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Economic Analysis
of Invasive Species
Module 3:
Impacts of invasive species
and ways to address them
what this module covers
1. Understanding the
impacts of invasive
species
2. Types of impacts of
species invasions
3. Prevention of biological
invasions
4. Managing invasions
5. Ecosystem restoration
after invasion
about
invasive species
Module 1
understanding the economic
causes of invasions
Module 2
impacts of invasive species
and ways to address them
Module 3
defining invasive-related
costs & benefits
Module 4
valuing
ecosystem impacts
Module 5
informing actions
to address invasives
Module 6
invasive species impacts on
ecosystems
Invasives threaten
*terrestrial,
*freshwater &
*marine
ecosystems with
increasing or
continuing
impacts
Invasives will have
increased
impacts with
increasing
climate change
general impacts of IAS
Invading species affect ecosystems by
altering or replacing natural systems
through:
competition, exclusion, predation,
parasitism, pathogenesis,
Alteration of: micro-climate, nutrient
availability, ecosystem cycles (energy,
water, minerals, organics) – affecting:
Ecosystem function, health, goods and
services livelihoods, well-being, health, development
an example of spread and invasion impacts
Kafue Floodplain, Zambia, dry
1974
Kafue Floodplain flooded
1974
The Kafue
Floodplain
was home to
many wild
animals and
plants +
cattle
grazing,
fishing,
conservation
& tourism
In 1974 there was an
occasional plant of
Mimosa pigra on the
edges of the Kafue River
Mimosa pigra continued
A heavy flood in 1981/2 brought a few
plants of Mimosa pigra on to the
floodplain
(which was
a new
ecosystem
changed by
a dam
upstream)
1982
Mimosa pigra continued
After a slow
start in the
late 1980s,
M. pigra
began to
spread
By 2000 it was
covering a
few hundred
hectares
2001
Mimosa pigra continued
By 2007 it was
growing up to 4m
high and covering
3,000 hectares
2007
2007
…. and excluding
almost every other
plant and most
animals ….
Mimosa pigra continued
3,000 ha of an available 12,000 ha are now covered
Today:
No livestock
No fisheries
No tourism
on this
part of the
Kafue
Floodplain
Costs to
livelihoods
and
production
examples of invasion impacts
terrestrial impacts
Old World Climbing Fern (Lygodium
microphyllum), smothering bald cypress in Florida
examples of invasion impacts
terrestrial
The Indian House Crow (Corvus splendens) has
invaded most coastal cities in Eastern Africa
kills domestic and wild birds, spreads human
diseases, raids food, destroys radio aerials, etc.
freshwater
Red Water Fern, Azolla
filiculoides from South
America – becoming
widespread in Africa
Aquatic invasive plants foul
drinking water, reduce fisheries,
exclude other biodiversity, block
waterways and water pipes,
reduce oxygen, reduce sunlight…
freshwater
Freshwater fish
Introduced for
aquaculture,
escape into wild
water systems,
destroy vegetation
and fish faunas
and hybridize with
local species – but
benefit to some!
Nile tilapia, Oreochromis niloticus, far from the Nile in Zambia
impacts on production (eco)systems
Tall trees of Senna
spectabilis from
S. America
replacing native
forest in Uganda
Ecosystems, native or
cultured, that are used for
food and commodity
production can also be
invaded by alien species.
Forestry, fisheries,
agriculture, aquaculture
Parasitism, pathogenesis,
predation, competition,
exclusion and destruction
of productive systems are
all recorded – most known
from farming, horticulture
and livestock production
impacts on marine systems
Such as:
fish
crabs
oysters
prawns
barnacles
mussels
comb jellies
seaweeds
plankton
competition, exclusion, predation, fouling
Seaweed (Caulerpa taxifolia) invading a new site in the Mediterranean – D. Luguet, France
invasion impacts – human development
Water hyacinth affecting Kafue Gorge Dam and hydropower station, Zambia
(photo
M. Mumba)
invasion impacts – human development
e.g. water hyacinth:
• Increases water loss in dams
• Blocks water flows
• Jams hydropower generators
• Prevents water traffic
• Encourages snakes, crocodiles, etc.
• Suppresses fisheries and aquaculture
• Harbours vectors of human diseases
and there are invasives that are themselves human
pathogens – e.g. ebola, SARS, H5N1, etc.
management of invasions
To avoid or lessen the impacts of invasion, it makes
sense to take one of the following courses of action:
1. Prevent their introduction
2. Eradicate a new invasion soonest
3. Contain a small, expanding invasion
4. Manage the impacts and the presence
of an established invasion
The CBD tells us that No.1 is best and cheapest;
No. 4 is “the last resort” – all have costs
prevention of invasions
Prevention is best done by stopping the
introduction of likely invasive species – at
the end of a pathway (module 1 and pathway types)
This requires a means to stop introduction, e.g.
border inspections, quarantine, and a
method to assess likely invasibility
Rigorous Risk Assessment can identify
species that may become invasive in the
intended area or ecosystem – then they can
be stopped
Prevention of establishment, naturalisation and spread,
once a species is introduced is possible in some cases,
but more costly, needing capacity for “rapid response”
management/control of invasions
“Management” is required once a species
has established an invasion and the
impacts are becoming obvious and need
to be reduced or removed = controlled
There are 4 main types of IAS control:
• Mechanical
• Chemical
• Biological control (biocontrol)
• Integrated control involving two or three
Management requires agreed objectives by
stakeholders to ensure successful results
mechanical control
Clearing, cutting,
catching, trapping
mechanically – by
hand or with tools
and traps or,
sometimes with
heavy and
sophisticated
machinery
Mechanical clearance of
Lantana camara by hand
Little non-target
impact but often not
sustainable –
especially in plants
with significant seed
banks
chemical control
As the name implies, this involves herbicides,
poisons, pharmaceuticals, hormones (and
pheromones), or any other chemicals that
can reduce the population or vitality of
invading micro-organisms, plants or animals
Chemical control has to be cautious to lessen
the risk of affecting non-target organisms
and polluting the environment – but can be
very effective in some cases
While complete eradication of small invasive
animals on islands has been effected with
poisons, this method has drawbacks
associated with dosages and applications in
the field – especially on organisms that are
not well-known
biological control
Many invading species are able to invade
because they have come to a new ecosystem
without their native control organisms such
as parasites, pathogens and predators
Biocontrol seeks to fill that void by using
organisms from the invaders original “home”
where it was “held in check”
Such organisms are tested for species
specificity, introduced through quarantine,
bred in large numbers, released on or near
the target invasive species ….
… and left to carry out control (with monitoring
to measure survival, spread and success)
Biocontrol of agricultural invaders are best known – as
are the insect control agents for invading water hyacinth
integrated control
This is a combination of control measures
designed to make the most of the benefits of
each method
For example, effective biocontrol can weaken
the ability of an invading species to complete
with local biota. If this is combined with
mechanical and chemical control to stop
expansion, or to manage critical habitats, the
overall effect can be beneficial to the invaded
ecosystem – as well as becoming selfsustaining
but all control has costs:
Mechanical clearing and burning of Mimosa
pigra on the Kafue Floodplain (discussed earlier)
40 field workers worked for 17 weeks to clear 31 ha of
mimosa for a total cost of $34,250 – invasion is 30,000 ha
Photos by Griffin Shanungu, Pilot site coordinator, Barriers project, Zambia
benefits of invasive species
Some biological invasions bring benefits as
well as costs – to local people and
development, e.g.
• Water hyacinth can be used for biogas,
compost, stock food, furniture
• Mesquite can reduce erosion, produce timber
and charcoal
• Lantana stems are used for chicken cages
• Australian rabbits can be eaten – as well as
feral pigs and goats
But it is rare that the benefits exceed the
costs or can pay for the necessary control
ecosystem restoration
Amongst the objectives for invasive
species management, there is often a
wish to return the affected system to its
original status
This requires a set of actions together
referred to as ecosystem restoration –
including:- returning lost species,
understanding biological succession,
and, addressing needs of stakeholders
The use of other potentially invasive species should not be
used – even if it can speed up the restoration!
THANK YOU
for listening