country. This chapter explores how these environmental features influence biological invasions (focusing on terrestrial ecosystems). We first discuss broad features of
the different landscapes, and then discuss how different environmental factors
[geomorphology, soils, climate (including rainfall seasonality), extreme events (specifically droughts and floods), fire, freshwater, and land use] determine which
species can establish, spread, and cause adverse impacts. The high diversity of
invasive species in South Africa is partly due to the variety of environmental
conditions, but some conditions (e.g. fire and aridity) also limit invasions. With
reference to plants, invasive species assemblages seem to be co-incident with native
species assemblages at a broad-scale (although the driving mechanisms are unclear).
However, finer-scale influences of anthropogenic factors (e.g. introduction effort and
disturbance) also play important roles in shaping invasive biotas. Together these
factors suggest that climate-based species distribution models (with an additional fire
filter) can accurately predict the broad-scale potential range of invaders in
South Africa. However, at finer scales and for management purposes, we need to
understand how humans directly and indirectly influence patterns of invasion.
13.1 What Does South Africa Look Like to an Alien
Species?
South Africa is a largely temperate and sub-tropical country covering over 1.2
million km
2 . While most of the country is arid to semi-arid, there are significant
gradients in rainfall amounts and seasonality (Fig. 13.1). Elevation varies from sea
level to over 3000 m asl. Conditions climatically analogous to those that exist in
South Africa occur over approximately a fifth of the world’s land surface (Richardson and Thuiller 2007; Fig. 1.1 in van Wilgen et al. 2020a, Chap. 1) [in this chapter
we only consider continental South Africa, see Greve et al. (2020), Chap. 8 for a
discussion of South Africa’s sub-Antarctic islands]. There are nine terrestrial biomes
within continental South Africa (Mucina and Rutherford 2006), with each biome
largely contiguous to itself. Importantly, the major points of entry of goods coming
into the country are in different biomes [Cape Town’s ports and airports are in the
Fynbos Biome, Durban’s in the Indian Ocean Coastal Belt, Port Elizabeth’s in the
Thicket; the airports in Gauteng (i.e. Johannesburg/Pretoria) are in the Grassland; the
land borders of both Beit Bridge and Lebombo are in the Savanna; and the land
borders with Namibia are in the Desert] (Fig. 12.1 in Faulkner et al. 2020, Chap. 12)
chapter. While human population density is much lower in the more arid biomes (the
Desert, Nama-Karoo, and Succulent Karoo Biomes), even in these biomes alien
species have been introduced due to farming, as ornamentals and pets, or due to
mining activities (e.g. construction, the movement of equipment, and
phytoremediation). This means there is a large pool of potential invaders, many
opportunities for introduction and dissemination, and a range of environmental
factors that can promote or limit invasions.
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the different landscapes, and then discuss how different environmental factors
[geomorphology, soils, climate (including rainfall seasonality), extreme events (specifically droughts and floods), fire, freshwater, and land use] determine which
species can establish, spread, and cause adverse impacts. The high diversity of
invasive species in South Africa is partly due to the variety of environmental
conditions, but some conditions (e.g. fire and aridity) also limit invasions. With
reference to plants, invasive species assemblages seem to be co-incident with native
species assemblages at a broad-scale (although the driving mechanisms are unclear).
However, finer-scale influences of anthropogenic factors (e.g. introduction effort and
disturbance) also play important roles in shaping invasive biotas. Together these
factors suggest that climate-based species distribution models (with an additional fire
filter) can accurately predict the broad-scale potential range of invaders in
South Africa. However, at finer scales and for management purposes, we need to
understand how humans directly and indirectly influence patterns of invasion.
13.1 What Does South Africa Look Like to an Alien
Species?
South Africa is a largely temperate and sub-tropical country covering over 1.2
million km
2 . While most of the country is arid to semi-arid, there are significant
gradients in rainfall amounts and seasonality (Fig. 13.1). Elevation varies from sea
level to over 3000 m asl. Conditions climatically analogous to those that exist in
South Africa occur over approximately a fifth of the world’s land surface (Richardson and Thuiller 2007; Fig. 1.1 in van Wilgen et al. 2020a, Chap. 1) [in this chapter
we only consider continental South Africa, see Greve et al. (2020), Chap. 8 for a
discussion of South Africa’s sub-Antarctic islands]. There are nine terrestrial biomes
within continental South Africa (Mucina and Rutherford 2006), with each biome
largely contiguous to itself. Importantly, the major points of entry of goods coming
into the country are in different biomes [Cape Town’s ports and airports are in the
Fynbos Biome, Durban’s in the Indian Ocean Coastal Belt, Port Elizabeth’s in the
Thicket; the airports in Gauteng (i.e. Johannesburg/Pretoria) are in the Grassland; the
land borders of both Beit Bridge and Lebombo are in the Savanna; and the land
borders with Namibia are in the Desert] (Fig. 12.1 in Faulkner et al. 2020, Chap. 12)
chapter. While human population density is much lower in the more arid biomes (the
Desert, Nama-Karoo, and Succulent Karoo Biomes), even in these biomes alien
species have been introduced due to farming, as ornamentals and pets, or due to
mining activities (e.g. construction, the movement of equipment, and
phytoremediation). This means there is a large pool of potential invaders, many
opportunities for introduction and dissemination, and a range of environmental
factors that can promote or limit invasions.
356
J. R. Wilson et al.