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Risks of alien plant infestations to land owners
Christo Fabricius
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(Kotze et al., 2010)
National Invasive Alien Plant Survey
Initial clearing = 48 years/R52 billion
16%
9%
20% 8%
1%
51% 5%
8%
22%
20%
39%
1. Acacia mearnsii, A. dealbata & A. decurrens 2. Eucalyptus spp. 3. Pinus spp. 4. Opuntia spp.
5. Salix spp.
Economic impact = R13 billion/annum
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Pines invading the watersheds of the Western Cape
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If we do not clear invasive alien plants …
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Infested
Not infestedNitrogen
levelsFuel load Soil loss
after fireStream
flowCropyields
Carryingcapacity
Infested Not infested
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Negative impacts on agriculture
• More evaporation
– Reduced stream flow
– Less water = higher concentrations of polluting nutrients
• Reduced ground water quantity, quality
• More intense fires
• Increased soil erosion
• Serious water quality and quantity problems
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COSTS (Chemicals; fuel; labour; ALIEN PLANT MANAGEMENT)
YIEL
D p
er H
ecta
re
Profitable
Unprofitable
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Species
Benefit :cost ratio
Red sesbania
45 : 1
Lantana
34 : 1 Long-leaved wattle
1 465 : 1
Golden wattle
4 333 : 1
Silky hakea
611 : 1
4. Biological Control
Melanterius weevil on Acacia cyclops
For many invading species, in many parts of the world, it is the only hope.