Alnus alnus (L.) Britton, Betula alnus var. glutinosa L., Betula glutinosa (L.) Lam., European alder, Black European alder

Several cultivars including pyramidal forms and trees with finely dissected leaves.

European alder is similar to the native shrub alders found along the streams in the American Northwest but can be distinguished by the notch at the apex of its leaves (Gubanov et al. 2003). Speckled alder (Alnus rugosa) has leaves with a distinct (acute) tip, usually shrubbier than A. glutinosa.

In the UK, A. glutinosa starts to flower in February when the temperature reaches 10-13°C (McVean 1953). Alnus glutinosa is a light-demanding species and seedlings do not usually survive in the shade of mature trees (Pancer-Kotejowa and Zarzycki 1980). Trees may live up to 100 years (Jaworski 1995), but sometimes on poor sites it may only live for 20-25 years (Savill 1991). The presence of symbiotic bacteria in the root nodules (Akkermans 1978; Van Dijk 1978) enables A. glutinosa to grow on soils that are poor in nitrogen. The root system of specimens growing on flooded soils is differentiated into horizontal roots (with nodules) and the stronger, almost vertical ones that grow deeper. The oxygen conditions in the roots are also improved by aerenchymatic tissue inside roots which have developed under water (McVean 1956). The species is monoecious. Reproduction is mainly by seed, but coppices readily after felling. The seeds are orthodox. Alnus glutinosa grows naturally in various temperate localities with the climate ranging from seasonally cold to warm. Climate data are based on the natural distribution and relevant climatic information (Walter and Lieth 1960).

According to Jurkevic et al. (1968), A. glutinosa grows well where there is a mean annual temperature from 4.0 to 7.5 C, and a mean annual rainfall from 400 to 700 mm. If climatic data from the whole natural range of the species is taken into account, the ecological amplitude of A. glutinosa appears much broader. The estimated mean annual temperature range is 1-18 C and mean annual rainfall range 400-1300 mm. Alnus glutinosa is highly resistant to seasonal frost as it grows in areas where the temperatures drop to -40 C, with the absolute minimum being -49 C, though extremely cold temperatures result in lower annual growth (Jurkevic et al. 1968).  Alnus glutinosa is, however, susceptible to drought (Fabijanowski and Zarzycki 1961). Alnus glutinosa grows naturally mainly on histosols and sometimes on gleysols or fluvisols (FAO 1988; Pancer-Kotejowa and Zarzycki 1980). The species is very resistant to flooding and waterlogging.

Alnus glutinosa grows better on flat areas or even in hollows, and it is one of the most suited species for planting on the banks of the lowland rivers, streams, along ditches, lakes and ponds. The altitudinal distribution ranges from sea level (sometimes even below, in depressions) up to high altitude sites, especially in the mountains located in the south of its range. The maximum altitude for the natural occurrence of A. glutinosa differs in various mountains: up to 1800 m altitude in the Alps (Hegi 1957), 1500 m in Macedonia (Jovanovic 1970), 1300 m in the Carpathians (Blattny and Stastny 1959; Savulescu 1952).

Dozens of insects and diseases have been observed in association with black alder, but few cause serious damage (Funk 1990).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Beneficial

Current research on the environmental impact of Alnus glutinosa in the Great Lakes is inadequate to support proper assessment.

Realized:
Alnus glutinosa has been identified as an invasive plant capable of displacing desirable vegetation (Herron et al. 2007, NatureServe 2010). It is associated with a number of nitrogen-fixing actinomycetes fungi that directly increase soil nitrogen concentrations (Hall et al. 1979). In general, black alder is an ornamental species, but its use in the Great Lakes varies. It may be discouraged for use in natural areas due to its reported ability to form monocultures (Eckel 2003, NatureServe 2010). With the potential to dominate wetland communities, the Ontario Invasive Plants Working Group has labeled A. glutinosa as a top priority for management (Havinga 2000).

Potential:
Black alder is a pioneer species capable of modifying the environment by colonizing exposed soils, fixing nitrogen, and producing copious amounts of litter (Funk 1990, USDA NRCS 2006). Black alder leaf litter easily leaches water-soluble organic substances that may alter soil conditions and impact nearby plants (Funk 1990). Areas planted with black alder at a mine restoration site in Kentucky had twice as much leaf litter and higher concentrations of soluble salts than areas without black alder. This leaf litter also resulted in significantly more acidic spring soil (Plass 1977).
Results from a study conducted by Vogel et al. (1997) suggest that as atmospheric carbon dioxide concentration increases, nitrogen fixing species such as black alder will be able to fix more atmospheric nitrogen. This will lead to an increase in nitrogen concentration (above current fixation rates) in leaves and, ultimately, in soils via leaf litter decomposition (Vogel et al. 1997).

Black alder could further impact water courses by de-oxygenating the water, shading out other species, and degrading habitat. Black alder’s dense root system is capable of trapping sediment and subsequently altering water flow in wetland ecosystems (Funk 1990). European alder hybridizes readily with many other alders (Funk 1990).

There is little or no evidence to support that Alnus glutinosa has significant socio-economic impacts in the Great Lakes.

Current research on the beneficial effects of Alnus glutinosa in the Great Lakes is inadequate to support proper assessment.
Potential:
This tree has both ornamental and practical value. While it is not considered a commercially-valuable hardwood, Alnus glutinosa is kept by some US nurseries to meet the demand for use in orchards (as a windbreak) and at mine revegetation sites (Mikola 1958, USDA NRCS 2006). However, the wood may be used for carving and the leaves for medicinal purposes (Mills et al. 1993). Within its native range, black alder is used for furniture, wooden-ware, cooperage, charcoal, and wood fiber industries (Genys 1988).

In a supercritical carbon dioxide extraction of A. glutinosa, β-sitosterol and eleven pentacyclic triterpenes were identified (Felföldi-Gáva et al. 2012). These compounds have a variety of potential pharmacological applications, including stunting cancer tumor growth and protecting against the side effects of chemotherapy and radiation treatment (Laszvzyk 2009, MDidea 2010). This group of compounds has also been found to have anti-inflammatory, antioxidant, antimicrobial, and antiviral properties, as well as cardiovascular benefits (MDidea 2010, Patocka 2003). One identified compound, betulinic acid, has been demonstrated to have antiviral properties against HIV (DeClercq 2000).

Black alder acts as a significant source of nitrogen that typically becomes available for other species and has been shown to increase growth in nearby trees (Funk 1990, Mikola 1958, Plass 1977). For this reason, black alder is sometimes recommended as a nurse crop (a species interplanted with the species of interest in order to assist in its growth) for numerous hardwood tree species (Bohanek and Groninger 2005, Plass 1977, Shepperd and Jones 1985, Vogel 1981).

Due to its ability to fix nitrogen and its capability to colonize acidic soils, black alder can aid in the restoration of disturbed sites and spoil banks (Funk 1990). In an evaluation of the soil remediation ability of trees, A. glutinosa not only caused the largest accumulation of organic carbon and total nitrogen of all examined tree species, but also was associated with the most acidic soils (Chodak and Niklinska 2010). When interplanted on coal mine reclamation sites, black alder’s presence was associated with the doubling in size of adjacent yellow-poplar (Liriodendron tulipifera), white ash (Fraxinus americana), and American sycamore (Plantanus occidentalis) (Vogel 1981). In a seven year study of shale mining reclamation sites in Estonia, black alder stands showed high survival and productivity rates, as well as reduced soil pH and phosphorous concentration (Kuznetsova et al. 2011). Notably, black alder may escape from reclaimed mine soils and grow naturally in surrounding areas.

Black alder may provide food for deer, rabbits, hares, and several bird species. Black alder seeds are released from cones throughout the winter, potentially benefiting seed-eating birds. Additionally, black alder could improve earthworm habitat (Funk 1990).

Regulations (pertaining to the Great Lakes region)
There are conflicting recommendations on the regulation of black alder. Indiana recommends that this species be inter-planted to improve soil quality and “protect other valuable trees” (IDNR n.d.). The state also includes black alder on a list of invasive exotics plants whose “use in landscaping and re-vegetation projects should be avoided or limited when possible” (Homoya 2010). Black alder is also listed as a “plant to avoid” in Wisconsin’s planting guide (WDNR n.d.). It is a recommended tree for urban environments in Minnesota (Johnson and Himanga 2009).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
For the most effective control, the US Forest Service (2006) recommends treating black alder with a combination of physical and chemical methods.

Biological
There are no known biological control methods for this species.

Physical
Trees should be felled and then herbicide applied to the stumps to prevent sprouting (USDA NRCS 2006).

Chemical
Effective herbicides include napropamide (preemergence) (Willoughby et al. 2007), glyphosate via exposed stump application (Kelly and Southwood 2006) triclopyr triethylamine via foliar application (Champion et al. 2008).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label directions.