Invasive species are among the top threats to biodiversity globally and are reported to be affecting livelihoods in 70% of African countries. Invasive alien species are plants and animals introduced by people, accidentally or intentionally, to new locations where they cause harm. They are among the top threats to biodiversity and ecosystems globally, yet few countries consider biosecurity measures to be a high priority.
Today, the term “invasive species” is the universal definition of animals, plants, and microbes introduced accidentally or deliberately outside their natural habitats or countries of origin. In sub-Saharan Africa (SSA), one of the most susceptible regions, the list of invasive species is long and diverse; their destruction is often horrendous.
While the CBD targets the control or elimination of priority invasive alien species by 2020, there has been little or no progress recorded in some African countries. The barriers to progress are varied, including constrained financial resources and the lack of legal frameworks and related operational systems.
Africa is one of the continents expected to be hit hardest by climate change, which is likely to compound existing problems of invasive species, Egoh worries. Invasive species threaten food security by negatively impacting fish production, agricultural productivity, grazing, and water supplies, she says.
Key Challenges in Africa
Africa's key challenges are a lack of capacity, mainly at ports of entry, which are mostly ill-equipped from a biosecurity perspective to detect invasive species, says Albi Modise, communications chief director of South Africa's Department of Environment, Forestry and Fisheries. Some areas in the region still have to enhance their management plans for effective control of invasive species. These include introductions, control, and identification of common invasive species affecting the region, Modise says.
Read also: Property Practitioners Regulatory Authority
Several invasive species occur across neighboring countries. For example, the shrub Parthenium hysterophorus is suspected to have accidentally been introduced to Ethiopia through relief food donations in the mid-1980s but has since spread to Kenya, Uganda, Tanzania, Somalia, and South Sudan, says Dr. Staline Kibet, an expert in botany, range, and dryland management at the University of Nairobi, Kenya. There is a lack of regional coordination in approaches to management across borders, he says.
Dr. Kibet explains that litigation involving invasive species remains a grey area in law, due to clashes in cultural ethics, self-interest, or desire to protect the environment. To investigate the level of African invasion biology expertise, Dr. Benis Egoh at the University of California Irvine reviewed national reports and scientific literature from July 2018 to August 2019, as indexed in the Scopus and Web of Science databases; of the 48 countries sampled, 35 (73%) had negative impacts from invasive species. In 21 countries the water hyacinth was the most common invasive species.
“The study hasn't really highlighted anything new”, says Dr. Arne Witt, invasion biologist for the Centre for Agriculture and Bioscience International (CABI) based in Nairobi, Kenya. Witt started his first invasive species project in Africa working in Ethiopia, Ghana, Uganda, and Zambia in 2005, trying to strengthen the countries' ability to manage invasive species. The barriers then were identified as a lack of policy or enforcement thereof, and a serious lack of capacity and awareness, as well as the absence of effective management practices. 15 years later, Witt suggests that these conditions have improved in terms of programs and experts addressing these gaps, but notes that invasive species are still a significant barrier to development.
“Africans are not only losing food, but culture and Indigenous knowledge that cannot be quantified in monetary terms”, Witt says. To try and quantify the loss, CABI is in the process of evaluating the economic damage due to invasive species across Africa. Although there is little local information or capacity, Witt says they are taking studies done elsewhere and extrapolating them for Africa, with the results expected by the end of this year.
Examples of Invasive Species and Their Impacts
The yield losses attributed to Asian citrus greening disease once established can be devastating. If the disease continues to spread unabated in the citrus-growing regions of East Africa, the annual value of lost production could potentially reach up to US $127 million over the next ten to 15 years, according to a recent paper published by CABI.
Read also: Amazing Facts About Africa
Some that have been the subject of icipe research in the recent past include the maize lethal necrosis disease (MLDN), caused by the maize chlorotic mottle virus and sugarcane mosaic virus. Africa’s backup staples, like potato, have not been spared from the invasion peril. Two years ago, the potato cyst nematode (PCN), microscopic, soil-dwelling roundworm that are highly destructive to potatoes worldwide was reported in eastern Africa.
Aside from ruining fruit and vegetable yield, at times up to 100%, B. dorsalis, like other fruit fly species, is also a quarantine pest, and its presence in Africa restricts the export of produce from the continent to European markets and emerging markets in North America. Other invasive fruit fly species on the continent include B. zonata, B. cucurbitae and B. latifrons.
Further, icipe and partners have recently detected the Asian citrus psyllid, Diaphorina citri, a sap-sucking insect that can transmit the lethal citrus disease huanglongbing, also known as ‘citrus greening’. In addition, Tuta absoluta, a devastating leafminer originating from Peru has swept across Africa, leading to the declaration of a state of emergency in some of the continent’s main tomato-producing areas.
Meanwhile, emerging infectious diseases like malaria, Rift Valley fever, yellow fever, and dengue, pose constant and growing threats to the continent. This is because, while these diseases are already causing significant problems in endemic zones, they are now also spreading to new geographical areas in Africa, and due to a number of factors, including climate change, they also represent a constant threat to regions beyond the continent.
Further, the Centre has focused attention on invasive weeds, like the Prosopis genus, enlisted for rehabilitation of African dry lands in the 1970s, but has since turned out to be a noxious, extremely aggressive invader that replaces native vegetation and colonizes important ecosystems like rangelands. A native of North and South America, Parthenium is considered one of the world’s most serious invasive plants. In East Africa, Parthenium is extensively spread over cultivated and pastoral lands.
Read also: Discover Thula Thula
Common invasive species, especially plants in Nigeria include Tithonia diversifolia, Chromolina odorata, Leucaena leucocephala, Gliricidia sepium. Fall armyworm (FAW), was recognized as a serious economic pest two centuries ago. long distance migratory and transboundary pest, FAW has invaded and spread into Africa. Recent reports have confirmed that FAW has emerged as a great challenge to Maize production, threatening food security for most households in Africa.
Siam weed (Chromolaena odorata) belongs to the family Asteraceae and is another invasive species in Africa. It propagates from seeds and basal shoots. It is a troublesome weed of open cultivated fields, roadsides, plantain crops and cocoa plantation. It is widespread in Africa from the coastal fringes to the rainforest to the southern edge of the Guinea Savanna.
Mexican sunflower or tree marigold (Tithonia diversifolia) is a bushy, perennial weed growing up to 2-5m. It can reproduce from seeds and from vegetative regrowth of the basal stem when the plant is cut. The inflorescence is a solitary capitulum on a peduncle 7-15cm long with large orange-yellow florets 5-10 cm across. The plant was probably introduced into West Africa as an ornamental plant but later become invasive.
Subabul (Leucaena leucocephala) belongs to the family Fabaceae and subfamily ceasapiniodeae. It is another invasive species in Nigeria - a small fast growing mimosoid tree native to southern Mexico and north-central America (Belize and Guatemala) and is now naturalized throughout the tropics.
The threat of invasive species - Jennifer Klos
Lessons from South Africa
Egoh's study finds South Africa to have the most scientific studies on invasive alien species with 22 of the 36 studies, followed by Ethiopia (six), and Kenya (four). South Africa came out top because it has been doing work on invasive species for much longer than other African countries, Witt says.
“South Africa was unfortunate in that we had a huge problem with invasions earlier than most other parts of Africa and had to make a start in managing invasive species”, says Professor David Richardson, director of the Centre for Invasion Biology at Stellenbosch University.
Richardson explains that the South African Government invested in science and technology, especially centers of excellence, which allowed researchers to engage with the problem in a multidisciplinary way. This led to the development of new knowledge and boosted capacity by producing many students who now work in governments and agencies across Africa.
Dr. David Le Maître, ecologist and hydrologist at the Council for Scientific and Industrial Research (CSIR) says it was all a fortunate combination of events: the new South African Government wanted to find ways of empowering the poor and they accepted scientific findings that clearing alien plant invasions could save water and provide meaningful work. Kader Asmal, Minister of Water Affairs who acted on this information and the influence of his advisor Dr. Guy Preston was largely responsible for growing the program to its current scope and budget.
South Africa has one of the largest invasive species clearing programs, Working for Water, which started in 1995 and focuses on invasive plant species, such as the water hyacinth.
Richardson says South Africa is the only country in Africa that has a reasonably comprehensive and accurate list of invasive species of all types; most other countries on the continent have relatively rudimentary research on which species were introduced and have become invasive. Researchers in South Africa have also assessed and quantified the impact of invasive species on biodiversity and human livelihoods.
A new open access encyclopedic book, Biological Invasions in South Africa published in June 2020, suggests 1422 alien species have become naturalized in the country. Some species have serious negative impacts on South African ecosystems, for example, some invasive tree species like the pines, eucalyptus, and wattles use much larger quantities of water than the native trees they are displacing.
While there may be a lack of peer-reviewed research on invasive species in Africa, Dr. Cathy Sutherland, a geographer of ecological infrastructure at the University of KwaZulu-Natal, says that in South Africa, there is extensive work being done on the ground, some of which is experimental and involves significant social learning, but “Given the actors that are engaged in this work, including the local state and environmental NGOs, this work is not being published in the scientific realm.”
“It would be important to explore other ways in which this knowledge and expertise is shared, for example in municipal reports… I would also imagine that work of this nature is occurring elsewhere in Africa but it is not being published in the form that Dr. Egoh's paper has assessed, which does not mean it does not exist”, Sutherland explains.
Post-2020 Biodiversity Adaptation
A one-size-fits-all target does not work particularly well for countries in Africa, says Egoh. “African countries should push for a more flexible target based on the specific situations in their countries”, she says. Some issues that need urgent attention in Africa include capacity building in addressing knowledge gaps and co-production of knowledge, putting in place robust financing mechanisms, addressing poor governance issues and identifying national biodiversity priorities that align with other national priorities for joint implementation.
“I think we need to work harder on drawing on multiple forms of knowledge and practices, right down to the local level where so much is being done, so that all people are drawn in and acknowledged for their contribution to the maintenance and enhancement of ecosystem services”, says Sutherland.
The challenges lie in doing the right thing where it really matters and in making sure that interventions are done efficiently and effectively. “Even so, the South African government does not have the resources to make sufficient progress, invasions are spreading at a faster rate than they are being addressed; private investment is needed as well”, says Le Maitre.
After 15 years of research in all aspects of invasions, marine, freshwater and terrestrial ecosystems, ecology and impact of invasive species, and policy development, Richardson says the CIB Centre of Excellency feels the time is ripe to expand their footprint by establishing hubs and centers of excellence across Africa.
“In [some] African countries there is some investment in dealing with invasive species but it's not well coordinated, it's not across all sectors, for example that includes education, training, creating governance structures, allowing for the transfer of scientific information into policy development is lacking,” says Richardson.
Kibet sees reliance on external financial support to run invasive species program not yielding much but, “African governments must, as a matter of urgency, establish a financial resource mobilization strategy that is sustainable”.
As the threat of alien invasive species continues, Africa has several models to learn from. A shift in approach from reactive to more proactive interventions based on the internationally recognized three-stage approach should be adopted: that is prevention, early detection and rapid response and control.
Examples of Invasive Species in Africa
Here are some examples of invasive species in Africa, categorized by type:
- Plants: Tithonia diversifolia, Chromolina odorata, Leucaena leucocephala, Gliricidia sepium, Prosopis spp., Parthenium hysterophorus, Water hyacinth
- Insects: Fall Armyworm, Asian citrus psyllid, Fruit flies (Bactrocera dorsalis, B. zonata, B. cucurbitae, B. latifrons), Tuta absoluta
- Diseases: Maize lethal necrosis disease, Potato cyst nematode, Asian citrus greening disease, Malaria, Rift Valley fever, Yellow fever, Dengue
- Marine Species: Fish, Jellyfish, Prawns
This list is not exhaustive, but it provides an overview of the diverse range of invasive species affecting Africa.
The Mediterranean Sea Invasion
The Mediterranean Sea is being invaded by hundreds of fish, jellyfish, prawns, and other marine species from outside the region. More than 1,000 non-indigenous species have been identified in the Mediterranean and the Black Sea.
“Climate change and human activities have had a profound impact on the Mediterranean and the Black Sea,” says Stefano Lelli, a fishery expert for the eastern Mediterranean working for the General Fisheries Commission for the Mediterranean (GFCM).
Prevention and Management
The degree of invasive pests introductions, globally but especially in Africa, suggests a lack of adequate contingency planning, preparedness, and management measures. Prevention involves pest risk analysis by relevant regulatory authorities to predict possible arrival, potential pathways, and the chances of a particular pest or pathogen becoming established in a new location. This information should allow regulators to determine the risk mitigation steps and the necessary phytosanitary measures to ensure that the risk is kept at acceptable levels.
Unfortunately, in many cases in SSA, the response to invasive pests has been reactive and ad hoc rather than proactive. As discussed later in this publication, icipe has been collaborating with a number of partners to rectify this situation.
Popular articles:
tags: #Africa
