The Galápagos Islands are a pelagic archipelago of 233 islands, islets, and emerged rocks produced through spreading of the Eastern Pacific sea floor. Each island was formed serially from east to west by underwater volcanic activity as the crust and mantle of a southeasterly rafting Nazca plate melted while passing over a stationary and intense hot spot. Forming almost 8000 km² of land surface and 1688 km of coastline, the archipelago is dominated by five islands, Fernandina, Isabela, Santiago, Santa Cruz, and the most easterly and geologically oldest island, San Cristóbal, which lies 928 km from the westernmost point of the Ecuadorian mainland.

Lower Elevation Coastal Vegetation San Cristóbal 2014
Laguna El Junco 2015
Wetland Lagoons Below El Junco 2015
Highland Vegetation on San Cristóbal 2014
Highland Vegetation in the Zone of Special Use (ZUE) 2014
View Southwest from El Junco 2016
View North from El Junco 2016
View to NW from Loma del Consuelo, El Progreso 2014
Invasive Regrowth, View from Loma del Consuelo, El Progreso, 2014

Vegetation on San Cristóbal Island

Straddling the equator, the islands experience relatively warm temperatures with seasonal rainfall regimes governed by migrating atmospheric pressure and modulated by ocean currents. Each island’s distinctive flora and fauna have evolved in relative isolation for much of their 2.5 million year history. Only a few of the larger islands have permanent freshwater, and those with sufficient elevation to support humid highlands support intergrading altitudinal vegetation zones: 1. A narrow Littoral Zone dominated by shrubs or small trees and salt-tolerant herbs and grasses; 2. An Arid Zone dominated by deciduous plants, cacti, shrubs, herbs, and smaller trees up to 100 m asl; 3. Transitioning by 200 m asl into a Scalesia Zone seasonally engulfed in garúa fogs and characterized by small trees and a shrub understory with herbs, vines, epiphytic ferns, orchids, liverworts and, mosses; 4. A higher Miconia Zone dominated by epiphyte-covered shrubs with open stands of Miconia, clubmosses, and tree ferns above 500m asl.; and 5. the Fern-Sedge, Pampa, or Grassy Zone that can persist to the tops of island peaks with clubmosses, ferns, lichens, occasional tree ferns, and peat bogs.

Sea Lions on Playa Mann and Cruise Ships in Wreck Bay, 2012
Sea Lions on Playa Mann and Cruise Ships in Wreck Bay, 2012

Biodiversity and Science

Converging along the equator, diverse ocean currents support conditions that can promote environmental variability throughout the islands in addition to providing possibilities for introducing rafting organisms. The numerous islands and rock outcrops present opportunities for multiple isolation events, and together with their relatively small size and low ecological complexity contribute to the development of unique insular adaptations. Coupled with their isolation from continental habitats and their relatively late human colonization, the islands provided a setting which enabled the local evolution of endemic plants and animals. Historically, Galápagos has become an internationally renowned testing ground for evolutionary principles in an isolated, pristine setting. The early inspiration for this narrative is generally attributed to the 1835 visit by a then 22 year-old Charles Darwin, who as naturalist on board the HMS Beagle spent 19 days ashore on San Cristóbal, Floreana, Santiago, and Isabela Islands. Darwin was of course well aware that humans were already present in the islands but their presence dates back to at least 300 years before this brief encounter.