Alien Invasive Plants in South Africa: Management and Challenges

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1 Alien Invasive Plants in South Africa: Management and Challenges Carl Reinhardt University of Pretoria Republic of South Africa

2 Africa in relation to Europe

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4 Contrast between small and commercial scale farming in Africa is large

5 Maize and cassava are staple crops, here with peanuts as intercrop to contribute nitrogen. Subsistence farming is a way of life for the majority of Africans living in rural areas.

6 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

7 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 m 3 ) 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.

8 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

9 Indigenous species can densify and dominate due to disturbance of vegetation in this case due to overgrazing Stoebe spp Asparagus spp

10 South America origin: Opuntia ficus-indica Biocontrol with insect, Dactylopius opuntiae

11 Examples of alien species deliberately planted for shelter, fuel (firewood), building material Populus canescens Eucalyptus spp

12 European origin: Populus canescens Typically invades wet habitats

13 Campuloclinium macrocephalum imported for horticulture, but devastating to grassland Origin: South America

14 Conyza spp on fallow crop fields

15 Solanum elaeagnifolium in Roundup Ready maize

16 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 km 2. More than 350 alien plants occur in KNP, of which about 30 are highly invasive.

17 Parthenium hysterophorus (Asteraceae) annual/biannual; herbaceous A recent invader whose spread is promoted by humans and natural forces

18 Parthenium preferentially invades disturbed areas.

19 Field trial: Interference potential of P. hysterophorus with indigenous grass species in the KNP

20 Parthenium plants on 18 Jan 2004

21 10 Feb 2004 One meter height increase in 3 weeks!

22 Lettuce grown together with Parthenium plants in hydroponic solution Control 2 Parthenium 4 Parthenium

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25 Parthenin content in various parts of P. hysterophorus Parthenin mg/g root stem leaf flower fruit pollen

26 dip homogenisate Parthenin [mg/g] Parthenin in TBME leaf-dips, and in leaf-homogenates after dipping In TBME (organic solvent) In leaves post-tbme Old Intermediate Young Old Intermediate Young Leaves of different age Leaves of different age REINHARDT, C.F., VAN DER LAAN, M., BELZ, R.G., HURLE, K. & FOXCROFT, L., Production dynamics of the allelochemical parthenin in leaves of Parthenium hysterophorus L. J. Plant Diseases and Protection 20, BELZ, R.G., REINHARDT, C.F., intermediate FOXCROFT L.C. & HURLE, K., Residue allelopathy intermediate Parthenium hysterophorus L. Does parthenin play a leading role? Crop Protection 26, VAN DER LAAN, M., REINHARDT, C.F., BELZ, R.G., TRUTER, W.F., FOXCROFT, L.C. & HURLE, K., Interference potential of the perennial grasses Eragrostis curvula, Panicum maximum and Digitaria eriantha with Parthenium hysterophorus. Tropical Grasslands 42, old leaf leaf juvenile leaf old leaf leaf juvenile leaf

27 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.

28 Before biocontrol Aquatic alien invader Pistia stratiotes in Sunset Dam, KNP Insect biocontrol agent After biocontrol

29 Special thanks to THE TEAM