Ascension : Conservation Weekly-contributed by Phil Lambdon
Submitted by The Islander (Conservation Office) 18.06.2009 (Article Archived on 02.07.2009)

Following on from the invasive species conference which was held on Ascension this month, it seems appropriate that one very topical issue has caught the attention of the South Atlantic Invasive Species Project team recently.

Wild mango – an unwelcome visitor to Ascension

Following on from the invasive species conference which was held on Ascension this month, it seems appropriate that one very topical issue has caught the attention of the South Atlantic Invasive Species Project team recently. The rights and wrongs of removing invasive plants often cause public controversy – should we encourage the greenery, or preserve natural habitats as they are? Whatever your opinion on greenery, Ascension now has plenty of it, and any more of the wrong sort could certainly cause substantial problems. Not only does it threaten some of the island’s unique plant and insect species which are in severe danger of disappearing from the planet completely, but vigorous weeds cause all manner of havoc, including blocking paths, overgrowing heritage sites, drying-out the water table and creating a fire risk. All of these problems require management, and the creeping costs may rise un-noticed into the £millions over several decades.

Unfortunately, the truth of the matter is that once a species has become widely established, the costs of removal are usually well beyond meagre conservation budgets. Mexican thorn, for example, would require further £millions to eradicate. The only realistic hope of achieving such a goal is to catch a new invader before it has a chance to establish. Removal of a few dozen plants won’t raise many headlines, but it may be an extremely cost-effective way of preserving the environment for future generations.

The relevance of this issue has been brought to the forefront by one particular species: wild mango (Schinus terebinthifolius). Those who have visited St. Helena will be very familiar with the name; introduced in 1870 as a garden plant and now ubiquitous across the island, both over barren hillsides and also forming dense, impenetrable scrub in more humid areas such as river valleys. It is a vigorous shrub or tree which can spread rapidly via underground suckers and soon excludes most other species.

Known elsewhere in the world as ‘Brazilian pepper tree’, it is native to tropical South America but has been widely introduced to many other parts of the tropics. Due to its invasive nature, has often become a serious pest: particularly in Florida, northern Australia and South Africa. For the record, wild mango is not the same as the true mango. It belongs to the same family (Anacardiaceae), but is more closely-related to species of pistacio.

With the large infestation already present on St. Helena, it has long been a concern that wild mango would eventually arrive on Ascension. It is not clear how the species eventually managed to sneak in; possibly from a shrub grown in a garden, or from a berry snagged in clothing. However, one plant has been known on Sister’s Peak since 2002. It was long thought that this was the only individual, but the recent botanical survey, conducted by the EU funded South Atlantic Species Project, located a small pocket in an isolated valley below the mountain road, opposite Middleton’s Ridge. This population was already well established, spreading vigorously by root suckers and producing large amounts of fruits.

Overall, 55 plants were counted. It is likely that the colony reached this inaccessible area via a bird dropping, because the small, scarlet berries can be produced in great quantities, and are avidly dispersed by mynahs and other species.

In the U.S.A., the sale or cultivation of Brazilian pepper is prohibited, and many states require immediate notification and eradication of any populations discovered. In lieu of similar legislation on Ascension, the Conservation Department, in cooperation with the South Atlantic Invasive Project, decided to implement their own eradication plan. The initial 

phase started on 22nd May.

The trees were cut-back to ground level with a hand brush saw. Because this merely stimulates greater suckering from the underground stems, it is therefore essential to apply herbicide immediately to the cut stumps before a callus develops to seal the wound. Unfortunately, the initial removal of the plants is not sufficient to ensure 100% eradication, as there may be many berries in the seed bank which could provide the capacity for future regeneration. The chances of new germination may decrease considerably after a few years, but it will be more than a decade before the eradication can be deemed a success.

In the mean time, there is a further risk that additional populations may have not yet been found, or that further new sources of seed could arrive from St. Helena. However, everyone can help keep Ascension free of wild mango by following two simple steps:

· Take care not to bring berries onto the island, either deliberately or accidentally carried at the bottom of a bag or in a pocket, especially when arriving from St. Helena.

· Keep an eye out for any shrubs which fit the description of wild mango whilst travelling around Ascension. Report any sightings to the Conservation Department together with a note of where you saw the plant, and if possible, a photograph.