Contributors: Leonie Twentyman-Jones
& Esther Townsend.
Invading alien plants (IAPs) are one of the biggest threats to plant and animal biodiversity. IAPs have become established in over 10 million hectares of land in South Africa, and the cost of controlling them is estimated at R600 million a year over 20 years. If IAPs are left uncontrolled, the problem will double within 15 years. IAPs waste 7% of our water resources, reduce our ability to farm, intensify flooding and fires, cause erosion, destruction of rivers, siltation of dams and estuaries, reduction of water quality and can cause the mass extinction of indigenous plants and animals.
- 750 tree species and 8 000 herbaceous species have been introduced into South Africa
- 1 000 introduced species are naturalised, 279 are invasive
History of plant introductions in South Africa
Long ago the Cape was a land of immeasurable beauty, a landscape of rivers and flowers, majestic forests and an abundance of wild life roamed the land. On June 18th 1580,Vice Admiral Sir Francis Drake rounded the Cape of Good Hope on his voyage around the world and described the Cape as ‘… a most stately thing, and the fairest Cape we saw in the whole circumference of the earth.’
Sad to say, things have changed. Our famed fynbos is being invaded by alien plants, some of our rivers have dried up because of invader plants, our forests are threatened because of bad management and invader plants, and our wildlife’s natural habitat has largely disappeared because of invader plants as well as the growth of agriculture and industry and the spread of urbanisation. The Western Cape has the dubious record of being the province with the largest number of Invasive alien species in the country.
How did this happen? Like us, all former colonies such as America, Australia & New Zealand have a history of plant introductions going back hundreds of years. Some of the introduced tree species quickly naturalised in their new environment, reproducing consistently and sustaining populations over many life cycles without direct human intervention. Some have become invasive in their new environment where, without their natural enemies (mostly left behind in the country of origin), they are able to survive, reproduce and spread unaided at alarming rates across the landscape.
Dutch East India Company (VOC) representatives arrived at the Cape in 1652 to establish a re-supply and layover port for vessels of the Company trading with Asia. Reports from the 1550s had described the Cape as having limited woodland, and thus being unable to supply European wood requirements for construction and fuel. First governor at the Cape, Jan van Riebeeck, therefore, brought a cargo of Norwegian and Swedish planks and beams as well as seed of alder (Alnus glutinosa), Norway spruce (Picea abies), Scots pine (Pinus sylvestris), ash (Franxinus excelsior) and oak (Quercus robur). The small settlement used a great deal of firewood for the Company’s ships, kitchens, bakery and lime kilns as well as wood for ship repair, building, wagon and furniture making. The indigenous forests growing on Table Mountain and shrubs growing on the Cape Flats were soon drastically depleted. Indigenous trees were slow growing, taking at least ten years to grow, so inevitably faster-growing alien trees were planted. The earliest source of tree planting material was the Company Garden in Cape Town, established in 1652. Later governors like Simon van der Stel, claimed to have planted 28,987 oak, 459 alder and 81 ash trees by 1694, as well as introducing a policy of compulsory tree planting by colonists. His son and successor, Willem Adriaan, was responsible for planting 30,000 oaks in the Company’s plantation and sending 20,000 inland to Stellenbosch and Drakenstein, as well as experimenting with Norway spruce, Scots pine, lime trees, black poplar and elm. However there was no bureaucracy for enforcing either tree protection or planting. Two species of pine, Pinus pinaster (maritime pine, native of the Mediterranean basin) and Pinus pinea (stone pine, native to Iberian Peninsula/southern Europe) reached the Cape in the late seventeenth century, possibly introduced by the Huguenots.
During the 18th century Europeans explored the country east of Cape Town for a variety of purposes, travelling across landscapes covered with mimosa and oak trees and shrubs like aloe, cacti and many kinds of Euphorbia. Free burghers wanted land and timber; missionaries wanted to convert the indigenous inhabitants; botanists were searching for new and exotic plant species; naturalists were hunting for exotic birds and animals. Some took seeds and planting stock for vegetables, grape vines and fruit trees, including orange, fig, apple, stone fruits, pomegranate and almond. For example, the first Moravian missionary, who settled in Genadendal in 1737, planted the famous pear tree, under whose branches his converts kept the faith until the next Moravians arrived 50 years later.
After using all available indigenous timber around Cape Town, the Dutch East India Company searched for sources further afield, and in 1726 established a Company post to fell timber in the Riviersonderend district. Grootvadersbosch was next and in 1777 the Company established a woodcutters’ post in Outeniqualand, followed by one at Plettenberg Bay nine years later. The exploitation and decimation of the indigenous forests was to continue unchecked for many years.
Specimens of our indigenous plants were sent to Europe as were plants from Asia and South America. All these needed to be described and categorised and ‘collections’ of such exotica were fashionable amongst the educated classes. Similarly in Cape Town there were individuals who were interested in importing and cultivating ‘exotic’ plants.
As the settlement grew, farms and small towns were established east of Cape Town. Water supplies were limited and farmers could only support small vegetable gardens and wheat fields, but towns such as Graaff-Reinet, situated on river banks, had irrigated tree-lined streets and fruit-filled gardens. With an increasing settler population, demand for wood products grew, far exceeding local supplies. By 1810 pine boards and beams were being imported from the United States of America. Although pines had first taken root in the seventeenth century, it was not until 1825–1830 that the first commercial plantation of P. pinaster was established at Genadendal. A Eucalyptus genus, E. globulus (Blue Gum), which became widespread later in the century, arrived at the Cape in 1828. By 1846 ‘gums’ and acacias were reportedly growing in the town of Howick in KwaZulu-Natal.
An interest in the exotic plants of other countries was encouraged by individuals who imported plants and established gardens in Cape Town. By 1831 Baron Carl von Ludwig’s garden in Kloof Road was one of the show places of Cape Town and he was lauded for his efforts in acclimatising ornamental trees and shrubs at the Cape. Von Ludwig introduced some 1,600 plants to South Africa, including the well-known South American Jacaranda mimosifolia and Cestrum nocturnum – now of course invasive aliens. Timber merchant Ralph Henry Arderne was another who established a garden at his home in Claremont with trees, shrubs and plants from all over the world, including Australasia, Asia, India and North America. Now called the Arderne Garden. (see ‘A Country Garden’ by Carol Kennedy).
The post of Colonial Botanist was created in 1858 to ‘determine the Cape Colony’s economic resources and its future for the growth of exotic trees, as well as perfecting the knowledge of South African flora’. By the end of the 1850s, Cape Town’s Botanic Garden was well respected and understood to be a major advertiser for, and encourager of, tree introductions and tree planting, as well as a cheap and reliable source of seed and seedlings. It issued a fruit tree catalogue as early as 1864.
Botanic gardens were also established at Graham’s Town, Graaff-Reinet and Durban and were all active in promoting tree planting by providing seeds and seedlings locally as well as exchanging plants with botanical gardens in India and Australia.
With the growth in urbanisation and industrialisation from the late 19th century onwards, more timber was needed for many industries including mining and the railways. Pinus radiata from North America was successfully grown commercially. The dunes on the Cape Flats and near the Port Elizabeth harbour were stabilised and reclaimed by planting Acacia saligna (Port Jackson willow) and Acacia cyclops (Rooikrans) from Australia. Those who worked hard to solve one problem did not realise they were creating another for future generations. Some aliens were introduced inadvertently, like the seeds of weeds and flowers imported in horse fodder from Argentina during the Anglo-Boer War. Today Khakibos, Blackjacks and Cosmos can be seen growing in profusion especially along roads and near old battle fields.
After the Second World War a strong nursery industry developed in South Africa. A growing middle class wanted to plant ornamental plants which were fast growing, evergreen and colourful. Imports of these plants were unregulated, and by early 1970 most ornamentals that are on the current Invasive Species list were the norm in nurseries. Some of these plants are frequently seen today in older suburbs, along roads and in municipal parks.
In 1987 South Africa had 198 species of plants on the declared weeds and alien invader plant list. In 2014 we have 379, an increase of 181 species in 27 years! Most of these species occur on our doorstep; in our gardens, on municipal lands, along our roads, on our farms, in our forests and mountains and along our coastline.
As the article above indicates, many IAPs are products of unwise and unintentional plant introductions. The problem is vast, and it requires active public and private participation to combat the ecological treat. Agricultural landowners, municipalities and other ‘organs’ of state as well as the gardening public should be aware of those invasive plant species that they may have on their properties and remove them. By doing so we can all make a small contribution to rectify the ‘wrongs’ of the past and help to secure the future existence of our wonderful flora and fauna.
More information can be found about specific invasive aliens at various websites including www.invasives.org.za, www.sanbi.org and www.environment.co.za. The latter list indicates the category as well as the botanical and common names of the plant. Category 1 invader plants must be removed and destroyed; category 2 may be grown under controlled conditions only; category 3 may no longer be planted.