Why are such beautiful plants like Garland Chrysanthemum and Crystal Ice Plant being uprooted, chopped down, sprayed and disposed of at the Tijuana Estuary? Such plants, though very attractive are non-native (exotic) to San Diego. They are also invasive which means they displace or replace native plants such as cottonwood, willow and coastal sage scrub, which is a threatened plant community. Not all exotics are invasive. Some, though not beneficial, don't become destructive. Invasive exotics, however, are very destructive. When invasive exotic plants displace the native ones, native animals also get displaced, causing great disturbances in the ecosystem. Plants provide habitat, or homes, for insects, birds, reptiles, invertebrates and mammals. Exotic plants are not designed to provide for our native animals so without the native plants as shelter and food sources, these animals have difficulty surviving. Native plants and animals have co-adapted to each other so well that they need each other for survival.

How did these exotic plants get here? There are various ways plants are displaced. Of course, some of these plants are intentionally brought into the region by gardeners and landscapers. Often seeds and cuttings of these imported plants are spread much farther than intended when they attach to our shoes, pets, vehicles, etc. One example is pampas grass which, used frequently in road side landscaping, has spread dramatically.

With the increasing ease of overseas travel, and globalization, more exotics are arriving by ship and by plane. In addition to coming over with and later being distributed by humans, seeds and plants come over in ballast water, grain shipments and with livestock, especially in the hooves of pigs. Ballast water is water added to the ballast of a boat in order to counter balance it. This water contains seeds and invertebrates which get released and later distributed at the new port or along the way.

non-native pampas grass

What is caulerpa taxifolia and why is it called "killer algae"?
Caulerpa taxifolia is a green alga, which is native to the tropics. As a fast-growing and hardy plant, it is widely used in saltwater aquariums. If released outside the tropics, this highly invasive non-native seaweed quickly takes over native plants. Caulerpa taxifolia has already infested the Mediterranean, growing uncontrollably and causing ecological devastation by eliminating native seaweeds, seagrasses, reefs and other communitites. Infestations of caulerpa taxifolia have been found in California: in a coastal lagoon in Carlsbad and in Huntington Harbour. These infestation were probably caused by pieces of the seaweed being inadvertently released from household aquariums. For more information on caulerpa taxifolia and how to help control it, visit:
http://www.fishingnj.org/artcaule.htm and http://www.mcbi.org/caulerpa/babbitt.html

Why do exotic plants do so well here? Far from their natural habitat, non native plants live and reproduce freely without having to protect themselves against their natural predators, giving these plants a significant advantage over the native ones and making it easy for non natives to quickly take over. The exotics we have at the Tijuana Estuary also like our disturbed soil. In addition, some exotics have specialized defenses that native plants are not designed to compete with. For example, the Tamarisk, a non-native tree, has a high tolerance for salt. This allows the seeds to germinate for longer periods of time and in salty water. This ability gives the Tamarix an advantage over native cottonwood trees which do not tolerate the salt as well and whose seeds germinate for a shorter period of time. Tamarisk have another advantage; animals prefer to eat cottonwood and leave Tamarisk alone.

What does it mean when a plant has a high or low wildlife value? Plants in their native habitat provide animal species with various necessities such as food, water, shelter and material for nesting. The more a plant provides the higher its wildlife value. Non native plants have a lower wildlife value than native plants. Plants with higher wildlife values help ensure a higher bio-diversity. Bio-diversity is the measure of species richness in an area. Wetlands, like those of the Tijuana Estuary, support an incredible variety of inter-dependant species making wetlands some of the richest habitats on earth. The lack of native coast live oak and sycamore trees in the Tijuana Estuary has negatively affected our bio-diversity.

Is it destructive to use exotics in my gardening and landscaping at home? As mentioned above, not all exotics are invasive. Some exotics can be used and contained in your yard without damaging or displacing our native vegetation. However, invasive exotics, even when only a small amount is planted, can spread rapidly and cause damage to native species of plants and animals in your yard and beyond. If you would like more information on landscaping with native plants, consult the California Native Plants Society's web page: www.cnps.org/.
Or click here for a list of nurseries that specialize in plants native to the area.

How do I know which exotics are harmful? Contact your local nurseries or consult the California Exotic Pest Plant Council's website: http://www.caleppc.org/.