GALAPAGOS FLORA
native flora | introduced species | the rarest plants | alcedo volcano | solutions
The plant life of Galapagos is just as extraordinary as its wildlife, although it has received less attention and publicity. There are many threats facing the vegetation, however, and world attention is currently focussed on raising funds for botany campaigns to safeguard endangered species and control the many invasive plants introduced to the islands by humans.
There are about 560 native species of plants in the islands, in other words, plants which arrived in the islands by natural means. Of these, almost one third are endemic to the islands, meaning they are found nowhere else on earth. For example, Galapagos has its very own, endemic species of cotton, pepper, guava, passion flower and tomato. Not only that but many species are so different from others elsewhere that they are grouped in their own endemic genera. These include Scalesia, the endemic 'daisy tree', which has evolved into a whole host of different species in a direct botanical parallel of the Darwin's finches. Other endemic genera in the daisy family are Darwin's aster Darwiniothamnus, the cut-leaf daisy Lecocarpus and needle-leaf daisy Macraea. There are also some endemic genera of cacti, Brachycereus, the lava cactus and Jasminocereus, the candelabra cactus.
On the whole, Galapagos plants tend to be 'pioneer' species, hardy plants which successfully cross oceans and manage to establish themselves in the often hostile environment of islands. Because relatively few plants succeed in doing this, the flora is 'depauperate' - there are far fewer species here than in similar environments on the South American mainland. Plants are also adapted to having very few insects or other animals to pollinate their flowers or disperse their fruits and seeds. This means there are few big, showy flowers to attract pollinators and few specialised fleshy fruits. But there are some fascinating relationships between plants and animals. The giant tortoises and land iguanas, for example, feed on Opuntia, the prickly pear cactus, and have influenced its growth form on different islands.
..Top
One of the biggest problems in Galapagos comes from foreign plant species introduced to the islands by people, which then become pests and 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 10 new arrivals each year. At the current rate, it is estimated that introduced plant species will outnumber native species by the year 2007. About 40 of these are already seriously invading the native vegetation and another 70 introduced plants are likely to cause problems in the future.
Different introduced plants are problems on different islands around the archipelago. On Santa Cruz island, 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 it could completely wipe out this whole zone. The guava tree, being drought-resistant, can invade just about anywhere, replacing native trees and shading out all the smaller plants underneath. 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. Insects and other invertebrates are also a major problem. 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.
..Top
Many of Galapagos' endemic plants are rare and endangered but there are two species which perhaps best deserve this title. The endemic daisy tree Scalesia atractyloides is only found on Santiago island. The species was believed extinct until five plants were discovered in a crater in 1995 where feral goats couldn't reach them. During the 1997-8 El Niño, all five plants died but more germinated from seeds in the soil due to all the rain. The crater was surrounded by a fence in late 1997 to keep out the goats and protect the plants. In November 1998, two more adult plants were discovered at another site on Santiago, again on a cliff out of the reach of goats, and the hill on which they were growing was immediately fenced off. The fencing work cost in total about £15,000 and it is hoped that the remaining plants will be able to reproduce inside these protected sites.
There is a similar story with the Floreana Flax, Linum cratericola. This species was only discovered in 1968 and was feared to have gone extinct some time after 1981 when it was last seen. Then in April 1997, two scientists from the Charles Darwin Research Station (CDRS) discovered a tiny population of the flax in a volcanic crater on the island. There were just thirteen plants, only eight fully grown, in a tiny area 2 m by 1m. The site was very vulnerable, lying on a path used by feral animals and with invasive introduced plants growing nearby. In July 1997, the botanists visited again and found that the smaller plants had died leaving only eight, but five new ones were discovered on the cliff above. The sites were fenced in 1998 but the number of plants has continued to decline, with only six present at the last count. A project began in June 1999 to study these few remaining plants in an attempt to discover what is causing the decline and to control the problem. The project may include cultivation and reintroduction work.
..Top
This volcano on the island of Isabela in the west of the archipelago is one of the worst hit areas in Galapagos. Large numbers of feral goats have invaded the area with a catastrophic effect on the native vegetation, reducing the plant food available for the giant tortoises which inhabit the volcano. Goats strip the bark off trees which then die, and the forests that once covered the southern slopes of the volcano have been reduced to small patches. There is only one small patch of the endemic tree fern left, which has now been fenced off. A huge campaign is under way to control the feral goats. However, it is calculated that £3 million is needed to completely eradicate them and resolve the problem.
..Top
The task of eliminating or controlling the invasive plant species is huge. For example, it was estimated in 1998 that it would take a team of fifteen people about 15 to 20 years to completely eradicate quinine from Galapagos at a total cost of about US$2 million. It may not be possible to completely eliminate guava so continuous control costing about US$250,000 (at 1997 prices) would be necessary after an initial 5 or 10 years to reduce it to levels where it is no longer a threat. The Galapagos National Park Service has virtually no funds for this so no major control work is currently taking place. The CDRS's role is to carry out research into the ecology of the invading species and methods for their control. Again, almost no funding is available for this and little is known about how exactly the introduced species are affecting native plant communities. There is therefore an urgent need for a properly funded research group at the CDRS and a dedicated plant control unit with secure funding at the Park Service. It was estimated in 1997 that the Park needs between half a million and a million dollars a year, over a five year period, to make a real impact on invasive plants, while a research team and operational equipment at the CDRS would cost about US$150,000 per year.
There are some hopeful developments for the future of Galapagos' plant life. In 1998 the Government of Ecuador implemented a Special Law for Galapagos, restricting immigration and giving the Park Service more powers. A vital quarantine programme was instigated to stop, or at least slow down, the rate at which foreign species are introduced to Galapagos by humans. Meanwhile, survey work continues to assess the status of Galapagos' flora and hopefully discover and safeguard populations of threatened species while funds are raised to tackle the underlying causes.
..Top
|
