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Jeremy Goodall Plant Protection Research Institute
Managing Chromolaena odorata (chromolaena) in subtropical grasslands in KwaZulu-Natal, South Africa Jeremy Goodall Plant Protection Research Institute
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Introduction Most abundant & destructive in KZN
Invades forest, savanna and grassland to 800 m Coastal lowlands most affected Impacts and management summarised
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Coastal Grassland Ecology
Secondary Iron Age (BP 2000) vegetation Maintained by pastoralists for 1000 years Diverse flora dependant on fire Now relic & fragmented, often in mosaics Rapid succession to forest or savanna
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Impacts Invades moribund grassland
Monospecific thickets in 5 to 10 years Composition & biomass inverse to density Dense thickets are monospecific Sward does not recover to original state
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21 15 11 5 10 5
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Control by fire 95% control of dense stands when:
grass cover >30% grass fuel load >1 t ha-1 dry matter 95% kill of dense stands by slash and burn: zero grass cover follow-up with herbicide until 30% grass Annual burning controls seedlings indefinitely Dense stands zero ‘weed’ after 6 burns
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Adaptive grassland management
Resilient on Regic Sands (marine origin): rapid restoration to open grassland with burning grasses dominated by palatable species Unstable on Glenrosa (glacial origin): invasion with savanna species savanna trees resistant to fire Vegetation managed in multiple states
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S & T model: Regic Sands 1 grassland 2 moribund 5 chromolaena thicket
4 forest 6 palm & wild banana Natural succession Chromolaena succession Fire Chemical & mechanical
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S & T model: Glenrosa 1 grassland 3 savanna 6 ruderal savanna 5
chromolaena thicket 4 forest Natural succession Chromolaena succession Fire Chemical & mechanical
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Conclusions IMPACT MANAGEMENT Invades under nil burning
Suppresses succession Transforms vegetation Threatens coastal habitats Forest prospects poor MANAGEMENT Manage in multiple states Fire in grassland & savanna Integrated control in dense stands on clays Urgent biocontrol for use in indigenous forest
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