Invasive non-native plants refer to plants growing outside of their native habitat. Once introduced into a new area, these plants grow without their natural checks and balances, such as predators and climate. Because of this, invasive plants often spread rapidly, displacing native plants and reducing biodiversity in critical habitats. Introduction of invasive species can cause economic or environmental harm, or harm to human health.  Japanese Knotweed, Scotch and French Brooms, English ivy, and Star Thistle pose the greatest threats to the Mattole, and are the focus of most removal projects.