Invasive Alien Plants in South Africa PDF

INVASIVE ALIEN PLANTS INVASIVE ALIEN PLANTS INVASIVE ALIEN PLANTS INVASIVE ALIEN PLANTS  Plants species introduced to S.A. for a range of purposes. Food Hylocereus undatus Cat2 Ornamental Structural material Acacia melanoxylon Cat2 INVASIVE ALIEN PLANTS  Oth...

INVASIVE ALIEN PLANTS INVASIVE ALIEN PLANTS INVASIVE ALIEN PLANTS INVASIVE ALIEN PLANTS  Plants species introduced to S.A. for a range of purposes. Food Hylocereus undatus Cat2 Ornamental Structural material Acacia melanoxylon Cat2 INVASIVE ALIEN PLANTS  Others arrived unannounced.  INVASIVE ALIEN PLANTS Many alien species have become naturalized. Some have become invasive. Invasive alien species are able to survive, reproduce and spread, unaided and sometimes at high rates. (National Biodiversity Assessment 2011) CHARACTERISTICS OF INVASIVE ALIEN SPECIES.  Similar climate and soils. CHARACTERISTICS OF INVASIVE ALIEN SPECIES.  Similar ecology. CHARACTERISTICS OF INVASIVE ALIEN SPECIES.  Produce large numbers of seeds, grow fast. CHARACTERISTICS OF INVASIVE ALIEN SPECIES.  Seeds can easily be spread by wind, birds or water. CHARACTERISTICS OF INVASIVE ALIEN SPECIES.  No natural predators.  INVASIVE ALIEN PLANTS  Introduced to S.A. – 750 tree species and 8000 shrubby / herbaceous species.  161 species – invasive  44 species – declared as noxious weeds *.  31 species – declared as invaders.  Not all alien species are invasive! * A noxious weed is any plant designated by federal, state or local government officials as injurious to public health, agriculture, recreation, wildlife or property.  Density of 27 established invasive plant species in South Africa (2010). Increased from 10 million ha in 1990s to ~20 million ha in 2007. (National Biodiversity Assessment 2011)  6% 3% 3% 1.5% 1.5% 1% 0.5% 0.5% 0.4% 0.3% 17.8% (National Biodiversity Assessment 2011) THE MOST WIDESPREAD ALIEN PLANTS IN SOUTH AFRICA. Species Origin Reasons for Approximate Area Invaded Introduction Syringa Asia Ornamental, shade Occurs in 3 million hectares of Melia azedarach savanna, along river banks, disturbed areas, roadsides, urban open spaces. Pines North America Timber, poles, Occurs in 3 million hectares; Pinus species Europe firewood, ornamental, widespread in mountain shade catchments, forest fringes, grasslands, fynbos. Black Wattle Australia Shelter, tanbark, Occurs in 2.5 million hectares Acacia mearnsii shade,firewood widespread except in arid areas. Lantana Central America Ornamental, hedging Occurs in 2.2 million hectares of Lantana camara South America forest and plantation margins, water courses, savanna. Rooikrans Australia Dune reclamation, Occurs in 1.9 million hectares of Acacia cyclops shelter, firewood mainly coastal belt of the Western and Eastern Cape. THE MOST WIDESPREAD INVADING ALIEN PLANTS IN SOUTH AFRICA CONT. Species Origin Reason for Approximate Area Invaded Introduction Port Jackson Willow Australia Dune reclamation, Occurs in 1.9 million hectares of Acacia saligna shelter, tanbark, Western Cape coastal lowlands. fodder Prickly Pear / Cactus North America Ornamental, edible Occurs in 1.8 million hectares of Opuntia species Central America fruits, animal fodder Karoo, dry savanna and pastoral South America lands. Mesquite North America Fodder, shade and Occurs in 1.8 million hectares of Prosopis species firewood in dry the Northern Cape and Northwest areas Province. Bugweed South America Ornamental Occurs in 1.8 million hectares; Solanum mauritianum widespread except for driest parts of country. Hakea Australia Shelter, dune Occurs in 0.7 million hectares of Hakea species reclamation, mountain and lowland fynbos. ornamental, hedging firewood  Syringa Asia Ornamental, shade Occurs in 3 million hectares of Melia azedarach (ca. 12 m tall) savanna, along river banks, disturbed areas, roadsides, urban open spaces. Melia azedarach http://bgis.sanbi.org/projectsearch.asp  Pines North America Timber, poles, Occurs in 3 million hectares; Pinus species Europe firewood, ornamental, widespread in mountain shade catchments, forest fringes, (ca. 20 m) grasslands, fynbos. Pinus sp.  Black Wattle Australia Shelter, tanbark, Occurs in 2.5 million hectares Acacia mearnsii shade,firewood widespread except in arid areas. (ca. 15 m) Acacia mearnsii  Lantana Central America Ornamental, hedging Occurs in 2.2 million hectares of Lantana camara South America (ca. 1.5 m tall) forest and plantation margins, water courses, savanna. Lantana camara  Rooikrans Australia Dune reclamation, Occurs in 1.9 million hectares of Acacia cyclops shelter, firewood mainly coastal belt of the (up to 4 m tall) Western and Eastern Cape. Acacia cyclops Port Jackson Willow Australia Dune reclamation, Occurs in 1.9 million hectares of Acacia saligna shelter, tanbark, Western Cape coastal lowlands. fodder (ca. 6 m tall) With midrib Acacia saligna  Mesquite North America Fodder, shade and Occurs in 1.8 million hectares of Prosopis species firewood in dry areas the Northern Cape and Northwest (ca. 3-5 m tall) Province. Prosopis sp. Prickly Pear / Cactus North America Ornamental, edible Occurs in 1.8 million hectares of Opuntia species Central America fruits, animal fodder Karoo, dry savanna and pastoral South America (ca. 3 m) lands. Opuntia sp.  Bugweed South America Ornamental Occurs in 1.8 million hectares; Solanum mauritianum (ca. 4 m tall) widespread except for driest parts of country. Solanum mauritianum  Hakea Australia Dune reclamation, Occurs in 0.7 million hectares of Hakea species ornamental, mountain and lowland fynbos. hedging firewood (ca. 3 m tall) Hakea sp. All 10 (SANBI BGIS: National Invasive Plant Survey 2010) Negative impacts  Ecological impacts  Loss of riparian habitat  Changes in littoral active zone  Reduction in fresh water availability  Biodiversity loss  Loss of grazing potential & livestock production  Altered fire regimes (frequency & intensity) Ecological impacts (Van Wilgen et al. 2001) Ecological impacts of alien invasive plants  In aquatic ecosystems -changes in physical habitat (e.g. waterweeds) and habitat loss. Pontederia crassipes Salvinia molesta Ecological impacts of alien invasive plants Ecological impacts of alien invasive plants Ecological impacts of alien invasive plants Ecological impacts of alien invasive plants  In Fynbos - rapidly reduces the abundance and diversity of native plants.  Dense stands of Acacia saligna result in a decline of soil- stored seed banks of native plants, resulting in the local extinction of species.  Ecological impacts of alien invasive plants  In arid savannas - widespread replacement of native Vachellia (Acacia) dominated communities by alien Prosopis.  Altered bird habitats Reduced species richness and diversity. Elimination of raptors. Reductions in frugivores and insectivores.  Ecological impacts of alien invasive plants  In Mesic savannas - Chromolaena odorata  Riparian invasions = increase shading on river banks  Altered sex ratios of native crocodiles due to reduced soil temperatures in nests  Cooler temps (30 °C) = females  Warmer temps (34 °C) = males  DESTRUCTION OF THE RIPARIAN HABITAT.  Grasses and sedges replaced by woody aliens.  Results in change over from stable community to an unstable community.  DESTRUCTION OF THE RIPARIAN HABITAT.  Leads to increased erosion.  More water available in riparian zones, thus water use of these trees tend to be almost double that of the same trees when growing away from rivers. Impacts on Littoral active zone In coastal zones- stabilization of natural mobile sand dunes has altered coastal sediment movement e.g. development on the Cape St Francis Headland Bypass Dune field, Cape Recife dunes – Port Elizabeth Sand movement (Port Elizabeth) Sand movement (Cape St Francis) NEGATIVE ECONOMIC IMPACTS: REDUCTIONS IN AVAILABLE WATER (Le Maitre et al. 1996) NEGATIVE ECONOMIC IMPACTS: REDUCTIONS IN AVAILABLE WATER (Van Wilgen 2008) Rainy season Rainy Season – Stand of invasive trees use same amount of water as grassland. Stream Flow Dry Dry Season – Grasses become dormant; Alien trees continue to transpire. season Water table recedes below trees; remain at a higher level under grasses. No Stream Stream Flow Flow NEGATIVE ECONOMIC IMPACTS: REDUCTIONS IN AVAILABLE WATER  Rainy Season – Stand of invasive trees use same amount of water as grassland.  Dry Season – Grasses become dormant; Alien trees continue to transpire.  Water table recede below trees; remain at a higher level under grasses.  Next rainy season – Groundwater will need to be replenished before streams can start to flow.  REDUCTIONS IN AVAILABLE WATER CONT.  Reductions in runoff impact on the economy in two ways:  Reduces the ability of existing water supply schemes to deliver sufficient water to meet demands.  Reduces the total amount of water available for human use. LOSS OF BIODIVERSITY AND ECOSYSTEM RESILIENCE.  Biodiversity – basis for life on Earth & thus a resource to be used and preserved.  Invading alien organisms – second largest threat to biodiversity  Due to displacement by direct competition, reduced structural diversity, increased biomass and disruption of the prevailing vegetation dynamics. LOSS OF BIODIVERSITY AND ECOSYSTEM RESILIENCE CONT. Number of species per 1 000 km2 South Africa Africa World Vascular plants 16 1.5 1.7 Amphibians 0.07 0.02 0.03 Reptiles 0.23 0.03 0.04 Birds (Breeding) 0.47 0.05 0.06 Birds (Non- 0.10 0.01 - Breeding) Mammals 0.18 0.03 0.03  LOSS OF GRAZING POTENTIAL AND LIVESTOCK PRODUCTION.  Alien plants cause the degradation of semi-natural rangelands.  Results in a loss of grazing through replacement of palatable species or reduced access.  Examples – Opuntia aurantiaca, triffid weed, ink berry. https://www.youtube.com/watch?v=ggqseLRvlfY INCREASED COSTS OF FIRE PROTECTION AND DAMAGE IN WILDFIRES. Hakea sericea  Aliens change the structure of the fuel beds.  More dry material (lower moisture content).  Fires become less frequent and more intense.  INCREASED COSTS OF FIRE PROTECTION AND DAMAGE IN WILDFIRES CONT. Acacia saligna  Detrimental effects:  A reduction in viability of indigenous seeds = poor regeneration from seed banks.  Damage to physical structures.  Human / livestock mortality Podalyria calyptrata  Indirect effects – Invaded areas are impenetrable; restricted access makes fires more difficult to contain. http://ewn.co.za/Media/2015/03/04/Inside-the-flames WILDFIRES EROSION FOLLOWING FIRES IN HEAVILY INVADED AREAS.  Higher intensity fires cause physical damage to the soil.  Loss of organic matter and moisture holding capacity.  Results in soil water repellence and increased erosion after fire.