were the rise in introductions for forestry in the nineteenth century that declined
towards the end of the twentieth century; and introductions of ornamental plants that
started in the mid-twentieth century and continue today.
Because of the paucity of trees suitable for forestry in South Africa’s flora, and the
small area of native forest, hundreds of tree species have been introduced to the
country (see Richardson et al. 2003 for a detailed review, and Box 3.1). Experimental introductions of trees began during the Dutch and British colonial periods with
the aim of providing timber for construction, shipbuilding, and for amenity plantings, shelter, windbreaks, and fuelwood. Organised government involvement in
forestry began in 1872 with the establishment of a forestry department at the
Cape. This led to the establishment of plantations of many alien trees, especially
species in the genera Acacia, Eucalyptus and Pinus. Wood shortages during World
War I stimulated major afforestation efforts. Poynton (1984) lists more than 400 tree
species that were successfully cultivated in South Africa, including more than
100 Eucalyptus species, 80 Pinus species and 70 Australian Acacia species (see
also Poynton 1979a, b; Poynton 2009). Besides species that were intended for
commercial forestry and woodlots, many other trees that were not grown in plantations were introduced, propagated, and promoted by government forestry organisations; these included Acacia cyclops (Rooikrans) and A. saligna (Port Jackson
Willow), Jacaranda mimosifolia (Jacaranda), Melia azedarach (Syringa), and
Prosopis (Mesquite) species (Poynton 1990, 2009). Widespread planting of many
alien tree species for dune stabilisation started in 1830; this created another major
pathway for the dissemination of woody alien plants in South Africa. Australian
Acacia species (wattles), Casuarina cunninghamiana (Beefwood), Hakea drupacea
(Sweet Hakea), Leptospermum laevigatum (Australian Myrtle) and Pinus pinaster
(Cluster Pine) were the most extensively planted species for this purpose (Avis
1989). Many alien species were introduced as barrier plants to support agricultural
production. Prominent examples of species that were widely planted as hedges or
windbreaks in agricultural and rural landscapes and that are now invasive are
Eucalyptus camaldulensis (River Red Gum), Biancaea decapetala (syn.
Caesalpinia decapetala; Mauritius Thorn), Leptospermum laevigatum, Ligustrum
lucidum (Chinese Wax-leaved Privet), Pyracantha angustifolia (Yellow Firethorn),
and many species of Cactaceae (Cacti) (Henderson 1983).
The introduction of alien plant species for ornamentation dates back to the
establishment of the Cape Colony in 1652 and the Company Gardens in Cape
Town, but most initial introductions (as discussed above) were strictly or mainly
for utilitarian purposes. The horticultural industry has grown over time and, although
South Africa has a rich native flora, the demand for new alien plant species has not
abated. Many of South Africa’s most widespread invasive plants, especially in areas
around human settlements, were introduced and disseminated for their ornamental
value (Alston and Richardson 2006; Foxcroft et al. 2008; Donaldson et al. 2014;
Jacobs et al. 2014; Cronin et al. 2017; Kaplan et al. 2017; McLean et al. 2017;
Canavan et al. 2019).
70
D. M. Richardson et al.
towards the end of the twentieth century; and introductions of ornamental plants that
started in the mid-twentieth century and continue today.
Because of the paucity of trees suitable for forestry in South Africa’s flora, and the
small area of native forest, hundreds of tree species have been introduced to the
country (see Richardson et al. 2003 for a detailed review, and Box 3.1). Experimental introductions of trees began during the Dutch and British colonial periods with
the aim of providing timber for construction, shipbuilding, and for amenity plantings, shelter, windbreaks, and fuelwood. Organised government involvement in
forestry began in 1872 with the establishment of a forestry department at the
Cape. This led to the establishment of plantations of many alien trees, especially
species in the genera Acacia, Eucalyptus and Pinus. Wood shortages during World
War I stimulated major afforestation efforts. Poynton (1984) lists more than 400 tree
species that were successfully cultivated in South Africa, including more than
100 Eucalyptus species, 80 Pinus species and 70 Australian Acacia species (see
also Poynton 1979a, b; Poynton 2009). Besides species that were intended for
commercial forestry and woodlots, many other trees that were not grown in plantations were introduced, propagated, and promoted by government forestry organisations; these included Acacia cyclops (Rooikrans) and A. saligna (Port Jackson
Willow), Jacaranda mimosifolia (Jacaranda), Melia azedarach (Syringa), and
Prosopis (Mesquite) species (Poynton 1990, 2009). Widespread planting of many
alien tree species for dune stabilisation started in 1830; this created another major
pathway for the dissemination of woody alien plants in South Africa. Australian
Acacia species (wattles), Casuarina cunninghamiana (Beefwood), Hakea drupacea
(Sweet Hakea), Leptospermum laevigatum (Australian Myrtle) and Pinus pinaster
(Cluster Pine) were the most extensively planted species for this purpose (Avis
1989). Many alien species were introduced as barrier plants to support agricultural
production. Prominent examples of species that were widely planted as hedges or
windbreaks in agricultural and rural landscapes and that are now invasive are
Eucalyptus camaldulensis (River Red Gum), Biancaea decapetala (syn.
Caesalpinia decapetala; Mauritius Thorn), Leptospermum laevigatum, Ligustrum
lucidum (Chinese Wax-leaved Privet), Pyracantha angustifolia (Yellow Firethorn),
and many species of Cactaceae (Cacti) (Henderson 1983).
The introduction of alien plant species for ornamentation dates back to the
establishment of the Cape Colony in 1652 and the Company Gardens in Cape
Town, but most initial introductions (as discussed above) were strictly or mainly
for utilitarian purposes. The horticultural industry has grown over time and, although
South Africa has a rich native flora, the demand for new alien plant species has not
abated. Many of South Africa’s most widespread invasive plants, especially in areas
around human settlements, were introduced and disseminated for their ornamental
value (Alston and Richardson 2006; Foxcroft et al. 2008; Donaldson et al. 2014;
Jacobs et al. 2014; Cronin et al. 2017; Kaplan et al. 2017; McLean et al. 2017;
Canavan et al. 2019).
70
D. M. Richardson et al.