What is the Concern with European Buckthorn
European (Common) Buckthorn (Rhamnus carthartica) is a deciduous small tree or shrub, native to Europe. In the 1930s, the former Dominion Tree Nursery (at the location of the current Saskatoon Forestry Farm) evaluated European Buckthorn as a potential shelterbelt tree. The species was of interest due to its hardiness and ability to tolerate a variety of soil and site conditions. It was discontinued as it is an alternate host to Oat Crown Rust (Puccinia coronata). Unfortunately, the species escaped from cultivation before the program was cancelled. It has been found up to 60 km north, 20 km south and throughout the city of Saskatoon.
European Buckthorn is prevalent in riparian forests of the Meewasin Valley, in upland sites in Aspen, Chokecherry and Saskatoon patches and in shelterbelts of other non-native species such as Caragana. It is found in urban parks, natural areas, and in backyards within Saskatoon and surrounding area. Seeds typically fall from parent trees forming dense, even-aged stands which crowd and shade out native understory plants, reducing natural cover of native understory plants eventually displacing native trees and shrubs. Seed dispersal is aided by rodents and birds. Fruit eating birds have been observed eating European Buckthorn fruits and it is speculated that this may be the major vector for seed dispersal in the Meewasin Valley.
In 2010, it was designed as a Noxious Weed under the Saskatchewan Weed Control Act. Meewasin’s 2017-2027 Meewasin Valley-wide Resource Management Plan identified invasive species the greatest threat to biodiversity in the Meewasin Valley.
What Does European Buckthorn Look Like?
European Buckthorn can be either shrub or trees; shrubs are 1-4 m tall with many stems and branches while in tree form it can be 5-8 m tall with a single main stem and ascending branches. Most branches are tipped with a small thorn. Leaves often remain green well into late autumn or early winter, making it is easy to detect after most tree species have shed their leaves. The fruits are single or clustered black berries that persist on the branches throughout most of the winter and are strongly laxative. Seeds germinate best in disturbed sites and only survive in the seed bank for a few years.
European Buckthorn Control Program – 2015 to 2018
In 2015, Meewasin received funding from Environment and Climate Change Canada’s Habitat Stewardship Program, Prevention Stream to expand its European Buckthorn Control Program that was first initiated in 1998. From 1998 to 2015, Meewasin, in partnership with the City of Saskatoon, controlled approximately 704,000 stems along the Meewasin Valley and within the City of Saskatoon. The expansion of the program has allowed Meewasin and the City of Saskatoon to provide a greater focus on control efforts with an additional 504,000 stems controlled in first two years of the program (over 1.2 million controlled from 1998 to 2016!).
2017 European Buckthorn Control Program
The objective for 2017 is for Meewasin and the City of Saskatoon, Parks Division to focus on several critical areas starting in mid- October 2017. These include: City of Saskatoon Parks, Natural Areas within city limits (Saskatoon Natural Grasslands, Peggy McKercher Conservation Area), Natural Areas outside of city limits (Cranberry Flats Conservation Area, Poplar Bluffs Conservation Area) and the South Saskatchewan River Valley.
Over the years, various control techniques have been tried and researched, with the most cost and time effective control method being a basal bark herbicide application. This technique involves directly applying a herbicide called Garlon RTU to the stem of the European Buckthorn at approximately 5 cm above the soil surface. This herbicide penetrates the bark of the stem and translocate down to the roots. The herbicide is oil based, therefore can be applied during colder temperatures (up to -15C).
The control efforts are conducted by City of Saskatoon, Parks Division and Meewasin Resource Management staff who are certified herbicide spray applicators with the Government of Saskatchewan.