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The role of resource economics in the control
of invasive alien plants in South Africa
Author: Jane Turpie
Turpie, J. (2004).The role of resource economics in the control
of invasive alien plants in South Africa. S. Afr. Sci. 100, 87-93.
General:
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8750 introduced species.
Over 200 considered to be seriously invasive.
By 1997, 180 woody plant species covered 10 million
hectares of land.
The biomes effected:
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The Fynbos biome is hardest hit.
Grassland and Savanna biomes worst hit in the moister
areas.
Semi-arid Nama and Succulent Karoo biomes invaded
by saltbushes, cacti, and mesquite trees.
Extent of invasions in forests is unknown.
Why established and successes:
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Realisation of implications of invasive species for water
supply.
Placed it into an economic context.
This led to the establishment of the WfW.
Have cleared over 171 000 ha.
Follow up weeding of 183 000 ha.
24 000 people employed in 2000.
Spent over R3 billion.
Ecological-economics:
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In a strict sense the term biodiversity
should include ecosystem functioning
as well as species richness.
Ecological-economics recognises the
important role played by ecosystems in
the economy.
Ecosystems have both tangible and
non-consumptive values.
Tangible goods carry the most political
weight.
Direct-consumptive values:
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Structural diversity and organisation of ecosystems must
be maintained.
This maintains the systems primary productivity, which in
turn adds to its direct consumptive value.
Non-consumptive values:
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Include things like water purification and regulation as
well as carbon sequestration.
Genetic diversity and organisation also maintains
ecosystems economic worth in terms of recreational
value, option value, and existence value.
Focus of studies:
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Initial studies focused on the economic consequences of
water loss.
The scope then expanded to include losses incurred in
tourism, natural resource harvest, pollination services,
option value, and existence value.
Recently studied have also included the effect of
invasions on fires.
Monetary costs of clearings:
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It is very costly.
Would cost about R650 million per year for the next 20
years.
Not enough is being spent on it which simply amplifies
the problem over time.
In some areas the cost of clearing is easy to justify.
Natural resources do not always have a high economic
worth.
Also varies with control method.
Some alien invasives carry an economic worth.
Short-comings of previous studies:
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The total cost of alien invasives has not been calculated
due to differences in approaches used.
Virtually all the studies have targeted riparian or
terrestrial invaders.
Studies have also varied in terms of the types of impacts
assessed.
Secondary effects of alien invaders have not been
analysed.
What about changing demands?
Two methods:
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Two methods used to value water losses, replacement
costs and opportunity costs.
Alien invasions can actually lead to the breakdown of the
entire ecosystem.
Effects other than on water loss:
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The easiest to estimate are impacts on direct
consumptive values.
Recreational value of biodiversity usually measured
using the travel-cost method.
No studies have looked at effects of alien vegetation on
biodiversity as a whole.
The effects of fire have been well researched.
The deleterious effects of fire are increased with
invasions.
Fynbos is also important for commercial fruit orchards as
well as the local honey industry.
Two available options:
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The other options
available are regulatory
and incentive methods.
Regulatory methods have
been shown to be
ineffective as well as not
socially optimal.
Incentives will therefore
be the best.