Non-Native Plants Along the Los Angeles River
Non-native plants can become accepted as hallmarks of a region or culture, e.g. the palm trees in Los Angeles, the tumbleweeds of the wild west, and the grass covering suburban lawns. But these and many other plants were introduced deliberately or accidentally by people. The problem that non-native plants create is that they often push out native plants and reduce biodiversity. Often native animals suffer too since they do not use these plants for food or shelter. For example many California animals find no nurishment from the thousands of introduced eucalyptus trees now found in parks and open spaces. The native oaks and cottonwoods that they replaced produced food for many animals.
Biologist E. O. Wilson of Harvard says that next to destruction of habitat, the introduction of exotic species by humans is the most destructive activity that humans engage in. The richness of our planet's bio-diversity is being so throughly diminished, that ecologist Gordon H. Orians says our era should be known as the "homogecene", after the habits of homogenized plant and animal life that we are creating. 17
The river's cooridor provides an interesting mix of native and non-native plants. Here are some of the more common non-native plants.
Fountain Grass, Pennisetum setaceum. This native of South Africa is now so common along stretches of the river and in openings in the concrete, that it almost seems as if it was deliberately landscaped.
Black mustard, Brassica nigra, often used to reseed hills after wild fires.
Arundo, Arundo donax, or Giant Reed, the great invader. This fast growing riparian reed in the grass family does better in flooded areas than native species. It is vigorously invading the arroyos of Southern California. Notice the inflorescence. This is NOT bamboo!
Tumbleweed, Salsola australis, from Russia. This non-native has become a symbol of the western frontier. However, it was introduced in South Dakota in the 1870s when Russian thistle seeds were probably mixed in with a shipment of flax seeds from Europe. Over the next 20 years it spread to 12 other states. This hardy invader does well in areas already cleared of native species. It was often the first plant to reestablish a popluation in the Nevada desert after nuclear weapons tests. However, the original population in Eurasia from which these plants came from no longer exists. 21
Tree Tobacco, Nicotiana glauca Grah. This was
brought here from South America by the Spanish. Taken as medicine.
Castor bean, Ricinus communis, in bloom. This non-native is poisonous.
Bottlebrush, Callistemon, Common in many southern California gardens, this brightly colored non-native made its way to a sand bar in Frogtown and has survived a few floods.
The Army Corps of Engineers announced in the summer of 1996 that it would be issuing permits to remove invasive, non-native plants. This program could help restore some of the native habitat in the river. Much of the vegetation was not cleared out until the fall of 1997 in anticipation of the El Niño storms. Eleven species targeted include: Giant Reed Arundo donax, Tree Tobacco Nicotiana glauca, Castor Bean Ricinus communis, Pampas Grass Cortaderia selloana, Salt Cedar Tamarix spp., Common Reed Phragmites australis, Star Thistle Centaurea solstitialis, Artichoke Thistle Cynara cardunculus, Thistle Cirsium spp., Fountain Grass Pennisetum setaceum, and Cocklebur Xanthium strumarium. 18. Many of these plants are pictured above.
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