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Invasive autumn olive produces 200,000 seeds per plant

Autumn olive can be found at Scanlon Creek Conservation Area in Bradford West Gwillimbury

Back in the 1970s, when well-meaning land managers looked for a species of shrub that could be planted in nutrient-poor soils to provide wildlife habitat, prevent erosion, and provide a food source for birds, they thought they had found the perfect plant in Elaeagnus umbellata, the autumn olive.

Unfortunately, as nature conservancies discovered across the U.S. and Canada, the shrub – native to Asia – could become an aggressive invader and a threat to native species.

Autumn olive was introduced in the early 1900s as a garden ornamental, and quickly caught the attention of managers, as suitable for erosion control and wildlife habitat, a “roadside refurbisher” that could be used to re-vegetate disturbed habitat, that was both drought-resistant and hardy.

The shrubs can grow to five to six metres in height, distinguished by their leathery foliage – a shiny green on the upper side, and silvery underneath. The plant fixes its own nitrogen, making it an effective colonizer of poor soils and even mine tailings, and produces pink to red fruits that are enjoyed by birds.

And therein lies the problem. The nitrogen-fixing properties of autumn olive change the soils, making it more difficult for native colonizers of nutrient-poor soils to take hold. It is fast-growing, and prolific: according to some sources, a single plant can produce up to 80 pounds of berries each year – about 200,000 seeds per plant.

Birds, including cardinals, sparrows and wild turkeys, love them – spreading the seeds, which remain viable for up to three years, in their droppings.

The plant may even release allelopathic chemicals, suppressing the growth of other plants, and can form dense colonies, creating heavy shade that excludes native species. The result: autumn olive has spread, especially in grasslands and disturbed areas, outcompeting native plants for light, space, and nutrients.

While it has become a real problem in some states, including Indiana, where it can produce stands with up to 125,000 plants per hectare, it’s not that prevalent in Ontario - yet.

“It definitely is here. I’ve seen pockets of it,” said Paul Cottenden, forestry technician with the Lake Simcoe Region Conservation Authority (LSRCA).

Autumn olive can be found at Scanlon Creek Conservation Area, between the workshop and Education Centre – and had to be cleared out when the conservation authority was creating its leash-free Bark Park. But compared to some other invasives, it’s not even on the radar.

“It’s not prevalent, like some invasive species,” Cottenden said.

The LSRCA is currently monitoring the presence and spread of autumn olive, recognizing that other species pose a bigger threat.

“Buckthorn is a bigger issue right now, not only with us, but across Ontario,” said Cottenden – noting that common buckthorn (Rhamnus cathartica) was introduced for many of the same reasons as autumn olive: it’s a fast-growing species, able to establish quickly and provide erosion control, wildlife habitat, and windbreaks.

“They weren’t doing it maliciously,” said Cottenden of the introduction of the shrubs. “All these plants have negatives and positives… I don’t think anybody realized the consequences.”

With buckthorn, the problem is “where do we start? There’s so much of it,” he noted.

Attempts to control Autumn olive have met with mixed success. The plant produces a deep tap root; cutting back the branches just spurs new shoots, and burning also was found by the U.S. Nature Conservancy to encourage the shrub’s spread.

In fact, the Nature Conservancy noted, “autumn Olive is quickly becoming one of the most troublesome shrubs in central and eastern U.S.” Once established, “it is almost impossible to eradicate completely.”

Most recommendations call for a combination of cutting, and the direct application of glyphosate herbicides to prevent the production of new suckers from the roots.

In Ontario, best practices proposed by the Ontario Invasive Plant Council call for repeated pruning, and even uprooting the plant – which Cottenden acknowledged is difficult – along with a recommendation that those hiking or biking on woodland trails clean their shoes and bicycle tires, to prevent the transfer of seeds of this and other invasive species.

When pruning or removing plants, the advice is to wear protective clothing and gloves; autumn olive has thorns, which can grow up to 2.6-centimetres long.

Best practices also call for the planting of native species instead of introduced shrubs – including dogwoods, serviceberry, choke cherry and native viburnums, which provide an equivalent supply of berries for the birds.

Sightings of Autumn olive should be reported to eddmaps.org/ontario and invadingspecies.com.


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Miriam King

About the Author: Miriam King

Miriam King is a journalist and photographer with Bradford Today, covering news and events in Bradford West Gwillimbury and Innisfil.
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