Institute of Biodiversity Conservation

Global Invasive Species Programme (GISP) promotes the ecosystem approach as being essential to the effective management of biological invasions

Water Hycinth (Eichornia crassipes) invading water ways (Photo: RBIPMA Ethiopia Project)

Invasive alien species are plants, animals or micro-organisms whose introduction and/or spread into a new ecosystem to which they are not native threatens biodiversity as well as food security, human health, trade, transport and economic development. Biodiversity is impacted negatively in a number of different ways including; competition, predation and herbivory, parasitism and pathogenesis, hybridization, facilitation e.g. by changing nutrients, air or water, and ecosystem processes but in all cases, the impact of the invasions and indeed the reason for the invasion phenomenon, is the interaction of the invasive species and the recipient ecosystem.

For this reason, GISP actively promotes the ecosystem approach in the management of invasive species so that the target is not just the reduction or eradication of the invading species but involves the recipient ecosystem and includes community involvement in a multisectoral, multi-tiered approach. A good example can be found in the UNEP/GEF-funded project, ‘Removing barriers to invasive plant management in Africa’, currently being executed by CAB International (CABI) and the International Union for Conservation of Nature (IUCN), which has adopted the ecosystem approach in managing invasive species at pilot sites in four countries in Africa.

The project focuses on managing invasives at the lowest level appropriate with the involvement of all stakeholders but notably, the local community (principle 2). A great deal of emphasis has also been attached to the importance of ensuring inter-sectoral co-operation including the formation of inter-ministerial bodies, which is consistent with the 5th operational guidance point in CBD decision V/6. Another important aspect of the ecosystem approach is that it encourages consideration of why management of a biological invasion is necessary and why it should take place before developing a management process. This latter aspect is necessary in order that stakeholders can debate and decide the expected outcome of management options for such targets e.g. returning the affected ecosystem to its original state (if that is known), or to a state where the invading species is diminished in extent, vigour, spread and/or impact on either the whole ecosystem and the surrounding local community, or the revitalization of selected important species and populations within it.

GISP has experienced many examples where the management of invasive species, which is based solely on eliminating the target species, has not yielded the desired result. Most common is the situation where the removal of an invader is achieved and then the degraded ecosystem becomes susceptible to further invasion by another invasive species e.g. removal of the aquatic invasive, water hyacinth (Eichhornia crassipes) from a lake often results in an invasion by another invasive species such as the water fern, Salvinia molesta. This type of problem can be addressed by careful planning for an agreed and desired outcome of management – using the ecosystem approach. Ironically, there are also examples where the continued presence of an invasive species at a lower density can be of value to the ecosystem e.g. by providing new nesting sites, or to people reliant on ecosystem goods and services that have been enhanced by the invasion such as provision of novel food sources, fibre, fuel, materials for artifacts, etc.

Use of the ecosystem approach in planning and implementing the management of invasive species on islands is a good example, in which many types of stakeholders can be consulted as well as components of the affected ecosystem analysed and outcomes debated. Nevertheless we still see some situations, especially where the total eradication of predators is concerned, where secondary and tertiary impacts of their removal have had deleterious effects on species of special importance. This is increasingly being addressed using the ecosystem approach to model possible outcomes of management and to better define the expected outcomes in terms of ecosystem indicators rather than the survival and population growth of selected species.

As more work is done to understand biological invasions on larger landmasses, often with more complex matrices of habitats and species, it is clear that the ecosystem approach can assist to define and achieve desired outcomes.

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