Sour Fig

sour FigSour Fig

Latin name: Carpobrotus edulis

Sour Fig  is the single biggest threat to Alderney’s coastal habitats. Also known as Ice plant or Sea Fig C. edulis is a robust, flat-growing trailing perennial herb. It forms dense mats. The leaves are yellowish to grass-green or reddish when older, succulent and crowded along the stem, sharply angled and triangular in cross-section, with tiny serrations along the outermost edge. Flowers are solitary, yellow fading to pink. Two similar species, Sally-my-handsome, Carpobrotus acinaciformis and Angular Sea Fig, Carpobrotus glaucescen, are also present and invasive in Alderney.

The Sour Fig is native to South Africa, but has been introduced to many parts of the world. In Europe it is known from the Mediterranean region and further north in Germany, the UK and Ireland. It was first recorded in Alderney in 1953, but it is thought to have been introduced before this date, as ornamental ground cover. It spreads through vegetative propagation; and new patches can form from a very small piece of broken stem. Broken pieces can be moved by rabbits, birds and the wind. Many people, both locals and tourists, also like the appearance of the plant, and cuttings are often taken for gardens. This is likely to contribute to its spread. It is now present throughout the island, in all coastal areas, and poses a major threat to native flora.

The Sour Fig competes aggressively with native species such as Bastard Toadflax, Small Restharrow, Stemless Thistle and Wild Thyme, and often smothers rare and endangered species. Once established, it reproduces at a high rate; and appears to be unaffected by grazing or competition. It is also known to modify soil properties and nutrient dynamics, by increasing soil N and organic C, and reducing soil pH. This can hinder native regeneration after the plant has been removed; and increases the likelihood of invasion of scrub species such as bracken and bramble. Finally, sour Fig can decrease species diversity by preventing sand movement, hindering the natural processes of disturbance and change in dune environments.

Action Plan

The Alderney Wildlife Trust (AWT) undertook GPS mapping, to chart the distribution of Sour Fig on the island, and to identify priority areas for removal. Soil sampling was also carried out to investigate the plant’s impact on soil pH. The results of this exercise revealed that a total of 206km² of Alderney’s coastline, 2.6% of the island’s total area, is covered by the invasive fig. Many of the largest areas covered by Sour Fig are inaccessible due to thick scrub and steep cliffs. Therefore, in prioritising sites for action, the conservation value of sites affected was taken into consideration. Thus, areas of coastal and dune grassland have been selected for targeted action. These include Saye Bay and Cats Bay.

Regarding soil pH, results confirmed a lowering in areas covered by Sour Fig. This confirms the plant’s ability to alter environmental conditions, and potentially species composition. Furthermore, it was observed that insects, such as bees, were not frequently found on the plant. The spread of Sour fig could therefore have a further adverse effect on the already declining bee population.

In light of these findings, the AWT continues to co-ordinate a programme of removal by hand. This is one of the most effective methods of controlling and reducing coverage by the species. Often, large mats can simply be rolled up, but it is important that all plant material is collected, with none left on site. This material must be kept separate from other green waste and it generally burnt. Post-pull raking of the site is recommended to encourage native regeneration. Finally, fig re-growth is expected, and new growth must be pulled in post-removal sites as it appears.