Invasive Plants

When exotic plants begin to colonize natural landscapes, each ecosystem is subject to changes that threaten the integrity and longevity of that system. As a result, the native flora and fauna is often displaced with less desirable species.

Around the globe and here in California, invasive plants (usually introduced from other parts of the world) pose serious threats to the environment. The native plants, animals, and other biota that co-evolved and characterize the many natural landscapes on earth are often unable to survive once invasive species are introduced - whether intentionally or accidentally - into these wild lands. When exotics begin to colonize these places, each ecosystem is subject to changes that threaten the integrity and longevity of that system.

Ecosystem changes caused by Invasive Plants include:

  • Competition with native species for pollinators, space, light, nutrients, and water
  • Changes in hydrology that favor the invasive species
  • Changes in soil chemistry due to allelopathy, a phenomenon that occurs when plants release chemicals into the soil that inhibit the germination and growth of other plants
  • Conversion of vegetation. For example, a shift from perennial species to annuals can affect the intensity and spread of fires, causing increased erosion and flooding
  • Hazards for native animals due to loss of food supply, protective cover, and physical harm caused by certain invasive plants (e.g. foxtails)
  • Potentially devastating new diseases or insect pests that hitch a ride on the invasive exotics, eventually spreading to the native flora

Invasive Plant Lists & Resources

The immediate consequences of these invasions are not often readily perceptible, and before we know it, damage has already occurred. Due to our incomplete understanding of how ecosystems function, it is difficult to determine appropriate control measures to eliminate these invasive exotics, let alone curb further spread. Implementation often involves a long-term financial commitment to solve the problem. Although models have been developed to help predict which plant species are likely to become noxious weeds, these are not foolproof.

Worst Invasive Plants in Santa Barbara County

The Santa Barbara Botanic Garden encourages home gardeners and design professionals to become more knowledgeable about invasive plants. To this end the Garden has prepared a list of invasive plants of concern to the Santa Barbara area, and a list of landscape plants that are suitable alternatives to invasive exotics. Worst Invasive Plants in Santa Barbara County

Exotic Pest plants of Greatest Ecological Concern in California

Whether intentionally or accidentally, a wide array of weedy plants have found their way into natural and designed landscapes. Both here in Santa Barbara and around the globe, invasive plants are a serious environmental problem due to their enormous negative impact on ecosystems. You can make a difference, by removing undesirable weeds from your property and by not planting certain species of ornamentals that are known to be invasive in some parts of our region. Please note that the following lists apply specifically to the Santa Barbara area; some of these species are not a problem elsewhere. The list of ornamental shrubs contains invasive plants most typically encountered in urban gardens, as opposed to weeds commonly found in agricultural or wildland situations, although there is overlap in several cases. CalIPC list of Exotic Pest Plants of Greatest Ecological Concern in California 

Native Alternatives to Weedy Exotics

This SBBG handout lists common, weedy, exotic species that have been planted in the Santa Barbara area. Several plants native to California are suggested as better alternatives for the designed landscape. Native Alternatives to Weedy Exotics

Additional Web Resources:

We suggest visiting the following web sites for more information on this vitally important issue:

Interactive guide to invasive plant alternatives at PlantRight
California Weed Mapper - online tool by CalFlora
California Department of Food and Agriculture Encycloweedia
California Invasive Plant Inventory - by the California Invasive Plant Council (Cal-IPC)