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Alien Invasive Plants in South Africa: Management and Challenges
Carl Reinhardt
University of Pretoria
Republic of South Africa
E-mail: [email protected]
Africa in relation to Europe
Contrast between small and commercial scale farming in Africa is large
Subsistence farming is a way of life for the majority of Africans living in rural areas.
Maize and cassava are staple crops, here with peanuts as intercrop to contribute nitrogen.
Many projects in Africa fail due to lack of appropriate knowledge ‒ resulting in disturbance of ecosystems
Failed biodiesel project in Mozambique – Jatropha curcas on 10,000 ha
South Africa is for the greater part a water-stressed country. Most regions receive <750 mm rain, which is concentrated in either the summer or the winter season, and usually in the form of low frequency rain events. About 7% (3300 million m3) of South Africa’s mean annual water runoff is lost through transpiration of woody alien species in water catchments, riparian zones and wetlands. Partly due to their high water usage, alien plants compete strongly with indigenous plants. Alien plants interfere with desirable species: Interference = Competition + Allelopathy.
Disturbance of natural habitats:
• Fire is a natural factor which is exploited by humans for vegetation management
• Mechanical clearing of vegetation is most destructive ‒ creates space for alien invasive plants
Indigenous species can “densify” and dominate due to disturbance of vegetation – in this case due to overgrazing
Stoebe spp
Asparagus spp
South America origin: Opuntia ficus-indica
Biocontrol with insect, Dactylopius opuntiae
Populus canescens Eucalyptus spp
Examples of alien species deliberately planted for shelter, fuel (firewood), building material
European origin: Populus canescens Typically invades wet habitats
Campuloclinium macrocephalum ‒ imported for horticulture, but devastating to grassland Origin: South America
Conyza spp on fallow crop fields
Solanum elaeagnifolium in Roundup Ready® maize
Alien Invasive Plants in the Kruger National Park, South Africa
Alien invasive plants represent a serious threat to natural biodiversity in this conservation area of 20,000 km2.
More than 350 alien plants occur in KNP, of which about 30 are highly invasive.
Parthenium hysterophorus (Asteraceae) ‒ annual/biannual; herbaceous
A recent invader whose spread is promoted by humans and natural forces
Parthenium preferentially invades disturbed areas.
Field trial: Interference potential of P. hysterophorus with indigenous grass species in the KNP
Parthenium plants on 18 Jan 2004
10 Feb 2004One meter height increase in 3 weeks!
Lettuce grown together with Parthenium plants in hydroponic solution
Control 2 Parthenium 4 Parthenium
1.1
3.7
0.17 0.1
4.5
14.5
0
2
4
6
8
10
12
14
16
root stem leaf flower fruit pollen
Parthenin
mg/g
Parthenin content in various parts of P. hysterophorus
12.011.2
1.2 1.0
13.4
1.4
02
468
10
1214
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intermediate intermediate
old leaf leaf juvenile
leaf
old leaf leaf juvenile
leaf
Parth
en
in [
mg/g
]Parthenin in TBME leaf-dips, and in leaf-homogenates after dipping
Old Intermediate Young Leaves of different age
Old Intermediate Young Leaves of different age
•REINHARDT, C.F., VAN DER LAAN, M., BELZ, R.G., HURLE, K. & FOXCROFT, L., 2006. Production dynamics of the allelochemical parthenin in leaves of Parthenium hysterophorus L. J. Plant Diseases and Protection 20, 427-433. •BELZ, R.G., REINHARDT, C.F., FOXCROFT L.C. & HURLE, K., 2007. Residue allelopathy in Parthenium hysterophorus L. – Does parthenin play a leading role? Crop Protection 26, 237-245. •VAN DER LAAN, M., REINHARDT, C.F., BELZ, R.G., TRUTER, W.F., FOXCROFT, L.C. & HURLE, K., 2008. Interference potential of the perennial grasses Eragrostis curvula, Panicum maximum and Digitaria eriantha with Parthenium hysterophorus. Tropical Grasslands 42, 88-95.
In TBME (organic solvent) In leaves post-TBME
Management of alien invasive plant species • Maintaining natural biodiversity is key ‒ disturbance/degradation directly or indirectly by humans is a major destroyer of diversity. • Chemical control (herbicides) has limitations in natural ecosystems: non-selectivity; environmental contamination. • Biocontrol using natural enemies are highly selective and takes a long time to be effective.
Aquatic alien invader Pistia stratiotes in Sunset Dam, KNP
Before biocontrol
After biocontrol
Insect biocontrol agent
Special thanks to THE TEAM
