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Cytisus scoparius(Scotch broom) – Can it be Controlled Using Sewage Biosolids?

Jacqueline Shaben, MS candidate, Dr. Judy Myers
Department of Zoology, University of British Columbia, Vancouver, B.C., shaben@zoology.ubc.ca

Cytisus scoparius (Scotch broom) is a leguminous, nitrogen-fixing shrub that is native to the Mediterranean. It has invaded open, coastal meadows and disturbed sites in the Pacific Northwest. Dense broom stands produce a prolific seedbank which typically results in re-invasion following shrub removal. To determine if seedling recruitment can be suppressed by increasing the nitrogen levels of the soil I have compared the efficacy of fertilization with sewage biosolids and of ammonium nitrate.  Experiments were conducted at three sites in South-Western British Columbia; one on a sandy dredge till site and two on powerline rights-of-way. Site establishment consisted of hand removal of broom, soil tillage by roto-tiller and seeding with native grass seed following treatment. Treatments consisted of biosolids, applied at a rate of 20 dry tonnes/hectare (approximately equivalent to 400kg available N/hectare), ammonium nitrate (applied at an equivalent rate of 400kg available N/ha/year) and a control.
Results from the first year’s data suggest that at two of the three sites (Iona Beach and Burnaby), significantly fewer broom seedlings emerged in the biosolid-treated plots, percent cover of broom seedlings was significantly lower in biosolid-treated plots and that the overall biomass of competitive vegetation tended to be greater under the biosolid treatment. The second year’s data will be collected and analyzed by September, 2006. If these patterns hold, increasing soil nitrogen through fertilization could be used as a tool in the control of invasive Scotch broom in non-environmentally sensitive sites.