Dec 20 2019
One million years ago, a volcano broke the surface in the middle of the Atlantic Ocean, forming Ascension Island. Like other oceanic islands, Ascension relied on colonization of plant species from nearby landmasses. Located about 1,000 miles from the coast of Africa and 1,400 miles from the coast of Brazil, it is one of the most isolated islands on earth.¹
Any plant that became established on the island overcame nearly impossible odds—traveling thousands of miles on the wind or in the plumage of seabirds, plus the spores and seeds that made it to the island intact needed to survive a hot, dry climate and a rocky terrain. These obstacles were so great that the colonization rate for flowering plants was only one species per 10,000 years.
Because of its young geological age and slow colonization rate, Ascension Island was relatively barren when discovered by humans in 1501. Early explorer Peter Mundy described the island as “the most desolate, barren (and like a land that God had cursed) that ever my eyes beheld.”¹
One of the most valuable accounts of the flora of the island before major human intervention comes from the diary of a Dutch sailor, Leendert Hasenbosch, who was excommunicated to Ascension in 1725 by his commanders as a punishment for his homosexuality. Hasenbosch’s account, discovered and published by British sailors the following year, is the tragic account of a man slowly dying from thirst, starvation, and the madness that followed. The sailor writes of finding few edible plants, except purslane (likely Portulaca oleracea), and laments, “in the whole island…there is not a drop of water to be found, wherefore if God Almighty does not please to send some rain, I must inevitable perish.”²
Although Dutch and British sailors altered the island’s ecology with the introduction of goats, rats, and a few crops, the landscape that had killed Hasenbosch was much the same more than a century later, when Charles Darwin visited on the second voyage of the Beagle in 1836. Darwin and Joseph D. Hooker, who visited in 1843, called Ascension “treeless” and hatched a plan to increase rainfall to the island by importing tropical tree species.¹ Darwin, Hooker, and gardener John C. Bell began one of the world’s most ambitious ecosystem creation plans. Using imports from Kew Royal Botanic Gardens, they created a tropical cloud forest, today named Green Mountain, on land that was once considered barren.
The efforts of Hooker and Darwin, though successful in increasing rainfall to the island, also disrupted the natural succession of a geologically young island, imperiling the island’s native flora. At least two endemic plant species, Sporobolus durus and Oldenlandia adscensionis, were driven to extinction by the introduction of foreign plants.³ The legacy of Green Mountain is now considered a cautionary tale of the damaging effects intervention can have on a pristine ecosystem. Modern authorities strive to protect the island’s seven remaining endemic plant species through the removal of certain invasive species and intentional planting.