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.