The Invasive Species Specialist Group (ISSG) of the Species Survival Commission (SSC) of the World Conservation Union (IUCN) has compiled a list of the One Hundred of the World’s Worst Invasive Alien Species (www.issg.org/database/species/search.asp?st=100ss&fr=1&sts=#SpeciesList) which aims to collectively illustrate the range of impacts caused by biological invasion. Although incomplete, this list is a first attempt to rank the impact of alien invasive species. Included in this list are 62 alien invasive species that impact forests and forestry. This annex provides an overview of these species.
Unless otherwise noted, the information in this annex is taken from the Global Invasive Species Database developed by ISSG (www.issg.org/database [accessed on 23 August 2005]). More detailed information on these species can be found there.
Batrachochytrium dendrobatidis is a parasitic fungus that causes fungal skin infections (chytridiomycosis) in wild and captive amphibians which has been associated with population declines in endemic amphibian species in montane rain forests (Daszak et al., 1999; Weldon et al., 2004). Chytridiomycosis has been reported in 38 amphibian species from 12 families, including frogs, toads and salamanders.
Although the fungus has been found on every continent that has amphibians except Asia, Africa is suggested as the origin of B. dendrobatidis (Speare and Berger, 2000; Weldon et al., 2004). The fungus can be found in lakes, natural forests, riparian areas and water courses and can remain viable in the environment, especially aquatic environments, for weeks.
Cryphonectria parasitica, known commonly as chestnut blight, is a fungus that primarily attacks chestnut trees (Castanea spp.) but can also cause damage to oak trees (Quercus spp.) and other hardwood tree species. It occurs in natural and planted forests where it infects the above-ground parts of trees only, creating cankers that expand, girdle and eventually kill tree branches and trunks. The native range of C. parasitica is Asia and it is considered invasive in Europe and North America.
First observed killing trees in the Bronx Zoo in New York City in 1904, the fungus was likely introduced to North America on nursery stock from Asia (Canadian Chestnut Council, undated). From there, chestnut blight spread throughout eastern North America and by 1940, three and half billion chestnut trees had perished (Cock, 2003).
Dutch elm disease is a wilt disease caused by a pathogenic fungus, Ophiostoma ulmi sensu lato, which is spread by specialized bark beetles that breed under the bark of dying elm trees (Stack, McBride and Lamey, 1996). The young adult beetles fly from infected pupal chambers to feed on healthy elm trees carrying fungal spores on their bodies and depositing them in healthy plant tissue. The fungus can also spread via root grafts.
The symptoms and progression of the disease differ among trees which are infected through beetle feeding and those which are infected through root grafts (Stack, McBride and Lamey, 1996). Trees infected by beetles first show wilting, curling and yellowing of leaves on one or more branches in the upper crown of the tree. Large trees may survive and progressively show more symptoms for years after initial infection. Trees infected through root grafts tend to wilt and die rapidly as the disease progresses from the base of the tree upward, typically in the spring after leaves have developed.
During the last century, there have been two destructive pandemics of this disease in Europe and North America, caused by the successive introduction of two fungal pathogens: Ophiostoma ulmi and the much more aggressive, Ophiostoma novo-ulmi. The fungus occurs in natural and planted forests and urban areas. Host trees include all the Euro-American native elms such as field elm (Ulmus minor), wych elm (Ulmus glabra), European white elm (Ulmus laevis), American elm (Ulmus americana), red or slippery elm (Ulmus rubra), rock elm (Ulmus thomasii) and cedar elm (Ulmus crassifolia). Asian elm species are generally much less susceptible than Euro-American native elms and although the Chinese elm (Ulmus parvifloia) is occasionally infected by the disease, it is much less susceptible than American elm.
Phytophthora ramorum is the causal agent of sudden oak death which until 2000 was undiscovered and unnamed. This fungus is the cause of much concern in Europe and North America because of the high level of local destruction it causes, the lack of knowledge of its epidemiology, and its high prevalence in nurseries which increases the potential of spread to new areas (Garbelotto, 2004).
P. ramorum occurs in natural and planted forests and has an extensive host range, covering many plant genera and several families, including trees, shrubs and woody and herbaceous perennials. The hosts can be broken down into two categories - bark canker hosts and foliar hosts - depending on the part of the plant or tree most susceptible to the disease (Rizzo and Garbelotto, 2003; Garbelotto, 2004). Bark canker hosts become infected on their trunks and in highly susceptible species, the cankers eventually girdle the tree, resulting in starvation and death. Mortality may occur in as little as two years. Foliar hosts become infected on their leaves and twigs and may be accompanied by branch infections and dieback in some foliar hosts; such hosts only occasionally die from infection.
The fungus spreads to new locations primarily through the nursery trade and are locally spread by vectors, and infected soil, water and tools. Infestations of P. ramorum have been reported in nurseries in most European countries, the United States (Oregon and Washington) and Canada (British Columbia) (Garbelotto, 2004). It is unknown how this fungus originally entered Europe and North America, but genetic analysis suggests the pathogen is from a third location (Rizzo et al., 2002; Garbelotto, 2004).
Platydemus manokwari is a predatory species of flatworm that has been intentionally and unintentionally introduced to many islands throughout the Pacific and Indian Oceans as a biological control agent for the giant African snail (Achatina fulica) (Lydeard et al., 2004). It now poses a serious threat to native gastropods, including many endemic snail species. This flatworm occurs in agricultural areas, coastland, disturbed areas, natural forest, planted forests, riparian zones, scrublands, shrublands, urban areas, and wetlands though is generally found in leaf litter in both undisturbed forests and habitats heavily modified by humans. Originating from New Guinea, P. manokwari now occurs in Australia, Guam, Hawaii, Japan, Maldives, Northern Mariana Islands, Palau, Philippines, Samoa, Tonga and Vanuatu (Lydeard et al., 2004).
Aedes albopictus, the Asian tiger mosquito, was introduced to the United States and other countries via used tire imports. This mosquito attacks more hosts than any other mosquito in the world, including many mammals, birds and reptiles, and is associated with the transmission of dengue fever, yellow fever, eastern equine encephalitis, dog heartworm and possibly St. Louis and LaCrosse encephalitis viruses (Wittenberg and Cock, 2001). A. albopictus occurs in natural forests and urban areas.
Believed to be indigenous to West Africa, Anoplolepis gracilipes or the yellow crazy ant, has been introduced, primarily through cargo shipments, into Africa, Asia, Australia, South America and many islands in the Caribbean, Indian and Pacific Oceans (Holway et al., 2002; Matthews, 2004). In some cases, however, the ant was intentionally introduced as a biological control agent against insect pests in cocoa, coconut and coffee plantations (Matthews, 2004). Because of its mutualistic relationship with Homoptera, A. gracilipes has itself become a pest of the agriculture and forest sectors. In exchange for their sugary honeydew secretions, the ant protects scale insects from predators and spreads them to new host plants. At high densities, these scale insects weaken plants and, combined with a sooty mould that inhabits the honeydew, can cause canopy dieback or even the death of the tree (Secretariat of the Convention on Biological Diversity, 2003b; Matthews, 2004).
The yellow crazy ant affects native fauna by competing for food resources, altering the habitat or direct predation. In at least one case its removal of a keystone species, the red land crab on Christmas Island, has resulted in a significant change in forest composition and structure and a decrease in nutrient cycling (Secretariat of the Convention on Biological Diversity, 2003b; Matthews, 2004). A. gracilipes can also affect the reproductive success of many mammals, reptiles and birds, such as the Christmas Island thrush (Turdus poliocephalus erythropleurus) (Secretariat of the Convention on Biological Diversity, 2003b). Such impacts have also affected the tourism sector in many areas. For example, on Bird Island in the Seychelles, the ant has displaced approximately 60 000 pairs of sooty terns (Sterna fuscata), which are a major tourist attraction of the island (Secretariat of the Convention on Biological Diversity, 2003b).
A. gracilipes occurs in agricultural areas, coastland, disturbed areas, natural and planted forests, rangelands, grasslands, riparian zones, scrublands and shrublands, urban areas and water courses.
The Asian longhorned beetle, Anoplophora glabripennis, native to China and Korea, occurs in agricultural areas, disturbed areas, natural and planted forests, scrublands and shrublands, and urban areas. They attack hardwood trees, feed on the leaves, petioles and twigs and then bore into the tree trunk to lay their eggs (Matthews, 2004). After hatching, the larvae tunnel under the bark and feed on plant tissue until they are ready to pupate. Adult beetles emerge through small exit holes. Repeated attacks cause tree dieback and eventually kill the tree, typically over an estimated 3-5 year period, though some tree species may live longer (Matthews, 2004).
Infestations were first discovered in North America in New York City in 1996 and in Chicago in 1998, about ten years after the beetle first entered the United States. As of May 2001, 5 286 and 1 547 infested trees have been cut in New York and Chicago respectively. An infestation was also discovered in Austria in 2001, an estimated 2-3 years after its introduction, and as of August 2001, approximately 47 infested trees have been felled. Asian longhorned beetles were also noted in New Jersey, United States in 2002 and in an industrial park in the Toronto-Vaughan area, Canada in 2003. In Poland, a single specimen was found on a bonsai tree (Acer palmatum) in 2003 and the beetles were also discovered in France in 2003 and 2004, about 100 km south of Paris and near Nante Port. In its native China, Asian longhorned beetles have damaged about 40 percent (approximately 2.3 million ha) of poplar plantations - over 240 cities or counties have been infested in five provinces alone (totalling 230 thousand ha) - and an estimated 50 million trees were cut down over a three year period (1991-1993) in Ningxia Province alone.
Cinara cupressivora, the cypress aphid previously referred to as C. cupressi, is a brownish soft-bodied insect that has been observed around the world feeding on various trees species from several genera including Austrocedrus, Callitris, Chamaecyparis, Cupressus, Juniperus, Thuja, Widdringtonia and the hybrid Cupressocyparis (Watson et al., 1999; Mwangi, 2002). The species occurs in natural and planted forests where it sucks the sap from twigs causing yellowing to browning of foliage. Depending on the severity and duration of the infestation, the overall effects range from partial damage to eventual tree death (O'Neil, 1998).
The cypress aphid has critically damaged commercial and ornamental plantings and native stands of Cupressus, Juniperus, Widdringtonia and other Cupressaceae in Africa, Colombia, Italy, Jordan, Mauritius and Yemen (Watson et al., 1999). Up to 1990, it was estimated that C. cupressivora had killed approximately US$44 million worth of trees throughout southern and eastern Africa and was causing an additional loss of approximately US$14.6 million per year through reductions in annual growth increment (Cock, 2003). In Kenya, approximately 5 153 ha of 86 000 ha of industrial forest plantations of Cupressus lusitanica have been infested by the aphid to varying degrees ranging from slight to severe (Mwangi, 2002). A study conducted by the Kenya Forestry Institute estimated that the cypress aphid in Kenya might kill as many as 50 percent of all cypress trees during the 30-year harvest cycle (Cock, 2003).
C. cupressivora probably originated in a region from eastern Greece to just south of the Caspian Sea and is now known to exist in Africa, Asia, Europe, North America and South America (Watson et al., 1999).
Linepithema humile, commonly known as the Argentine ant, is a very successful colonizer that produces large numbers of aggressive workers capable of invading both disturbed and undisturbed habitats. In favourable environments, the Argentine ant can attain high densities and displace native and introduced ant species, significantly reduce the abundance of other arthropods, and alter ecosystem level processes such as plant pollination and seed dispersal (Cole et al., 1992; Human and Gordon, 1996; Human and Gordon, 1997; Holway, 1998; Christian, 2001).
The native range of the Argentine ant is South America and the species can now be found on all continents except Antarctica, as well as a number of oceanic islands (Suarez, Holway and Case, 2001). Southern Europe is home to the world's largest colony of L. humile. It occurs in agricultural areas, coastal areas, disturbed areas, natural and planted forests, rangelands and grasslands, riparian zones, scrublands and shrublands, urban areas and wetlands.
The gypsy moth, Lymantria dispar, is one of the most destructive pests of hardwood forests and shade, fruit and ornamental trees throughout the northern hemisphere. The caterpillars cause extensive defoliation, leading to reduced growth or even death of the host tree. They destroy the aesthetic beauty of natural areas by defoliating and killing the trees and covering the area with their waste products and silk. Gypsy moth also has impacts on human health as the hairs on larvae and egg masses have been known to cause allergies in some people.
Cyclical outbreaks generally only occur in stands where primary hosts, such as Quercus and Populus, comprise more than 20 percent of the basal area and where environmental conditions are favourable to generation explosions. Outbreaks (of several generations) can be every 7-10 years, however more recently the period between outbreaks is apparently becoming shorter.
L. dispar can be found in natural and planted forests, riparian zones and urban areas. The native range of the European gypsy moth is southern Europe and northern Africa. It was introduced to the United States by a scientist searching for silk-producing caterpillars (Wittenberg and Cock, 2001; Ciesla, 2002). This form soon moved to Canada and is now present in most of northeastern North America and its range is expanding to the south and west. The native range of the Asian gypsy moth is central and southern Asia and Japan. This form is considered a greater threat as adult females are capable of flight and can therefore disperse greater distances. It is classified as a potential threat by many countries and is covered by phytosanitary regulations. Regular monitoring, generally through the use of pheromone traps, is carried out to intercept establishment of the gypsy moth.
Pheidole megacephala, commonly called the big-headed ant, is one of the most invasive species of ant, having attained a pantropical distribution. It is a serious threat to biodiversity as it aggressively displaces most native invertebrate species (Hoffmann, Andersen and Hill, 1999). Reductions in vertebrate populations have also been observed where this ant is extremely abundant. The big-headed ant is also a domestic pest since it chews on telephone cabling and electrical wires and an agricultural pest as it harbours phytophagous insects that reduce crop productivity (Hoffmann, Andersen and Hill, 1999). P. megacephala can also facilitate the invasion of non-native plant species.
P. megacephala occurs in agricultural areas, coastal areas, disturbed areas, natural and planted forests, rangelands, grasslands, riparian zones, scrublands and shrublands, urban areas and wetlands. The native range is believed to be southern Africa and it is now widespread throughout the temperate and tropical zones of the world. It favours shaded and moist environments but can exist wherever there is anthropogenic disturbance (Hoffmann, Andersen and Hill, 1999).
Red imported fire ants (RIFA), Solenopsis invicta, are aggressive generalist foragers that occur in very high densities thereby allowing them to dominate food sources. Their stinging ability allows them to subdue prey and repel even large vertebrate competitors from resources. They have considerable impacts on native invertebrates. In the southeastern United States, for example, S. invicta has reduced native ant abundance by 90 percent and species richness by 70 percent and has had a serious impact on other invertebrates (Hoffmann, Andersen and Hill, 1999). This species breeds and spreads rapidly and if disturbed, can relocate rapidly in order to ensure colony survival.
Native to South America, the red imported fire ant has been introduced into parts of Australia, New Zealand, North America and some Caribbean islands, notably Puerto Rico and the Virgin Islands (Holway et al. 2002). S. invicta occurs in agricultural areas, coastal areas, deserts, disturbed areas, natural and planted forests, rangelands, grasslands, riparian zones, scrublands, shrublands, urban areas and water courses.
S. invicta inhabits hot arid regions however it may survive colder climates in human habitations or infrastructure such as climate-controlled buildings or greenhouses. Invasive ants are usually more likely to establish in disturbed habitats, including the edges of forests or agricultural areas (Ness and Bronstein, 2004). Deforested areas are particularly at risk of being invaded by red imported fire ants (Morrison et al., 2004). This ant constructs earthen mounds for brood thermoregulation, which are easier to build in open, sunny areas; as a result it is less abundant in, and poses a smaller threat to, dense forests (Morrison et al., 2004). Tropical regions that are warm, wet and densely forested are not suitable habitats for fire ants (Morrison et al., 2004).
Vespula vulgaris, the common wasp or yellowjacket, occurs in natural and planted forests, scrublands and shrublands and urban areas where they nest underground and in tree cavities and buildings. The common wasp is a Holarctic species and has been introduced into New Zealand and Australia. In addition to causing painful stings to humans, they compete with birds and other insects for insect prey and sugar sources. They will also eat fruit crops and scavenge around rubbish bins and picnic sites. This species impacts a wide range of sectors including conservation, forestry, beekeeping, horticulture, and human health. V. vulgaris is a major threat to insect and bird populations in native beech forests on New Zealand’s South Island (Matthews et al., 2000).
Wasmannia auropunctata, or the little fire ant, is native to Central and South America and has been introduced into parts of Africa, North America, South America and onto some islands in the Caribbean and the Pacific Oceans including the Galapagos, Hawaii, New Caledonia, Vanuatu and the Solomon Islands (Roque-Albelo and Causton, 1999; Holway et al., 2002). The ant occurs in agricultural areas, coastlands, deserts, disturbed areas, natural and planted forests, rangelands and grasslands, riparian zones, scrublands and shrublands, urban areas and wetlands.
The little fire ant reduces species diversity and abundance of flying and tree-dwelling insects and eliminates arachnid populations. In agricultural areas, the ant is considered a great nuisance to humans because it is more likely to reach high densities and sting people working in the field. In human habitations, it may sting and even blind domestic pets (Romanski, 2001). In New Caledonia and the Galapagos, W. auropunctata has been blamed for a decrease in reptile populations, where it eats tortoise hatchlings and attacks the eyes and cloacae of adult tortoises (Nishida and Evenhuis, 2000). The ant is probably the most aggressive species that has been introduced into the Galapagos where a marked reduction of scorpions, spiders and native ant species in infested areas has been observed (Roque-Albelo and Causton, 1999; Nishida and Evenhuis, 2000). The species has also led to a decrease in local arthropod biodiversity in the Solomon Islands (Romanski, 2001). In its native range the little fire ant decreases herbivorous arthropods, increasing plant growth and fruit and seed production, and decreasing pathogen attacks. W. auropunctata may also however exclude arthropod plant mutualists such as plant tenders or seed dispersers (Ness and Bronstein, 2004). It is considered to be perhaps the greatest ant species threat in the Pacific Region.
Environmental stresses, including human practices such as monoculture plantings, may cause explosions of some ant populations. For example, in its native range in South America, W. auropunctata is a pest in disturbed forests and agricultural areas where it can reach higher densities. High densities of this species have been linked with sugar cane monocultures in Colombia and cocoa farms in Brazil. In Colombia, a high abundance of the little fire ant in forest fragments has also been linked with low native ant diversity. The little fire ant efficiently exploits resources including shelter, nectar, and honeydew residues of Homopteran insects and may outcompete and displace native ants (Armbrecht and Ulloa-Chacón, 2003).
Achatina fulica, the giant African snail, is native to East Africa and has been introduced into most regions of the humid tropics, including many Pacific islands, eastern and southern Asia, and the Caribbean. It has also been intercepted widely by quarantine officials and initial invasions have been eradicated in many countries. The species occurs in agricultural areas, coastal areas and wetlands, disturbed areas, natural and planted forests, riparian zones, scrublands and shrublands, and urban areas
A. fulica has been considered the most important snail pest in the tropics and subtropics and perhaps the world. A major agricultural and garden pest, and a general nuisance, the giant African snail eats native plants, modifies habitats and out-competes native snails (Matthews, 2004). A. fulica is also a vector for eosinophilic meningitis, a disease caused by the parasite rat lungworm that is passed to humans through the consumption of raw or improperly cooked snails (Matthews, 2004). Often the introduction of the giant African snail has lead to the subsequent introduction of predatory snails and flatworms as biological control agents that can also have devastating effects on native land snail diversity.
The predatory rosy wolf snail, Euglandina rosea, is native to the southeastern United States and has been introduced to islands in the Caribbean, Pacific and Indian Oceans as a biological control agent for another alien invasive species, the giant African snail (Achatina fulica) (Stein and Flack, 1996). This snail has caused the extinction of numerous endemic tree snails in French Polynesia and has been heavily implicated in the extinction or decline of other snail species wherever it has been introduced, notably in Hawaii (Stein and Flack, 1996). E. rosea occurs in disturbed areas, natural and planted forests, scrublands and shrublands, and urban areas.
Bufo marinus, or cane toads, are indigenous to northern South America, Central America, and Mexico northward to the southern United States and have been introduced throughout the world as a biological control agent for various insect pests of sugarcane and other crops. In its introduced range, it has become a serious pest feeding on a wide variety of insects, frogs, reptiles, birds and mammals (Department of Natural Resources and Mines, 2003). It also preys on and competes with native amphibians for food and breeding habitat. Glandular secretions excreted when the toad is provoked or pressure is applied, are toxic and are known to cause illness and death in domestic animals and wildlife that come into contact with toads. B. marinus inhabits agricultural areas, disturbed areas, lakes, water courses, wetlands and riparian zones, natural forests and urban areas.
Eleutherodactylus coqui is a small tree frog native to Puerto Rico that has been introduced into the Asia-Pacific region, North America and the Galapagos Islands. The Caribbean tree frog is highly adaptable to different ecological zones and altitudes and inhabits agricultural areas, natural and planted forests, wetlands and riparian zones, and urban areas.
Their loud call is the main reason they are considered pests and in some regions there are fears that this may negatively impact the tourism industry (HEAR, 2004). These frogs have a voracious appetite and in Hawaii, there is concern that E. coqui may put endemic insect and spider species at risk and compete with endemic birds and other native fauna which rely on insects for food (Campbell, 2000).
Boiga irregularis, the brown treesnake, is native to eastern Indonesia, the Solomon Islands, New Guinea, and the northern and eastern coasts of Australia and has been introduced to Guam and the Northern Mariana Islands. They have also been sighted on Saipan, Tinian, Rota, Kwajalein, Wake Oahu, Pohnpei, Okinawa, and Diego Garcia. The brown treesnake occurs in agricultural areas, wetlands, riparian and coastal zones, disturbed areas, natural and planted forests, rangelands and grasslands, scrublands and shrublands, and urban areas.
The brown snake is notorious for concealing itself in international freight and aircraft. It is nocturnal, secretive and arboreal, hunting for food at all levels within a forest. It is an effective generalized predator that has decimated the avifauna, greatly impacted other terrestrial vertebrates, caused cascading ecological perturbations, and disrupted the electrical supply in Guam.
Pycnonotus cafer is a noisy, gregarious bird that occurs naturally from Pakistan to southwest China and has been introduced to many Pacific Islands where it is considered highly invasive. Commonly known as the red-vented bulbul, it is an agricultural pest that destroys fruits, flowers, beans, tomatoes and peas. It may also help to spread the seeds of other alien invasive species. The bulbul is aggressive and chases off other bird species. It occurs in agricultural areas, natural and planted forests, scrublands and shrublands, and urban areas.
Sturnus vulgaris, the European starling, is an aggressive omnivore native to Asia, Europe and North Africa and has been introduced into Australia, New Zealand, North America and South Africa. The starling prefers lowland habitats to more mountainous terrain and inhabits agricultural areas, coastal areas, disturbed areas, natural and planted forests, rangelands, grasslands, riparian zones and wetlands, scrublands and shrublands, tundra and urban areas.
European starlings cost hundreds of millions of dollars in agricultural damage each year and contribute to the decline of local native bird species through competition for resources and nesting space. They are also a public nuisance, can damage infrastructure, negatively affect aesthetics, and can pose public heath risks by transmitting diseases to humans as well as livestock (Adeney, 2001).
Goats, Capra hircus, are destructive herbivores with a highly diverse diet that includes plant species often avoided by sheep or cattle. They prevent successful regeneration of favoured plant species and their overbrowsing also decreases biomass and percent cover of vegetation, resulting in a decrease or extinction of animal species, and often severe erosion on the devegetated landscape. In New Zealand, for example, 35 years of overgrazing, overbrowsing and trampling by goats reduced the number of plant species from 143 to only 70 (Courchamp, Chapuis and Pascal, 2003). Goats easily become feral and can spread disease to native wildlife. Grasslands, scrublands and forests are all used extensively as feeding areas.
Cervus elaphus, or red deer, are a Eurasian species that have been introduced to Australia, New Zealand, North America and South America. They inhabit natural and planted forests, rangelands and grasslands, scrublands and shrublands, and tundra. Deer prevent regeneration of preferred plant species, thereby creating significant changes to the structure and composition of native ecosystems (Department of Conservation, 2002). In some areas, non-replacement of canopy species can lead to canopy collapse. Even at low densities, red deer inhibit forest regeneration (Department of Conservation, 2002). In Argentina, they have invaded several national parks where they negatively affect native flora and fauna and possibly disrupt ecological processes (Jaksic et al., 2002). In Chile, there is a concern over red deer competition with endangered endemic deer species such as the huemul, Hippocamelus bisulcus, and the pudu, Pudu pudu (Jaksic et al., 2002). Red deer also compete with livestock.
Cats, Felis catus, occur in almost all geographical regions but are usually absent from true desert, high mountain and frozen areas due to an absence of suitable prey and wetlands and rainforests as they prefer to stay dry. Their preferred prey is small mammals, amphibians, lizards and snakes but they also prey on birds, particularly those that nest or feed on or near to the ground. They have significant impacts on the abundance of such species, even to the point of extinction, thus causing considerable ecological impacts (Courchamp, Chapuis and Pascal, 2003).
Herpestes javanicus, or mongooses, occur in agricultural areas, coastal areas and wetlands, deserts, disturbed areas, natural and planted forests, rangelands and grasslands, riparian zones, scrublands and shrublands, and urban areas. They were introduced to many islands in the West Indies beginning in 1872 and to Fiji and several of the larger Hawaiian Islands in 1883 to control rats in sugar cane fields (Atkinson and Atkinson, 2000). Mongooses prey on birds, small mammals and reptiles and have caused the decline or extinction of many endemic vertebrates (Courchamp, Chapuis and Pascal, 2003). They cause significant losses to industries involving game species and livestock and are also a vector of rabies.
Macaca fascicularis, commonly known as the crab-eating or long-tailed macaque, is native to mainland Southeast Asia, the Philippines, and parts of Indonesia and has been introduced into Mauritius, Palau, Hong Kong and other parts of Indonesia (Tinjil Island and Papua) where it is considered to be invasive or potentially invasive. They inhabit a wide range of habitats including riparian, secondary and primary forests, coastal forests, forest edges, swamps, and urban and agricultural settings. Highly adaptive to new environments, macaques often prefer secondary habitats which have been disturbed by human activity.
It is an opportunistic mammal and reaches higher densities in degraded forest areas. In its introduced ranges, macaques have few natural predators and negatively affect native biodiversity by consuming native plants and competing with birds for fruit and seed resources. They also facilitate the spread of alien invasive plants through seed dispersal. Macaques may impact the agriculture and forest sectors by feeding on commercially important crops, plants and trees. They may also carry potentially fatal human diseases including B-virus.
The house mouse, Mus musculus, probably has the most extensive global distribution than any other mammal with the exception of humans. Native to the Indian subcontinent, the geographic spread of the house mouse has been facilitated by its commensal relationship with humans and they have colonized tropical, temperate, semi-desert, desert and subantarctic regions throughout the world. They are common in agricultural areas, coastal areas, disturbed areas, natural and planted forests, rangelands and grasslands, riparian zones, scrublands and shrublands, and urban areas.
House mice are major economic pests; consuming, destroying and contaminating crops and food supplies intended for human consumption. They have also been implicated in the extirpation or extinction of many indigenous species. They are host to a range of human diseases and parasites, the most serious being bubonic plague (Yersinia pestis) and salmonella (Salmonella spp.).
Mustela erminea, or stoat, is native to northern parts of Eurasia and North America and has been introduced into New Zealand and some small European islands. They live anywhere they can find suitable prey but prefer forests or shrublands to protect them from their avian predators. They also inhabit agricultural areas, coastal areas, disturbed areas, riparian zones, scrublands and shrublands, tundra and wetlands. An intelligent, resourceful predator, the stoat specializes in small mammals and birds though they also attack animals larger than themselves. They have contributed to the loss of native birds in New Zealand, including the northern brown kiwi, Apteryx mantelli, and hole-nesting forest birds (O'Donnell, 1996; Basse, McLennan and Wake, 1999). Research and management of stoats in New Zealand costs millions of dollars every year.
Native to southern Europe and North Africa, rabbits, Oryctolagus cuniculus, have been introduced to all continents except Antarctica and Asia. They are found in agricultural areas, desert, disturbed areas, natural and planted forests, rangelands and grasslands, scrublands and shrublands, and urban areas. Rabbits cause considerable damage to the environment and agricultural areas. They compete with native wildlife for food and shelter, contribute to a decline of many native plants and animals, and by supporting large populations of predators such as cats and foxes, they can also enhance their negative impacts on native species (Courchamp, Chapuis and Pascal, 2003). Rabbits cause extensive erosion through browsing and loss of plant cover and often destroy the habitats of many animals (Courchamp, Chapuis and Pascal, 2003). They also compete with livestock for food.
Rattus rattus is a native of the Indian subcontinent that has spread worldwide inhabiting agricultural areas, coastal areas, disturbed areas, natural and planted forests, rangelands and grasslands, riparian zones, scrublands and shrublands, and urban areas. Ship rats are omnivorous and capable of eating a wide range of plants and animals including the eggs and young of forest birds (Innes, 2001; Courchamp, Chapuis and Pascal, 2003; Robertson and Saul, 2004). They are known to impact the regeneration of maritime forest due to their consumption of inland podocarp seeds and their competition with and predation of many bird species that disperse seeds (Courchamp, Chapuis and Pascal, 2003). They have directly caused or contributed to the extinction of many species of wildlife including birds, small mammals, reptiles, invertebrates and plants, particularly on islands. The ship rat is the species most frequently identified with catastrophic declines of birds on islands as evidenced on Midway Island in the Leeward Islands of Hawaii, Lord Howe Island, and Big South Cape Island, New Zealand (Atkinson and Atkinson, 2000; Courchamp, Chapuis and Pascal, 2003). They are known to prey on many bird species including the endangered kakerori (Pomarea dimidiata) in the Cook Islands, sooty terns in the Seychelles, Bonin petrels in Hawaii, Galapagos dark-rumped petrels in the Galapagos Islands, and white-tailed tropicbirds in Bermuda (Atkinson and Atkinson, 2000; Robertson and Saul, 2004).
Native to the eastern United States, grey squirrels, Sciurus carolinensis, were imported into Italy, South Africa and the United Kingdom for the pet industry. They have subsequently been released or have escaped into the wild and are known to live in agricultural areas, disturbed areas, natural and planted forests, scrublands and shrublands, and urban areas. In the United Kingdom and Italy, the grey squirrel is expanding its range resulting in a decrease of the native red squirrel. It causes considerable damage to woodlands by stripping the bark from trees. The grey squirrel is also suspected to be a vector for the parapoxvirus which is fatal to red squirrels.
Feral pigs, Sus scrofa, are escaped or released domestic animals that are now found in many parts of the world. They cause significant damage to crops and property and transmit many diseases to domestic and wild animals. Pigs damage forests by eating or uprooting tree and plant seedlings and by opening tree-fern trunks in searching for starch (Atkinson and Atkinson, 2000). Pigs can spread alien invasive weeds by feeding on some species of fruit such as guava; the seeds pass through the gut and into droppings (Atkinson and Atkinson, 2000). They can also affect large native invertebrates, such as earthworms and land snails, through direct predation and habitat destruction (Atkinson and Atkinson, 2000). Pigs are very effective predators of seabirds such as albatrosses, shags and boobies (Atkinson and Atkinson, 2000). They are suspected to facilitate infestation of trees by the dieback disease caused by the fungus, Phytophthora cinnamomi (Atkinson and Atkinson, 2000).
The brushtail possum, Trichosurus vulpecula, is a solitary, nocturnal, arboreal marsupial from Australia that was introduced into New Zealand where it is causing considerable damage to native forests by selective feeding on foliage and fruits. Persistent possum browsing pressure can result in long-term changes in forest structure and composition (Courchamp, Chapuis and Pascal, 2003). This species also competes for tree hollows with endemic hole-nesting species, such as kiwi (Apteryx spp.), preys on invertebrates and the eggs and chicks of birds, and transmits bovine tuberculosis to cattle and deer (Courchamp, Chapuis and Pascal, 2003).
The red fox,Vulpes vulpes, is one of the most widely distributed carnivores in the world inhabiting agricultural areas, deserts, disturbed areas, natural and planted forests, rangelands and grasslands, riparian zones, scrublands and shrublands, tundra and urban areas. Native to Asia, Europe, North Africa and the boreal regions of North America, this species has been introduced into Australia and temperate regions of North America. Red foxes are generalist predators that attain relatively high densities and negatively impact many native species, including smaller canids and ground nesting birds in North America, and many small and medium-sized rodent and marsupial species in Australia (Kamler and Ballard, 2002). They also prey on livestock. In Canada, introduced red foxes may have already replaced several native subspecies of red foxes. They also pose a threat to the health of humans and domestic animals through the transmission of diseases such as rabies, distemper, parvo virus and mange.
Arundo donax is a tall perennial grass that has been widely introduced into riparian zones and wetlands in subtropical and temperate areas around the world. Considered native to the Indian subcontinent, the giant reed is now present in the Federated States of Micronesia, Fiji, Guam, Hawaii, Nauru, New Caledonia, Norfolk Island, Palau, Samoa and Christmas Island.
Once the reed becomes established, it forms impenetrable, homogenous stands which displaces native plant species and thus alters the habitat of native wildlife (Benton, Bell and Swearingen, undated). It is also both a fire and flood hazard. Giant reed traps sediments and narrows flood channels, leading to erosion and flooding, and promotes wildfire. It may also reduce water availability through high evapotranspiration rates.
Native to Southeast Asia, Imperata cylindrica, or cogongrass, can flourish in virtually all ecosystem types including degraded forests, grasslands, arable land and young plantations, in both temperate and tropical regions. It is a considerable nuisance species that displaces native plant species, disrupts the habits of wildlife, and alters natural fire cycles by causing more frequent and intense fires (van Loan, Meeker and Minno, 2002). The costs of controlling cogongrass amount to hundreds of millions of dollars annually.
Commonly called chromolaena, triffid weed or Siam weed, Chromolaena odorata is a fast-growing perennial shrub native to Central and South America that has been introduced into much of Africa, tropical Asia and the Pacific. An aggressive invasive weed, it forms dense stands which prevent the establishment of other species through competition and allelopathic effects. Chromolaena can be found in agricultural areas, disturbed areas, natural and planted forests, rangelands and grasslands, scrublands and shrublands, and riparian zones. In South Africa, it is considered a considerable threat to conservation and ecotourism, as it has primarily invaded natural areas, reducing the biodiversity of grasslands, savannahs and forests, and compromising game-viewing in nature reserves and national parks (Matthews and Brand, 2004). It has also been shown to threaten the breeding habitat of the Nile crocodile in South Africa and the decrease in temperature caused by the shading and crowding of nesting sites can induce female-biased sex ratios or may even prevent embryonic development altogether (Leslie and Spotila, 2001; Matthews and Brand, 2004). In Asia, chromolaena decreases agricultural productivity by readily invading subsistence food gardens, cultivated crops, and young or neglected plantations of cocoa, coconut, oil palm, rubber and tobacco (Matthews, 2004). This weed is a considerable problem in commercial tree plantations as it suppresses the growth of young pine and eucalypt trees and allows fire to penetrate deeper into plantations (Matthews, 2004; Matthews and Brand, 2004). It can also promote wildland fires (PIER, 2004a; Department of Natural Resources and Mines, 2005). Chromolaena may also cause skin problems and asthma in allergy-prone people.
Euphorbia esula or leafy spurge is perennial plant native to Europe and temperate Asia that can now be found throughout the world with the exception of Australia. It occurs in agricultural areas, disturbed areas, natural forest, rangelands and grasslands, scrublands and shrublands, and urban areas. E. esula is an aggressive invader that displaces native vegetation by shading sunlight, exhausting water and nutrient supplies and excreting toxins that prevent the growth of surrounding plants. Contact with the milky sap contained in leafy spurge can have impacts on human health ranging from minor skin irritations to blindness if the liquid reaches the eyes.
Planted in many parts of the world, Hedychium gardnerianum is a native plant of India that has escaped from gardens and can now be found in the Cook Islands, the Federated States of Micronesia, French Polynesia, Hawaii, Jamaica, New Zealand, Réunion and South Africa. It forms dense colonies in native forests that chokes understorey plants and prevents young native seedlings from establishing thus changing the function and structure of native forests and in some instances resulting in the death of the entire forest (Environment Bay of Plenty, 1998).
Mikania micrantha is a perennial, climbing plant that is commonly called the mile-a-minute weed because of its incredible growth rate. It grows best in areas with high fertility, organic matter, soil moisture and humidity. M. micrantha is a particular threat to young plantations and nurseries where it damages or kills other plants by blocking sunlight and suffocating them, by competing for water and nutrients, and by releasing substances that inhibit their growth (Matthews, 2004). The weed is especially problematic in tea crops in India and Indonesia and in rubber plantations in Malaysia and Sri Lanka (Matthews, 2004). It also causes serious problems in pastures and in oil palm, banana, cacao and forest plantations.
It its native habitat in Central and South America, M. micrantha grows in and near forests, and in riparian and disturbed areas. Widely introduced as a cover crop and garden ornamental, it has since spread readily due to its efficient reproduction and can now be found in Bangladesh, India, Indonesia, Malaysia, Mauritius, Papua New Guinea, the Philippines, Sri Lanka, Thailand and many of the Pacific islands (Matthews, 2004).
Pueraria montana var. lobata, commonly known as kudzu, is a semiwoody vine with a twining and trailing growth habit that forms dense infestations that covers the ground and trees. A native of Asia, kudzu has spread and established in temperate zones and higher altitudes in the tropics and can be found growing in almost all ecosystem types including agricultural areas, disturbed areas, natural and planted forests, rangelands and grasslands, riparian areas, scrublands and shrublands, and urban areas. In the eastern United States, kudzu has infested 2 to 3 million hectares of land costing approximately US$500 million per year in land productivity losses and control costs.
Native to the tropical areas of Central America, Sphagneticola trilobata is a creeping herb that has established in many wet tropical areas worldwide. Often planted as an ornamental plant and for groundcover, it can rapidly escape from gardens to roadsides, riparian areas, natural forests, grasslands, scrublands, and plantations where it forms a dense ground cover that crowds out and prevents regeneration of other plant species (PIER, 2004b). In plantations, it competes with crops for nutrients, light and water, and reduces crop yields.
Acacia mearnsii, commonly called black wattle, is a fast-growing, nitrogen-fixing tree often used as a commercial source of tannin and as a source of fuelwood and timber for local communities (Matthews and Brand, 2004). A serious threat to native habitats and species, this tree competes with indigenous vegetation, replaces grass communities, reduces native biodiversity and increases water loss from riparian zones. Native to Australia, black wattle can now be found in Africa, Asia and the Pacific, Europe, North America and South America. It occurs in disturbed areas, rangelands and grasslands, riparian areas, urban areas, and water courses.
Ardisia elliptica is a fast-growing, shade-tolerant evergreen tree that forms dense stands that prevent the establishment of other plant species. A popular ornamental plant because of its fast growth and attractive fruit, it spreads from gardens and readily invades moist disturbed forests and also undisturbed sites. A. elliptica is native to the west coast of India, Indonesia, Malaysia, New Guinea and Sri Lanka and has become established in southern Florida, Hawaii, Jamaica and Okinawa.
Cecropia peltata, commonly known as the trumpet tree, is native to tropical Central and South America and has been introduced to French Polynesia, Hawaii, Malaysia and West Africa where it has subsequently become invasive. It is known to spread and establish in disturbed areas, lava flows and forest gaps.
Cinchona pubescens is a widely planted tropical forest tree from Central and South America that has invaded a variety of forested and non-forested habitats in French Polynesia, the Galapagos Islands, Hawaii, St. Helena and Tanzania. Its fast growth, rapid spread and dense canopies result in a replacement of native vegetation in naturally treeless environments and a significant loss of species diversity of shrubs and herbs with very few species able to grow below the canopy in forests.
Clidemia hirta is a toxic weedy shrub from Central America that has been introduced to almost all tropical islands and Southeast Asia. An aggressive invader in rangelands and grasslands, scrublands and shrublands, disturbed areas and natural forests, it grows up to two metres tall forming almost impenetrable thickets which thus shade out all other vegetation (Wester and Wood, 1977).
A native of temperate and tropical Asia, Hiptage benghalensis is a high-climbing vine to large shrub that has been cultivated in the tropics as an ornamental and for medicinal purposes (GRIN-CA, 2002; Starr, Starr and Loope, 2003). It has been a problem species in parts of Australia and the United States and is considered an extremely invasive species on the Mascarene Islands. On the islands of Mauritius and Réunion, H. benghalensis flourishes in drier lowland forests and forms dense thickets that smother native vegetation and choke trees.
Widely grown as an ornamental shrub throughout tropical, subtropical and temperate zones, Lantana camara has established in these regions and become a major weed of pastures, roadsides, wastelands and plantations (Matthews, 2004; Matthews and Brand, 2004). L. camara has many beneficial uses: it is grown as a hedge plant; its stalks are used for paper pulp; its bark is used as an astringent; and its leaves are used for many medicinal purposes. It also has many negative impacts on the environments in which it invades including: decreases in pasture productivity; cattle can be poisoned when lantana is ingested; exclusion of understorey species; and changes in wildlife composition through the provision of perch sites and cover (Matthews, 2004; Matthews and Brand, 2004). Access problems are also often experienced which affects recreation and forest harvesting activities.
Leucaena leucocephala is a fast growing, nitrogen-fixing and drought-tolerant tree native to Mexico and Central America (Matthews, 2004; Matthews and Brand, 2004). Subspecies leucocephala was introduced to Asia over two centuries ago and is now established around the world (Matthews, 2004). Subspecies glabrata was widely introduced across the tropics in the 1970s and 1980s by agroforestry groups and organizations and is now widely cultivated throughout the tropics and subtropics (Matthews, 2004). Leucaena is considered a conflict tree because although it is invasive and destructive, it can also provide many positive benefits. Widely promoted as a miracle tree, leucaena has been planted for the provision of wood and non-wood products and for reforestation purposes.
Leucaena is spreading naturally and is considered a weed in more then 20 countries across all continents except Europe and Antarctica. It invades open, often coastal or riverine, habitats, disturbed sites and agricultural lands. It forms dense thickets which in some areas are replacing native forests and threatening endemic species of conservation concern. Such dense thickets also render extensive areas of land unusable and inaccessible, and once established the species is very difficult to eradicate.
Ligustrum robustum subspecies walkeri is native to Sri Lanka and is now present on all three of the Mascarene Islands – Mauritius, Réunion and Rodrigues (Lavergne, Rameau and Figier, 1999; Milne and Abbott, 2004). Commonly known as Sri Lankan privet, this species exhibits rapid growth rates, high tolerance to shade and high seedling recruitment, and depends on birds to distribute its seeds. It can invade primary forests which poses a serious threat to native ecosystems (Lavergne, Rameau and Figier, 1999). Its dense foliage reduces the amount of light reaching the forest floor and prevents the regeneration of light-demanding plants. L. robustum can also alter forest structure and composition by upsetting nutrient and water cycles and by competing with native species for space and nutrients, thus displacing them and affecting successional patterns.
The benefits of L. robustum are diverse which makes this a conflict species. In its native range, its stems are made into tool handles and the plant reduces erosion along streams and rivers. It was introduced into Rodrigues and Réunion as a hedge plant and into Mauritius as an ornamental plant as well as to protect conifer plantations from deer, provide firewood and control invasions of other invasive weeds (Lavergne, Rameau and Figier, 1999).
Melaleuca quinquenervia, commonly known as melaleuca or the paper bark tree, is native to Australia, New Caledonia and New Guinea. It was originally introduced into South Florida at the beginning of the twentieth century as an ornamental and to provide a useful crop capable of growing in an area subject to drought, flooding and periodic fires (Cock, 2003). It has since invaded across much of the state and has the potential to invade all of that region's wetlands within the next 50 years (OTA, 1993; FAO, 2000a). Melaleuca is rapidly degrading the wetlands system of the Florida Everglades by outcompeting indigenous plants and altering hydrology, topography and soils (OTA, 1993). Its dense impenetrable stands provide poor habitat and forage for wildlife and the altered hydrology has decreased populations of nesting wading birds and accelerated the proliferation and spread of alien fishes and aquatic plants (OTA, 1993). Melaleuca has also replaced sawgrass marshes, forests and other natural habitats (OTA, 1993).
Miconia calvescens is a small South American tree initially introduced into Hawaii and Tahiti as an ornamental that, facilitated by hurricanes, feral pigs and hikers, has subsequently invaded other areas. It invades the understorey of native rain forests, eventually growing through the canopy and suppressing native trees (Denslow, 2002). In Tahiti, M. calvescens has homogenized the landscape as Miconia stands replace native forest, create barren understoreys and facilitate erosion on steep slopes (Denslow, 2002). It has spread over several of the Hawaiian Islands and the state is now spending US$1.5 million per year to protect its native rain forests (Denslow, 2002).
Native to Mexico, Central and South America, Mimosa pigra has been introduced to Australia and many countries in both Africa and Asia. The giant mimosa is an aggressive woody shrub that grows rapidly, produces large quantities of seeds, and flourishes in both aquatic and terrestrial environments, allowing it to invade watercourses, floodplains and wetlands (Matthews, 2004). It forms impenetrable, prickly thickets up to four or five metres high which make invaded areas inaccessible to humans and wildlife, block irrigation channels, cause silting of dams, interfere with recreational uses of waterways, and create safety hazards along roadways.
In Northern Australia, M. pigra covers about 450 km2 of river floodplain and swamp forest and these thickets have been observed to contain fewer birds and lizards, less herbaceous vegetation and fewer tree seedlings than native areas free of this species. It also prevents traditional food gathering by Aborigines and threatens pastoral industries (Binggeli, 1997).
Morella faya, commonly called the fire tree, is native to the Azores, the Madeira Islands and the Canary Islands and has been introduced to Australia, New Zealand and the United States, including Hawaii. A fast growing tree whose dispersal is facilitated by introduced frugivorous birds, the fire tree rapidly forms dense stands and negatively impacts the recruitment and survival of native plant species in volcanic sites, agricultural areas, disturbed areas, forests and shrublands (Walker and Vitousek, 1991). Capable of fixing nitrogen, the fire tree has been shown to alter primary successional ecosystems by increasing nitrogen levels in the soils (Vitousek, 1990).
Native to the Mediterranean Basin, Pinus pinaster or maritime pine was widely planted in temperate regions within and outside its natural range for a variety of purposes. It readily regenerates almost everywhere it has been planted and has escaped and established in agricultural areas, disturbed areas, natural forests, rangelands and grasslands, riparian zones, scrublands and shrublands, and urban areas. After fire, it also regenerates profusely often resulting in dense thickets that suppress native plants, change fire regimes and hydrological properties, and alter wildlife habitats (van Wilgen et al., 2001).
Native to Brazil, Psidium cattleianum or strawberry guava, has been introduced into the Mascarene Islands, Norfolk Island, Polynesia and the United States (Florida). It occurs in agricultural areas, coastal areas, disturbed areas, natural and planted forests, rangelands and grasslands, riparian zones, scrublands and shrublands, urban areas and wetlands. Strawberry guava is a major threat to flora and fauna, especially rare and endemic species, by forming shade-casting thickets with dense mats of surface roots that make it difficult for other species to establish.
Rubus ellipticus is a prickly shrub, a wild raspberry, which invades natural forests, agricultural areas, disturbed areas, and rangelands and grasslands. It spreads vegetatively by way of underground shoots and the seeds are dispersed by frugivorous birds and mammals. Hawaii has faced many infestations and this species has displaced the native Hawaiian raspberry (Rubus hawaiiensis).
Native to Argentina, Paraguay and Brazil, Schinus terebinthifolius has invaded Mauritius, Norfolk Island, St. Helena, and the United States (Florida, Hawaii) (Cronk and Fuller, 1995). This tree, commonly called the Brazilian pepper tree, is a successful invader of both disturbed sites and undisturbed natural environments including forests. An aggressive weed, S. terebinthifolius displaces native vegetation and can also cause severe health and respiratory problems for humans (Kendle and Rose, 2001).
The African tulip tree, Spathodea campanulata, is an evergreen tree native to West Africa that has been widely planted throughout the tropics and has established in many parts of the Pacific including American Samoa, the Cook Islands, Fiji, Guam, Hawaii and Vanuatu. It invades agricultural areas, forest plantations and natural ecosystems where it smothers trees and crops and eventually displaces them.
Ulex europaeus, or gorse, is a spiny, perennial, evergreen shrub commonly found in disturbed areas, grasslands, shrublands, forest margins and coastal habitats. Once established, it is a very successful and persistent plant that forms dense and impenetrable thickets capable of displacing native plant and tree species. In British Columbia, Canada, for example, gorse represses the regrowth of the commercially important Douglas fir (Pseudotsuga menziesii) (FAO, 2000a).
