This document summarizes the risks of alien plant infestations to land owners. It notes that initial clearing of major invasive species like acacia, eucalyptus, and pines could cost R52 billion over 48 years. Invasive plants negatively impact agriculture through increased evaporation, reduced stream flows and water quality, more intense fires, and increased soil erosion. They can also make land unprofitable by increasing costs from needed management of the invaders. The document advocates for biological control as the best hope for many invading species, and provides examples of high benefit-cost ratios from successful biological control agents.

1. Risks of alien plant infestations
to land owners
Christo Fabricius

2. National Invasive Alien Plant Survey
Initial clearing = 48 years/R52 billion
1.
2.
3.
4.
5.
Acacia mearnsii, A. dealbata & A. decurrens
Eucalyptus spp.
Pinus spp.
Opuntia spp.
Salix spp.
Economic impact = R13
billion/annum
8%
51%
5%
39%
20%
8%
22%
1%
16%
9%
(Kotze et al., 2010)
20%

3. Pines invading the watersheds of the Western Cape

4. If we do not clear invasive alien plants …

5. Nitrogen Fuel load
Soil loss
levels
after fire
Stream
flow
Infested
Not infested
Infested
Crop
yields
Carrying
capacity
Not infested

6. 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

7. YIELD per Hectare
Profitable
Unprofitable
COSTS (Chemicals; fuel; labour; ALIEN PLANT MANAGEMENT)

8. 4. Biological Control
For many invading species, in many parts of
the world, it is the only hope.
Melanterius weevil on Acacia cyclops
Species
Red sesbania
Benefit :cost ratio
45 : 1
Lantana
Long-leaved wattle
34 : 1
1 465 : 1
Golden wattle
4 333 : 1
Silky hakea
611 : 1