Plants of the Galapagos Islands
In recent years, introduced Galapagos plants have taken center stage, threatening native species and upsetting the natural balance of life on the islands. Conservation programs supported by responsible tourism are helping to reduce the impact of introduced Galapagos plants on the islands’ fragile ecosystems and protect native plants and wildlife.
Native Plants of the GalapagosMany of the plant species found in the Galapagos Islands are as interesting and unique as the islands’ renowned animal life. Still, many first-time visitors are surprised by the arid, almost lunar landscape that greets them as they step off of the plane. When compared to many parts of mainland South America or to other tropical island groups throughout the world, the Galapagos Islands are home to relatively few native plant species and are not particularly lush, except at higher elevations on the larger islands.
Scientists believe that there are around 600 native species of vascular plants here – not many when you consider that mainland Ecuador alone is home to over 20,000!
This discrepancy makes sense when you consider the obstacles that the ancestors of today’s Galapagos plants faced in getting there. First, seeds had to somehow make it across 600 miles of salty ocean from the mainland, carried by birds, the wind, or on rafts of wood and vegetation. And because the islands lie within the Pacific dry belt, they receive little rainfall at lower elevations in normal years, resulting in semi-desert conditions throughout much of the archipelago. Once on land, the newly-arrived seeds had to establish themselves and adapt to this foreign and often harsh environment. Finally, because the islands are relatively young in geologic terms, the plants that did make it have had relatively little time to branch out, evolutionarily speaking, into new varieties and species.
In spite of all of this, the flora of the Galapagos is endlessly complex and fascinating. Thirty percent of the native vascular plants here are found nowhere else on Earth and there are seven entirely distinct endemic genera. The endemic genus Scalesia, for example, is comprised of fifteen different species of trees found nowhere else on earth. They have been called "the Darwin's finches of the plant world" because of their remarkable pattern of adaptive radiation.
Because of the variation in plant life found at different elevations and from island to island, the flora of the Galapagos is generally categorized into seven distinct vegetation zones:
Littoral (or Coastal) ZoneThis zone extends from the edge of the ocean to around fifty to one hundred miles inland and is populated by plants that are well adapted to living in salty conditions. Four species of mangrove can be found along the edges of the numerous saltwater lagoons in this area. In addition to limiting erosion caused by waves and storms, mangroves provide habitat and nesting places for many bird species, including finches, herons and mockingbirds. The shallow waters of mangrove swamps also provide safe nurseries for young fish, mollusks, shrimps and other species that are crucial links in the Galapagos food chain.
Arid ZoneThe arid zone is the next vegetation zone you’ll encounter as you move inland from the littoral zone. It is the largest vegetation zone in the archipelago, extending to 300 feet on the wetter, southern sides of the islands, and as high as 1,600 feet on the drier, northern sides. Some of the smaller and lower islands are located entirely within this zone. Three types of endemic cacti dominate the landscape here; lava, candelabra, and prickly pear, the staple diet of land iguanas and giant tortoises.
Transition ZoneAs you move up from the arid zone, you will encounter the transition zone. As its name implies, this zone lies between the arid lowlands and the cooler, moister highlands and is home to species from both. As such, this zone has the greatest plant diversity among the seven vegetation zones. Small trees and shrubs, including the endemic pega pega and the native hardwood matazarno, dominate this landscape.
Scalesia ZoneThis zone is often referred to as the “rain forest of the Galapagos.” Sitting at elevations ranging from about 650 to 1,300 feet on the larger islands, the Scalesia zone is notably cooler, moister and more lush than the zones below it. It is named for the Scalesia forests found here. Some of the trees can grow to over sixty feet tall and are covered in ferns, mosses and orchids. Unfortunately, introduced pigs, goats and plants have decimated these once great forests.
Zanthoxylum (or Brown) ZoneThe Zanthoxylum zone is named after the predominant plant found here: the Zanthoxylum fagara, or “cat’s claw.” It is also sometimes referred to as the “brown zone” because the brown lichens that cling to the trees give them a brownish hue. This zone has largely been destroyed by agriculture, unfortunately.
Miconia ZoneThe Miconia zone can be found at elevations starting around 3,200 feet on the islands of Santa Cruz and San Cristóbal. It is named for the Miconia shrub, which once carpeted the region, but is now one of the most endangered plants in the archipelago due cattle grazing and the impact of invasive plants. The Miconia robinsoniana can grow to sixteen feet and has purple and pink flowers.
Pampa or Fern-Sedge ZoneHere in the highest elevations of the Galapagos (above 3,200 feet) exists an otherworldly realm of ferns, grasses, mosses, lichens and orchids. The plants in this zone crowd around temporary pools of water and disappear and reappear seasonally based on rainfall. The only tree found here is the endemic Galapagos fern tree, which can grow to nine feet tall and has a trunk that can grow to eleven inches in diameter.
Invasive Plants of the Galapagos
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.