An indigenous plant or animal is one which occurs
naturally in the place in which it is currently
found, and has not been assisted in its travels
by people. Being indigenous does not mean that a
species has always occurred where it is now found
- some species shift their distribution quite
quickly, for example, when blown by strong winds
of naturally transported by ocean currents.
The indigenous concept also
applies to habitat, and does not refer just to a
geographical area. For example, the birds
indigenous to dry thornveld are very different
from the birds indigenous to mistbelt forest,
even though they may be only 10 km apart.
An endemic species is not only
indigenous, but is restricted to a particular
area. The blue crane, for example, is indigenous
to southern Africa, and is found nowhere else.
This makes it endemic. The wattled crane is also
indigenous, but it is not endemic to southern
Africa as it is also found further north in
A species which does not occur naturally in an
area (i.e. is not indigenous), but which has been
introduced there by people, is called an alien.
Sometimes people use the word "exotic"
instead of alien, but this is not the best word
as it has many other meanings.
A few alien species reproduce and spread,
unassisted by man, into areas where they are not
wanted - these invasive aliens pose a serious
threat to nature conservation. Expensive and
drastic measures are required to control
Some indigenous species also
invade new areas but these invasions are brought
about by changes in the area invaded, e.g. Acacia
karoo rapidly takes over overgrazed grassland.
Control of such invasions involves correcting the
management of the area, in addition to control of
the invading species itself.
WHY DO SOME ALIENS
There are several reasons, but most important is
that aliens find themselves in an environment
different from that in which they evolved.
Usually such a drastic change in environment is
fatal to an alien. Occasionally, however,
conditions are superior to those in the native
land. In particular the alien animal or plant is
normally free of the diseases, parasites and
predators which keep its numbers in check in its
natural environment. Under these conditions
populations can explode with the invaders
overwhelming the indigenous fauna and flora,
usually by crowding it out.
In southern Africa very few
mammals have become invaders. Alien fish,
however, pose a serious threat to the indigenous
fish of our inland waters. For example,
smallmouth and largemouth bass prey heavily on
indigenous fish. Fish parasites accidentally
introduced with some aquarium species cause even
greater problems. Parasites such as `white spot'
are alien to southern Africa.
Plant invaders are plentiful,
especially in the southwestern Cape,
KwaZulu/Natal, and the eastern Transvaal. Cape
fynbos, a unique floral kingdom, is severely
threatened by Australian acacias, which were
originally introduced for timber, bark products,
or to stabilise sand dunes. In the eastern Cape,
KwaZulu/Natal, and the Transvaal lowveld the
worst invaders are lantana, chromolaena (triffid
weed), seringa, and pereskia (Barbados
gooseberry), black wattle, prickly pear, bugweed,
and bramble. Many alien plants have been declared
undesirable and may not be grown on any public or
private property. These alien plants were
originally introduced as commercial plants or as
ornamental garden plants. Many rivers and dams
are clogged with water hyacinth, Kariba weed or
parrot's feather, also escaped ornamentals.
Highveld areas suffer most from wattle and
bramble, and the arid west is being invaded by
mesquite. There are more than 700 alien plant
species in southern Africa and 10% of these are
None of these plants and
animals cause problems in their native lands.
Their invasive qualities were unsuspected, which
goes to show that no alien plant or animal should
ever be released into the veld without screening
for its invasive potential. Almost any alien
could become an invader.
THINGS TO DO
* List and map all the invaders in your area and
find out how to control each invader.
* Draw up a report outlining an
overall control plan (specialist advice will be
needed for this) and present it to your local
* Check all gardens and
nurseries to ensure that none are cultivating
invaders - bring offenders to the attention of
your local conservation authority.
* Do not move any aquatic plant
or animal (including fish) from one water body to
another - to do so is illegal. * Never release
unwanted pets into the wild - rather give them to
a pet shop.
* Abide by the regulations
regarding the importation of plant and animal
material when returning from abroad, and
encourage friends to do so.
UNDERWATER INVADERS. I.J. de Moor and M.N.
Bruton. African Wildlife 42(4), 1988.
INVASIVE ALIEN PLANTS
AND NATURE CONSERVATION. I.A.W.
Macdonald. in African Wildlife 42: 333-335, 1988.
ATLAS OF ALIEN AND
TRANSLOCATED INDIGENOUS AQUATIC ANIMALS IN
SOUTHERN AFRICA. Southern African
National Scientific Programme Report No. 144. CSIR, Pretoria. 1988.
NATIONAL LIST OF
INDIGENOUS TREES. F. von Breitenbach.
Dendrological Foundation, Pretoria, 1990.
NATIONAL LIST OF
INTRODUCED TREES. F. von Breitenbach.
Dendrological Foundation, Pretoria, 1989.
CATCHMENT ACTION: 28
ALIEN PLANT INVADERS IN NATAL. P.
Caldwell. Share-Net, 1992. PO Box 394, Howick,
BEAUTIFUL BUT DANGEROUS. C. H. Stirton
(ed.) Department of Nature and Environmental
Conservation of the C.P.A. Cape Town, 1987.
* A CATALOGUE OF
PROBLEM PLANTS IN SOUTHERN AFRICA INCORPORATING
THE NATIONAL WEED LIST OF SOUTHERN AFRICA.
M. Wells et al. Memoirs of the Botanical Survey
of South Africa, no. 53. Botanical Research
Institute and Department of Agricultural and
* PLANT INVADERS OF THE
TRANSVAAL. L. Henderson and K.J. Musil.
Department of Agriculture and Water Supply,
Bulletin 412. Government Printer, Pretoria, 1987.
* DECLARED WEEDS AND
ALIEN INVADER PLANTS IN SOUTH AFRICA.
Henderson et al. Dept. Agriculture & Water
Supply, Pretoria, 1987.
* Available from the National
Botanical Institute, address below.
Dept. Water Affairs and
Forestry, Forestry Branch. P. Bag X313,
Pretoria, 0001. Tel. 012-299 9111. Publish
various pamphlets on invasive plants.
Agricultural Information. P. Bag X144,
Pretoria, 0001. Tel. 012-206 2829/206 2181.
Publish a selection of pamphlets on weeds.
The National Botanic
Institute. P. Bag X101, Pretoria, 0001.
Tel. 012-804 3200, ask for Information Officer.
Institute. P. Bag X134, Pretoria, 0001.
Tel. 012-206 9112. Branches in Pietermaritzburg,