Risks of alien plant infestations to land owners

Christo Fabricius

(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

Pines invading the watersheds of the Western Cape

If we do not clear invasive alien plants …

Infested

Not infestedNitrogen

levelsFuel load Soil loss

after fireStream

flowCropyields

Carryingcapacity

Infested Not infested

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

COSTS (Chemicals; fuel; labour; ALIEN PLANT MANAGEMENT)

YIEL

D p

er H

ecta

re

Profitable

Unprofitable

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.