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Glossy Buckthorn

Frangula alnus

Summary 6

Frangula alnus, commonly known as alder buckthorn, glossy buckthorn, or breaking buckthorn, is a tall deciduous shrub in the family Rhamnaceae. Unlike other "buckthorns", alder buckthorn does not have thorns. It is native to Europe, northernmost Africa, and western Asia, from Ireland and Great Britain north to the 68th parallel in Scandinavia, east to central Siberia and Xinjiang in western China, and south to northern Morocco, Turkey, and the Alborz in Iran and the Caucasus Mountains; in the northwest of its range (Ireland, Scotland), it is rare and scattered. It is also introduced and naturalised in eastern North America.

Short Description 7

Non-spiny deciduous shrub, usually multi-stemmed that grows to 3 to 6 m (10-20 ft) tall. Alternate, ovate leaves 3 to 7cm (2-3 in) long by 2.5 to 4 cm (1-2 in) wide. The entire leaf margin shows 6-10 pairs of grooved veins.

Source: EwA Invasive Pocket Fieldguide | © Earthwise Aware

Description 6

Alder buckthorn is a non-spiny deciduous shrub, growing to 3–6 m (10–20 ft), occasionally to 7 m (23 ft) tall. It is usually multistemmed but rarely forms a small tree with a trunk diameter of up to 20 cm (8 in). The bark is dark blackish-brown, with bright lemon-yellow inner bark exposed if cut. The shoots are dark brown, the winter buds without bud scales, protected only by the densely hairy outer leaves.

The leaves are arranged alternately on .mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}8–15-millimetre (5⁄16–19⁄32-inch) petioles. They are ovate, 3–7 cm (1+1⁄4–2+3⁄4 in) long by 2.5–4 cm (1–1+5⁄8 in) wide (rarely to 11 cm or 4+1⁄4 in by 6 cm or 2+1⁄4 in). They have 6–10 pairs of prominently grooved and slightly downy veins and an entire margin.

The flowers are small, 3–5 mm (1⁄8–3⁄16 inch) in diameter, star-shaped with five greenish-white acute triangular petals, hermaphroditic, and insect-pollinated, flowering in May to June in clusters of two to ten in the leaf axils.

The fruit is a small black berry 6–10 mm (1⁄4–13⁄32 inch) in diameter, ripening from green through red in late summer to dark purple or black in early autumn, containing two or three pale brown 5-millimetre (3⁄16-inch) seeds. The seeds are primarily dispersed by frugivorous birds, which readily eat the fruit.

Invasiveness 8

Alder buckthorn grows in wet soils in open woods, scrub, hedgerows and bogs, thriving well in sunlight and moderate shade, but less vigorously in dense shade; it prefers acidic soils though will also grow on neutral soils.

Frangula alnus was probably introduced to North America about 200 years ago, and in Canada about 100 years ago. It was planted for hedgerows, forestry plantings, and wildlife habitat, but has become an invasive species, invading forests in the northeastern United States and wetlands and moist forest in the Midwestern United States. It is predicted to continue to expand its North American range with time. Its invasiveness is assisted by its high adaptability and pollution tolerance. It is one of three species of buckthorn that occurs without cultivation in eastern Canada.

It invades forests and grows in the understory in spots with a lot of light. These areas, usually where a tree has fallen, normally allow locally native tree seedlings to grow and eventually fill in the gap in the canopy. But when Frangula alnus invades and grows in these locations, its dense canopy prevents light from reaching the ground and therefore prevents other seedlings from growing. It tends to grow more densely and with larger individuals in lower topographical areas with moist, fertile soils, and is very problematic for land managers. Uplands forests are not invaded as easily as lower lying ones. Hemlock-oak stands, which tend to be older stands of trees, are much less suitable for Frangula alnus because the density of the tree canopy creates a more shady environment that is not as suitable for Frangula alnus. Eastern white pine stands are easily invaded because they allow more light to reach the forest floor, and tree stands that are cut are very quickly invaded while undisturbed stands are rarely invaded.

⭕ Control Methods (EwA Content) 9

Glossy buckthorn is one of the most challenging invasive shrubs to control (a). Effective management requires preventing seed production and dispersal (b, c). Small seedlings and plants can be hand-pulled or dug up (c). The most effective approach for well-established populations is a combination of mechanical and chemical methods. In extensive infestations, prioritize the removal of the largest seed-producing plants first (d). Monitoring is vital to prevent the resprouting of treated stumps and shrubs and the depletion of the seed bank (a). Management goals are achieved through the diligent repetition of control measures over several years (e).

Mechanical Treatment

Hand-pulling and digging up seedlings and young plants is recommended during the early invasion stage (a). In large infestations with mature shrubs, mechanical methods alone are ineffective; however, they can be strategically integrated into management plans (a, d). Monitor sites annually and reapply control measures as needed to prevent rapid reinvasion. Minimize soil disturbance whenever feasible and avoid winter pruning to deter vigorous regrowth (d).

Pulling, digging, and mowing → Manually pull out small seedlings when the soil is moist and the population is limited. Pull steadily and slowly to minimize soil disturbance, then compact the soil. In heavier soil or when seedlings are more oversized, use tools like Weed Wrench® or Root Talon® for removal (a, e).

Cutting or mowing mature shrubs quickly removes the plant canopy but stimulates resprouting from the stump. To prevent resprouting, apply herbicide on the cut surfaces or take girdling measures (a, e).

Girdling → Girdling can be employed either independently with limited efficacy or in conjunction with herbicides. When used alone, girdling has the potential to induce tree mortality, though over an extended period, often spanning several years (a, e).

For mature trees, use an axe or saw to make two parallel horizontal cuts around the trunk several inches apart, cutting through the bark and cambium (a thin layer inside the bark responsible for transporting water and nutrients between the plant's roots and leaves) and removing the bark between the cuts. Check the tree periodically until it dies to remove any resprouts and ensure the bark does not heal over. Girdling is more effective when combined with herbicide application (a).

Girdling on stumps is an effective method for reducing the number of new sprouts after cutting. Stumps of glossy buckthorn with a girdle anywhere exhibit a reduction of 40%-50% in sprouts compared to those without girdles. Ensure effectiveness by applying girdling to each stem individually. Moreover, using herbicides on the girdled band can accelerate the plant's decline (e).

Chemical Treatment⚠

Chemical treatments include herbicide application through foliar spraying, basal bark, and herbicide injection (a, e). The optimal time for herbicide treatment is in the fall, once native plants are dormant. This minimizes the impact of herbicides on desirable species and makes it easier to identify the target species (a, d). Additionally, winter application of herbicides has also been proven effective (d). Triclopyr, ester, and amine formulations are the primary herbicides used to treat glossy buckthorn. The amine formula is suitable for use in humid areas (e). Glyphosate can also be used if considered more appropriate for the site (b, c). Always consult the product label for application guidelines.

Foliar treatment → Foliar spray applications involve applying the herbicide directly to the plant’s leaves (e). The most suitable times for foliar application are after spring sap flow and when native plants are dormant in autumn (a, e). Foliar application is recommended in areas with a substantial glossy buckthorn population and few desirable species (a). To apply the herbicide, utilize squirt bottles, backpack sprayers, or boom-mounted sprayers, depending on the site’s characteristics (a).

Cut-stump treatment → Cut-stump treatment is viable in any season except spring when sap flows upward (a). However, the optimal period is from August to October, when the plant transports nutrients to the root system (d).

To perform the treatment, cut the stem horizontally and apply concentrated herbicide using a squirt bottle or absorbent applicator (a, d). Cut near the ground for large stems and treat only the cambium with herbicide. For small stems, cut several inches above the ground and treat the cut surface and sides of the stem with herbicide (a).

Apply a solution of 20-25% triclopyr or glyphosate mixed with water to the stump, covering at least 20% of the top of the cut stem. The herbicide should be applied immediately after cutting (d). Another effective combination is triclopyr ester and 3% Imazapyr with penetrating oil (PS: not approved in humid areas). Imazapyr is effective against glossy buckthorn resprouting for a long time; however, it persists in the soil and can kill native vegetation (e).

Girdling treatment → After girdling, paint the entire exposed cambium with concentrated herbicide. Monitor treated plants, as they may still resprout. Treat new steams by either applying a foliar spray or cutting and applying herbicide (a). Apply a mixture of 25% triclopyr and 75% horticultural oil to the entire girdling area (d).

Basal bark treatment → This method involves applying concentrated herbicide to a strip of bark around the stems in the basal part of the plant (a). Use this method on stems less than 15 cm (2 in) in diameter at any time except during heavy spring sap flow (a). This method is most effective during the dormant season but remains viable year-round as long as snow cover does not impede ground-level spraying, and the bark is not wet from rain (a, d, e).

Apply a mixture of 25% triclopyr and 75% horticultural oil to the basal parts of the plant at a height of 30-15 cm (12-6 in) from the soil. Continue spraying until runoff is noticeable at the soil line. Treat the entire stem circumference in a strip at least 30 cm (12 in) wide (d).
Basal bark treatment is most effective on younger stems with thin bark (a).

Injections/Drill and fill → These methods are effective on larger trees and can be implemented at any time of the year except during spring sap flow (a).

For injection, use a specialized tool to apply the herbicide to the plant stem, roots, or rhizome. Triclopyr is the most suitable herbicide for this technique (a, e). However, the injection technique requires considerable labor (e).

For drilling and filling, drill holes in the tree every 2.5 cm (1 in) at a downward angle and fill them with a measured amount of concentrated herbicide (a).

Disposal

Dispose of uprooted seedlings and shrubs in a manner that ensures their roots dry completely (a). Small bushes can be hung from trees for this purpose. Larger shrubs can be piled with the roots facing up or piled and burned. The same applies to cut stems (d). If fruit is present, it must be burned or bagged and placed in a landfill by state law (a).

⚠ Disclaimers

Disclaimer #1: Harmless chemicals do not exist. Any chemical use is likely to harm non-target species and affect the soil. However, in some circumstances, chemicals might be the only way to succeed in removing an invasive species permanently. Researching and understanding the latest scientific literature before using a specific chemical or a mix of several is critical to reducing negative impact.

Disclaimer #2: Independently, several European countries recently announced future bans or massive restrictions on the use of glyphosate (e.g., Austria, Germany, France). The EU, at large, is expected to decide on the renewal of the approval of glyphosate Ultimo 2023 (More here).

Sources

[a] - Invasive Species—Best Control Practices. Glossy buckthorn Frangula alnus, 2012; Available in: https://mnfi.anr.msu.edu/invasive-species/GlossyBuckthornBCP.pdf
[b] - Invasive in the Spotlight: Glossy Buckthorn. A canopy invader best controlled with early detection, 2019; Available in:
https://extension.unh.edu/blog/2019/07/invasive-spotlight-glossy-buckthorn
[c] - Glossy Buckthorn. Available in: https://www.natickma.gov/1837/Glossy-Buckthorn
[d] - Pest Management – Invasive Plant Control Buckthorns. Available in: https://www.townofbolton.com/sites/g/files/vyhlif2836/f/uploads/buckthornnrcs.pdf.
[e] - State of Michigan’s. Status and Strategy for Glossy Buckthorn (Frangula alnus Mill.) Management. Available in: https://www.michigan.gov/-/media/Project/Websites/invasives/Documents/Response/Status/egle-ais-frangula-alnus.pdf.

Sources and Credits

  1. (c) Kate Danziger, some rights reserved (CC BY-NC), uploaded by Kate Danziger, https://www.inaturalist.org/observations/89076102
  2. (c) Claire O'Neill, some rights reserved (CC BY-NC), uploaded by Claire O'Neill, https://www.inaturalist.org/observations/116682510
  3. (c) Kate Danziger, some rights reserved (CC BY-NC), uploaded by Kate Danziger, https://www.inaturalist.org/observations/89077248
  4. (c) Claire O'Neill, some rights reserved (CC BY-NC), uploaded by Claire O'Neill, https://www.inaturalist.org/observations/138278887
  5. (c) Louisa Dixon, some rights reserved (CC BY-NC), uploaded by Louisa Dixon, https://www.inaturalist.org/observations/120972027
  6. (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Frangula_alnus
  7. (c) Claire O'Neill, some rights reserved (CC BY-SA)
  8. Adapted by Claire O'Neill from a work by (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Frangula_alnus
  9. Adapted by Esther Meirelles from a work by (c) Claire O'Neill, some rights reserved (CC BY-SA)

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