Invasive Plants, Pacific Northwest
Scotch broom is an escaped garden ornamental, common west of the Coast Mountains in southwest BC, and is out of control on the BC coast. It is an evergreen shrub, with bright yellow, pea like flowers that may have red markings in the middle.
Stems are woody and 5 angled, with lower leaves composed of 3 leaflets. The flat seedpods are initially green, turning dark brown to black with maturity and are hairy. It grows up to 3 metres in height at maturity.
It spreads by seed and lateral bud growth, and mature plants can produce up to 3500 seed pods, each containing 5 to 12 seeds. As seedpods dry, they split and spiral, expelling the contained seeds up to 5 metres. The plant can also spread to new areas through seed transport by animal, bird, hikers and vehicles.
Due to its affinity for light dominated, disturbed areas, any disturbance activity, such as road or home construction near infested areas, can enhance spread. Scotch Broom invades range lands, replacing forage plants, and is a serious competitor to conifer seedlings. Douglas fir plantation failures in Oregon and Washington have been credited to infestations of this plant.
High density infestations can increase wildfire fuel loads, thereby escalating wildfire intensity and dense thickets may be impacting Garry Oak woodlands in southern Vancouver Island and limiting movement of large animals.
Year round growth gives scotch broom the ability to displace native plant species.