Many visitors to Galapagos are surprised to be greeted by desert-like vegetation—most are expecting a continuation of the lush greenery they witnessed on mainland Ecuador. In fact, the majority of the archipelago’s land area is covered by the brown and grey vegetation often found in deserts. The Galapagos Islands are situated in the Pacific Dry Belt, and in average years only the highest altitudes of the larger islands receive enough rainfall to support tropical plant life.
Geologically speaking, the islands are young, and much of the island’s plant life reflects this; many species seem to be in the midst of the evolutionary process, which makes classifying them a difficult task. To date, the islands are believed to be home to between 552 and 614 native species of vascular plants and approximately 825 introduced species, the majority introduced by humans. More than 100 of the introduced species have become established in the wild, with many of them extremely invasive and of major concern. Three introduced plant species have been eradicated. Mainland Ecuador, on the other hand, has about 20,000 species. The discrepancy between species number on the Islands and the mainland highlights the fact that the Galapagos Islands are separated from the continent by a hostile saltwater barrier reducing the potential for arrival and, once a plant has arrived, establishment is difficult due to the harsh environment. It is worthy of note that more than 30% of native plant species found in Galapagos are endemic (not found anywhere else on earth).
The flora of Galapagos can be grouped into three major vegetation zones: the coastal zone, the arid zone, and the humid highlands.
- Coastal plants are found in the narrow zone near the shore and are distinctive because of their tolerance to salty conditions. Mangrove trees are one of the most common plants found in this zone, and they serve an important role as the breeding sites for many birds, such as pelicans and frigatebirds. They also provide much needed shade regions for iguanas and sea lions, as well as refuges for sea turtles.
- The dry area is the most extensive zone in Galapagos and is comprised of plant species that are highly adapted to drought-like conditions, such as succulent cacti and leafless shrubs that flower and grow leaves only in the brief rainy season.
- Located above the dry zones are the very lush and green, humid zones. In portions of this zone, Scalesia trees form a very dense forest in the humid zone, with their branches adorned with mosses, liverworts, and epiphytes—non-parasitic plants that use larger trees only for support. The humid zone is only found on the larger, higher islands. The majority of islands in the archipelago do not rise in elevation above the arid zone.