ASCENSION iSLAND

Environment

Ascension Island has a smattering of different conditions; many areas are wastelands of lava flows and cinder cones that support only highly resistant plants. Such places are indeed in keeping with Darwin’s description of Ascension as a desolate island, which he made following the visit of the second Beagle voyage in 1836. In other areas, though, there is grassland, scrubland, and woodland, including, incredibly, lush cloud forest.

Yet, somewhat sadly, Ascension hosts one of the most invaded terrestrial ecosystems in the world, with more than 95% of the plant species considered to be non-native. This exceedingly high level of non-nativeness is largely down to botanist Sir Joseph Dalton Hooker, who, with a lot of encouragement from Darwin, advised the Royal Navy and Kew Gardens to plant huge swathes of non-native vegetation. The reasoning was that it would capture more rainwater and improve the soil, and thereby transform Ascension into a luscious garden. So, starting in the mid-19th century, trees were brought from across the world and planted on the island. After a couple of decades, an array of non-native vegetation, including pines, bamboo, and eucalyptus, grew on Ascension. An artificial cloud forest even developed in the area that is now aptly known as Green Mountain.

This programme, predictably, placed a mighty strain on Ascension’s native flora and fauna. Some Ascension endemics cling on, like the Critically Endangered fern, Pteris adscensionis, and the Vulnerable fern, Asplenium ascensionis. Interestingly, this latter fern was thought to be extinct, until a handful were found in 2010. They have since been successfully propagated and the future of the species looks promising. Also, native flora and fauna are actively conserved in Ascension’s oldest national park, Green Mountain National Park.

In terms of fauna, Ascension is one of the most important nesting areas for tropical seabirds in the whole of the Atlantic; hence its designation as an Important Bird Area. It supports around half a million pairs of over 10 breeding species, including the endemic and Vulnerable Ascension frigatebird, and swathes of boobies, noddies, petrels, terns, and tropicbirds. The island was also once home to the endemic Ascension crake, but it was driven to extinction by invasive rats in the 18th century, or, if it survived long enough, by both rats and cats in the 19th century.

What’s more, Ascension is an important site for turtles. Its beaches support the second largest number of nesting green turtles in the Atlantic – in fact, its three main beaches for these Endangered turtles support more than half of all nesting green turtles in the whole of the South Atlantic. Notably, Ascension’s nesting turtles experienced sharp declines in the 19th and 20th centuries as they were hunted for their meat. But, once this practice was stopped in the mid-20th century, their numbers shot up six-fold. Additionally, Ascension’s waters boast high abundance of various fish, including tuna, billfish, and sharks, as well as just over 10 endemics.

However, as touched upon, Ascension’s biodiversity faces pressing threats from invasive species. The Mexican thorn, for instance, is particularly aggressive in its establishment of thickets that suppress native flora and provide sustenance for invasive rats. On that note, Ascension remains plagued by invasive rats, which affect the breeding birds and turtles. In the past, invasive cats had a devastating impact on the breeding seabirds of Ascension. In fact, their presence led to the loss of many seabirds from the main island. Yet, following the eradication of cats in 2004, several seabird species have returned and, in general, their numbers on Ascension have been rising.

Biodiversity conservation efforts on Ascension are often spearheaded by the Conservation and Fisheries Directorate of the Ascension Island Government, and supported by a raft of overseas organisations, like the Royal Society for the Protection of Birds. One particularly impressive conservation initiative in the territory is the Ascension Island Marine Protected Area. For context, in 2016, the UK Government announced that a huge area around Ascension Island would become a marine reserve, and, then, in 2019, the Ascension Island Government announced that all of its exclusive economic zone would be a marine protected area. This equates to more than 445,000 km2, making the protected area one of the largest in the world.

Authors: Ben Parker & Robert Midgley