Invasive Species Program

Invasive Species in California

What are invasive species and why are they a problem?

Californians have benefited from the introduction of plant and animal species necessary for food or other human pursuits; however, there are many other introduced species that can wreak havoc on the state’s environment and economy.  Those species that cause harm and once established, spread quickly from their point of introduction are often called “invasive.”

Invasive species threaten the diversity or abundance of native species through competition for resources, predation, parasitism, interbreeding with native populations, transmitting diseases, or causing physical or chemical changes to the invaded habitat.  Through their impacts on natural ecosystems, agricultural and other developed lands, water delivery and flood protection systems, invasive species may also negatively affect human health and/or the economy.  Examples of direct impact to human activities include the clogging of navigable waterways and water delivery systems, weakening flood control structures, damaging crops, introducing diseases to animals that are raised or harvested commercially, and diminishing sportfish populations.

A large population of an invasive species can start from a very small number of individuals, and those individuals can be difficult to see, so they may easily go unnoticed.  The tiny young of invasive shellfish or insects, a fragment of an aquatic weed or a single plant ready to release its seeds can be enough to start off a population that will ultimately become a multimillion dollar headache for the state.  However these populations do not grow from a few individuals to damaging levels overnight, and if populations are detected early enough, there is a good likelihood that they can be eliminated before they cause damage and huge population control costs.  Early detection and rapid response are the most effective and cost efficient responses to invasive species, after prevention.

How did they get here?

Relatively few non-native species were introduced to California prior to its settlement by Spaniards that began in the 1700’s.   With the beginning of European settlement, non-native species were carried to California attached to the hulls of ships, submerged in the ships’ ballast, or carried along in shipments of grain. 

Today, there are many different ways in which non-native invasive species are introduced to the State.   Commercial shipping remains a major source of unintentional introductions, along with smaller commercial fishing boats and recreational watercraft.  People traveling between natural areas, farms or waterways for work or recreation unintentionally spread invasive species on their vehicles, boats, equipment and even clothing.

Both historically and today, non-native invasive species have also been introduced purposely, without an understanding of the potential consequences of those introductions.  This occurs most commonly with plants used for erosion control, livestock forage, and aquarium or garden ornamentals.  Some of the animals that in the past were or are currently brought into California as sources of food, fur or pets have turned into major pests.

What does the Invasive Species Program Do?

The mission of the Invasive Species Program is to reduce the negative effects of non-native invasive species on the wildlands and waterways of California.  We are involved in efforts to prevent the introduction of these species into the state, detect and respond to introductions when they occur, and prevent the spread of non-native invasive species that have become established.  Our projects address problems with introduced animals, plants and microbes, both terrestrial and aquatic.  More fundamentally, we try to address the ways by which the species are introduced, typically inadvertently, by human activities.  Studies show that preventing introductions is the most effective and cost efficient way to respond to the problem of invasive species.  We conduct our work in coordination with other government agencies and non-governmental organizations.