ALIEN PLANT INVADERS: Broom is Bad, and Gorse is Worse!

By Jean Wilkinson, Salt Spring Island Conservancy

Spring brings longer days, new growth and warm sunshine, but unfortunately it also brings the bright yellow blooms of gorse, and later broom. For people interested in the health of local ecosystems, those concerned about fire hazards, and folks with allergies, this heralds a major headache!

Broom and gorse are covered under the Invasive Plants Regulation of the Forest and Range Practices Act, and gorse is also listed as a provincial noxious weed under the BC Weed Control Act. This legislation imposes a duty on all land occupiers to control designated noxious weeds, due to the very serious economic and ecological problems they pose.

With its sharp thorns and aggressive dense growth, gorse is a huge problem in some regions, but it is currently limited to fairly small areas of Salt Spring. The local Highways contractor is making a special effort to mow gorse along roadways before it sets seed, and hopefully all property-owners will also do their part while it’s still possible to eliminate this fast-spreading invader. Unfortunately, Scotch Broom is very widespread, but with a determined effort it can be controlled and its negative impacts reduced.

Other species such as Portuguese Broom (Cystus striatus) Spanish Broom (Sparitum junceum) and French Broom (Genista monspessulana) are less common, but potentially invasive in this area. Please don’t plant them! There are many low-maintenance, non-invasive plants to choose instead.

SCOTCH BROOM and GORSE – QUICK FACTS ABOUT THESE HORTICULTURAL BULLIES

Identification – Cystus scoparius and Ulex europaeus– vigorous perennial shrubs 1 to 3 metres tall with tap-root, woody photosynthetic stems, small evergreen leaves, and bright yellow pea-like flowers. Hairy seed-pods ripen from green to dark brown or black. Mature gorse has distinctive long thick spines. Broom plants live 15-20 years, but gorse may live up to 45 years.

Impacts – Both species contain volatile oils and create a serious fire hazard wherever they grow. They out-compete native species in sunny locations, and prevent the growth of nearby plants by releasing toxins into the soil, thus reducing plant biodiversity and forage for wildlife. They can form dense, impenetrable thickets which reduce access for recreation, impact Garry Oak woodlands and limit movement of large wild and domestic animals. They invade pastures and replace forage plants, and can impair forest regeneration in logged areas. .

Found – in grasslands, pasture and rangelands, roadsides, forest clearings, coastal bluffs and other open, disturbed areas.

Spreads – each mature plant produces thousands of seeds which can remain viable up to 50 years. Mature seed-pods split and expel broom seeds up to 5 metres, and gorse seeds at least a metre. Seeds are spread widely by ants, mammals, birds, water, people, vehicles and machinery. Gorse is reported to also spread by rhizomes.

Prevent – Infestations develop easily when soil is disturbed, so avoid this as much as possible. Plant competitive species in susceptible areas to provide shade and thus inhibit germination of broom and gorse seeds.

Control – Stems thinner than a pencil can be pulled when the soil is wet. Avoid disturbing soil by placing feet beside plant while pulling, and tamping down afterwards. Larger plants and those growing on rock should be cut at or below ground surface with loppers or pruning saw. To reduce re-growth, cut during bloom before seed-set, or during a drought. For best results, promptly apply wood mulch, and re-vegetate with competitive grasses, alternative shrubs or red alder. Monitor area and repeat for at least 5 years. Grazing by goats can be effective in reducing infestations in pasture areas. Fire is sometimes used to control gorse, but plants can re-sprout and seeds in the soil often germinate following a burn. Although not a preferred method, for persistent infestations herbicides can be applied to gorse stumps or new shoots, as part of an integrated approach.

Disposal – Cuttings are extremely flammable, and large piles of them will leach toxins into the soil. Small amounts with no seeds can be scattered or piled in shady spots. Large amounts with no seeds can be chipped or taken to a goat farmer to use as feed. If seeds are present, avoid spreading them by putting cut or chipped material in strong bags or on tarps in securely covered loads, and take to the landfill.

Alternatives – (Grows in * sun, + part shade, or # full shade, M = Moist soil, D = Dry soil, DT =Drought Tolerant)

Nootka Rose *+M; Tall Oregon Grape *+D,DT; Salal +#M,DT ; Salmonberry *+#M,DT; Thimbleberry *+M,DT; Mountain Mahogany *D,DT; Snowberry *+#D, DT; Red Flowering Currant *+D,DT; Saskatoon *+D/M; Golden Currant *D,DT; Mock Orange *D,DT; California Lilac *D,DT; Forsythia *M,DT; Winter Jasmine *+# M,DT; Japanese Kerria *+# M/D; Hardy Dwarf Broom (Genista lydia) *D,DT; Warminster Broom (Cystisus x praecox) *D, DT; Yellow/Pontic Azalea *#M; Blue Spirea *D/M; Hebe *D.

More Info: Salt Spring Island Conservancy Stewardship Committee 250-537-4877, Coastal Invasive Species Committee www.coastalisc.com, Invasive Species Council of B.C. www.bcinvasives.ca