◆Zhang Fengchun

　　China has a vast territory, crossing approximately 50 latitudes and 5 climatic zones. Most alien species worldwide can find suitable habitats in China. Therefore, China has become one of the countries in the world that are severely harmed by alien invasive species.

　　50 of the 100 most threatening alien invasive species worldwide published by the International Union for Conservation of Nature have been found in China. By the end of 2014, China has 515 species of 285 genera in 72 families of alien invasive plants, distributing in all provinces (autonomous regions and municipalities directly under the Central Government). China's Southwest and Southeast coastal areas are "hard-hit areas" by alien invasive plants. According to the data released by the Ministry of Ecology and Environment in 2020, more than 660 alien invasive species have been found in China.

　　Alien invasive species can often bring all aspects of hazards, and these hazards are complicated and changeable. In general, the hazards of alien invasive species include impacts on water areas: blocking waterways and water channels, affecting irrigation and drainage, and affecting seawater exchange. Impacts on human health: inducing induction of hay asthma and central nervous system paralysis. Impacts on agriculture and aquaculture, etc.: endangering farmland, animal husbandry and fishery, destroying offshore habitats, threatening native fish, endangering cultivation of aquatic products, affecting mudflat environment, and threatening sericulture. Impacts on local territory plants: destroying the landscape, expelling native animals and plants, disturbing the ecological equilibrium, bacteria host, contributing to unordered hybridization, affecting natural forest restoration, community species simplification and allelochemical inhibitor, releasing toxic and harmful substances, gnawing, infecting, suffocating and expelling plants, hollowing tree trunk, pest host, inducing red tide; etc. As a matter of fact, the hazards of alien invasive species are far more than these.

　　These hazards of alien invasive species can be roughly summarized into several aspects: Causing economic losses, among which direct economic losses including hazards to agriculture and forestry production, such as the invasion of lissorhoptrus oryzophilus kuschel, ragweed, lolium temulentum and sorghum halepense, etc. into the farmland, causing reduced crop yield and product quality; for example, the invasion of pine wood nematode and fall webworm, etc. into the forest, causing damage to forestry. In addition, there are also indirect economic losses, such as expenditures for the prevention and elimination of alien invasive species, etc. Moreover, will destroy the local ecosystem, etc., such as the invasion of mikania micrantha into the Guangdong Ling Ding Island, resulting in the island's ecosystem being on the verge of collapse. The alien invasion will also decrease the diversity of species, such as the invasion of water hyacinth into the Dian Lake, causing reduced fish species in Dian Lake, and ageratina adenophora expelling local species in south China; affecting genetic diversity, genetic communication between alien invasive species and native species may cause genetic erosion to native species; endangering human health, such as killer bee, red imported fire ant, ragweed and ambrosia trifida endangering human health even human life; destroying the integrity of the landscape, such as the invasion of spartina alterniflora, water hyacinth and alternanthera philoxeroides, etc. into the aquatic ecosystem, destroying the integrity of the landscape, etc.

　　The pathways of alien invasive species can be roughly divided into 3 categories: The first pathway is control failure after intentional introduction. Mainly refer to people intentionally introducing certain species for the purposes of agriculture, animal husbandry and fishery production, environmental improvement, viewing and admiring and scientific research, etc., but widespread and uncurbed after control failure or escaping. Such as alternanthera philoxeroides and water hyacinth, etc. introduced by China as pasture or fodder. The second pathway is accidental introduction. It mainly includes alien invasive species be brought in with vehicles (such as ragweed), with international trade of agricultural products (such as imported food carrying sorghum halepense), with the introduction of animals and plants (such as imported seeds bringing lolium temulentum to China), with international tourists and their luggage (such as plantago virginica), with ballast water of international shipping (mainly including some microorganisms, planktons and their eggs, larvas and spores, etc.). The third pathway is natural communication. It includes dispersion by self-producing, and natural dispersion by media such as wind, streamflow and animals. The above is only a rough classification. In real life, the invasion pathways of species are far more complicated.

　　The prevention and control measures for alien invasive species are divided into two aspects which are prevention and control. Firstly, for prevention, it is required to establish and perfect the relevant laws and regulations, early warning mechanism and evaluation system, to enhance the risk assessment as well as supervision and administration of intentionally introduced alien species. Secondly, the inspection and quarantine works need to be enhanced to intercept alien invasive species that have unintentionally entered China through the main channel.

　　Methods of controlling alien invasive species can be divided into four categories: The first method is physical prevention and control. It includes manual elimination and removal, and mechanical removal, etc.; The second method is chemical prevention and control. Using chemical agents to control alien invasive species. This method has advantages such as quick effect, easy to use and generalize, but it is easy to affect the environment, native species, as well as human and livestock health. The third method is biological prevention and control. It includes biological alternatives and biological prevention and control. The biological alternative is selecting and using native species by means of alternative methods to control alien invasive species, the biological prevention and control are controlling alien invasive species through the introduction of natural enemies in the country of origin; The fourth method is comprehensive prevention and control. Organically combine the three above-mentioned methods, bring their superiorities into full play, offset the deficiencies of a single technique, and deal with alien invasive species comprehensively.

　　The author is the former chief expert of the Ecological Research Institute of the Chinese Research Academy of Environmental Sciences