-tone) foliage. Young bark is grey and mostly smooth with raised white pores (lenticels). Older bark is dark grey with flattened plates. Male flowers are 2 – 4” rust-colored catkins, while female flowers are small (½”) pinkish catkins. Fruits are woody brown cones, ½ – ¾” long, which form in mid-fall and persist through winter. (Dirr 2019)
Look-alikes: Black alder is related to and somewhat similar in appearance to three species that are native to parts of the Great Lakes region: speckled alder (A. incana subsp. rugosa), hazel alder (A. serrulata), and green alder (A. viridis). At maturity, black alder is taller than any of the natives; it is a large tree with a single main trunk, while the natives are all multi-stemmed shrubs (less than 25’ tall). All three natives have roughly elliptical leaves with a pointed tip. The leaves of black alder are more round and are either rounded or notched at the tip.
Black alder is reported occasionally throughout most of the Great Lakes Basin. It is not known to occur in Northern Minnesota, the Upper Peninsula of Michigan, or in Central-Western Ontario. There is some conflicting information regarding this species’ hardiness. The USDA Plants Database indicates a minimum winter temperature of -18oF (Zone 5a), indicating that it would not be able to grow in the coldest areas of the Great Lakes Basin. However, research on the species from its native range shows that it can withstand very low temperatures (Claessens 2010). Nationally, black alder is most commonly reported in the Great Lakes region, in the greater New York City area, and in coastal New England.
Additional invasive species distribution data for specific Great Lakes jurisdictions is available from:
Seeds are distributed locally by gravity leading to local thicket-like populations. Seeds can be carried long distances by running water, and by wildlife. Although black alder is capable of vegetative reproduction through the root system, this seems to play a relatively minor role in its spread (Funk 1990).
Black alder invades disturbed wetlands, including riparian corridors. It is very adaptable and can grow in nutrient-poor soils due to its ability to fix nitrogen as long as moisture is sufficient.
Black alder has been known to establish single species colonies as a result of its fast growth rate and high rate of seed production, out-competing native trees and other plants. Black alder is also known to change wetland ecosystems in a number of ways. It is a nitrogen fixing plant, meaning that bacteria that colonize the root system are able to transform nitrogen in the air into forms that are useable by plants. This species also produces a large amount of leaf litter, which can effect carbon cycling and soil acidity. Finally, the root system can trap sediment and change the way that water moves through wetland systems. All of these changes can have unpredictable impacts on the native plant community. (Anderson 2010, Cao et al, 2012).
It has been found through genetic testing that black alder freely hybridizes with European gray alder (Alnus incana subsp. incana) (Jurkšiene et al. 2021). It is unknown whether black alder hybridizes with the closely-related North American speckled alder (Alnus incana subsp. rugosa) or what the potential impacts on speckled alder populations might be. The two species do share considerable range and habitat types in North America (Kartesz 2015).
Black alder was introduced to North America as a landscape plant. It is commercially available today but is not popular in most developed landscapes due to its perceived lack of ornamental features, messy litter, and invasiveness (Dirr and Warren 2019). It is sometimes used in wet areas, such as riverside parks, or in moist sunny areas with low soil fertility (Dirr 1998). It is also occasionally used as a “nurse tree” for other species in areas with poor soil, particularly at extremely challenging sites like mine reclamations (Cao et al, 2012).
Please see our Landscape Alternatives pages for more information about how the WIGL Collaborative selected alternatives.
|Alternatives for Black Alder
Common name (Latin name)
(>40ft tall at maturity)
|Speckled alder (Alnus incana subsp. rugosa)||✔||✔|
|Yellow birch (Betula alleghaniensis)||✔||~||~|
|Black birch (Betula lenta)||✔||~|
|River birch (Betula nigra)
|American beech (Fagus grandifolia)||✔||✔||✔|
|Sycamore (Platanus occidentalis)||✔||✔|
|Sweet-gum (Liquidambar styraciflua)
~ = trait is somewhat present but not as pronounced as in check-marked examples
a Listed cultivar has the indicated trait, but the straight species may not. Straight species native plants may provide greater pollinator benefits.
b Only cold-hardy cultivars like the one listed are recommended for the upper Midwest/Great Lakes.
Green = native to part of the Great Lakes Basin
Yellow = native to the United States but not to the Basin
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 black alder. 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: Whenever possible, individual plants should be controlled before they form cones in order to prevent spread. If control is undertaken when cones are present, it is best not to remove the plants from the site to avoid spreading seed.
Physical control: Small plants can be hand-pulled from moist soil; larger plants can be dug or pulled using equipment such as a weed wrench. The root system must be removed to prevent regrowth. It should be noted that soil disturbance often triggers seed germination of this species, so monitoring and repeat treatment will be critical (Anderson 2010). Methods that top-kill the plant without impacting the root such as cutting and girdling are unlikely to be effective without follow-up herbicide treatment due to the potential for regrowth.
Chemical control and combined approaches: Foliar application may be practicable on dense growth of seedlings, but is not usually conducted on mature black alders due to the potential for drift in sensitive riparian areas. Cut stump, stem injection, and basal bark herbicide treatments are effective and can be applied during most times of the year (avoiding early spring). These treatments may be most effective when applied during the fall (Anderson 2010). In all cases, herbicide should be selected carefully based on site conditions, and label directions read and followed carefully. When treating in wetlands or adjacent to running water, managers should select herbicide that is approved for aquatic use.
With any treatment it will be necessary to monitor for and treat regrowth and new seedlings in subsequent years.
Resources on management of black alder:
- Anderson, H. 2010. European black alder: best management practices in Ontario. Peterborough, ON: Ontario Invasive Plant Council. 1/11/2019.
- Cao, L, Larson, J, Berent, and A Fusaro. 2012. Alnus glutinosa. In: Great Lakes Aquatic Nonindigenous Species Information System (Online). U.S. Geological Survey and National Oceanic and Atmospheric Administration. 1/11/2019.
- Claessens, H, Oosterbaan, A, Savill, P and J Rondeux. 2010. A review of the characteristics of black alder (Alnus glutinosa), and their implications for silvicultural practices. Forestry: International Journal of Forestry Research. 83(2): 163-175.
- Dirr, MA. 1998. Alnus glutinosa. In: Manual of Woody Landscape Plants, Fifth Edition. Champlain, IL: Stipes Publishing. 85-86.
- Dirr, MA and KS Warren. 2019. Alnus glutinosa. In: The Tree Book: Superior Selections for Landscapes, Streetscapes, and Gardens. Portland, OR: Timber Press. 157-158.
- Funk, DT. 1990. Alnus glutinosa. In: Silvics of North America, Volume 2: Hardwoods. U.S. Department of Agriculture, Forest Service. 4/8/2020.
- Jurkšiene, G, Tamošaitis, S, Kavaliauskas, D, Buchovska, J, Danusevicius, D, and V Baliuckas. 2021. Identification of Alnus glutinosa L. and A. incana (L.) Moench. hybrids in natural forests using nuclear DNA microsatellite and morphometricmarkers. Forests, 12, 1504, 1-18. https://doi.org/10.3390/f12111504
- Kartesz, JT. 2015. Alnus. In: The Biota of North America Program (BONAP), North American Plant Atlas. (http://bonap.net/napa). Chapel Hill, N.C.
Photo: Paul Wray, Iowa State University, via bugwood.org