INTRODUCED NON-NATIVE EXOTICS
When Europeans and other foreigners began to colonize the Alta California region in the 1800s, they brought with them plant species that they thought would thrive in the Mediterranean climate of Southern California and the Islands.
How did the plants reach California ? By boat.
Where did they come from ? the Mediterranean, South America, South Africa, and Austral-asia.
The reasons they brought these plants were mixed :
For building timber
These plants that were brought came from climates similar to Southern California with dry summers and mild, wet winters, and this helped them more easily establish in a new environment.
While they did create a new food source, or delicious wines, or beautiful flowers, they were not always immediately successful, and were often times not a wise choice to import from an ecosystem perspective. In fact, all of the islands have over 20% up to 48% non-native plants that compete with the native plants. Letís look at some of the short-term benefits of these introduced plants, and examine some of the short term and long term problems they have caused.
Foods, Spices and Wines
In particular the introduction of fennel to the Island has had a long term devastating effect. The fennel crowds out native plants, and has been assisted to proliferate by an introduced European honeybee. The fennel itself physically crowds out native plants, and it leads to diminishing the native bee population, which then lessens the number of native plants that can reproduce since they lose their natural pollinator, the native bees. Serious fennel eradication efforts are underway as a result.
Do you know where Tasmania is ? Look on a world map, it is down under, near Australia. Some of the eucalyptus trees on the California Islands were brought from Tasmania, an Island south of Australia. The Eucalyptus is now well know as the primary food source of the appealing Koala Bears in Australia, but back in the 1800s, it was hoped it would serve as a strong building materials for rail roads on the mainland. But when grown in California, this wood proved too soft for railroads ties, and so it began to be planted as a windbreak in coastal areas to protect crops from damaging winds blowing in off the pacific. Likewise on the islands, the eucalyptus trees are planted as wind breaks. One problem with the eucalyptus trees is that they release a substance into the soil that prevents other native plants from growing, and can in a generation form a grove of trees that crowds out native plants.
But there are several positive qualities about eucalyptus: it makes a reasonable firewood and regenerate quickly. It is very beautiful visually and its groves are very special habitats for owls and other creatures. And, it is a food that the orange and black monarch butterflies come back year after year from Mexico to enjoy thanks to its sweet nectar in the flowers on its young seed pods.
Other introduced plants competing with natives include these identified by the Catalina Island Conservancy:
Wild oat (Avena fatua
Wild mustard (Brassica kaber)
Barnaby's thistle (Centaurea solstitialis)
Bull thistle (Cirsium vulgare)
Broom or Dyer's greenwold (Cytisus linifolius)
Fennel (Foeniculum vulgare)
Horehound (Marrubium vulgare)
Crystalline iceplant (Mesembryanthemum crystallinum)
Tree tobacco (Nicotiana glauca)
Russian thistle (Salsola pestifera v. tenuifolia)
Tamarisk (Tamarix ramosissima)
Spiny clotbur (Xanthium spinosum)