However, among the huge biological species in China, how many exotic species are still unknown. At the same time, China is vulnerable to the influence of exotic species. Because China is 5,500 kilometers long from north to south and 5,200 kilometers wide from east to west, spanning 50 latitudes and 5 climatic zones (cold temperate zone, temperate zone, warm temperate zone, subtropical zone and tropical zone), most exotic species from all over the world may find suitable habitats in China.
Invasion of alien species in China has the following characteristics:
A. Coverage: Invasive species have been found in 34 provinces, municipalities and autonomous regions. As of May 2002, China has established 65,438+0,500 nature reserves, accounting for about 9% of the country's total area. Except for a few remote nature reserves, invasive species can be found more or less.
B there are many ecosystems involved: almost all ecosystems can be seen from forests, agricultural areas, waters, wetlands, grasslands and urban residential areas. Among them, the ecosystems in low-altitude areas and tropical islands are the most seriously damaged.
C. There are many species involved: examples can be found in vertebrates (mammals, birds, amphibians and reptiles, fish), invertebrates (insects, crustaceans, mollusks), plants, bacteria and viruses.
D. Serious harm: Many places in China have stopped cutting down virgin forests, and it is strictly forbidden to further destroy the ecology. Alien invasive species have become an important cause of ecological degradation and biodiversity loss at present, especially for aquatic ecosystems in the south and tropical and subtropical regions, and have risen to the top of the list.
2. The main ways (channels) of alien species invasion
The most fundamental reason of biological invasion is that human activities have brought these species to places where they should not appear. Therefore, we call these species "harmful", which is actually unfair to them. They just stay in the wrong place, and the cause of this mistake is often some irresponsible activities of human beings. The key to the problem of alien invasive species lies in human beings. Introduction means that species, subspecies or taxons below (including all parts, gametes or propagules that may survive and reproduce later) are transferred by humans to areas beyond their (past or present) natural distribution and diffusion potential. This transfer can be carried out within countries or between countries. Introduction can be divided into intentional introduction and unintentional introduction.
Intentional introduction refers to the intentional introduction (which can be authorized or unauthorized) by human beings to move a species out of its natural distribution range and diffusion potential.
Unintentional introduction refers to the unintentional introduction of a species through human or human-to-human transmission system and its spread beyond its natural distribution.
Exotic species are introduced into their non-native areas in these two ways.
Deliberately introduce
China has a long history of introducing excellent varieties from other places or abroad. Early introduction was usually achieved through ethnic migration and regional trade. The seeds of sour bean (sour horn), grape (grape), alfalfa, pomegranate (pomegranate) and safflower (safflower) originated in Africa passed through the ancient famous "Shu-Toxoplasma gondii (India) Road" in the 4th century BC and 1 century BC respectively. Since then, in the Northern Song Dynasty, Aloe vera (or A. vera var China sweet potato (native to northeastern Africa, now introduced to the southern coastal areas of China), and in the17th century, economic plants such as sweet potato, tobacco and passion fruit were introduced to China. Earlier, the Dutch introduced some American species (such as Leucaena, Acacia and pitaya) into Taiwan Province Province, and most of these species were later naturalized as wild plants. 1842 After the Opium War, Hongkong, Guangzhou, Xiamen, Shanghai, Qingdao, Yantai and Dalian became the main entrances for exotic weeds to enter China. Weeds such as Erigeron canadensis (1857), Erigeron canadensis (1862) and Erigeron annua (1886) landed in Hong Kong, Yantai and Shanghai successively, and gradually spread to the mainland. The introduction time and escape place of some cultivated plants are irregular. For example, French missionaries introduced Vitex negundo into the vicinity of Chengkou Church in Sichuan, and then a large number of Vitex negundo escaped.
At present, almost all planting and breeding units are imported from other places or abroad. These departments or units include agriculture, forestry, gardens, aquatic products, animal husbandry, special aquaculture and various breeding bases. Most of them are introduced to improve economic benefits, ornamental and environmental protection, but some species have become harmful because of improper introduction. Among the known exotic harmful plants in China, more than 50% are the result of artificial introduction.
The purpose of intentional introduction is varied, which can be mainly divided into the following aspects:
As pasture or feed
There are many examples of invasion caused by the introduction of pasture or feed. For example, Alternanthera philoxeroides, alfalfa, clover, sunflower, millet, Pennisetum, sorghum, ryegrass, water hyacinth, barley, Eichhornia crassipes and so on. Long-term overgrazing and grassland degradation in China's animal husbandry have increased the demand for new high-quality fast-growing grasses, which provides an excellent opportunity for foreign grass seed companies to dump grass seeds in China. A large number of new forage experiments are being carried out now, mainly to test whether the varieties provided by foreign grass seed companies can grow rapidly on our land. Worryingly, some of them have become dangerous alien invasive species. Alternanthera philoxeroides, commonly known as "Alternanthera philoxeroides", was introduced and popularized as pig feed in many places in southern China after 1950s, and later became wild. 1986 investigation shows that Alternanthera philoxeroides has a natural occurrence area of about 889,600 hm2, and has become the main weed in vegetable, sweet potato and other crop fields and citrus orchards.
As an ornamental plant
The pursuit of exotic flowers and herbs has prompted people to introduce exotic flowers and herbs or foreign varieties. These flowers and plants inevitably escape from the garden. Under natural growth, some exotic ornamental plants become dangerous alien invasive species after escaping. Such as Pogostemon rugosa, Coreopsis verticillata, cosmos, Heliqiu, Tagetes erecta, Solidago canadensis, Petunia hybrida, Petunia rotundifolia, Lantana, Mimosa, Oxalis purpurea, Allium tuberosum, Vitex negundo and Spider Orchid.
The popularity of aquariums and family aquariums also makes some exotic aquatic plants become invasive species. For example, Cabomba Carolina, which originated in the United States, has now appeared in rivers in Zhejiang; Aquatic Myriophyllum from South America has been introduced in Taiwan Province Province. Although the former only blooms without fruit, while the latter only has female plants, neither of them produces seeds, but they can spread rapidly through asexual reproduction. For example, the green algae (Caulerpa taxifolia) introduced into the French aquarium from the Adriatic Sea formed a dominant population in the French local marine ecosystem by releasing spores, which led to the mass extinction of local marine plants. Lantana is native to tropical America. During the period of 1645, it was introduced to Taiwan Province Province by the Dutch and cultivated as an ornamental plant. Now it is spreading in tropical and subtropical areas of China, crowding out local plants and blocking roads. Its plants have a bad smell and its stems have thorns, so it is a harmful shrub. Its fleshy fruit is further spread by local birds pecking. The scavengers that are often kept in aquariums are a species of the genus Catalpa, which is native to Latin America. Recently, it has been reported that it was collected in the Nanchanghe River in Beijing, the Pearl River and the Hanjiang River in the south. According to Dongshan River in Yilan County, Taiwan, this variety has no natural enemies in Yilan, but it has strong reproductive ability, laying 300-500 eggs at a time, and the hatching rate is almost 100%. Feeding on the eggs of other fish gradually reduced the native species in Taiwan Province Province. To this end, Yilan also launched a fish cleaning operation.
As a medicinal plant
More than12,000 kinds of organisms used in traditional Chinese medicine in China are mostly native to China, some are exotic species, and some have become invasive species. Such as soap grass, cassia obtusifolia, cassia obtusifolia, evergreen, wangjiangnan, Phytolacca acinosa, Datura stramonium, ice eggplant and so on.
As a plant for improve that environment
In order to quickly solve the problems of ecological environment degradation, vegetation destruction, soil erosion and water pollution that have plagued us for a long time, people often look at some characteristics of alien species unilaterally, which provides an excellent opportunity for the invasion of alien species. At present, many areas are actively carrying out vegetation restoration, but some species used are dangerous alien species. At present, some species have invaded, typical cases are Spartina alterniflora, Mikania micrantha and Eichhornia crassipes. Spartina alterniflora was introduced from the salt marsh vegetation on the east coast of the United States in 1979. First, 1980 and 10 were planted in Fujian coastal areas, and then widely publicized. 1982 expanded to Jiangsu, Guangdong, Zhejiang and Shandong. The purpose of introduction is to protect beaches and revetments, improve soil, green beaches and improve the ecological environment of beaches. Now this species has escaped from Zhejiang, Fujian, Guangdong and Hong Kong on a large scale. 1990, the loss of aquaculture in Dongwuyang, Ningde, Fujian Province alone reached 10 million yuan a year. This species has become a serious problem in coastal areas, affecting the local fishery output and threatening mangroves.
Exotic species are also widely used in urban landscape construction and beautification, which often leads to radical changes in local ecosystems and landscapes. Take the lawn industry as an example, with the large-scale construction of lawns with different functions (golf courses, football fields, parks and green spaces, etc.). ) In cities all over the country, it has promoted the rapid development of lawn industry in China, and the demand for lawn grass seeds has increased sharply. At present, the grass species used are mainly excellent lawn varieties from abroad. Except Zoysia japonica seeds, almost all other grass species are imported, and the import volume of 1997 alone is more than 2,000 tons. Up to 1990, China has introduced 1 14 different cool-season grasses, mainly from the United States. At present, some species have invaded, such as carpet grass. In fact, China has a vast territory and abundant germplasm resources, which has great potential in forage seed selection.
As food
Food is a part of China's traditional culture, and its emphasis on food diversity is unmatched by any other ethnic group in the world. In order to pursue the color, fragrance, taste, novelty and novelty of food, people introduce a large number of edible animals and plants, but they don't know that this will also cause biological invasion, such as sweet apricots, amaranth and sunflower introduced as vegetables; Psidium guajava, passion fruit, and pseudoPhysalis alkekengi are introduced as fruits, as raw materials for bean jelly production, as well as edible animals such as Ampullaria gigas and black-bellied pheasant. The skin of some mammals has high economic value, such as muskrat and nutria. People widely promote reproduction to obtain animal skins, and as a result, biological invasion has also formed. Pomacea canaliculata was introduced to Guangdong by a Brazilian Chinese in 198 1 for the purpose of being used as aquaculture food. Since 1984, Ampullaria canaliculata has been widely cultivated in Guangdong, Fujian and Yunnan. It was released into the wild because of excessive reproduction and bad taste. Ampullaria canaliculata has strong adaptability and reproductive ability, large appetite and many kinds of food. It spreads rapidly, destroying vegetables and aquatic crops. Since 1988, Ampullaria canaliculata has caused huge losses in 25 000 hm2 of land in 37 counties of Guangdong Province.
As a cannabis crop
Some hemp crops introduced in ancient times, such as abutilon and hemp, were gradually eliminated with the introduction of cotton and became weeds in many places.
As a pet
Some animals are widely farmed as pets in cities, and some parrots with strong viability, such as South African parrot (Cacacatua sulpurea) and Egyptian parrot (Trichoglossus haematotus), have greatly increased in number after being wild in the local area, and excessive use of fruiting shrubs or excessive consumption of young leaves has endangered local vegetation. Trachemys scripta is a global invasive species, which can be seen in almost all pet markets in China from north to south. Although China has not reported the harm of the Brazilian tortoise, it has been listed as one of the most dangerous 100 invasive species in the world by the World Conservation Union (IUCN, 200 1), and the Brazilian tortoise is also a vector of disease transmission. The introduction of "pet mice" from South America in Taiwan Province Province has also aroused people's concern about the spread of the disease.
As an aquaculture species
Aquaculture is one of the important industries with a long history in China. Almost all waters that can be used for aquaculture, such as rivers, lakes, ponds, reservoirs, rice fields and parks, are engaged in aquaculture to some extent. The exotic species involved include those introduced from abroad, such as Procambarus clarkii, Macrobrachium rosenbergii, red crayfish, rainbow trout and non-crucian carp (tilapia). ), European eel (Anguilla japonica), paddlefish (pomfret), freshwater pomfret (pomfret), channel catfish (channel catfish) and some carnivorous fish (especially small fish), such as California bass (California bass). Perch introduced from Irtysh River has led to the extinction of Xinjiang bighead carp in Bosten Lake, Xinjiang. In addition to these imported species, the native fish in southern China, such as "four big fish" (silver carp and bighead carp), were introduced into the high-altitude waters in northwest and southwest China, and these species and small miscellaneous fish (tiger fish, wheat ear fish, etc.) caused disasters. ) is no less harmful than alien species. The breeding of bighead carp in Qilu Lake and Xingyun Lake in Yunnan Province has led to a sharp decrease in the number of local species of bighead carp in Qilu Lake and Xingyun Lake, and now it has to rely on artificial breeding. For example, Procambarus clarkii was introduced from Japan to China for artificial culture in the early 1940s. Unlike most aquatic species, female Procambarus clarkii hatches her eggs by herself, so there is no need to spend money on artificial incubation. Once the Procambarus clarkii is put into the original seed, it can maintain itself, and it is not necessary to put it into the original seed after harvest. Procambarus clarkii is often mixed with other crops, especially rice Those who escaped during the harvest season dug holes in the dam to survive. In the next season, a breeding population will be formed, living on surplus crops and other foods. It was first cultivated in Nanjing and Chuxian, Anhui Province, and later spread to the central, northern and southern parts of China, and became a large population in the wild.
Issue in different places
In China, Viet Nam, Malaysia, Thailand, South Korea and Cambodia, people will be respected for releasing captured animals, especially birds, fish and turtles, but a study shows that 6% of the released birds are foreign; Most fish, turtles and sea turtles are kept in captivity abroad, and these species may be invasive [10]. Obviously, the cultural meaning of "doing good" does not take into account the harmful effects on the local ecosystem. The reason is that people don't have the concept of alien invasive species and don't understand the harm caused by alien invasive species.
There is a bad habit of eating wild animals in southern China. Wild animals are also used as pets and Chinese medicine ingredients. As a result, illegal wildlife trade is rampant. A large number of wild animals come from neighboring countries, especially Southeast Asian countries, and some wild animals are smuggled to China from distant Europe, Africa and America. Our government's trade management of illegal wild animals is also strengthening. But how to deal with the confiscated wild animals often becomes a worrying and headache problem. Because many smuggled wild animals are exotic species, or often carry exotic wildlife diseases. Releasing these confiscated wild animals at will may lead to the death of some species, while others are in danger of biological invasion, posing a serious threat to the local wildlife or ecosystem in China. These results run counter to the publisher's original intention.
Introduction of Botanical Gardens, Zoos and Wildlife Parks
Many cities in China have zoos, botanical gardens and bird parks. Many exotic plants have escaped from the botanical garden and naturalized, and some have invaded. Although there are no reports of invasions in zoos, some species naturally reproduce in the wild. For example, starlings have formed a natural population in Beijing. In particular, it has become fashionable to establish wildlife parks in various places, and a large number of species are scattered in natural areas. If management measures are not strengthened to prevent exotic species from escaping from zoos, botanical gardens, bird gardens and wildlife parks (which may carry exotic wildlife diseases), these potential alien invasive species sources may bring disastrous ecological invasion.
Unintentional introduction
Many alien invasive organisms were inadvertently introduced with human activities. Usually, people and their products are introduced to a new environment as stowaways or "hitchhikers" by planes, ships, trains, cars and other means of transportation. Especially in recent years, with the continuous increase of international trade, the continuous expansion of foreign exchanges and the rapid warming of international tourism, more and more alien invasive organisms have been introduced into China through these channels. In addition to transportation, construction and development, military transshipment, express delivery service, letter mailing, etc. Will inadvertently introduce alien species.
The following lists the main ways of unintentional introduction, but some invasive organisms are not introduced through only one way, but may be introduced through two or more ways, not just once, but two or more times. The introduction of multi-channel and multi-frequency increases the possibility of colonization and diffusion of alien organisms.
Brought by human transportation
Many alien species enter and spread along the traffic routes, and the vegetation around roads and railways is usually destroyed and degraded, so these places are usually the earliest or most frequent places where alien species appear. For example, ragweed mostly appears on both sides of railways and highways, and was originally introduced from North Korea by train; Rattus norvegicus and Rattus flavipectus in Xinjiang were also introduced from the mainland by railway.
Ship transportation
In the ocean, tens of thousands of species formed after hundreds of millions of years are limited by the external environment such as barriers between oceans, temperature differences and low-salt estuary runoff, so many species can only live in a local sea area and become local species or native species in this sea area. There are also some creatures, because their adults or larvae swim or float, the spread of ocean currents and tides, and the carrying of some animals (such as turtles, whales and seabirds), which expand their distribution and become widely distributed species. However, some transfers are related to the transportation of human ships.
The way of loading is mainly to discharge ballast water from different places. Ballast water usually comes from the coastal waters of the ship's port of origin or route. It is estimated that the world's ballast water is transported by ships every year as much as 654.38 billion tons. Therefore, many bacteria, animals and plants are also inhaled and moved to the next port of call. There are about 16 species of harmful red tide organisms in China's coastal waters, most of which are mainly spread in the global coastal waters through ballast water. Exotic red tide species have aggravated the occurrence of red tide in coastal areas of China [3]. Another way of introduction by ship is to attach creatures (such as barnacles) to the ship and bring them into new areas. After the introduction of these exotic creatures, some species fundamentally destroyed or changed the original ecological characteristics. For example, the carnivorous red snail Rapana Thomas iana migrated from the Sea of Japan to the Black Sea in 1947. After ten years, the oysters on the Taota beach in the Black Sea were almost completely eliminated.
The biological propagules loaded on the ship may sometimes be discarded, or escape after the ship sinks and rush out of the coast with the waves. Kalanshou and Aloe vera, which grow on some uninhabited islands in the East China Sea and South China Sea of China, may be discarded by early seagoing ships.
Marine garbage
With the floating of waste plastics and other man-made garbage, marine life is invading Antarctica and some tropical islands, posing a threat to local species. These wastes have increased the number of organisms spread to subtropical areas by 1 times, and even increased by more than 2 times in high latitudes. Compared with natural floating objects such as coconut or wood, marine life prefers to float on plastic containers and other non-degradable garbage. With these carriers, they can float almost anywhere in the world.