Invasive species

 

 

An invasive species is a species of animal, plant, or fungus, which is not native to a specific area, and which tends to spread beyond control, causing damage to the environment and often expelling native species. Most of these harmful species have been introduced by man, deliberately or accidentally. The term invasive is sometimes applied to native species, whose numbers increase to an extent that they become harmful to their environment. Three such examples are white-tailed deer (Odocoileus virginianus) in North America, and common broom (Cytisus scoparius) and bracken (Pteridium aquilinum) in Europe.

 

 

White-tailed Deer, Odocoileus virginianus, hind jumping over a fence, Great Smoky Mountains National Park, United States. Hind af Hvidhalet Hjort, Odocoileus virginianus, springer over et hegn, Great Smoky Mountains National Park, USA
The white-tailed deer (Odocoileus virginianus), a native of North and South America, has been introduced to several European countries, and in Finland it is now considered to be a pest, expelling native species of deer. In many parts of North America, it has now spread beyond control. As far back as 1949, Aldo Leopold wrote in A Sand County Almanac: “I now suspect that just as a deer herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer.” – In August 2012, The Bloomberg View published a staff editorial, entitled: ‘Deer Infestation Calls for Radical Free-Market Solution’. About two months later, The Wall Street Journal ran a story, entitled: ‘America Gone Wild’, noting the impact of overabundant deer. The Nature Conservancy then noted: “No native vertebrate species in the eastern United States has a more direct effect on habitat integrity than the white-tailed deer. (…) In many areas of the country, deer have changed the composition and structure of forests by preferentially feeding on select plant species.” – This hind is jumping over a fence in Great Smoky Mountains National Park, United States. (Photo copyright © by Kaj Halberg)

 

 

Taiwan 2018b
This species of bur-marigold, Bidens pilosa, is a pan-tropical and -subtropical weed of unknown origin, which in many places has become a pest, dispelling native species. In Taiwan, for instance, it covers huge areas, readily spreading by its hooked seeds, which has given it names like beggarticks and stickseed. – Taichung, Taiwan, January 17, 2013 Denne brøndsel-art, Bidens pilosa, er et pantropisk og -subtropisk ukrudt af ukendt oprindelse. Mange steder er den blevet en plage, som fordriver indfødte arter, fx i Taiwan, hvor den dækker kæmpestore områder. Arten spredes nemt ved hjælp af frøene, som har to kroge, der hægter sig fast i fx dyrepelse eller strømper. – Taichung, Taiwan, 17. januar 2013
Nepal 2009a
The downy bur-marigold (Bidens pilosa), also called blackjack, is a pan-tropical and -subtropical weed of unknown origin, which in many places has become a pest, expelling native species. One isolated plant can produce over 30,000 hooked seeds, which are readily spread by sticking to animals’ furs, socks, trousers, etc. These seeds have given it popular names like beggarticks, stickseed, cobbler’s pegs, duppy needles, farmer’s friend (ironic!), needle grass, Spanish needles, and stick-tight. This species is reported to be a weed of 31 crops in more than 40 countries, Latin America and eastern Africa having the worst infestations. (Source: cabi.org/isc/datasheet/9148) – The upper two pictures are from Taiwan, where downy bur-marigold covers huge areas, while the bottom picture, showing the hooked seeds, is from Pokhara, Nepal. (Photos copyright © by Kaj Halberg)

 

 

Taiwan 2012a
Balloon vine (Cardiospermum halicacabum) – also called heart pea or love-in-a-puff – is a climber, often covering huge areas. It is widely distributed in tropical and subtropical Africa and Asia, but has become naturalized in many other parts of the world. In New Zealand, where it is considered a pest, trading of its seeds is prohibited. Read more about this species on this website, see Traditional medicine: Cardiospermum halicacabum. – This picture shows a plant, growing in a dried-out riverbed in Taichung, Taiwan. (Photo copyright © by Kaj Halberg)

 

 

Jylland 1996-99
In an article, European Starlings: A Review of an Invasive Species with Far-Reaching Impacts, published in Managing Vertebrate Invasive Species: Proceedings of an International Symposium (USDA/APHIS/WS, National Wildlife Research Center, Fort Collins, Colorado, 2007), George M. Linz and others state the following: “The introduction of European starlings (Sturnus vulgaris) in New York City in 1890 and 1891 resulted in their permanent establishment in North America. The successful occupation of North America (and most other continents as well) has earned the starling a nomination in the Top 100 list of ‘Worlds Worst’ invaders. Pimentel et al. (2000) estimated that starling damage to agriculture crops in the United States was $800 million yearly, based on $5/ha damage. Starlings may spread infectious diseases that sicken humans and livestock, costing nearly $800 million in health treatment costs. Lastly, starlings perhaps have contributed to the decline of native cavity-nesting birds by usurping their nesting sites.” – This picture is from Denmark, where the starling is a native. Incidentally – as opposed to the situation in the United States – the species is declining in large parts of Europe, mainly because of persecution in its wintering areas. In later years, the species has begun to spend the night in cities, where it is considered a nuisance because of its droppings. It also does some damage on fruit trees and other crops. (Photo copyright © by Kaj Halberg)

 

 

USA-Canada 1992
The musk thistle, or nodding thistle (Carduus nutans), is native to parts of Eurasia and North Africa, but has spread to many other areas of the world. It grows in open areas, preferably on disturbed ground, such as agricultural areas (esp. fallow fields) and road sides. In the early 19th Century, musk thistle was introduced to North America, where it quickly became a nuisance in agricultural areas. It is declared a noxious weed in the U.S., Canada, Australia, New Zealand, and South Africa. – This picture was taken in Devil’s Tower National Park, Wyoming, United States. (Photo copyright © by Kaj Halberg)

 

 

Taiwan 2018
Taiwan 2012
The railroad creeper (Ipomoea cairica), also called coast morning-glory or mile-a-minute vine, is believed to be a native of Tropical Africa, but today it has a very wide distribution in tropical and subtropical areas around the world. This species is capable of very rapid growth, sometimes completely entwining trees and bushes, but it is also able to creep along the ground. It is regarded as an invasive in many areas, including eastern Australia, southern China, and Taiwan. These pictures are from Taiwan, where the species is extremely common. – Read more about this species and other members of the morning-glory family on this website, see Plants: The morning-glory family. (Photos copyright © by Kaj Halberg)

 

 

Traveller's Joy, Clematis vitalba, climbing on Noble Fir, Abies procera, Langeland, Funen, Denmark. Almindelig Skovranke, Clematis vitalba, klatrende på Nobilisgran, Abies procera, Langeland
Traveller’s joy (Clematis vitalba) is a climber with pretty, white flowers, which has been introduced into many countries. Due to its vitality, it has become naturalized in numerous areas, and is now listed as invasive in several countries, e.g. New Zealand, where it has been declared an ‘unwanted organism’. – This picture shows traveller’s joy, climbing over young noble firs (Abies procera) in a plantation in Denmark. (Photo copyright © by Kaj Halberg)

 

 

Myanmar 2007
The red-vented bulbul (Pycnonotus cafer) is a very common breeding bird in Pakistan, India, Nepal, Bangladesh, Sri Lanka, and Myanmar. It has been introduced to many other parts of the world and has become invasive in several Pacific countries, including Fiji, Samoa, Tonga, and Hawaii. It has also established itself in parts of southern Arabia, New Zealand, the United States, and Argentina. It is considered to be among the world’s one hundred worst invasive species (Lowe, Browne, Boudjelas, and de Poorter, 2000: 100 of the World’s Worst Invasive Species: A Selection from the Global Invasive Species Database. The Invasive Species Specialist Group, IUCN). – This picture is from Myanmar, where red-vented bulbul is indigenous. (Photo copyright © by Kaj Halberg)

 

 

Field bindweed (Convolvulus arvensis) – in America called 'Creeping Jenny' – is a Eurasian species, which is a troublesome weed in America and many other places. – Bornholm, Denmark, June 18, 2008 Ager-snerle (Convolvulus arvensis) – i USA kaldt 'Krybende Jenny' – er et besværligt ukrudt i Amerika og andre steder. – Sose Odde, Bornholm, 18. juni 2008
Field bindweed (Convolvulus arvensis) – in America also called ‘Creeping Jenny’ – is a Eurasian species, which twines around other plants to compete for sunlight and nutrients. It was probably accidentally introduced into North America around 1740. Today it is regarded as one of the world’s worst weeds (L.G. Holm, D.L. Plucknett, J.V. Pancho & J.P. Herberger, 1977. The World’s Worst Weeds. Distribution and Biology. University Press of Hawaii), invading agricultural fields and reducing crop yields by 20-80%. In 1998 alone, it was estimated that crop losses due to field bindweed in the U.S. exceeded US$ 377,000,000. This picture was taken on a beach – a natural habitat of the species – on the island of Bornholm, Denmark. – Read more about this plant, and many other members of the morning-glory family, on this website, see Plants: The morning-glory family. (Photo copyright © by Kaj Halberg)

 

 

An American plant, the horsetail fleabane (Conyza canadensis), has become a troublesome weed in Europe, especially in newly established coniferous plantations, where it is able to resist herbicides, growing to three metres tall. – Jutland, Denmark, August 22, 2012 En amerikansk plante, canadisk bakkestjerne (Conyza canadensis), er blevet et yderst besværligt ukrudt i Europa, specielt i nyanlagte granplantager, hvor den modstår sprøjtemidler og kan blive op til 3 m høj. – Laven, Jylland, 22. august 2012
Canadian fleabane (Conyza canadensis) – also called horsetail fleabane – is a native of North America and parts of Central America. It has been accidentally introduced to large parts of the world, in many places becoming a serious pest, especially in Europe and Australia, but also in its native North America. It prefers to grow in undisturbed areas and is particularly troublesome in newly established plantations, where it is able to resist herbicides, growing to three metres tall, thus depriving planted species of nutrients and sunlight. The plant contains an oil with a turpentine-like smell, which, supposedly, should deter fleas, hence its common name. Another popular name of this species is bloodstanch, given by herbalists, who claim that an extract from leaves and flowers arrests haemorrhages from the lungs and alimentary tract. – This picture is from Denmark, where horsetail fleabane is a serious pest in young coniferous plantations. (Photo copyright © by Kaj Halberg)

 

 

Bornholm 2016a
The European rabbit (Oryctolagus cuniculus) has been introduced to many countries as a hunting object. It was first brought to Britain by the Romans, following their invasion in A.D. 43, and today it is extremely common – an estimate in 2004 suggested about 40 million. In Australia, 24 European rabbits were introduced in Victoria in 1859. The vast farmlands were an ideal habitat for the rabbits, and the mild winters allowed them to breed year-round, so they quickly spread over most of the country. Australia’s equivalent to the rabbit, the greater bilby (Macrotis lagotis), could not compete with the fast-breeding rabbits, and today it is an endangered species. Other places of introduction include New Zealand, certain Hawaiian islands, and islands off the coast of South Africa. There are also many instances of pet rabbits, which have escaped, forming feral populations. In countless cases, the species has done severe damage to the environment, partly through overgrazing, partly through its system of underground tunnels, and partly through competition with local wildlife. In most countries, it is regarded as an invasive species. – The picture shows a dark rabbit (probably having genes from escaped pets) on the island of Bornholm, Denmark, nibbling at a flower of common broom (Cytisus scoparius). (Photo copyright © by Kaj Halberg)

 

 

Cultivated varieties of the common broom (Cytisus scoparius) are spreading over large parts of Europe, genetically polluting the natural varieties of this species. – Hammerknuden, Bornholm, Denmark, June 2, 2008 Dyrkede former af gyvel (Cytisus scoparius) spreder sig kraftigt over store områder i Europa, hvor de forurener de naturligt forekommende varieteter af denne art genetisk. – Hammerknuden, Bornholm, 2. juni 2008
Cultivated varieties of the common broom (Cytisus scoparius) are spreading over large parts of Europe, genetically polluting the natural varieties of this species. The picture also shows another alien invasive plant, the large-leaved lupine (Lupinus polyphyllus). – Sønder Vosborg Hede, Jutland, Denmark, June 29, 2015 Dyrkede former af gyvel (Cytisus scoparius) spreder sig kraftigt over store områder i Europa, hvor de forurener de naturligt forekommende varieteter af denne art genetisk. På billedet ses også en anden invasiv art, mangebladet lupin (Lupinus polyphyllus). – Tidligere hede nær Sønder Vosborg Hede, Jylland, 29. juni 2015
Jylland 2013-15
Cultivated varieties of the common broom (Cytisus scoparius) are spreading over large parts of Europe. In Denmark, for instance, many moors are invaded by this species, here on Hammerknuden, Bornholm (top), and on Sønder Vosborg Hede, Jutland (centre). – Genetically, introduced forms of common broom pollute the original, low and creeping variety of broom. Today, in Denmark, this form is only found in a few moors and dunes in western Jutland (bottom). – The picture in the centre also shows another alien invasive plant, the large-leaved lupine (Lupinus polyphyllus), from America. – Read more about common broom on this website, see Traditional medicine: Cytisus scoparius. (Photos copyright © by Kaj Halberg)

 

 

Flowering common cock's-foot (Dactylis glomerata), Cades Cove, Great Smoky Mountains National Park, Appalachians, Tennessee, United States. This species is invasive in many parts of America. – May 16, 2012 Blomstrende almindelig hundegræs (Dactylis glomerata), Cades Cove, Great Smoky Mountains National Park, Appalachians, Tennessee, USA. Denne art er invasiv i mange egne af Nordamerika. – 16. maj 2012
Common cock’s-foot (Dactylis glomerata) is indigenous to most of Europe, temperate parts of Asia, and northern Africa. Emigrants from Europe introduced the species as a pasture grass to many countries, notably the United States, Canada, Australia, and New Zealand. However, it easily spreads into natural plant communities, and in Australia, for instance, it has now become an invasive in heathlands, open woodlands, forests, and along rivers and wetlands, forming dense growths which dispel native flora. In the U.S., it has been characterized as “a desirable pasture grass, but it has escaped cultivation in many natural areas throughout the United States.” – This flowering common cock’s-foot was photographed in Great Smoky Mountains National Park, Tennessee. (Photo copyright © by Kaj Halberg)

 

 

Grazing Canada Geese, Branta canadensis, being a nuisance on a golf course, Glen Cove, Long Island, United States. Græssende Canadagæs, Branta canadensis, er en plage på mange golfbaner, Glen Cove, Long Island, USA
The Canada goose (Branta canadensis) is native to northern North America, but has been introduced to Britain, Sweden, New Zealand, Argentina and other places. Canada geese are very bold, and the species has been able to establish populations in urban areas, where it has no natural predators. In many areas, it has been declared a pest because of its noise, droppings and aggressive behaviour. – This picture is from a golf course on Long Island, United States. (Photo copyright © by Kaj Halberg)

 

 

Nepal 2009-2
Sydindien 1997-98
The pretty water hyacinth (Eichhornia crassipes) has invaded most tropical freshwater bodies outside its native South America, being a serious threat to the natural ecology, as it clogs water channels and lakes. In this picture, people are removing water hyacinth from a waterhole in Keoladeo National Park, Rajasthan, India, April 4, 1979 Den smukke vandhyacint (Eichhornia crassipes) har invaderet de fleste tropiske ferskvandsarealer uden for sit oprindelsesområde i Sydamerika. Arten er en alvorlig trussel mod de økologiske forhold, da den blokerer for vandstrømmen i vandløb og søer. På dette billede fjerner folk vandhyacinter fra et vandhul i Keoladeo Nationalpark, Rajasthan, Indien, 4. april 1979
The water hyacinth (Eichhornia crassipes) has pretty flowers (top), and from its native South America it has been introduced as an ornamental to many tropical and subtropical countries. Almost everywhere it has escaped cultivation, invading countless streams and lakes. Through its massive vegetative growth, it blocks the free flow of water, thus being a serious threat to the natural ecology, as in this picture, where it covers the entire surface of a lake near Rajnagar, Odisha (Orissa), India (centre). In Keoladeo National Park, Rajasthan, India, these people are removing water hyacinth from a waterhole (bottom). (Photos copyright © by Kaj Halberg)

 

 

The eastern gray squirrel (Sciurus carolinensis) is the most widespread squirrel in North America. It has also been successfully introduced to South Africa, Britain, and other places. In Britain, it has become a pest, as it competes with the native European red squirrel (S. sciurus), which is now scarce south of Scotland. – Kew Botanical Gardens, London, September 5, 1992 Det østlige gråegern (Sciurus carolinensis) er den egernart i Nordamerika, som har den største udbredelse. Arten er også blevet indført med succes til Sydafrika, England og andre steder. I England regnes den som et skadedyr, idet den udkonkurrerer det europæiske røde egern (S. sciurus), som nu er meget sjældent syd for Skotland. – Kew Botaniske Have, London, 5. september 1992
The eastern grey squirrel (Sciurus carolinensis) is the most widespread squirrel in North America. It has also been successfully introduced to South Africa, Britain, and other places. In Britain, it has become a pest, as it competes with the native European red squirrel (Sciurus vulgaris), which is now scarce south of Scotland. – Kew Botanical Gardens, London. – Read more about the eastern grey squirrel and other North American squirrels on this website, see Animals: Squirrels of North America. (Photo copyright © by Kaj Halberg)

 

 

Couch grass (Elytrigia repens) in evening sun, Jutland, Denmark Almindelig kvik (Elytrigia repens) i aftensol, Vorsø, Horsens Fjord
Couch grass (Elytrigia repens, also called Elymus repens), which is a native of Eurasia and north-western Africa, is a very troublesome weed in fields and gardens. Just a tiny bit of underground stem is able to produce a large colony of plants, sending up stems at regular intervals. Couch grass has become naturalized in North America, where it is considered to be invasive. Read more about this species on this website, see Traditional medicine: Elytrigia repens. – The picture shows couch grass in evening light, growing in a natural habitat of this species: a sandy beach in Jutland, Denmark. (Photo copyright © by Kaj Halberg)

 

 

USA 2016
In many parts of the Eastern and Northwestern United States, and in Canada, the lesser celandine (Ranunculus ficaria) – a native of Europe and western Asia – is an invasive, which has expelled native species in huge tracts of forest. – This picture is from Shu Swamp Preserve, Long Island, United States. In the foreground leaves of eastern skunk cabbage (Symplocarpus foetidus). (Photo copyright © by Kaj Halberg)

 

 

Himalayan Tahr, Hemitragus jemlahicus, Shomare, Khumbu, Nepal
The Himalayan tahr (Hemitragus jemlahicus) is a species of wild goat, which lives in the temperate zone of the Himalaya. This animal has been introduced to other parts of the world, e.g. New Zealand and South Africa, as a hunting object. But in these countries, numbers of tahrs have exploded, as they have no natural enemies there. The species has become a serious threat to the local environment through overgrazing. – This picture of grazing bucks was taken in the Khumbu area, E Nepal. (Photo copyright © by Kaj Halberg)

 

 

Seeds and autumn leaves of Variegated Japanese Knotweed, Fallopia japonica, Jutland, Denmark. Efterårsløv og frøstande hos Japansk Kæmpe-Pileurt, Fallopia japonica, Brabrand Sø, Jylland
Variegated Japanese knotweed (Fallopia japonica) – which is also known under the scientific names Reynoutria japonica and Polygonum cuspidatum – was introduced into Europe and North America in the 1800s. It soon became a popular garden plant because of its bamboo-like appearance, vigorous growth, and pretty inflorescences. However, it quickly became a menace, as it spread beyond control, its strong root system being able to “damage concrete foundations, buildings, flood defences, roads, paving, retaining walls and architectural sites.” (cited from gardenroots.co.uk). It is listed by the World Conservation Union as one of the world’s worst invasive species. – This picture shows seeds and autumn leaves, photographed in Denmark. (Photo copyright © by Kaj Halberg)

 

 

Large growth of Giant Hogweed, Heracleum mantegazzianum, Østerild Fjord, Thy, Denmark. Note the person. Stor bevoksning af Kæmpe-Bjørneklo, Heracleum mantegazzianum, Østerild Fjord, Thy. Bemærk personen
Giant hogweed, or giant cow-parsley (Heracleum mantegazzianum, also known as H. pubescens) is native to the Caucasus Mountains and Central Asia. In the 1800s, it was introduced as an ornamental to Europe, and later to the United States and Canada. It has become naturalized in many areas, especially wetlands, and due to its vigorous growth it often expels native species. Furthermore, its sap is toxic to the human skin, causing inflammation and blisters. In many countries, its spreading is inhibited by using herbicides – the only known efficient means to control this species. – Where undisturbed, giant hogweed grows to huge dimensions – note the person in the centre of this growth. (Photo copyright © by Kaj Halberg)

 

 

Coypu, Myocastor coypus, sitting on its nest, Lac de Grand Lieu, Loire Atlantique, France. Sumpbæver, Myocastor coypus, på sit bo, Lac de Grand Lieu, Loire Atlantique, Frankrig
The nutria, or coypu (Myocastor coypus), is native to South America, but was introduced to North America and Europe for fur production. Over the years, numerous animals have escaped, and the species has become naturalized in many places. They are considered a pest, as they compete with – and sometimes expel – native species, erode river banks, destroy irrigation channels, and chew up house panels etc. – This coypu is sitting on its nest in Lac de Grand Lieu, Loire Atlantique, France. (Photo copyright © by Kaj Halberg)

 

 

Himalayan Balsam, Impatiens glandulifera, Sissu, Lahaul, Himachal Pradesh, India. Kæmpe-Balsamin, Impatiens glandulifera, Sissu, Lahaul, Himachal Pradesh, Indien
Himalayan balsam (Impatiens glandulifera), a native of the Himalaya and Central Asia, was introduced to Europe and North America as an ornamental in the 1800s, but has since then become invasive in many countries, especially in Britain, where it is a menace along many rivers. Under the Alberta Weed Control Act 2010, it is characterized as a ‘prohibited noxious weed’. – This picture was taken in Lahaul, Himachal Pradesh, India, where the species is indigenous. (Photo copyright © by Kaj Halberg)

 

 

Japanese silverberry (Elaeagnus umbellata), Washington, New Jersey, United States Japansk sølvblad (Elaeagnus umbellata), Washington, New Jersey, USA
Japanese silverberry (Elaeagnus umbellata) – also called autumn olive – is indigenous to East Asia, from the Himalaya to Japan. As early as c. 1830, it was introduced into the United States. In the 1950s, it was widely promoted as a splendid species to control erosion in environmentally disturbed areas, at the same time providing food for wildlife. However, it soon became an invasive species, displacing native sun-loving plants by creating dense shade. One bush can produce up to 200,000 seeds a year, and its nitrogen-fixing root nodules allows it to grow in even the poorest soils. Attempts to remove bushes by cutting and/or burning are in vain, as it easily sprouts from its roots. Birds devour the seeds, thus aiding in the spreading of the species. Under the Alberta Weed Control Act of 2010, Japanese silverberry is characterized as a ‘prohibited noxious weed’. – This picture was taken in New Jersey. (Photo copyright © by Kaj Halberg)

 

 

Nordindien 1985-86
Crab’s eye (Abrus precatorius) has many other popular names, most of them referring to its colourful seeds. This shrub is possibly a native of India, but was introduced early into many other areas. Today, it has a pan-tropical and -subtropical distribution, and in many areas, e.g. Belize, West Indies, United States, Hawaii, and Polynesia, it is proclaimed an invasive weed. – Read more about this species on this website, see Traditional medicine: Abrus precatorius. (Photo copyright © by Kaj Halberg)

 

 

Taiwan 2008
Taiwan 2018
The white leadtree (Leucaena leucocephala), also called white popinac, is a member of the Mimosoideae, a subfamily of the huge pea family (Fabaceae). It is native to southern Mexico and parts of Central America, but has become naturalized throughout the tropics and parts of the subtropics. White leadtree is a prolific species, forming dense growths, often dispelling native vegetation. It is regarded as an invasive in numerous countries, e.g. Taiwan, Hong Kong, several Pacific islands, northern Australia, southern United States, Puerto Rico, and parts of Europe and South America. By the Invasive Species Specialist Group (IUCN) it is considered to be among the world’s one hundred worst invasive species. – Both pictures were taken in Taiwan, where white leadtree is extremely common. (Photos copyright © by Kaj Halberg)

 

 

Raccoon, Procyon lotor, coming to a house at night to feed, Long Island, New York State, USA. Vaskebjørn, Procyon lotor, ved fuglefoderplads om natten, Long Island, New York State, USA
The raccoon (Procyon lotor) has become naturalized and invasive in large parts of Europe, and in Japan. In many places, it is regarded as a pest, plundering birds’ nests and competing with local mammals. In America, it is a nuisance in urban areas, as it will turn over garbage cans, looking for food, and spread the garbage over large areas. It also consumes food at bird feeders, if the food is not being placed out of reach. – This raccoon has come to a house at night, eating from a dog’s feeding bowl, Long Island, United States. (Photo copyright © by Kaj Halberg)

 

 

The common gorse (Ulex europaeus) is a West European species, which has become a serious pest in many countries around the world. – Tomales Bay, California, United States, February 25, 2013 Tornblad (Ulex europaeus) er en vesteuropæisk plante, som er et alvorligt problem mange steder i verden. – Tomales Bay, Californien, USA, 25. februar 2013
Californien 2011a
The common gorse (Ulex europaeus) is a European species, which has been introduced to many other areas around the world, including North and South America, South Africa, Australia, and New Zealand. It spreads easily and has become invasive in numerous areas, notably the western United States, New Zealand, Sri Lanka, and Chile. To some extent, its spreading can be controlled by the gorse spider mite (Tetranychus lintearius) and the gorse seed weevil (Exapion ulicis). – These pictures were taken in California, in Tomales Bay (top) and Jughandle State Park. (Photos copyright © by Kaj Halberg)

 

 

Large growth of lesser periwinkle (Vinca minor), Oyster Bay Cove, Long Island, United States Stor bestand af liden singrøn (Vinca minor), Oyster Bay Cove, Long Island, USA
The lesser periwinkle (Vinca minor) of Europe was first introduced into North America in the 1700s as an ornamental. In many places throughout the eastern U.S., it has escaped cultivation and is invading natural areas, displacing native species. – In this picture, it is covering the entire forest floor of a copse in Oyster Bay Cove, Long Island. (Photo copyright © by Kaj Halberg)

 

 

Brown rat (Rattus norvegicus), caught in a trap, Vorsø, Horsens Fjord, Denmark Brun rotte (Rattus norvegicus), fanget i en fælde, Vorsø, Horsens Fjord
The brown rat (Rattus norvegicus) originated somewhere in Asia, but has spread with humans to almost all parts of the world. It is a serious pest, as it competes with native mammalian species, raids birds’ nests, and consumes huge amounts of cereals and other food items. Furthermore, it spreads various diseases among humans. During the Middle Ages, fleas of the brown rat were carrying bubonic plague, which in some places reduced the human population by 50 to 75%. This much feared disease was aptly named ‘The Black Death’. – The picture shows a brown rat, caught in a trap, Nature Reserve Vorsø, Denmark. (Photo copyright © by Kaj Halberg)

 

 

Japanese honeysuckle (Lonicera japonica) is invasive in large parts of eastern North America. – Cades Cove, Great Smoky Mountains National Park, Tennessee, United States, May 16, 2012 Japansk gedeblad (Lonicera japonica) er invasiv i mange egne af det østlige Nordamerika. – Cades Cove, Great Smoky Mountains Nationalpark, Tennessee, USA, 16. maj 2012
Japanese honeysuckle (Lonicera japonica) is a climber, which is native to eastern Asia, including China, Taiwan, Japan and Korea. It has been imported into many countries as an ornamental, but has become naturalized in e.g. the United States, Mexico, Brazil, Argentina, Australia, New Zealand, as well as a number of Pacific and Caribbean islands. Due to its vigorous growth, and the production of numerous seeds, it is extremely difficult to control. In many U.S. states, it is classified as a noxious weed, and it is banned in New Hampshire. In New Zealand, the National Pest Plant Accord has declared Japanese honeysuckle an unwanted organism. – This picture was taken in Great Smoky Mountains National Park, Tennessee. (Photo copyright © by Kaj Halberg)

 

 

 

A pair of Egyptian Goose, Alopochen aegyptiacus, grazing on a camp ground, Daan Viljoen National Park, Namibia. Et par af Nilgås, Alopochen aegyptiacus, græsser på en campingplads, Daan Viljoen National Park, Namibia
The Egyptian Goose (Alopochen aegyptiacus), a native of Africa south of the Sahara, was introduced to Britain in the 1700s, and later to other European countries. It has become naturalized in many areas, where it competes with indigenous geese and ducks. It was officially declared a pest in the U.K. in 2009. – Egyptian geese often become very confiding and bold. This picture was taken in a campground in Namibia. (Photo copyright © by Kaj Halberg)

 

 

Alperne 2016
A native of western North America, the large-leaved lupine (Lupinus polyphyllus) is a pretty garden plant, which readily escapes cultivation, forming large growths. It is regarded as an invasive species in many countries, e.g. New Zealand, Finland, Norway, Switzerland, Czech Republic, and Lithuania. – In this picture, it has taken over a large clearing in a forest near Sankt Peter am Kammersberg, Austria. (Photo copyright © by Kaj Halberg)

 

 

The alien red iceplant (Malephora crocea) has established itself on numerous beaches along the American Pacific Coast. – Border State Park, S of San Diego, California, March 12, 2013 Den invasive røde isplante (Malephora crocea) har etableret sig på mange strande i det vestlige USA. – Border State Park, syd for San Diego, Californien, 12. marts 2013
The red iceplant (Malephora crocea) is native to southern Africa, but has been introduced elsewhere as an ornamental. It is also widely planted along highways in California in areas prone to fire, as its succulent leaves do not easily catch fire. However, on numerous beaches in California and Baja California it has become a noxious weed, covering large areas. This picture is from Border State Park, south of San Diego, California. (Photo copyright © by Kaj Halberg)

 

 

Small Asian Mongoose, Herpestes javanicus, Keoladeo National Park, Rajasthan, India. Guldmangust, Herpestes javanicus, Keoladeo National Park, Rajasthan, Indien
To control populations of rats and other rodents, the small Asian mongoose (Herpestes javanicus) has been introduced to many parts of the world, mostly small islands. In most localities, however, the species has had negative impact on ground-nesting birds, and it is often able to outcompete smaller local carnivores. It is considered to be among the world’s one hundred worst invasive species (International Union for Conservation of Nature, 2000). – The picture is from Keoladeo National Park, Rajasthan, India. (Photo copyright © by Kaj Halberg)

 

 

Taiwan 2014b
Taiwan 2018
Persian lilac, or Chinaberry (Melia azedarach), is probably native to Iran and the Indian Subcontinent, but due to its beautiful flowers and fruits it has been widely planted elsewhere. It readily spreads and has become an invasive in e.g. North America, East Africa, some Pacific Islands, New Zealand, and Australia. – Both pictures are from Taiwan, where the species is commonly planted. (Photos copyright © by Kaj Halberg)

 

 

Little boy with a young Mink, Mustela vison, about 10 days old, Adaldal, Iceland. Lille dreng med en unge af Mink, Mustela vison, ca. 10 dage gammel, Adaldal, Island
The American mink (Neovison vison) is a semi-aquatic North American mustelid, which has been introduced in many parts of the world for fur production. In countless places it has escaped, and has become a serious threat to the native fauna, as it is a notorious predator of birds’ eggs. It is also blamed for the serious decline in populations of e.g. European mink (Mustela lutreola), Pyrenean desman (Galemys pyrenaicus), and European water vole (Arvicola amphibius). – This picture is from Iceland, where teams of professional ‘mink hunters’ control mink numbers by locating as many dens as possible, removing the young and, if possible, kill the mother. (Photo copyright © by Kaj Halberg)

 

 

The invasive African wood-sorrel (Oxalis pes-caprae) is a serious pest in many countries. – Cape San Martin, California, United States, February 21, 2013 Den invasive afrikanske surkløver (Oxalis pes-caprae) er en alvorlig plage i mange lande. – Cape San Martin, Californien, USA, 21. februar 2013
The invasive African wood-sorrel (Oxalis pes-caprae) has displaced natural vegetation on a littoral meadow, Cape San Martin, California, United States, February 21, 2013 Den invasive afrikanske surkløver (Oxalis pes-caprae) har fordrevet naturlig vegetation på en strandeng, Cape San Martin, Californien, USA, 21. februar 2013
African wood-sorrel (Oxalis pes-caprae) is a native of South Africa, but has been accidentally introduced to many corners of the planet. It is regarded as an invasive in e.g. North America, Israel, Australia, and several European countries. In this picture (bottom), it has displaced the natural vegetation on a littoral meadow, near Cape San Martin, California, United States. (Photos copyright © by Kaj Halberg)

 

 

Østafrika 1994-95
In Ancient Egypt, the sacred ibis (Threskiornis aethiopicus) was venerated as a symbol of the god of knowledge, Thoth, which is often depicted with the head of an ibis. Today, the sacred ibis is a common and popular species in zoological gardens worldwide. It often escapes, and populations in the wild have been established in e.g. France, Italy, Spain, the Canary Islands, Florida, and Taiwan. These populations are a great threat to many other birds, which breed in colonies. Ibises are predators, which can ravage e.g. colonies of terns by eating their eggs and young, and they also compete for nest sites with e.g. cattle egret (Bubulcus ibis) and little egret (Egretta garzetta). – The sacred ibis is very common in East Africa. This picture is from the Ngorongoro Crater, Tanzania. (Photo copyright © by Kaj Halberg)

 

 

USA 2012
Black cherry (Prunus serotina) – a native of North America – has been widely planted in Europe, and also in South Africa. It readily grows in shady places, thus being able to spread easily. In many European countries the species has become an invasive, and in threatened habitats like moors and grasslands it is a threat to indigenous plant species. Leaves and bark are toxic, and in South Africa black cherry is considered a leading cause of livestock illness. – This picture was taken at Cape May, New Jersey, United States. (Photo copyright © by Kaj Halberg)

 

 

Man, hand-feeding house sparrows (Passer domesticus), St. James' Park, London, June 2, 1993 Mand håndfodrer gråspurve (Passer domesticus), St. James' Park, London, 2. juni 1993
The house sparrow (Passer domesticus) was introduced to North America several times between 1851 and 1875, as it was thought it could control populations of harmful insects in cereal crops. However, the sparrows only catch insects when feeding their young, the rest of the year eating the very crops they were supposed to protect. Today, the house sparrow is found in most parts of North America, being a serious crop raider, and also competing with native passerines at bird feeders etc. – This man is hand-feeding house sparrows in St. James’ Park, London. (Photo copyright © by Kaj Halberg)

 

 

Tanzania 1989
Jylland 2016
Bracken (Pteridium aquilinum) has an almost cosmopolitan distribution, found in most temperate and subtropical regions of the world. Areas, which has been utilized for farming or grazing, and then abandoned, are readily invaded by bracken, which can cover huge areas, hindering growth of other species. – The upper picture shows a mountain top north of Songea, Tanzania, on which the forest has been felled, the clearing completely taken over by bracken. On the lower picture, brackens – despite being withered – almost hide young conifers in a plantation, Jutland, Denmark. (Photos copyright © by Kaj Halberg)

 

 

Taiwan 2014d
Taiwan 2012
The kudzu vine, or Japanese arrowroot (Pueraria montana ssp. lobata), a native of eastern Asia, was introduced to the United States in 1876 as a means to curb soil erosion. In the 1930s and 1940s, it was cultivated in an area covering more than a million acres. However, it soon escaped, spreading along roadsides to most of the eastern and south-eastern states, and also to southern Canada. It grows vigorously, often completely enveloping indigenous vegetation and over time suffocating it. Today, kudzu is regarded as a serious pest in e.g. the U.S. and New Zealand, and in New Zealand it has been declared an ‘unwanted organism’. Kudzu is widely used in Chinese traditional medicine, see elsewhere on this website, Traditional medicine: Pueraria montana ssp. lobata. – These pictures are from Taiwan, where kudzu is a native species. (Photos copyright © by Kaj Halberg)

 

 

USA 2012
Tall buttercup (Ranunculus acris) is native to temperate Eurasia, and to Greenland and Alaska. This species has been introduced accidentally by humans to many other parts of the world, and in North America (other than Alaska) it is regarded as an invasive. – The picture shows a horse, grazing in a field covered in tall buttercup, Maryland, United States. (Photo copyright © by Kaj Halberg)

 

 

Jylland 2016
The garlic mustard (Alliaria petiolata), a native of Eurasia and North Africa, was introduced to North America as a spice herb around 1860. Since then it has spread to most of the states of the U.S., and to Canada as well. Its natural enemies of the Old World, such as fungi and insects, are not present in North America, which leads to a much higher seed production. The garlic mustard has invaded numerous forests, where it is able to dominate the understorey, hereby expelling native plants. It is listed as a noxious species in at least nine American states. – This picture was taken in Denmark, where the species is native, but nevertheless has also been expanding during the last fifty years. The plant with the red flowers is red campion (Silene dioica). (Photo copyright © by Kaj Halberg)

 

 

The alien hottentot fig (Carpobrotis edulis) has established itself on numerous beaches along the American Pacific Coast. – Mac Kerricher State Park, California, United States, February 27, 2013 Den invasive gule middagsblomst (Carpobrotis edulis) har etableret sig på mange strande i det vestlige USA. – Mac Kerricher State Park, Californien, USA, 27. februar 2013
The hottentot fig (Carpobrotis edulis), a native of South Africa, has established itself on numerous coasts, especially around the Mediterranean, along the American Pacific coasts, and in Australia, where it covers huge areas, expelling native species. – This picture is from Mac Kerricher State Park, California. (Photo copyright © by Kaj Halberg)

 

 

Nepal 2009-2
Taiwan 2012a
Goat-weed (Ageratum conyzoides, top) and Mexican blueweed (A. houstonianum) are native to Central and South America, but have become naturalized worldwide in tropical and subtropical areas. Both are regarded as invasive weeds in numerous countries around the world, in Africa, Southeast Asia, China, Japan, Australia, New Zealand, and the United States. More about these two species is found on this website, see Traditional medicine: Ageratum. – Goat-weed was photographed in the Marsyangdi Valley, central Nepal, Mexican blueweed in Taiwan. (Photos copyright © by Kaj Halberg)

 

 

Taiwan 2018c
Taiwan 2018a
The Javan, or white-vented, myna (Acridotheres javanicus) has been introduced to numerous countries as a cage bird, escaping in many places to form wild populations. Two such places are Singapore and Taiwan, where Javan myna today is very common, competing with local species, in Taiwan with e.g. the native crested myna (A. cristatellus), which has become rare. – These pictures of Javan mynas are from the city of Taichung, Taiwan. The upper picture shows a bird, feeding in a flower of a silk-cotton tree (Bombax ceiba) in Tunghai University Park, while the bird in the lower picture is sitting in front of a water tower. (Photos copyright © by Kaj Halberg)

 

 

USA 2012a
USA 1998-99
An invasive climber, Oriental bittersweet (Celastrus orbiculatus), engulfing two conifers, Lenox, Massachusetts, United States. In the background autumn forest with e.g. sugar maple (Acer saccharum). – October 15, 1998 En invasiv klatreplante ved navn rundbladet celaster (Celastrus orbiculatus) omslynger to nåletræer, Lenox, Massachusetts, USA. I baggrunden efterårsskov med bl.a. sukkerløn (Acer saccharum). – 15. oktober 1998
Oriental bittersweet (Celastrus orbiculatus) is a climber, which is native to eastern Asia. It was introduced to North America from China around 1860 as an ornamental, but has since escaped cultivation and become widely naturalized. In the eastern part of the continent, it is a menace, affecting the ecology in about 33 states. Birds and other animals relish its fruits, which has contributed to its spreading. It closely resembles the native American bittersweet (C. scandens), with which it readily hybridizes, thus threatening the existence of this local species. – The bottom picture shows oriental bittersweet, enveloping two conifers near Lenox, Massachusetts. Autumn forest with e.g. sugar maple (Acer saccharum) is seen in the background. (Photos copyright © by Kaj Halberg)

 

 

The radish (Raphanus sativus var. radicula) has spread from cultivation and is now considered a pest in many parts of North America. – Montaña de Oro State Park, California, February 20, 2013 Radis (Raphanus sativus var. radicula) har spredt sig fra dyrkning og betragtes nu som en invasiv art i mange egne af Nordamerika. – Montaña de Oro State Park, Californien, 20. februar 2013
The radish (Raphanus sativus var. radicula) has spread from cultivation and is now considered a pest in many parts of North America. – Montaña de Oro State Park, California. (Photo copyright © by Kaj Halberg)

 

 

Due to its creeping underground stems, the creeping thistle (Cirsium arvense) – in America called 'Canada thistle' – is a Eurasian species, which is a very troublesome weed in most cooler parts of the World. Just a tiny bit of underground stem is able to produce a large colony of plants, sending up stems at regular intervals. – Jutland, Denmark, July 12, 2013 På grund af sine underjordiske udløbere er ager-tidsel (Cirsium arvense) et yderst besværligt ukrudt i de fleste kølige egne af kloden. Blot en lille stump af den underjordiske stængel kan producere en stor koloni af planter ved at sende stængler op med regelmæssige mellemrum. – Skanderborg, Jylland, 12. juli 2013
Sjælland_2017_065
Due to its numerous creeping underground stems, the Eurasian creeping thistle (Cirsium arvense) – in America called ‘Canada thistle’ – is a most troublesome weed in most cooler parts of the World. Just a tiny bit of underground stem is able to produce a large colony of plants, sending up stems at regular intervals. In his delightful book All about Weeds, American botanist Edwin Spencer (1881-1964) writes: “(…) it is, perhaps, the worst weed of the entire United States. (…) Its seeds serve as food for goldfinches and sparrows, but even this good turn is offset by the fact that the birds, in getting their food, set free the winged seeds, and wherever those seeds fall trouble begins. The plant is outlawed in every northern State; thirty-seven States in all legislate against this rogue, but outlawing it has had very little effect upon it.” – Fallow field, full of creeping thistles, Jutland, Denmark (top). One plant can spread thousands of seeds. – Zealand, Denmark (bottom). (Photos copyright © by Kaj Halberg)

 

 

Rhododendron ponticum is a native of the Caucasus, Bulgaria, Turkey, Lebanon, Spain, and Portugal. It was introduced to Britain in 1763, and is now a widespread menace, especially in Ireland, spreading vegetatively by suckers on the tips of the branches. – Espiye, Turkey, May 1, 1973 Rhododendron ponticum er vildtvoksende i Kaukasus, Bulgarien, Tyrkiet, Libanon, Spanien og Portugal. Den blev indført til England i 1763 og er i dag en vidt udbredt invasiv art, specielt i Irland. Den spredes vegetativt ved hjælp af sine rodslående grene. – Espiye, Tyrkiet, 1. maj 1973
Rhododendron ponticum is native to the Caucasus, Bulgaria, Turkey, Lebanon, Spain, and Portugal. In 1763, it was introduced to Britain, where it quickly became naturalized, spreading vegetatively by suckers on the tips of the branches. Today, it is a widespread menace, replacing local plant species, especially in Ireland. This picture is from Espiye, on the Turkish Black Sea coast. – More pictures of rhododendron species are found on this website, see Plants: Rhododendrons. (Photo copyright © by Kaj Halberg)

 

 

Multiflora Rose, Rosa multiflora, Sose Odde, Bornholm, Denmark. Mangeblomstret Rose, Rosa multiflora, Sose Odde, Bornholm
Taiwan 2018c
The many-flowered rose (Rosa multiflora) is a native of eastern China, Taiwan, Korea, and Japan, but has been introduced as an ornamental to e.g. the United States, Canada, South Africa, and most European countries. It is also used as a rootstock for other ornamental rose species, and in the U.S. it has been planted to prevent soil erosion. However, it readily escapes cultivation, forming dense thickets along roads, in abandoned fields, on grazing grounds and prairies, and in open forests. In numerous places, it has become a serious pest, spreading beyond control and expelling native plant species. Today, it is regarded as an invasive plant in many countries. – These pictures are from the island of Bornholm, Denmark (top), and from Taiwan, where a variety of this species, R. multiflora var. formosana, is a native. (Photos copyright © by Kaj Halberg)

 

 

Many species of cockroach have adapted to a life in cities, where they are often an immense nuisance. - Bontoc, Luzon, Philippines Mange kakkerlak-arter har tilpasset sig til at leve i byer, hvor de ofte er en voldsom plage. - Bontoc, Luzon, Filippinerne
Many species of cockroaches (family Blattidae) have been introduced by Man during his expansion to inhabit the entire planet. In countless homes, they are a true menace, consuming food, making a mess, and possibly spreading diseases to humans. This picture is from Luzon, Philippines. – Read about the usage of cockroaches in Chinese folk medicine on this website, see Traditional medicine: Blattidae. (Photo copyright © by Kaj Halberg)

 

 

Bramble, Rubus plicatus, Møn, Denmark. Brombær, Rubus plicatus, Ulvshale, Møn
Blackberry (Rubus plicatus, also called R. fruticosus) is a native of Europe. It is highly invasive in some countries, expelling native vegetation. It forms dense thickets, often threatening entire ecosystems. It is considered a noxious weed in e.g. Australia, New Zealand, and the U.S. – This picture was taken on the island of Møn, Denmark. (Photo copyright © by Kaj Halberg)

 

 

The South European giant reed (Arundo donax) has displaced natural vegetation in Julia Pfeiffer Burns State Park, Big Sur, California, United States, February 22, 2013 Den sydeuropæiske kæmperør (Arundo donax) har fordrevet naturlig vegetation i Julia Pfeiffer Burns State Park, Big Sur, Californien, USA, 22. februar 2013
The South European giant reed (Arundo donax) has been widely planted in western United States as a means to control erosion, and as a biomass plant. It has become highly invasive in numerous places, especially along rivers, where it will often displace natural vegetation. – In this picture, it grows on a bluff in Julia Pfeiffer Burns State Park, Big Sur, California. (Photo copyright © by Kaj Halberg)

 

 

The American razor clam (Ensis americanus) was introduced to European waters around 1979 and has since then spread to most of Europe. However, it is not a serious threat to native mussles, such as the other two species in this picture, the common cockle (Cardium edule) and the blue mussle (Mytilus edulis), as it lives in deeper waters. – Fanø, Jutland, Denmark, July 6, 2012 Den amerikanske knivmusling (Ensis americanus) blev indslæbt til europæiske farvande i 1979 og har siden bredt sig eksplosivt. Den er dog ikke nogen alvorlig trussel mod indfødte muslingearter, såsom de her viste hjertemusling (Cardium edule) og blåmusling (Mytilus edulis), da den lever på dybere vand end disse. – Hønen, Fanø, 6. juli 2012
The American razor clam (Ensis americanus) was introduced to European waters around 1979 and has since then spread to most of Europe. However, it is not a serious threat to native mussels, such as the other two species in this picture, the common cockle (Cardium edule) and the blue mussel (Mytilus edulis), as it lives in deeper waters. – Fanø, Jutland, Denmark. (Photo copyright © by Kaj Halberg)

 

 

Wild oat (Avena fatua) is a serious pest in many parts of the world. – Crystal Cove State Park, California, United States, March 13, 2013 Flyvehavre (Avena fatua) er et yderst besværlig ukrudt i mange egne af verden. – Crystal Cove State Park, Californien, USA, 13. marts 2013
Wild oat (Avena fatua) is a serious pest in crops in many parts of the world, and it has become naturalized numerous places, as here in Crystal Cove State Park, California, United States. (Photo copyright © by Kaj Halberg)

 

 

Giant goldenrod (Solidago gigantea) is an American plant, which has become invasive in Europe, often dispelling native vegetation. – Zealand, Denmark, August 13, 2012 Sildig gyldenris (Solidago gigantea) er en amerikansk plante, som i Europa opfører sig invasivt og ofte fordriver den naturlige vegetation. – Roskilde Fjord, Sjælland, 13. august 2012
Giant goldenrod (Solidago gigantea) is an American plant, which was introduced to Europe as an ornamental in the mid-1700s. The first naturalized populations were observed about a hundred years later, but it was not considered an invasive before the 1950s. Since then, it has spread rapidly, often expelling native vegetation over large areas, and today it is regarded as an invasive in all European countries. The name Solidago is from the Latin solido, meaning ‘to join’, or ‘make whole’. Formerly, several species of goldenrod were reputed to be able to heal wounds. – This population was photographed on the island of Zealand, Denmark. (Photo copyright © by Kaj Halberg)

 

 

Common cordgrass (Spartina anglica) is a new species, which has evolved as a hybrid between Spartina maritima of Western Europe and S. alterniflora of eastern North America. It has become fertile, and is now a serious pest, expelling natural vegetation on numerous tidal flats. – Fanø, Jutland, Denmark, August 2, 2011 Engelsk vadegræs (Spartina anglica) er en ny art, opstået som en krydsning mellem Spartina maritima fra Vesteuropa og S. alterniflora fra det østlige Nordamerika. Den er blevet fertil og betragtes nu som en alvorlig trussel, da den fordriver den naturlige vegetation på vadeflader. – Hønen, Fanø, 2. august 2011
Common cordgrass (Spartina anglica) is a European species, which has evolved as a fertile hybrid between Spartina maritima of Western Europe and S. alterniflora of eastern North America. It is a serious pest, expelling natural vegetation on numerous tidal flats, here on the island of Fanø, Jutland, Denmark. (Photo copyright © by Kaj Halberg)

 

 

Black mustard (Brassica nigra) is a widespread alien in North America, here growing on a beach in Montaña de Oro State Park, California, February 20, 2013 Sortehavskål (Brassica nigra) er en vidt udbredt invasiv art i Nordamerika. Her vokser den på en sandstrand i Montaña de Oro State Park, Californien, 20. februar 2013
Black mustard (Brassica nigra) is probably a native of southern Europe and possibly also the Middle East and the Indian Subcontinent, where it has been cultivated for thousands of years for its seeds, from which mustard is produced. It was introduced early to many other parts of the world and has become naturalized in numerous countries. It is classified as invasive in California, Hawaii, and some of the Great Lakes states in the U.S., in New Zealand, and on off-shore islands in Chile. – This plant was growing on a beach in Montaña de Oro State Park, California. (Photo copyright © by Kaj Halberg)

 

 

Taiwan 2010
Wandering Jew (Tradescantia zebrina) is a native of Mexico, Central America, and Colombia. It was named after John Tradescant, a Royal British horticulturist in the 17th Century. It is a popular garden plant, which, however, has a tendency to spread, mostly in disturbed forests, but also in native forests, e.g. in St. Lucia, West Indies, and in Hawaii. Stems, which have broken off, are able to take root, and, over the years, create veritable carpets on the forest floor. Today, it is regarded as an invasive in many places, e.g. South Africa, Brazil, Galapagos Islands, St. Lucia, Hawaii, and Taiwan. In South Africa, all trade in seeds and cuttings of the species is prohibited. – This picture is from Malabang National Forest, Taiwan, where it covers large areas. (Photo copyright © by Kaj Halberg)

 

 

Common elms (Ulmus glabra), killed by Dutch Elm disease, caused by the fungus Ceratocystis novo-ulmi, Vorsø, Horsens Fjord, Denmark Skovelme (Ulmus glabra), dræbt af elmesyge, forårsaget af sæksporesvampen Ceratocystis novo-ulmi, Vesterskov, Vorsø, Horsens Fjord
These common elms (Ulmus glabra) have been killed by Dutch Elm disease, caused by the sac fungus Ophiostoma (Ceratocystis) novo-ulmi, which is spread by elm bark beetles of the genera Scolytus and Hylurgopinus. It is generally believed that the disease originated in Asia, but was accidentally introduced to Europe and North America, where most native elm species had no resistance to the disease. – This picture was taken in a Danish nature reserve, Vorsø, where all larger elms have died from the disease. Read more on this website, see Vorsø on my mind – Dutch Elm disease on Vorsø. (Photo copyright © by Kaj Halberg)

 

 

Goat, feeding on a bush, standing on its hindlegs, Pokharan, Rajasthan, India. Ged står på bagbenene, mens den æder af en busk, Pokharan, Rajasthan, Indien
As a close follower of Man for thousands of years, the domestic goat (Capra hircus) is now found in almost every corner of the planet. In countless places, the goat is doing serious damage to the environment by overgrazing, and it is often the culprit in the increasing desertification, which takes place across the world. – This goat is standing on its hindlegs, feeding from a bush in the Thar Desert, Rajasthan, north-western India. – Read more about domestic goats on this website, see Animals: Animals as servants of Man – Sheep and goat. (Photo copyright © by Kaj Halberg)

 

 

Jylland 2016
The small-flowered balsam (Impatiens parviflora) is native to mountains of Central Asia, which has accidentally been introduced to most European countries, where it has successfully invaded numerous forests, dispelling indigenous species. In North America it is still very localized, but may be a potential invasive. – The picture was taken in a forest in central Jutland, Denmark. (Photo copyright © by Kaj Halberg)

 

 

Cat, resting on a tree stump, Jutland, Denmark, May 1997 Kat hviler sig på en træstub, Skanderborg, maj 1997
Feral domestic cats (Felis silvestris ssp. catus) are a serious threat to the wild fauna in many parts of the world. For instance, a study from 2013 by S.R. Loss, T. Will and P. Marra (“The impact of free-ranging domestic cats on wildlife in the United States,” Nature Communications 4:1396) suggested that free-ranging domestic cats (mostly feral) are the top human-caused threat to wildlife in the U.S., killing an estimated 1.3-4 billion birds and 6.3-22.3 billion mammals annually. – Read more about domestic cats on this website, see Animals: Animals as servants of Man – Cat. (Photo copyright © by Kaj Halberg)

 

 

Vorsø 2000-15
Bornholm 2016
The sycamore maple (Acer pseudoplatanus) is a native of Central Europe. It was introduced to Britain around 1500, and has also become naturalized in other parts of Europe, and in Australia, New Zealand, and North America. In many places, it has become invasive, easily spreading by its winged seeds, which are produced in the tens of thousands on a single large tree. – The upper picture shows a 25-year-old growth of sycamore maples in Nature Reserve Vorsø, Horsens Fjord, Denmark, which has sprung up on an abandoned field, where thousands of seeds, stemming from a few trees in a small plantation at the edge of the field, had been spread by the wind. Read more about the succession of this maple forest on this website, see Vorsø on my mind – Expanding wilderness. – In the lower picture, a sycamore maple has taken root in a crack in a quarry with Nexø sandstone on the island of Bornholm, Denmark. (Photo copyright © by Kaj Halberg)

 

 

Bornholm 2016a
Ramsons (Allium ursinum) is hardly a native of northern Europe, but was probably introduced by monks during the Middle Ages as a nourishing herb. Today, it is very common in forests and groves in northern Europe, where it often becomes an invasive, dispelling other plant species. As early as 1741, the famous Swedish botanist Carolus Linnaeus noticed this phenomenon on his journey to the Swedish islands Öland and Gotland. He writes about ramsons: ”The farmers told me that where this plant is growing, it dispels other species. We had clear evidence of this fact, because where ramsons was growing there were no other plants.” (C. Linnæus, 1745. Carl Linnæi Öländska och Gotländska Resa förrättad År 1741. – New edition by Wahlström & Widstrand, 1975). – The picture is from Bornholm, Denmark. (Photo copyright © by Kaj Halberg)

 

 

The invasive rugose rose (Rosa rugosa) is a serious pest along many European and North American beaches, displacing natural vegetation. – Bornholm, Denmark, June 14, 2008 Den invasive rynket rose (Rosa rugosa) er en alvorlig trussel langs mange europæiske og nordamerikanske strande, hvor den fortrænger den naturlige vegetation. – Melsted, Bornholm, 14. juni 2008
Bornholm 2008
The beach rose (Rosa rugosa), also called rugosa rose, Japanese rose, or wrinkled rose, is a native of south-eastern Siberia, north-eastern China, Korea, and Japan. This beautiful plant was first introduced as an ornamental to northern Europe in 1796, and to eastern North America in 1845. It began spreading to coastal habitats of Europe in the 1850s, and in North America in 1899, and today it is abundant on all North European and New England beaches, where it is considered a serious pest, expelling natural vegetation. – These pictures are from the island of Bornholm, Denmark. (Photos copyright © by Kaj Halberg)

 

 

The light-vented bulbul (Pycnonotus sinensis) is common in towns. – Taichung, Taiwan, January 1, 2009 Kinesisk bulbul (Pycnonotus sinensis) er almindelig i byer. – Taichung, Taiwan, 1. januar 2009
In many parts of eastern Taiwan, large numbers of light-vented, or Chinese, bulbuls (Pycnonotus sinensis) have been mass-released during Buddhist festivals. They have become naturalized in many areas, where they compete with – and also hybridize with – the local, endemic Styan’s bulbul (Pycnonotus taivanus), causing the latter to have declined drastically, and already gone extinct in the Yilan County. (Photo copyright © by Kaj Halberg)

 

 

Paper mulberry (Broussonetia papyrifera), growing near a playground, Taichung, Taiwan. This species is very common in Taiwanese towns, popping up in cracks everywhere. In many countries, the species is invasive, dispelling indigenous species. – October 19, 2012 Papir-morbær (Broussonetia papyrifera) vokser nær en legeplads, Taichung, Taiwan. Denne art er meget almindelig i taiwanesiske byer og dukker op i sprækker allevegne. I mange lande betragtes arten som invasiv. – 19. oktober 2012
Taiwan Broussonetia papyrifera_resize
Paper mulberry (Broussonetia papyrifera) is a small tree of the fig family (Moraceae), native to East and South Asia and possibly to some Pacific islands. It thrives in a wide range of habitats and climates, readily growing in disturbed areas. It is dioecious, spreading rapidly, when male and female plants grow together and seeds are produced. Birds and other animals eat the fruits and thus help dispersing the species. It can also form dense stands via its spreading root system. Paper mulberry is regarded as one of the worst weeds in Pakistan, as a highly significant invasive plant on the pampas of Argentina, and as one of the most dominant invasive species in the forests of Ghana and Uganda. – Paper mulberry is very common in Taiwanese towns, popping up in cracks everywhere. Both pictures are from Taichung. (Photos copyright © by Kaj Halberg)

 

 

(Uploaded March 2016)

 

(Revised continuously)