Ascension Island

Invasive species and biosecurity

A total of 232 non-native species (marine and terrestrial) was recorded for Ascension by the RSPB Stocktake (Churchyard et al 2014).

Taxon Total species Non-native species
Invertebrates 595 113
Vertebrates 140 16
Plants 324 103

Problems with invasive non-native species

Introduced non-native species on the island have caused significant ecological problems. For example, non-native spiders, centipedes and ants have had an impact on the endemic invertebrate species, causing some extinctions. A number of introduced plants are regarded as invasive. For example the Mexican thorn tree (Prosopis juliflora) dominates large parts of the island and out-competes native plants, also leading to soil erosion. (Acacia farnesiana), Guava (Psidium guajava), Prickly pear (Opuntia vulgaris) and Bermuda cedar (Juniperus bermudiaana), all regarded as invasive , are well established in some areas and are likely to exclude any surviving native plant species as are various grass species (eg Greasy grass (Melinis minutiflora), Cow grass (Paspalum scrobiculatum), Cape grass (Sporobolus africanus)). Cottony cushion scale (Icerya purchasi) damages the endemic Ascension Island Spurge (Euphorbia origainoides).

Mynah birds (Acridotheres tristis) prey extensively on the eggs of native sooty terns Sterna fuscata. Other species such as cats (now eradicated) and rats prey on seabirds and newly emerging turtles. Feral donkeys, sheep and rabbits cause damage to native vegetation and can spread seeds of invasive species.

Invasive non-native Prosopis juliflora showing damage from introduced rats; non-native Acridotheres tristis; native Sterna fuscata.

L-R: Invasive non-native Prosopis juliflora showing damage from introduced rats; non-native Acridotheres tristis; native Sterna fuscata.

Priority invasive non-native species and actions

The main priorities for action have been to clear invasive plant species in order to allow the regeneration of some endemic plants. Following an island wide botanical survey in 2008 all known examples of Bullgrass (Juncos capillaceus) and Wild Mango (Schinus terebinthifolium) have now been removed. Other action has focussed on the management of Mexican thorn which is widely established in the lowlands. Restoration of local vegetation has also involved excluding grazing animals such as rabbits.


In 2017 a biosecurity gap analysis (PDF) was completed. Biosecurity capacity is generally low, and particularly weak for pre-border and border controls. A biosecurity review was carried out for Ascension Island in 2016, which included a detailed pathway analysis. Subsequently, a part-time biosecurity post was created and a number of actions initiated to strengthen biosecurity on the island, targeting identified risks. This includes border and post-border operations, and the development of a biosecurity policy. Risk analysis is not included, however, and no capacity to do this exists on the island.

In 2018 a pathway analysis (PDF) was completed. Pathways of introduction remain relatively few.
There is one harbour, and a military airport operated by the US Airforce. Passenger flights arrive from South Africa around once a month via St Helena Island, and more frequently from the US through the military airbase. Cargo comes mainly from the UK and South Africa via a monthly cargo ship from South Africa, also via St Helena.

Horizon scanning was carried out in 2019, identifying a total of 42 new invasive species of concern which have the potential to arrive within the next 5 – 10 years; read a report on the horizon scanning (PDF).

Thin strip of image show tree trunk and bark