What is the introduction of trees?

(Shen Xihuan)

Introduce excellent tree species from other regions into this region, and select excellent tree species for propagation and popularization through experiments. Each tree species has a certain natural distribution range under natural conditions. When a tree species grows in its natural distribution area, it is called a native tree species; Those planted outside the natural distribution area are called exotic tree species. Introducing valuable tree species from home and abroad is of great significance to enrich tree species resources, increase wood output, provide new forest by-products, and play the role of forests in protecting nature and beautifying the environment.

The introduction work in Britain started earlier, and many exotic trees were introduced in the 9th century. Australia, New Zealand and the United States all started large-scale introduction from 65438 to 2009 in the 1950s. At present, Pinus radiata, Douglas fir, Picea sibirica and Eucalyptus have been widely planted in many countries and become important timber trees. Metasequoia glyptostroboides and Ginkgo biloba originated in China have also been introduced to many countries.

China introduced eucalyptus, Robinia pseudoacacia and clover rubber around the beginning of the 20th century. In 1930s, Pinus caribaea, Pinus elliottii and Pinus taeda were introduced. After 1949, forest introduction developed rapidly. Eucalyptus originated in Australia and other places, and has been planted in many southern provinces, becoming an important wood, firewood and greening tree species. Casuarina equisetifolia, native to Australia, Myanmar, Malaysia and other places, thrives on the long coastline from Beibu Gulf in China to Wenzhou in northern Zhejiang. Pinus elliottii, Pinus taeda and Pinus caribaea introduced from Jiangnan grow fast and have good dry shape. Populus euramericana (a hybrid of Populus deltoides and Populus deltoides) is widely spread in the lower reaches of the Yangtze River in North China, Southeast China, Jianghuai, Jianghan and other areas, and has become an important afforestation tree species. Robinia pseudoacacia originated in Qiya Mountain Area of Apara in the eastern United States, and has been widely planted in North China, Southeast China, Southwest China and East China, becoming an important tree species for soil and water conservation, sand-fixing afforestation, "four sides" greening and firewood forest in these areas. In addition, economic tree species such as rubber, oil palm, coffee, cinchona, and olive have performed well in some parts of southern China. At the same time, many excellent tree species from China have been popularized in China. Pinus sylvestris var. mongolica. Quercus mongolica is a native tree species in Daxing 'anling and Hulunbeier. Now it has been introduced in Zhanggutai, Liaoning, Hohhot, Inner Mongolia and Yulin, Shaanxi, and it grows well. It may become an important sand-fixing afforestation and barren mountain afforestation tree species in this arid area. Another example is the planting area of Metasequoia glyptostroboides and Paulownia, which has now expanded to Beijing and Shanxi.

Possibility of introduction

The natural distribution range of a tree species is closely related to its occurrence history, adaptability and reproduction conditions. There are great differences in tree species between the northern and southern hemispheres. Pinaceae trees, including pine, spruce, fir, Chinese fir, larch, money pine, hemlock, cedar, Metasequoia glyptostroboides, silver fir and other genera, are widely distributed in the northern hemisphere and are the dominant populations in plant communities in many areas. In the genus Pinus, there is no natural distribution of other tree species in the southern hemisphere, except South Asian pine which slightly crosses the equator and reaches Sumatra Island in Indonesia. However, among conifers, the two genera of Aralia and Concha are all distributed in the southern hemisphere, except for a few species crossing the equator to Indonesia, the Philippines and the Malay Peninsula. The introduction practice has proved that many kinds of pine trees originated in the northern hemisphere can fully adapt to the climate and soil conditions in this area and flourish after being introduced to the southern hemisphere. This shows that some tree species cannot go beyond the existing distribution area, which is probably the result of being blocked by oceans and mountains. The disappearance of some tree species in some areas may also be the result of historical climate change. Such as Metasequoia glyptostroboides, the natural distribution area is now limited to the narrow area at the junction of China, Hubei, Sichuan and Hunan provinces. However, according to fossil analysis, Metasequoia glyptostroboides was widely distributed in North America, Western Europe, Greenland, Siberia, Japan and other places during the Cretaceous period, but Metasequoia glyptostroboides in these areas became extinct during the Ice Age. Metasequoia glyptostroboides was discovered in China on 1945 and distributed to some countries. At present, Metasequoia glyptostroboides introduced from many countries in Asia, America and Europe grow normally, and some of them have already borne fruit.

The main basis of introduction

There are many kinds of trees, different economic characters and social benefits, and different ecological habits, so it is necessary to have a certain foundation when introducing them. ① According to the purpose of introduction, that is, the requirements of the introduction site for tree species, understand the performance of exotic tree species in the country of origin and conduct preliminary screening. The introduction practice shows that the characters of successfully introduced exotic tree species in the new area are similar to those in the origin. ② The possibility of alien tree species adapting to the new environment should be considered. Trees are perennial plants, and the rotation period varies from ten to several decades, so the growth environment is not easy to be controlled artificially. Therefore, it is very important to analyze the ecological factors of the origin and the new area, especially the climate factors. 1906, the German forester H.Mayr put forward the theory of climate similarity, and thought that the climatic conditions of the introduction place and the origin place must be similar in order to succeed in introduction. But in fact, in the world, it is impossible to have regions with exactly the same conditions. At the same time, many introduction experiments show that tree species with roughly the same distribution area sometimes behave differently after introduction: some have strong adaptability and can be widely popularized; Others can only be planted in small areas. Whether the selected exotic tree species can grow and spread in new areas needs to be tested by introduction experiments.

Main ecological factors to be considered in introduction

① Temperature: Extreme low temperature and absolute low temperature are often the main limiting factors for the distribution of a tree species. In the introduction of forest trees, we should also consider the rare low temperature and its duration for several years or even decades. The damage of high temperature and absolute high temperature to forest trees is not as obvious as that of low temperature, but the combination of high temperature and drought will have serious adverse effects. In addition, the alternation of seasons is often one of the reasons why the northern tree moves south. ② Precipitation: It is one of the important factors that determine the success or failure of exotic tree species introduction. The seasonal distribution type of rainfall, called rain type, is closely related to introduction. The subtropical region in eastern China belongs to summer rain type. The introduction of winter rain-type trees such as olive, coastal pine and radial pine from the Mediterranean region and the west coast of the United States was rarely successful, while summer rain-type Caribbean pine and slash pine grew well. ③ Illumination: The length of sunshine and the nature of illumination change with latitude and altitude, which affects the growth and development of plants. The normal growth and development of plants need a certain proportion of day and night alternation, which is called photoperiod. For tall perennial trees, in addition to the long development cycle, there is also the problem of wintering every year, so the response to the length of sunshine is more complicated than that of annual plants. For example, the southern tree moves northward, and the sunshine in the growing season is prolonged, which prolongs the growing period, affects the capping, hinders the lignification of tissues and the transformation of protective substances before winter, and reduces the cold resistance. However, when the northern trees move south, the sunshine length becomes shorter, which promotes the early capping, shortens the growth period, affects the normal physiological activities of trees, and sometimes causes secondary growth. ④ Soil: The chemical characteristics, physical structure and fertility of soil have a profound influence on the growth of trees. Among them, soil salt content and pH value play a decisive role in the success or failure of introduction. Salicaceae, Chenopodiaceae, Tribulus and some Polygonaceae plants are halophilic plants. Elm, willow, locust, Amorpha fruticosa, etc. Wide adaptability to soil pH value. Conifer species such as pine, spruce, fir and larch are suitable for growth in neutral and acidic soils. Soil structure is related to soil ventilation and drainage. Most tree species, such as pine trees, are suitable for growing in well-drained soil; Populus tomentosa and Paulownia require not only good drainage, but also deep soil layer. Taxodium ascendens, Taxodium ascendens and Metasequoia glyptostroboides are suitable for growing on aquatic wetlands, especially Taxodium ascendens, which has strong resistance to water and humidity. ⑤ Pests and diseases: Their occurrence and development involve the complex relationship and interaction among pathogens, hosts and environment. Some pests and diseases already exist in the country of origin, but they do not pose an important threat, but they become serious harmful factors under the new environmental conditions; Diseases and pests in some new areas have found new hosts that are more suitable for infection, making it impossible for exotic tree species to occupy new territories. Root tissues and fungi of some species of Pinus massoniana, Populus davidiana and Leguminosae are necessary biological conditions for the normal growth of trees, and should also be considered when introducing them.

Introduction measures

The criteria for successful introduction of trees are: normal growth and development, no special cultivation and protection measures; The quantity and quality of products provided can reach the average level of origin. In order to ensure the success of introduction, we must pay attention to the following matters: ① The introduction must adhere to the principle of long-term experiment and gradual popularization. The popularization of a tree species in production is the result of long-term introduction test. If it is popularized in production without trial, it is bound to take risks, and sometimes it will suffer heavy losses and waste manpower and material resources. Without the long-term natural test of several generations, it is difficult to say that the introduction of an exotic tree species is completely successful. In order to meet the needs of experiment and production, exotic tree species with development prospects have been preliminarily confirmed after several rounds of experiments, which can gradually expand the experimental area and transition to production and popularization. ② Attention should be paid to the intraspecific differences of introduced exotic tree species. In the past, the best introduction effect was often not achieved because of ignoring the variation within tree species. There are differences in growth and adaptability among different provenances of the same exotic tree species. Without provenance selection, it is impossible to introduce effectively, which is an important experience in introduction. ③ Different site conditions should be selected for experiments in the same area. Different topography and slope directions will cause significant differences in temperature and soil moisture, which will have an important impact on the success or failure of introduction. Suitable trees in the right place (see tree species selection) are also suitable for introducing exotic tree species. ④ Strengthen the quarantine of introduced seedlings. When introducing tree species from other places or abroad, we must strictly implement the seed quarantine system and do a good job in quarantine to prevent them from being brought into quarantine objects. Special care should be taken when introducing tree species that have been infected by quarantine objects or from epidemic areas. ⑤ Take the most suitable cultivation measures for exotic tree species. For example, southern trees move northward, and fertilization is required in the early stage of annual growth, and no fertilization or irrigation is required in the later stage. For 1 ~ 2-year-old southern saplings, wind barriers or soil burial can be set up in winter; Trees in the north move to the south, shade sheds should be built in summer, and Chinese fir should be inoculated with * * * bacteria.

philology

Wu et al. Introduction to Introduction of Foreign Tree Species, Science Press, 1983.