Invasive Plants

One of the biggest problems in the Galapagos comes from foreign plant species introduced to the islands, which invade the native vegetation. Most of these species were brought on purpose either for agriculture or gardens, and the problem is therefore greatest on the inhabited islands. There were 475 known introduced species by early 1999, and the process is still continuing at the rate of about ten new arrivals each year. At the current rate, it is estimated that introduced plant species will soon outnumber native species, if they haven’t done so already. About forty of these are already seriously hindering native vegetation growth, and another seventy introduced plants are likely to cause problems in the future.

Each island has its own issues regarding introduced plant species. On Santa Cruz, for example, the worst culprits are guava (Psidium guayaba), the curse of India (Lantana camara), a species of blackberry (Rubus niveus) and quinine (Cinchona pubesceris). Quinine trees have invaded a unique vegetation zone formed by the endemic plant (Miconia robinsoniana), which is found on only two islands. Quinine shades out Miconia and eventually all the other plants around it, so if not controlled, could completely wipe out this entire vegetation zone. Because it is drought-resistant, the guava tree can thrive just about anywhere, replacing native trees and shading out all the smaller plants. The endemic scalesia tree dies out in huge numbers during severe El Niño events and there are fears that it will never recover from the 1997–98 event, as the introduced guava will prevent its natural regrowth. Other problem plants are passionflower, elephant grass, and kalanchoe, the ornamental mother-of-thousands.

Introduced animals also have a detrimental effect on the native flora. Goats have decimated the vegetation on many islands and brought some plant species to the verge of extinction. Feral donkeys and cattle also graze on native plants or trample them, and insects and other invertebrates are a major problem as well. For example, in 1982 a scale insect, the cottony cushion scale, was first reported in Galapagos and spread to another seven islands by 1997. It infests and often kills many kinds of native plants, and scientists looked at biological methods of control to safeguard the vegetation. In January 2002 the Australian ladybug, the natural enemy of the cottony cushion scale, was released following extensive studies to ensure that the ladybug did not pose any threat to the Galapagos ecosystem.

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