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Individual study: A comparison of pulling vs. cutting as methods to control invasive broom Cytisus scoparius in Garry oak Quercus garryana meadow communities in Victoria, British Columbia, Canada

Published source details

Ussery J.G. & Krannitz P.G. (1998) Control of Scot's broom (Cytisus scoparius (L.) Link.): the relative conservation merits of pulling versus cutting. Northwest Science, 72, 268-273

Summary

Over the last 150 years in the pacific northwest of Canada and USA, agricultural and urban development has led to the loss of most Garry oak Quercus garryana ecosystems. These ecosystems are biologically rich and characterized by a mosaic of woodlands, meadows, grasslands and open rocky areas. Overgrazing by domestic and feral livestock has impaired Garry oak regeneration and this, coupled with fire suppression, has enabled non-native plant species such as Scot's broom Cytisus scoparius and orchard grass (or cock's-foot) Dactylis glomerata to take over. In British Columbia, only 1-5% of original Garry oak ecosystems are left and much of this has been strongly modified by invasive species.

A study was undertaken to investigate how the method and timing of the removal of the invasive shrub, Scot's broom, affected the level of site disturbance and subsequent broom regeneration from seed and resprouting in areas of remnant Garry oak meadow communities in Victoria, British Columbia.

Study site: The study was undertaken in remnant, high conservation value, Garry oak Quercus garryana meadow communities at the southern tip of Vancouver Island around the town of Victoria, southwest British Columbia.

Manual uprooting versus cutting: Manual uprooting versus cutting of invasive broom Cytisus scoparius was compared at two time periods, in May when the shrub was in flower, and in July just prior to seed dispersal. Pulled and cut material was removed from site for disposal.

Soil disturbance, trampling & seedling regeneration: Soil disturbance, trampling, and seedling regeneration were significantly higher in plots where broom plants were uprooted as compared to plots where broom plants were cut at the base. The amount of trampling damage to meadow plants was higher in July than in May, howevr, in July the trampled plants comprised mostly exotic grasses, while in May these included flowering and fruiting stalks of native plants such as common camas Camassia quamash.

Resprouting of cut broom stems: Resprouting of cut broom stems was observed in only seven (9%) of the 75 broom stems cut and all of these died-back within one year.

Conclusions: These results suggest that the preferred broom removal strategy in Garry oak meadow communities of high conservation value is to cut broom after native herbaceous species have flowered and set seed. This approach will minimize damage to native vegetation and should reduce the amount of broom seedling regeneration in the longterm if cutting is regularly repeated.


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