Prior to human settlement, the native ecosystems present on Ascension were almost certainly at a relatively early stage of development, making them particularly susceptible to invasion by introduced plants. With the first human inhabitants also came the destruction of large areas of native habitats and large scale re-planting e.g. with trees/ shrubs that provided a source of wood. Perhaps the most significant event in the process of transformation was brought about by the eminent botanist Joseph Dalton Hooker. He implemented the mass planting of organised forests, shrublands and pastures on Ascension, introducing over 220 exotic plant species from diverse parts of the world, with the aim of greatly increasing mist interception, soil development, water storage capacity and of reducing erosion. Today, Green Mountain is largely covered with dense invasive vegetation and man-mde cloud forest.
Artifical cloud forest on Green Mountain: a direct legacy of Hooker’s experiment
Even the lowland areas of Ascension have now been substantially invaded by non-native shrublands – guava (Psidium guajava) became widespread in the south-east of the island during the early 1800s, Mexican thorn (Prosopis juliflora) has spread rapidly since the 1970s and yellowboy (Tecoma stans) even more recently than this. Introduced species now comprise approximately 90% of the higher plant flora.
Endemic Higher Plants
Of the 10 known species endemic to Ascension, only 7 are thought to remain today, and all of these are considered to be threatened. Lower plants (bryophytes) have been poorly-studied on Ascension (but see progress on this as part of the new Darwin Initiative project here), and it is probable that several of the endemic mosses and liverworts are also now endangered.
The extinct species:
- Dryopteris adscensions – last observed 1889
- Oldenlandia adscensions – last observed 1888
- Sporobolus durus – last observed 1886
The extant species:
1) Anogramma ascensionis, Ascension Island parsley fern
This species was Red Listed as extinct in 2003, however, four seedling sporophytes were rediscovered by the Conservation Team in 2009. In collaboration with the Royal Botanical Gardens, Kew, intensive efforts have subsequently been made to secure the survival of cultivated stock from these. This has been successful and so now to focus is shifting to a successful program for reintroducing some of the specimens into the wild in the hope that the population can re-establish.
2) Asplenium ascensionis, Ascension Island spleenwort
Although relatively little work has been conducted on this species, it is the most abundant of the endemic species on Green Mountain with relatively persistent and stable populations.
3) Euphorbia origanoides, Ascension Island Spurge
This plant is now most prevalent in extremely marginal habitat: very barren and often composed of loose scree where few other species exist, but in the more stable localities where small, and most likely discrete subpopulations can still be found, plants can develop into larger sub-shrubs.
4) Ptisana purpurascens (formerly Marattia purpurascens)
This large fern is mostly confined to the highest, most heavily mist-drenched slopes on the south face of Green Mountain. As a cloud forest has developed around the summit area, the population has adapted to this environment and it now occurs both as an epiphyte and as an under-storey species in densely-shaded areas. For most recent conservation efforts of this fern see here.
5) Pteris adscensionis
The population of this plant is currently very restricted – two main relict areas persist, consisting of a small number of plants on dry, shady cinder bacnks at the bottom of Breakneck Valley, and a larger poulation widely scattered over the trachyte cliffs on the north side of Cricket Valley. However, this species is growing well in the Conservation nurseries and dedicated restoration areas and substantial progress has been made towards securing its future.
6) Sporobouls caespitosus
In its extant localities, this plant occurs under a narrow range or marginal ecological conditions. On Green Mountain, it is found on exposed, relatively bare banks, always facing into the south-easterly trade winds. Dispersal appears to occur largely down-wind, and seedlings seem to be relatively common which suggests a healthy establishment rate. The plant is very vulnerable to grazing, especially by sheep that can dislodge tufts from their fragile root-hold.
7) Xiphopteris ascensionense
This small fern currently occurs in two distinct habitat areas. Firstly in its original native habitat on the damp, exposed rocks and banks on the upper south side of Green Mountain. And secondly, this plan has more recently managed to colonise the trees of the man-made cloud forest which now dominate the summit area of Green Mountain (a habitat which is in keeping with that of its closest African relatives).
For more information about the endemic plants of Ascension please download:
Native Higher Plants
Around 25 vascular plant species are thought to be native to Ascension, and all are important in the preservation of the island’s ecological heritage and functioning. Most of the non-endemic natives remain locally widespread, and are not globally-threatened.
Some of Ascension’s native plants (Left to Right) Cyperus appendiculatus, a near endemic sedge, Hymenophyllum sp. a filmy fern, and Ophioglossum sp. a lily fern.
Photos and information from the 2009 report: A plan for the conservation of endemic and native flora on Ascension Island. This document is currently being updated as part of the Biodiversity Action Plan project and will be online soon.
Bryophytes (Lower Plants)
Bryophytes is the collective term for mosses, hornworts and liverworts – plants that do not have true vascular tissue. In the plast, these ‘lower plants’ have been comparatively less well studied on Ascension, but are now receiving more attention as part of the current OTEP and Darwin projects. In April 2013, Prof. Jeff Duckett and Dr Silvia Pressel of the Natural History Museum and Queen Mary University, London visited Ascension Island to lead a Darwin Project training workshop in bryophyte biology, collection and identification. The workshop included sessions on field identification, microscopy and the preparation of herbarium specimens, as well as a seminar on bryophyte biology, conservation and diversity on Ascension Island. During the 10 day workshop the teams developed the most comprehensive inventory of bryophytes on Ascension Island to date, including 65 native species, 13 new records for the island and 1 species that is believed to be new to science. Specimens of all species were taken for DNA barcoding and for inclusion in a host country herbarium collection that is currently under development. High quality photographs and locations of all species were also taken for inclusion in a Darwin Project field guide.
Learn more about the trip and Ascension’s bryophytes here: Desert Island Delights: the Bryophytes of Ascension Island
Examples of bryophytes found on Ascension. Top Left: The endemic liverwort Fossombronia hamato-hirta. Top Right: The hornwort Phaeoceros sp. Bottom Left: Calymperes sp. Bottom Right: Campylopus sp. growing on bamboo. (Photos: Dr Sylvia Pressel)