Impacts in Africa
Agriculture provides 60% of all employment in Africa, and about 80% in rural areas. Africa's 120 million smallholder farmers play a major role in food security. Invasive species cause severe losses in two widely-grown staple crops of particular importance in the region: cassava and maize.
An estimated 70 million people in Africa are dependent on cassava as a primary food source. It is grown as a famine reserve, due to its resilience and ability to resist drought. Invasive weed species present a serious threat to cassava, smothering crops and reducing growth, while plant diseases are a major constraint to production.
Infestations of invasive plants, diseases and pests are also causing a decline in maize yields. In sub-Saharan Africa – where an estimated 200 million people are chronically undernourished – maize is a staple food, yet the region has the lowest maize yields in the world.
Post-harvest losses are also an extensive problem in Africa, with insect pests such as the larger grain borer devastating produce in storage.
Goods and services supplied by the ecosystems in which people live also contribute significantly to income generation – for instance, in South Africa at least 133,000 people trade in 771 different medicinal plant species (Mander et al.) – and many native forest plants have a domestic or pastoral use, with an important role to play as a source of food, drink, construction materials, tools, firewood and medicines.
Seyam et al. (2001) calculated that the annual economic values of the Zambezi basin wetlands are, amongst others, US$50 million for flood plain recession agriculture, US$78.6 million for fish production, US$70.6 million for livestock grazing, and US$2.6 million for natural products and medicine.
Invasive plant species often block access to these ecosystem services or outcompete them so they become scarce.
Preventing fishing and reducing water quality
Aquatic weeds such as water hyacinth, salvinia molesta and water pistia stratiotes affect communities that rely on fishing by blocking waterways and diminishing fish stocks. They also reduce water quality, disturb the supply needed for households, agriculture and industry, and present a human health risk by increasing stagnation and harbouring mosquitoes.
Livestock production is affected when invasive weeds colonise prime grazing land. Farmers are driven into marginal areas, use pasture beyond its capacity, or have to take their herds long distances to find fodder. This can lead to conflicts between communities, due to competition for access to resources and fear of the plant spreading.
Agriculture generates more than 40% of Africa’s foreign exchange earnings, and pests and diseases threaten economic development by restricting international exports. The presence of an invasive fruit fly (Bactrocera dorsalis), for instance, has resulted in severe restrictions in the trade of mango and banana, and some countries have already banned the import of these fruits from Kenya and Uganda.