Glossy Buckthorn, Frangula alnus, is a member of the Rhamnaceae family. This family is commonly known as the buckthorn family and it contains over 950 species.
Glossy buckthorn was introduced from Europe as an ornamental shrub some time before 1800.
It is an aggressive, invasive shrub with multiple stems and can grow to be 20’ tall.
Glossy buckthorn tolerates a wide range of habitats like wetlands, woodland edges, old fields, ditches, and grassy areas.
Spreads mainly by sexual reproduction, with seeds often being spread by birds.
On PEI, glossy buckthorn is widespread throughout the Charlottetown area.
Glossy buckthorn is a large perennial deciduous shrub.
Its leaves emerge early in the spring and remain on twigs into late fall after other species have died back.
This shrub has multiple stems with grey-brown spotted bark.
The spots are known as lenticels
With maturity these stems merge into a larger single central trunk.
Leaves are alternate, shiny, and oval-shaped with smooth edges.
Flowers bloom in June. They are tiny, star-shaped, white to whitish-green and are found growing along leaf axils in small clusters.
Red berries called “drupes” replace the flowers beginning in July.
As they ripen, they turn black.
The drupes are produced from July-September and persist into the winter.
Drupes tend to mature at different times along the same branch.
Common buckthorn, Rhamnus cathartica, is a related lookalike of glossy buckthorn.
Common buckthorn is also invasive and found on PEI.
Common buckthorn has slightly toothed leaf edges, while glossy buckthorn does not.
Common buckthorn has a thorn at the end of each branch, while glossy buckthorn lacks thorns.
The drupes of common buckthorn grow in large clusters, while glossy buckthorn drupes grow in smaller clusters.
The immature fruit of common buckthorn is green, whereas glossy buckthorn immature fruit is red.
The leaf veins of glossy buckthorn extend straight toward the leaf edge (in a herringbone pattern), whereas common buckthorn leaf veins are curved and end near the leaf tip.
What it does in the ecosystem
Like many invasive species, glossy buckthorn has adapted to thrive in a wide range of habitats and growing conditions.
Suitable growing conditions include both open areas with full sun and shady, forested areas.
It grows in wetter, less shaded, and more acidic soils than some other buckthorn species and is especially aggressive in alkaline bogs and swamps.
You can find this species in bogs, marshes, fens, wetlands, riverbanks, forests, abandoned farmland, and roadsides.
Glossy buckthorn is fast-growing and densely leafed.
It can monopolize light in a canopy and out-compete native species.
The leaves on larger buckthorn shrubs emerge early in the spring, blocking sunlight from reaching lower-growing species such as native wildflowers.
Buckthorns are allelopathic, which means they release chemicals from their roots that the growth of competing plants and increase the buckthorn’s fitness.
Glossy buckthorn seed production is prolific.
Seedlings germinate early in spring, before most other understory plants.
The berries stay on the shrubs over winter, increasing the chance that foraging birds will eat them.
Unfortunately, buckthorn berries are low in nutrients and contain a natural laxative.
The laxative ensures that seeds are quickly dispersed by birds who eat buckthorn berries.
Low nutritional value and the added laxative means that birds have to expend much more energy to feed.
This can be a serious concern for birds leading into the winter months.
Weakened energy reserves can impact successful migration or the overwintering of resident birds.
Before selecting a control method, consider the size of the infestation, your available resources, and the amount of effort you are willing to expend.
Often, multiple control methods are used simultaneously.
Surveying and management for glossy buckthorn is best done in the spring, as this plant produces leaves very early.
This way, you will avoid trampling native species that might be present in the area.
You will have plenty of time in early summer for your management before glossy buckthorn goes to seed.
The most important aspect of glossy buckthorn management is that the berries are prevented from establishing.
Berries are glossy buckthorn’s main method of spread.
Cutting and burning tend to lead to vigorous re-sprouting from left-behind stumps, so these methods are not recommended control measures.
While these treatments temporarily prevent seed production, they do not kill the buckthorn.
Removal sites must be closely monitored for regrowth, and regularly repeated control efforts will likely be required to effectively control an infestation.
PULLING OR DIGGING
Physical removal of buckthorn infestations is the most effective method of manual control available.
Plants less than 1 inch in diameter and about a metre in height can be pulled by hand or with the help of tools.
The Extractigator® is a tool designed specifically for this purpose.
This is a lever system designed to uproot tough shrubs and bushes.
Spades and shovels can be used to cut a circle 1-2ft out from the shrub’s trunk.
Another person rocks the shrub back and forth to show what remains necessary to cut.
Using an axe can help to chop through the roots making it easier to remove large shrubs.
Regeneration is unlikely if a portion of the root system is removed.
Tap disturbed soils back into place and plant suitable native species to discourage the further establishment of invaders.
The right species to plant will vary site to site. Reach out for advice on selecting a replacement to plant. Native alder and willow grow similarly.
Pulling buckthorn plants early in the season is ideal, as it helps to reduce competition for the light and nutrients needed by other plants.
If the plant has berries, it is important to remove the branches and bag them before pulling the stem out.
You do not want to shake the berries off the branch during management, as this will make the seed bank longer-lasting.
Laying out a ground sheet below your work area can help catch any berries that detach.
Pulling buckthorn infestations is labour intensive, so this method may not be possible for large infestations.
Girdling involves removing a two-inch-wide ring of bark from near the base of a tree.
Remove the outer bark and the green cambium layer, but avoid cutting into the hard core of the trunk.
If the xylem layer in the core is disturbed the shrub will respond by resprouting. If the cut is not deep enough the tree will heal.
This is why it is key to cut to the appropriate depth.
This technique allows the roots to nourish the crown but prevents the crown from sending nourishment back to the roots, leading to eventual root death.
Trees that have been girdled should continue to be monitored and new sprouts that develop below the girdled site should be removed.
Girdling buckthorn infestations is labour-intensive, so this method may not be feasible for large infestations.
Girdling should be reserved for large individuals that cannot be pulled or along waterways where it is the only species along the bank.
Chemical control methods exist for glossy buckthorn, but the PEI Invasive Species Council does not provide advice on these measures at this time.
Surrounding vegetation and wildlife may be damaged by the herbicides.
Herbicide use is prohibited near wetlands and watercourses on PEI.
If using chemical control methods, it is imperative that all local legislation and manufacturer’s instructions be followed.
FOLLOW-UP AND DISPOSAL
After work is completed, it is imperative that all equipment be thoroughly cleaned and that all plant parts are removed from boots and clothing before leaving the area.
If the plants have fruit, all branches with berries must be bagged and properly disposed of.
If management occurs before berries are formed, or if the plants have not yet matured to produce berries, the most important thing is that the roots of the plant are left in such a way that they cannot root themselves back in the soil.
The PEIISC often hangs buckthorn plants upside down by their roots from nearby trees.
Each time you manage the site, collect, bag, mark, and dispose of all berried branched properly.
Bag the branches in clear plastic bags.
Mark the bags boldly with a permanent marker. Write “INVASIVE PLANT” or “GLOSSY BUCKTHORN” on the bags.
If the bags are thin, double bag them to prevent accidental dispersal later on.
Tie the bags tightly and place them in your usual residential waste collection (THE BLACK BIN)
Never place invasive plants into the compost. This may allow them to become established once they reach the heap.
With any treatment option, the site will need to be revisited regularly to control any new growth which may appear.