The Tijuana River Comprehensive Management Plan states that "The control of exotic species is critically important to maintaining and enhancing resource values throughout the reserve." It further states that arundo and tamarisk threaten the viability of the native habitat. (CONCUR, 1999)

In the struggle to preserve the estuary's native habitat, volunteers and staff participate regularly in trail clean-ups, invasive plant removal and native plant propagation. When planting native vegetation, the seeds and cuttings are taken from adjacent areas. Some seeds are collected for various seed banks. Though many non-native plants threaten the estuary's native plants, six of these invasive intruders particularly stand out because they have taken over our natives to the largest extent. They are listed here by their common name, their Latin name and their name in Spanish: Giant Reed (Arundo donax), Sp. Caña brava; Salt Cedar (Tamarix spp.), Sp. Tamarisco; Sea Fig or Freeway ice plant (Carpobrotus endulis), Sp. Escarchada; Castor Bean (Ricinus communis); Garland Chrysanthemum (Chrysanthemum coronaruim), Sp. Crisantemo; and Sweet Fennel (Foeniculum vulgare), Sp. Hinojo.

1. Giant Reed (Arundo donax) Sp. Caña brava

Description: robust, perennial bamboo like plant that can grow as tall as 30 feet, has hollow stems, produces cluster of cream or brown flowers in early summer to early fall
How it spreads: rhizomes (underground stems that often send out roots and shoots) and fragments that can survive and replant themselves after being exposed to extreme conditions such as ocean water
Native habitat: Mediterranean
Native species most affected at the Tijuana Estuary: both giant reed and salt cedar take over riparian habitat (habitat along rivers, streams, etc.) and effects flora and fauna that live in the riparian community. For example: non-native giant reed and salt cedar can out compete the native willow and cottonwood trees. As the native plants disappear so do the animals that depend on them such as the grosbeak and the endangered least Bell's vireo.
Additional information: they have a thick root mass that causes erosion resulting in increased sedimentation that fills in streambeds. They also require extensive amounts of water.

2. Salt Cedar (Tamarix spp.) Sp. Tamarisco

Description: woody, long-lived tree with reddish brown bark, needle like leaves and a feathery overall appearance, produces small pink flowers
How it spreads: seeds
Native habitat: Africa, Asia and (Southern) Europe
Native species most affected at the Tijuana Estuary: both giant reed and salt cedar take over riparian habitat (habitat along rivers, streams, etc.) and effects flora and fauna that live in the riparian community. For example: non-native giant reed and salt cedar can out compete the native willow and cottonwood trees. As the native plants disappear so do the animals that depend on them such as the grosbeak and the endangered least Bell's vireo.
Additional information: uses a great deal of water; can tolerate high saline concentrations

3. Sea Fig or Freeway Ice Plant (Carpobrotus endulis) Sp. Escarchada

Description: perennial succulent, produces yellow flowers April to September (hybrid plants at the Tijuana Estuary produce yellow, pink and purple flowers)
How it spreads: seeds and vegetatively
Native habitat: South Africa
Native species most affected at the Tijuana Estuary: affects the horned lizard because it lowers the temperature of the sand; steals nutrients and water that would normally be available for native plants
Additional information: ironically, ice plant was sometimes intentionally planted to stabilize dunes; hybridizes easily with Carpobrotus chilensis, a close relative to Carpobrotus endulis, throughout California

4. Castor Bean (Ricinus communis)

Description: perennial shrub up to 15 feet tall with large, dark green-purple palmate leaves, produces a soft-spined fruit
How it spreads: seeds and root crown
Native habitat: Asia, Africa
Native species most affected at the Tijuana Estuary: grows so rapidly that it shades out native seeds and seedlings
Additional information: seeds are highly toxic; causes contact dermatitis

5. Garland Chrysanthemum (Chrysanthemum coronaruim) Sp. Crisantemo

Description: annual, produces yellow or white flowers April to August
How it spreads: seeds
Native habitat: Southern Europe
Native species most affected at the Tijuana Estuary: chrysanthemum forms fields that overtake native plants such as California buckwheat and sagebrush - both these plants provide food and shelter for native birds, insects and other animals
Additional information: looks very much like a native species of sunflower called encelia - look at the leaves to tell the difference

6. Sweet Fennel (Foeniculum vulgare) Sp. Hinojo

Description: perennial herb related to anise, can grow up to 10 feet tall, leaves look almost like feathers produces small, yellow flower clusters April to July
How it spreads: seeds and root crown
Native habitat: Europe and Mediterranean area
Native species most affected at the Tijuana Estuary: alters composition of coastal scrub and riparian wetland plant communities
Additional information: has a large root mass similar to that of Arundo; can germinate any time of the year and seeds are viable for years

For more information on these and other non-native plants, visit the California Exotic Pest Plant Council's website: http://www.caleppc.org/