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Invasive Species |
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Tree Killers
Black Locust
(Robinia pseudoacacia)
 Photo 1: Dan Tenaglia (www.missouriplants.com) Biology
- a medium-sized tree (up to 25 m or 80 ft tall) with long compound leaves
- belongs to the Pea family
- like many other species in the Pea family, it has nitrogen-fixing bacteria in its roots enabling the tree to grow vigorously in poor soil
- reproduces by root suckers to form dense clones of interconnected trees
- in spring the trees produce large, drooping clusters of fragrant, white flowers
- large, hanging, multi-seeded pods form in the summer and remain on the tree until the next year
- seeds rarely germinate although they are produced in large numbers
- branches contain pairs of short, sharp spines
- prefers open areas with well-drained soil and lots of light but tolerates a wide range of growing conditions
- stumps will re-sprout vigorously if cut
History in Canada
- introduced from the southern United States as an ornamental tree and as a source of hard, rot-resistant wood
- still available from nurseries
- most abundant in southern Ontario but occurs east to Nova Scotia as well as in British Columbia
 Photo 18: Mandy Tu /The Nature Conservancy Impact on Trees
- may grow in dense stands in open woodland, forest openings, and forest edges
- suppresses native tree seedlings due to shade
- enables invasion by other non-native species by enriching the soil with nitrogen
Control
- cutting or girdling stems followed by herbicide application to the cut stems or later removal of sprouts that develop after cutting
- several years of control may be needed since stumps can resprout one or more years after treatment
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