Natural invasion
Natural invasion refers to the expansion of natural distribution areas without human influence at all. Spreading weed seeds through the natural introduction of wind and water and the migration of animals such as birds is the main way of natural invasion. For example, Mikania micrantha may have been introduced into Guangdong from Southeast Asia by air, and rice weevil may have been introduced into China by air.
Unconscious introduction
Many alien invasive organisms were inadvertently introduced with human activities. Usually, people or products are introduced to a new environment as "stowaways" or "hitchhikers" by planes, ships, trains, cars and other means of transportation. 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 are introduced into China through these channels. 1. Enter by human transport. Many alien species enter and spread along the traffic routes, and the vegetation around roads and railways is usually destroyed and degraded, which makes these places the earliest or frequent places where alien species appear. For example, ragweed mostly occurs 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. 2. Shipping. Ocean-going cargo ships need to be filled with ballast water when they leave the shore empty, and they need to be discharged when they are loaded in different places. A large number of organisms move to different places with ballast water, which leads to seawater pollution and biological invasion. There are about 16 species of harmful red tide organisms in China's offshore waters, most of which are introduced through ballast water. 3. Marine garbage. More and more wastes are discharged into the ocean by human beings, and floating marine organisms adsorbed on the wastes flow around the world and invade these countries and regions, thus posing a threat to invasive species. For example, marine debris has increased the number of organisms spread to subtropical areas by 1 time, and even increased it by more than 2 times in high latitudes. 4. With the import of agricultural products and goods, many alien invasive species are brought in with the introduction of other species. For example, a large number of weed seeds are imported with grain, poisonous wheat is introduced into China with wheat introduction, and some forestry pests come with wooden packaging materials. 5. Take it with tourists. With the opening of the international tourism market, transnational tourism is increasing. Living things carried by tourists in different places, such as fruits, vegetables or pets, may carry dangerous alien invasive species. China Customs has repeatedly seized Mediterranean fruit flies from fruits carried by immigrants. In addition, some species may be brought into China due to the adhesion of tourists' luggage.
Soap grass humans introduce new species or varieties for a certain purpose, so that a species can be purposefully transferred to areas beyond its natural distribution and diffusion potential. China is a country deeply invaded by exotic species, and one of the most fundamental reasons is that China is the country that has introduced the most exotic species. China has a long history of introduction, and it has a long history of introducing excellent varieties from other places or abroad. Early introduction was usually achieved through ethnic migration and regional trade. With the economic development and reform and opening up, almost all units related to breeding, breeding and planting have a large number of exotic species introduction projects. Due to over-belief that "foreign monks can recite scriptures", the introduction of China is blind, disorderly and short-sighted, which leads to a large number of biological invasion incidents. Among the known exotic harmful plants in China, more than 50% species are the result of artificial introduction.
Intentional introduction has various purposes, which can be divided into the following aspects: 1. Introduced as pasture, feed or human food. Such as Alternanthera philoxeroides (also known as Alternanthera philoxeroides), alfalfa and Eichhornia crassipes introduced as pasture and feed; Apricot, amaranth and sunflower introduced as vegetables; Guava and egg fruit introduced as fruits; As edible animals, there are large bottle snail, brown cloud agate snail and so on. 2. Introduced as an ornamental animal. Curiosity makes people constantly introduce animals and plants from outside the local area as ornamental plants or pets. When these creatures escape or are abandoned in the wild, they may become dangerous alien invasive species, such as Solidago canadensis, mimosa, Oxalis rubra and piranha. 3. Introduced as a medicinal plant. Most of the traditional Chinese medicines in China are native to China, but some of them are exotic species, and some of them have become invasive species, such as Gleditsia sinensis, talinum, Phytolacca acinosa and Datura stramonium. 4. Introduction of plants to improve the environment. For example, in order to repair the damaged environment, human beings treat some characteristics of alien species unilaterally and introduce some dangerous alien species. Such as Spartina alterniflora and Mikania micrantha.