Invasive alien species – harmful species introduced by human activity to an area in which they are not native – are estimated to cost the African agricultural sector $3.66 trillion per year – approximately 1.5 times the gross domestic product of all African countries combined. The findings are published in the open access journal CABI Agriculture and Bioscience.
A team of researchers from CABI, in Ghana, Kenya, the UK and Switzerland, estimate that the average cost of invasive alien species to the agricultural sector of each African country is $76.3 billion per year. However, substantial variation exists between countries with costs of $1 trillion in Nigeria, $317 billion in the Democratic Republic of the Congo, $248 billion in Niger and $229 billion in South Africa. The combined costs for Djibouti, Equatorial Guinea and Guinea-Bissau are estimated to be $82 million per year. Economic losses caused by invasive alien species were found to exceed the gross domestic product of 27 out of 49 countries included in the authors’ analysis.
The authors found that removing invasive alien weeds from crops accounts for 99.2% ($3.63 trillion) of the estimated total costs incurred by the African agricultural sector each year by invasive alien species. Of the total weeding costs, weeding cereal crops accounts for 72% ($2.61 trillion), weeding maize and root crops accounts for 14% ($508 billion) and weeding vegetables accounts for 3.3% ($120 billion). Grassland losses caused by invasive alien species throughout Africa are estimated to result in losses of livestock income of $172 million per year. The amount of money spent on researching invasive alien species in 2019 was found to be $1.9 million.
The invasive alien species that was found to cause the most substantial crop losses was the moth Phthorimaea absoluta, which affects tomato plants and is estimated to cost the agricultural sector $11.4 billion in crop losses per year. The estimated annual crop losses caused by other species include $9.4 billion by the moth Spodoptera frugiperda, $6.3 billion by the mealybug Phenacoccus manihoti and $5.8 billion by the fruit fly Bactrocera dorsalis. These species affect maize, cassava and mango/citrus crops, respectively.
René Eschen, the corresponding author said: “Our findings reveal the substantial cost of invasive alien species to farmers and other land users, as well as the major impact that these species have on people’s livelihoods. The removal of invasive alien weeds is largely unpaid work and is primarily carried out by women and children, reducing the amount of time they are able to spend on income-generating and community activities or education. Our study demonstrates that there is an urgent need for measures to mitigate current impacts of invasive alien species and prevent the spread of new alien species across Africa.”
The costs of invasive alien species were estimated using data obtained from literature on the impact of these species on the agricultural sector and a survey of 110 individuals from 30 countries who either worked with or studied invasive alien species in Africa. During the survey, participants were asked to estimate crop losses caused by invasive alien species and report the cost of research into these species for the organisations they represented. For countries with insufficient data, the authors estimated the economic costs of invasive alien species using data on the costs incurred in similar habitats and climates.
The authors caution that their findings may underestimate the true economic cost of invasive alien species to the agricultural sector, as their analysis focused on the species that are currently having the greatest economic impact and did not include costs related to chemical herbicides used to control pests and diseases. Further research could assess the cost of invasive alien species to other economic sectors in Africa.