Managing invasive species in a biodiversity hotspot: the Juan Fernández Archipelago, Chile
Globally, species are disappearing at an alarming rate. Nowhere is this more evident than on islands, where over 90% of recorded bird and reptile extinctions and around two-thirds of plant and mammal extinctions have occurred. Many of these losses are attributable either directly or indirectly to invasive species.
Recently Al Glen and Alan Saunders took part in a study on how to minimise the impacts of invasive species on the flora and fauna of the Juan Fernández Archipelago, a cluster of three islands several hundred kilometres west of mainland Chile and home to around 700 people. It is also home to a spectacular and unique range of plants and animals, and is recognised as a global biodiversity hotspot. Over 60% of the native plants occur nowhere else on Earth. In addition, 6 of the 7 native land birds occur only on the islands, and some of these species, such as the Másafuera rayadito and the Juan Fernández firecrown, are critically endangered. Threatened seabirds such as petrels and shearwaters also breed on the islands. These outstanding naturalvalues have led to the Archipelago being designated a national park and a UNESCO biosphere reserve.
However, the islands are rapidly being degraded by invasive plants and animals. Weeds such as blackberry and Chilean wineberry are displacing native plants, altering entire communities and hreatening many native species with extinction. Rats and mice eat native seeds and seedlings, preventing forest regeneration and endangering remaining areas of forest. Introduced rabbits, goats and cattle not only disperse seeds of introduced species but also overgraze native vegetation and trample the soil, causing severe erosion and further loss of vegetation. The combined impacts of these herbivores have reduced some areas to a lifeless moonscape (Fig. 1). Cats and coatis (a South American relative of the raccoon) prey upon critically endangered native birds. The gravity of these impacts led the International Union for Conservation of Nature (IUCN) to list the archipelago as one of the world’s most threatened protected natural areas.
Al and Alan were members of an international team of scientists that investigated how to manage the invasive species in the archipelago and halt the decline of its biodiversity. The team adopted a broad approach, covering invasive plants, mammals, birds and invertebrates. Members visited the archipelago in May and November 2010 to consult with the local community and management agencies, and to see first-hand the impacts of the invasive species. The team judged that restoration of the islands is feasible but will involve significant costs and risks. Because a wide variety of invasive species are well established in the archipelago, the invaders are likely to interact with one another, and with native species (Fig. 2). A multi-species approach is therefore thought to be necessary so that attempts to manage one pest do not exacerbate the impacts of others. For example, removing goats and rabbits could allow weeds to grow unchecked. Island biosecurity will also be important to prevent further introductions of invasive species.
There are also complicating social challenges in managing invasive species on inhabited islands. The project must be acceptable to, and supported by, the local community and they must be engaged in both planning and execution stages. Public safety must be assured. Fortunately the team observed a large measure of awareness and support for the management of at least some of the invasive species present.
Managing diverse communities of invasive plants and animals, and community expectations, for island restoration presents major challenges. However, as much of the world’s biodiversity is found on such islands, it is a challenge that must be met.
This work was commissioned and funded by Island Conservation.