Alien weeds and Invader plants:
why the fuss?
What are
alien invader plants? These
are plant species that are non-native, non-indigenous, foreign or exotic
occurring outside of their natural range (past or present) and dispersal
potential (i.e. outside the range they occupy naturally or could not occupy
without direct or indirect introduction or care by humans). Furthermore, they
have become established in natural or semi-natural ecosystems or habitat, are
agents of change, and threaten native biological diversity.
How substantial is the threat? With
increasing globalisation, free trade and tourism, natural barriers to species
movements are being ameliorated or eliminated. Over 900 species of alien plants
can be found within South Africa. Although many of these species are introduced
for beneficial (e.g. food crops) or benign (e.g. ornamental plants) reasons,
many of the species have the potential to spread to land where they were not
planted. This process is termed
invasion. Unfortunately, the South
African environment is particularly prone to invasions. With
increasing globalisation, free trade and tourism, natural barriers to species
movements are being ameliorated or eliminated. Over 900 species of alien plants
can be found within South Africa. Although many of these species are introduced
for beneficial (e.g. food crops) or benign (e.g. ornamental plants) reasons,
many of the species have the potential to spread to land where they were not
planted. This process is termed
invasion. Unfortunately, the South
African environment is particularly prone to invasions. The total landmass of South Africa is some 1 221 040 km2 and
all of this land is potentially subject to invasions. Alien plant invasions have a major impact on the natural resources of
South Africa. In 1998, geographical information systems analysis assessed that
alien plants had invaded over 10 million hectares, an area larger than the
province of KwaZulu-Natal, or approximately 8% of South Africa. In KwaZulu-Natal the assessment was even more disparaging: 9.75% of the
province assessed as invaded. Worst
still was that anecdotal evidence suggested that the total invaded areas maybe
as much as 2-3 times as extensive as the reported assessment. Hotspots identified for KwaZulu-Natal by the mapping experts
were Zululand, the Natal Midlands, and the Coastal Zone. Reasons for
intervention to combat alien invader plants are fivefold.
One: an ecological imperative. Alien invader plant
species have an adverse effect on biodiversity. Natural communities consist of a multitude of species and the
sustainability of a community depends upon the interactions between species,
climate and soil. A factor or event that disrupts this interaction can change
the community. Such a factor is the
invasion by alien invader plant species. The
introduction and establishment of plant invaders in complex multi-species plant
communities upsets the intricate set of competitive balances that are in
operation. This disruption often
results in dominance by the invader over the other species. Over time the rich multi-species community is transformed into a
species-poor community within a degraded environment. South Africa, as a
signatory to the Convention on Biodiversity, makes the conservation of
biodiversity a national commitment and therefore also the responsibility of
every landowner.
Two: an economical imperative. Alien invader plant
species incur economic costs. An
official estimate suggests that the costs of mounting a one-year, ‘once off’
eradication campaign would be R6.97 billion, including the necessary follow-up
costs. This, however, is impossible
in practice. If alien invader plant
species are conservatively estimated to spread at 5% per annum, a 20-year
programme would cost approximately R600 million per annum and the total cost (at
net present value) would be R5.44 billion. While the cost of clearance is high, the alternative may be
even more costly. Economists use
the term ‘opportunity costs’ for losses incurred through certain choices
made over others, including ignorance and inaction. For alien invader plant species, or more precisely the neglect of the
problems posed by alien invader plant species, these costs may well prove to be
very high. For example, a delay of
10 years in launching such a programme would increase the projected costs by
55%. Furthermore, increased costs
may be expected in the agricultural sector as the cost of managing land and
livestock rises due to bush encroachment and livestock poisoning. Communities living in areas infested by alien invader plant species may
also experience health problems. Some
species are toxic to humans, e.g. lantana, particularly among children, has been
known to cause death through neuro-circulatory collapse. Symptoms include stomach and intestinal irritation, muscular weakness and
circulatory collapse. Hospitalisation
is essential. A far-reaching
economic, as well as ecological and social, concern is the depletion of South
Africa’s water resource that alien invader plant species incur. In KwaZulu-Natal alone, alien invader plants use
approximately 576 million m3 per annum more than the natural
vegetation they have invaded or replaced.
Three: an
aesthetical imperative. South Africa’s flora and fauna are unique.
For example, the Cape Floral Kingdom is one of only six floral kingdoms
in the world with a high-level of endemism. Without doubt this rich and beautiful flora is worth saving for its own
sake. One of the ways in which
humans spend their intellectual energies is in the pursuit and enlightenment of
taste and pleasure by aesthetic exercises that may be referred to as the
‘humanities’. Each year, local
and overseas tourists visit, and take delight at, the natural marvels that may
be witnessed throughout the country. However,
the South African landscape is being transformed at a rate unprecedented
throughout history. A major
precursor to this is the invasion of alien plant species. Due to a lack of
public-awareness, the danger to these harbingers of the aesthetics is being
underestimated. Millions of Rand is
spent on conserving cultural artifacts and old buildings, but living things have
beauty too, and once lost they are much harder to replace.
Four: a moral imperative. Moral consideration for other species is a relatively new concept.
Many in the past have blindly accepted and preached that moral considerations
towards other species need to be taken into account. However, an overriding
rationale for moral considerations to all non-human life on Earth does exist.
Humanity, with its ballooning population and increasing influence within the
ecosphere, has become the guardians, or stewards, of the world and its wildlife.
Even in anthropocentric terms a moral imperative exists – to conserve as much
as possible for future generations. The renown, Harvard ecologist, E.O. Wilson
warned that “no comfort should be drawn from the spurious belief that because
extinction is a natural process, humans are merely another Darwinian agent”,
as the rate of extinction is now 400 times of that recorded through recent
geological time and is accelerating rapidly. A major role–player in this
accelerated process are alien invader plant species. Thus, conserving
biodiversity is, amongst other reasons, an obligate moral responsibility, if
humanity wishes to co-exist on this planet with other species.
Five: a legal imperative. As signatories to the
Convention on Biological Diversity, signed in Rio de Janeiro in June 1992, we
have a legal obligation in conserving biodiversity. South Africa has pledged a
commitment to Article 8(h), which stipulates: “Each contracting Party, shall
as far as possible and as appropriate… Prevent the introduction of, control or
eradicate those alien species which threaten ecosystems, habitats or species”.
Recently, the
South African Government made steps to fulfill this obligation. On 8 March 2001,
the Minister of Agriculture, Thoko Didiza, signed the new alien invasive
regulations under the Conservation of Agriculture Resources Act (1983). These
constitute an important first step in combating the social, economic and
ecological threats posed by alien invasive plant species in South Africa. Effectively, the regulations update the register of plant species that are
considered as alien invaders and classifies them accordingly into three
categories. This legislation increases the list of legally declared alien
invader plant species to 198 plant species.
The three categories are:
Category One: Plant species that
may not be grown and must be eradicated.
Category Two: Plant species with
commercial or utility value, which may only be grown with a permit under
controlled circumstances.
Category Three: Plant species,
which have amenity value and which may be grown, but not planted, propagated,
imported or traded.
Landowners found
to contravene any section of the Act are liable to be penalised, with matters
taken to court in cases of non-compliance. The penalties range from fines of R500 to R5000 to imprisonment.
Further consequences for landowners can be expected after the
Conservation of Agricultural Resources Act is rewritten. It is anticipated that the rewritten legislation will be promulgated in
mid-2002. This will have further
ramifications for landowners. Property
will not be able to be transferred, or subdivided unless the property complies
with the Conservation of Agriculture Resources Act and a certified clearance is
obtained stating that the property is clear of alien invader plants. The Wildlife &
Environment Society of SA (WESSA), generously sponsored by Hillside Aluminium of
Richards Bay, has initiated an Alien Invader Plants Project. The Project’s objective is to combat the threats of alien invasive
plants in KwaZulu-Natal. This
objective will be achieved through increasing public awareness of alien species
and means to control and eradicate them. Environmental Education will,
initially, be the focus of the project. A
course providing an introduction to Alien Invader Plant Management has been
developed and is being offered by WESSA’s Environmental Education Projects.
Interested parties
can contact me on (031) 201-3126. The comprehensive list of declared weeds and alien invader plants, complete with
their categorisation and the new regulations may be obtained by e-mailing me on edenjw@mweb.co.za.
The list and the regulations are in MS Word. Alternatively, one can follow the links through this web page to download
both the plant species list and amended regulations.
This page was last edited on
22 April, 2006
