Background
Scotch broom was introduced as a garden ornamental by early settlers of the Pacific Coast. It has spread far beyond the bounds of cultivation and now covers many acres west of the Cascades from British Columbia to California. It has established in northern Idaho as well. Scotch broom reduces establishment rates of conifer seedlings in Oregon and Washington.
Wherever it grows, this aggressive plant spreads to form pure stands at the expense of desirable forbs, grasses, and young trees. Because it is a threat to native plant species and indirectly to animals that feed on the displaced plants, Scotch broom is a Class B noxious weed in Washington and Oregon.
Locally, Scotch broom spreads slowly but persistently. Seed pods split suddenly at maturity and eject the seeds.
Also, it is reported that ants aggressively collect the seed of Scotch broom, assisting in dispersal. Birds also assist with spread, but how well the seeds survive digestion varies with the species of bird.