Farmer's Weekly (South Africa)
– Know your invasive species: Part 3 – Caring for your tractor tyres
In this issue, we look at the arsenic bush, the ash-leaved maple, the wild Asian raspberry and the Australian blackwood.
The following species are regarded as invasive alien species under the National Environmental Management: Biodiversity Act (NEMBA), No. 10 of 2004:
• Arsenic bush ( Senna septemtrionalis)
The arsenic bush is a toxic shrub that can grow up to 3m tall. Yellow flowers appear from October to March. The leaves are arranged in pairs opposite each other. The pods are between 7cm and 10cm long and contain shiny seeds.
In addition to being toxic, the bush invades forest margins, savanna, riverbanks, roadsides, waste ground and plantations, where it establishes itself and suppresses the regeneration of desirable species.
Invasive status: NEMBA Category 1b. A particular problem in Limpopo, Mpumalanga, Gauteng, KwaZulu-Natal, the Eastern Cape and the Western Cape.
• Ash-leaved maple ( Acer negundo)
A fast-growing, deciduous tree 10m to 20m high with a spreading crown and often more than one trunk. The bark is greenish and smooth at first, ageing to brown and rough. The leaves are bright green and sometimes densely hairy beneath; they turn yellow in autumn.
Large trees that are cut or damaged will reshoot vigorously and can develop dense stands. The fruit is relatively light and spread by water and dumped garden waste. The seeds are also dispersed by birds and animals.
The maple crowds and shades out native plants in sensitive bushland along watercourses.
It is also thought that dense, long-term infestations may cause damage to waterways by trapping sediment, causing erosion and shedding masses of autumn leaves that deplete oxygen levels.
Invasive status: NEMBA Category 3. A particular problem in the Free State, KwaZulu-Natal and Limpopo.
• Asian wild raspberry ( Rubus ellipticus)
A stout, evergreen shrub with a prickly stem that grows about 4,5m high. The stems are covered with prickles and reddish hairs. The fruit is yellow, edible and highly sought-after.
R. ellipticus can form impenetrable thickets, threatening indigenous lowland wet forests and displacing indigenous plant species.
Invasive status: NEMBA Category 1a. It is a particular problem in the Western Cape. • Australian blackwood ( Acacia melanoxylon)
The tree grows up to 20m high, with a trunk of about 150cm in diameter. The bark on older trunks is dark greyishblack, deeply fissured and somewhat scaly. Younger branches are ribbed, angular, or flattened towards their tips and are greenish in colour.
The seeds are spread by animals, particularly birds, and by dumped garden waste.
In South Africa, A. melanoxylon is a major invader of forests and is a serious threat to fynbos and grasslands. It transforms these plant communities by replacing the native non-tree vegetation.
A. melanoxylon is difficult to control due to its fast growth, vigorous regrowth from root suckers, and prolific regeneration from seed.
Invasive status: NEMBA Category 2. A particular problem in the Western Cape, Free State, Eastern Cape, KZN, Mpumalanga and Limpopo.
• Source: ‘Invasive plants’. Invasive Species South Africa (2018). Retrieved from http://invasives. org.za/plants/plants-a-z. Click on ‘Legislation’ to download the NEMBA Invasive Species Regulations, Declaration of Invasive Species forms, and other key documents.
• For contact lists of accredited invasive species consultants, landscapers and garden centres, visit invasives.org.za, sagic.co.za, sali.co.za, sana.co.za or wessa.org.za.