Invasion EcologySaint Helena, Ascension and Tristan da Cunha
The 1850s Man-Made Cloud Forest
A barren volcanic island where Victorians deliberately planted 300+ exotic species in the 1840s. Now a thriving self-sustaining forest that 'shouldn't' exist.
LordHarris, CC BY-SA 3.0
An Experiment in Terraforming
When Charles Darwin visited Ascension Island in 1836, he described the volcanic landscape as "destitute of trees". The island was a barren rock in the middle of the Atlantic, useful as a naval outpost but inhospitable. Its highest point, a volcanic peak rising 859 meters (2,817 feet), was ironically named Green Mountain. Before human intervention, only about 25 to 30 plant species, mostly ferns and mosses, survived on its upper slopes. The primary challenge for the British garrison established in 1815 was the lack of fresh water.
This problem prompted an unprecedented ecological experiment. Following a visit in 1843, botanist Joseph Dalton Hooker, a close friend of Darwin, proposed a radical plan. He theorized that planting trees on a large scale would capture moisture from the frequent mists, increase rainfall, reduce soil erosion, and make the island more habitable. Beginning around 1850, the Royal Navy, with guidance from Hooker and Kew Gardens in London, began systematically shipping hundreds of different plant species to the island.
A Thriving, Unnatural Ecosystem
Over the next few decades, ships delivered more than 330 species of plants from botanical gardens in Europe, Argentina, and South Africa. Between 1860 and 1870 alone, an estimated 5,000 trees were planted. Species were chosen for their hardiness and ability to thrive. Among the introductions were Norfolk Island Pines (Araucaria heterophylla), multiple species of Eucalyptus, bamboo (Bambusa sp.), and guava (Psidium guajava).
By the late 1870s, the experiment had succeeded beyond expectations. The slopes of Green Mountain, once bare volcanic ash, were covered in a dense, multi-layered forest. The new vegetation trapped moisture from the trade winds, creating a self-sustaining microclimate. This artificial cloud forest is a large and most successful examples of deliberate "terra-forming" ever recorded. Today, the ecosystem is so effective that a water catchment system built in the 19th century is no longer needed. The area was designated Green Mountain National Park in 2005. The novel ecosystem is a case study for invasion ecology; while it made the island habitable, the introduced plants displaced some of the rare, native flora.
💡Fun Facts
Charles Darwin's visit in 1836 and subsequent correspondence with Joseph Hooker were instrumental in forming the plan to vegetate the island.
The island is a critical nesting ground for one of the Atlantic's largest populations of Green Turtles (*Chelonia mydas*).
A unique local pastime is "letterboxing," where hikers follow clues to find hidden boxes containing a logbook and a unique rubber stamp to mark their guidebooks.
The island hosts a giant land crab, *Johngarthia lagostoma*, which migrates from the heights of Green Mountain to the sea to breed.
The National Park is accessible 24/7, but paths should only be used in daylight hours.
Admission
Free
Accessibility
The park is mountainous with steep, winding roads and hiking trails. Some paths can be slippery, especially the boardwalk through the bamboo forest near the summit. A vehicle is necessary to reach the main trailheads.
