According to Geoffrey Howard of the World Conservation Union (IUCN), the problem of invasive alien species (IAS) is far greater than most people imagine.
Dr Howard, why is the issue of invasive alien species important for agriculture in ACP countries?
Invasive alien species are those that come from outside a particular ecosystem, area or country and which are capable of damaging local biodiversity, food production, development in general, and even human health.
The fact that they are ‘alien’ usually means that they have been introduced to an area, either intentionally or unintentionally, but have come without their own predators, parasites and pathogens and so are able to breed and disperse very rapidly. Many of the most familiar agricultural pests are invasive species that have established in new areas. Without their natural predators they can multiply and spread unabated, wreaking havoc on crops, livestock or food stores – until we develop control measures.
Most ACP countries lack the facilities and the experience to deal with the three phases of tackling IAS: prevention (mainly stopping introductions), eradication (of newly established invasive species) or control (of invasions that are already underway). While awareness is slowly growing of the concept of ‘invasiveness’ and of the potential impacts of IAS, there is often very little a developing country can do to stem a problem before it becomes critical and impacts basic food production and/or human development.
How serious is the problem of IAS?
The ‘IAS problem’ in general is far greater than most people imagine. A recent IUCN analysis of threatened species has shown that IAS are the third most common cause of extinctions, after habitat loss and over-exploitation, of mammals, birds and amphibians.  IAS are becoming more common worldwide and more destructive as international trade, air transport, travel and tourism increase with globalization. We are finding more and more invasive species turning up and establishing themselves in previously unaffected areas all around the world. In fact, some places on opposite sides of the world but with similar climates are beginning to ‘look alike’ as the invasive species take over from the natural flora and fauna, wherever they may be.
A classic example is the Water hyacinth (Eichornia crassipes) which is a native of wetlands in South America. But is has spread to most tropical countries of the world, causing serious problems in many parts of Africa, Asia and Oceania
How do IAS differ from other pests and parasites?
It would be better to think of pests and parasites as types of IAS – if they cause serious and increasing problems, such as replacing local species, hampering development and affecting human health. Many invasive species may impact ecosystems rapidly, with numerous negative effects. But other species may take years, decades or even centuries to pass through the stages of introduction, establishment, spread and invasion. Some invasive plants, such as large trees, may take decades before they start to spread and become a problem, while others may have been around for so long that people no longer recognize them as exotic or alien, and learn to live with them, to their great disadvantage.
It serves no purpose to try to distinguish a pest or parasite from an invasive species. Rather, it is better to think of them all as problems that need to be addressed by controlling introductions, preventing their spread, and managing invasions or outbreaks whenever and wherever they occur as a matter of urgency.
What is being done to address IAS at the international level?
The Global Invasive Species Programme ( GISP) is an international organization that has taken on the responsibility for increasing awareness of invasive species and for disseminating information and building capacity for their prevention and control in developing countries and elsewhere. The GISP is a network of global and local organizations with an interest and expertise in IAS issues which is dedicated to their control. Several other organizations have assembled valuable information on IAS, including the IUCN Global Invasive Species Database and CAB International, which has devoted an entire section of 2004 edition of the Crop Protection Compendium to the management of IAS.
Dr Geoffrey Howard is the East Africa regional programme coordinator for the World Conservation Union (IUCN), and IUCN representative with the Global Invasive Species Programme (GISP).
 Baillie, J.E.M., Hilton-Taylor, C. and Stuart, S.N. (Eds) 2004 IUCN Red List of Threatened Species. A Global Species Assessment. IUCN, Gland, Switzerland.