Alien invaders are usually the subject of science fiction and anti-immigration pundits. Rarely is the imagined threat considered real, and never is the dangerous intruder thought to be lurking in the bushes considered to be the bushes themselves. Those days are over.

After an extended period of fire and flood in the San Luis Rey watershed, a council majority of Esther Sanchez, Rocky Chavez and Mayor Jim Wood voted to pick up the mantle of environmental stewardship by banning three species of exotic invasives that long ago lived out their welcome.

If tamarisk, arundo donax and pampas grass sound exotic, they are. Those plants are a threat to human communities, causing property damage and posing a fire risk, and a threat to native plant and animal biodiversity by crowding out indigenous species and forever altering Southern California habitats.

This ecological catastrophe has long been in the making and is highly encouraged by commercial growers, clueless gardeners and lazy landscapers for more than a century. Thankfully state and local government have now acknowledged the threat, and are doing something about it.

Hopefully it’s not too late.

In the mid-1800s, these species were imported to the United States for use in erosion control, roofing, reeds for woodwind instruments and garden ornamentation. More than a century later, these prolific species have completely displaced native plants reducing habitat and forage for native bird and animal species.

Tamarisk, of the plant genus tamarix, is comprised of about 54 species native to North Africa, the Mediterranean and the Middle East. Also known as “salt cedar,” it usually grows as a woody shrub or small tree in areas where water is at or near the surface. Tamarisk has invaded almost all watercourses and more than 1 million acres of wetland habitat throughout the Southwest.

Tamarisk species are fire-adapted, and have long tap roots allowing them to intercept deep water tables and exploit natural water resources. These species also limit competition from other plants by taking up salt from deep ground water, accumulating it in their foliage, and depositing it in the surface soil where increased salinity deters native plants.

Recent floods and fires have revealed arundo donax, among the fastest growing terrestrial plants in the world, poses a significant risk to municipal infrastructure and private property. Introduced from the Mediterranean to California by the Spanish as erosion control, arundo now threatens California’s riparian ecosystems by out competing native species for water. Stems and leaves of arundo contain a variety of harmful chemicals that protect it from most insect herbivores and deter wildlife from feeding on it.

Both species of Patagonia native pampas grass, cortaderia selloana and cortaderia jubatais, are highly adaptable and grow in a wide range of environments and climates. Each plant is able to produce more than 1 million seeds during its lifetime. The spread of pampas promotes the spread of wildfires into riparian corridors.

The best way for residents of Southern California to prevent the spread of tamarisk, arundo, pampas grass and other exotic invaders, is not to invite them into the community by purchasing and planting them, or allow them to remain in existing landscaping when native species are readily available and better suited to the ecological balance of indigenous habitats.

Environmental restoration begins at home.