Invasive Alien Species in Zimbabwe

June 4, 2021
Paddy Pacey
Vegetation

By Clare Davies, Ecologist

As humans have moved about the planet they have taken with them, deliberately or accidentally, pathogens, animals and plants. Some of these have caused havoc where they have spread and “invaded” the new territories, damaging or squeezing out what was indigenous. Smallpox, for example, wiped out huge sections of the native populations of the Americas. And we are all keenly aware of the effects of human movement around the planet and COVID-19. Rabbits have become a major pest in Australia and New Zealand.

Rabbit problem in Australia

The Japanese kudzu vine rapidly smothers all other vegetation in many places in the United states. (There are species that are introduced into a country from elsewhere but do not spread like wildfire – they remain “alien” or non-indigenous, but they do not become invasive, i.e. they do not become widespread or a problem.)

Invasive species were often originally introduced for agriculture/cultivation (e.g. crops, forestry or fisheries) or for ornamental purposes. Alternatively, some species are introduced accidentally, being transported in trucks, animal feed or contaminated wood, usually in the form of seeds or pods. These species escape their enclosures or fields and establish in neighbouring places as viable populations. The plants then spread via wind, water, animals or humans. They find conditions in the new country particularly favourable and/or they have none of the pests that would have kept them under control back in their native country.

There are several characteristics or circumstances that cause an introduced species (plant or animal) to become an invasive. These include:

Similar conditions to the area/region where they originated.
Prolific seed or offspring production,
Individuals (plants or animals) living a long time.
Effective dispersal of seeds (wind, water and/or birds) or offspring.
Absence or reduced predators or enemies.
Vegetative reproducers, as in the case of many plant species.
Opportunistic species – invasive plants often establish themselves in areas with a lot of bare ground that is degraded and/or over-grazed.

Invasive alien species cause environmental harm. They affect biodiversity by competing with native species, causing their decline and/or elimination. Species like pine, wattle and eucalyptus change the chemical composition of the soil in which they are growing to discourage any competition so that indigenous species can no longer grow in that soil.

The end result is the disruption of the balance of ecosystems and their functions. The impacts are environmental, economic and social, affecting agriculture and forestry, fisheries and countless other ecosystems and then affecting peoples’ livelihoods, especially in developing countries. The result of this is an increase in poverty. This situation is all compounded by climate change, other human impacts on ecosystems, habitat loss and, of course, pollution.

Invasive Species in Zimbabwe

The following are the main invasive species of plants and animals in Zimbabwe.

Invasive Land Plants

Black wattle in flower — Black wattle tree *Acacia mearnsii*, native to Australia & densely populating about 200 000 hectares in the Eastern Highlands

Pine trees – especially *Pinus patula* or Mexican weeping pine – from Mexico. Another major invader in the Eastern Highlands

Guava, strawberry or cherry — Cherry, cattley or Chinese guava tree – *Psidium cattlensis* – originally from Brazil

Jacarandas flowering — Jacaranda, *Jacaranda* *mimosifolia*, imported, understandably, for ornamental purposes, from South America

guava — Guava tree, *Psidium guajava* – from South and Central America and the Caribbean

Dodder, strangleweed, witch’s hair, love vine etc. – *Cuscutaspp species of* parasitic creepers – thought to come from Cthe Americas.

Mysore raspberry — Mysore or Ceylon raspberry, *Rubus niveus*, commonly known in Zimbabwe as “Dustyberry”, from India and Malaysia

Jointed prickly pear or jointed cactus – *Opuntia Aurantiaca* from the Americas

Lantana flower — Lantana – *Lantana camara* is a shrub from the American tropics/West Indies

Queen of the Night creeper — Moonflower cactus – *Eriocereus martini* – originates from South America

Avena fatua, common wild oats — Wild oats – *Avena fatua spp.* – originates from the Mediterranean, Ethiopia, North Africa, Europe and Asia

Khakibos flowers — Khakibos, African marigold or Stinkbos – *Tagetes minuta* from South America.

Madagascan periwinkle – *Ammocallis rosea* – native to Madagascar

Blackjacks — Black-jack (*Bidens pilosa*). Probably originally from South America

Chain fruit cholla — Chain fruit or jumping cholla – *Cylindropuntia fulgida, Cylindropuntia rosea* or *Opuntia rosea* – originates in Southwest USA and Mexico

cosmos — Cosmos or Mexican aster (chocolate, pink or white, or yellow) – *Cosmos bipinnatus, C. sulphureu* or C. caudatus – from Mexico and northern South America

Bee bush – *Vernonanthura Polyathes* – originating from Brazil

Red or Mexican sunflower – *Tithonia rotundifolia* – probably from Mexico.

Invasive aquatic (water) plants

Kariba weed – *Salvinia molesta* – originates from south-eastern Brazil, South America

Water hyacinth clogging a waterway — Water hyacinth – *Eichhornia crassipes* – originates from South America

Water lettuce — Water cabbage, water lettuce, Nile cabbage or shellflower – *Pistia stratiotes* – native location origin is uncertain, first discovered from the Nile, near Lake Victoria

Water fern, Azolla filiculoides — Water fern – *Azolla filiculoides* – originates from the Americas

Giant Salvinia – *Salvinia auriculata* – originates from South and Central America

Invasive creatures

khapra beetle in grain — Khapra beetle – *Trogoderma granarium* – from South Asia, destroying stored maize and other grains

Larger grain borer & its work — Larger grain borer beetle – *Prostephanus trancates* – from Tanzania, destroying stored maize and other grains

Large-mouth bass — Largemouth bass – *Micropterus salmoides* – native to North and Central America

Oreochromis niloticus — Cichlid – *Oreochromis species* – originates from Africa and the Middle East, but has been introduced far outside its native range

Brook trout – *Salvelinus fontinalis* (fish) – originates in Eastern North America, in the United States and Canada

Tinca or doctor-fish — Tench or doctor fish – *Tinca* *tinca* – from Eurasia

Australian red-claw crayfish, *Cherax quadricarinatus*, feeds on eggs of fish and other species and burrows into dam walls and banks causing structural damage

Kapenta catch — Kapenta or Lake Tanganika sardine L– *Limnothrissa miodon*, and Lake Tanganyika sprat – *Stolothrissa tanganicae* – originate from Lake Tanganyika

We will talk in other articles about specific examples of invasive species, e.g. what is happening in the Eastern Highlands and what is happening in our dams and rivers.

Invasive species and the law in Zimbabwe

The Zimbabwean Environmental Management Act (2002), Chapter 20:27, Part XIII, sections 118 – 127 deals with the legal and control aspects of alien invasive species in Zimbabwe. The following species have been declared ‘Invasive Alien Species’ (IAS) by law:

(EMA, refer to References section).

What you need to know?

You cannot know and deal with all the invasive species – but you have probably got a feeling of those plants or insects or fish which are causing a problem in your area. It would be a very good idea to go onto the internet and look up the negative effects of these particular species – and what the suggestions are for beginning to get some control of the populations. If we all make an effort to fight invaders in our little patch we could begin to turn around the situation.

Paddy Pacey

Zimbabwean field guide and trainer of aspiring guides