Invasive plants have a variety of negative effects on the watershed.
- They out- compete and displace native plants that are the food source for native wildlife.
- They often grow rapidly, and the high volume of vegetation can result in reduction and diversion of stream flows.
- Some invasive plants, like the brooms, are flammable even when green. Thickets of broom can enable the spread of wildfire along roadsides and gravel bars and into tree stands.
Invasive plants are found throughout the watershed. At least 19 species have been found on the neighboring lower Pit River. Several problematic species have become established on the gravel bars and stream banks along the Upper Sacramento River. The primary invasives of concern on the Upper Sacramento include French and Scotch Broom, Dyer’s Woad (also known as Marlahan Mustard), Perennial Sweet Pea, Whitetop, Tree of Heaven, and Himalaya Blackberry. Scotch Broom was widely used for erosion control in the past, but has spread to become a dominant plant along the river. Other weeds have been accidentally introduced in hay bales used to control erosion in construction and road maintenance. Once these plants are firmly established, the river itself carries seeds down stream to new locations.