The sustainability of natural resources and environment is the foundation of urban sustainable development. In the process of accelerating urbanization, resources provide impetus for economic development, which naturally determines the boundary of sustainable development of urban economy. With the continuous improvement of urbanization level, the demand for water resources in most cities in China has increased sharply, and the contradiction between supply and demand has become increasingly acute. As one of the indispensable resources for urban development, water resources have become one of the important factors restricting the sustainable development of cities.
Keywords: urban sustainable development; Water resource limitation; Institutional innovation
1 Introduction
The 16th National Congress of the Communist Party of China regards "the ability of sustainable development has been continuously enhanced, the ecological environment has been improved, the efficiency of resource utilization has been significantly improved, the harmony between man and nature has been promoted, and the whole society has embarked on the development road of production development, affluent life and good ecology" as one of the goals of building a well-off society in an all-round way in China. It can be highlighted that resources and environmental problems are the core issues of sustainable development, and the essence of this problem is that social and economic activities exceed the carrying capacity of natural ecosystems. Studying the problem of resource constraints, seeking effective ways to get rid of the constraints of environment and energy, and realizing the sustainable development of economy and society have become the primary problems of local economic and social development in China during the Eleventh Five-Year Plan period.
City is the core of regional system and the key to realize sustainable development. In the process of accelerating urbanization in China, resources provide impetus for economic development, which naturally determines the boundary of sustainable development of urban economy. The sustainability of natural resources and environment is the foundation of urban sustainable development. With the continuous improvement of urbanization level, the demand for water resources in most cities in China has increased sharply, and the contradiction between supply and demand has become increasingly acute. As one of the indispensable resources for urban development, water resources have become one of the important factors restricting the sustainable development of cities.
2 Resource constraints for sustainable economic development
2. 1 Internal energy consumption and supply constraints
From the physical point of view, everything is produced by energy, and sustainable development fundamentally involves the sustainable utilization of energy and its various specific material resources. In the process of economic development, there are three systematic problems: internal energy consumption, entropy increase and ecosystem carrying capacity, from which the problem of sustainable development actually arises.
According to the first law of thermodynamics, the amount of energy in nature is constant in the process of transmission and transformation, that is, energy conservation. But in fact, the more important significance of the law of conservation of energy is that the increase of internal energy in a system is equal to the heat Q absorbed by the system and the work W done by the outside world to the system. Namely:
△U = Q + W
In order to do work, the system either consumes internal energy or absorbs energy from outside the system. Social and economic development is essentially an act of energy use, consumption and transformation. If a city is regarded as a system, it must provide production and living services for the population within the city by consuming various renewable and non-renewable resources. Due to the unreasonable or over-quota use of resources by cities, the consumption of resources by cities not only meets the development needs of contemporary cities, but also sets constraints for the long-term stability and sustainable development in the future, and this constraint is becoming more and more obvious.
At present, the developed countries in the world, because of their "pioneer" position in economy, show the input of resources in international trade, thus consuming 80% of the world's energy with 10% population, showing the advantages of absorbing external resources and increasing "internal energy". Since the industrial revolution, the rapid economic development of western countries is largely based on the continuous absorption of resources from economically backward countries. However, due to the backward economy and technology, international trade in developing countries is characterized by the export of resource-based primary products, and the internal energy consumption and supplement in economic development are mainly limited to domestic solutions. This is why developing countries will encounter serious resource carrying capacity constraints when they consume a lot of energy, while developed countries will not, or the symptoms are much lighter. This is also the first constraint on the economic development of developing countries, that is, internal energy consumption and supply constraints.
2.2 entropy increase and negative externalities constraints
According to the second law of thermodynamics, entropy is also a quantity representing the internal characteristics of a system. In a system, with the continuous utilization of energy, the useless energy that can no longer do work is increasing, that is, the total entropy is increasing, thus forming the law of entropy increase. The only way for an organism system to get rid of death is to constantly absorb negative entropy from the environment, so as to balance the entropy increase mechanism and maintain the system balance. In an urban system, economic growth depends on the support of a large amount of energy consumption, which will lead to the continuous accumulation of entropy, including a large increase of wastewater, waste gas and waste related to the specific form of entropy. The increase of entropy will greatly expand the negative externality of economic development, lead to the imbalance of ecosystem and the weakening of life support system, and produce the problem of ecological sustainability. Ecological sustainability is the basis of economic sustainability and social sustainability, which makes maintaining the balance of ecosystem in the process of economic development a basic condition for achieving sustainable development.
In the aspect of entropy balance mechanism, developed countries use their scientific and technological advantages and economic upstream position to absorb a lot of negative entropy (resources and profits) from developing countries with low economy and potential, and transfer a lot of negative externalities such as high pollution and high energy consumption industries and entropy diffusion, thus maintaining the balanced development of economic systems and ecosystems in developed countries. Developing countries are completely different, because of their low economic potential, their ability to absorb negative economic entropy and transfer negative externalities from outside the system, especially from developed countries, is much weaker. It is this difference in development constraints that leads some developed countries to squander energy almost unscrupulously, while developing countries with low economic status have to absorb more negative entropy from their own countries to promote their economic development and accumulate negative externalities such as entropy increase brought about by economic development at home. This constitutes another important constraint in the process of economic development in developing countries, namely, entropy increase and negative externality constraint. Controlling internal energy consumption within the limits of economic resources and controlling entropy increase within the carrying capacity of the biosphere is not only a concrete explanation of these two constraints, but also a long-term condition for developing countries to achieve sustainable development.
It is concluded that sustainability is essentially a "constraint" problem. Both developed and developing countries have different levels of understanding and effectiveness of sustainable development due to economic differences, but cities as the core of regional systems, especially those in developing countries, are in an unfavorable sustainable environment due to the dual constraints of internal energy supplement and entropy increase, so it is more important to implement sustainable development strategies.
3 the relationship between water resources and urban sustainable development
3. 1 Concept and basic characteristics of urban water resources [1][2]
Urban water resources refer to all water sources that can be used by the city, have sufficient quantity and quality, and can supply water for urban residents' life and industrial and agricultural production, including local natural fresh water resources, external water transfer resources, renewable water, used water and treated sewage. Urban water resources are an important material basis for urban survival and development, a prerequisite for the normal and stable operation of urban social production and people's lives, an objective guarantee for giving full play to the multi-functional role of cities and promoting the realization of economic benefits of urban agglomerations, and one of the basic elements for measuring urban attractiveness and radiation and evaluating urban investment environment.
Generally speaking, urban water resources show the following characteristics because of its special status and function:
(1) large concentration, mainly manifested in the large and concentrated demand for water resources in cities;
(2) Sustained stability means that the water demand and water quality requirements of the city are relatively stable in different seasons;
(3) High efficiency, indicating that the same amount of water has higher social and economic benefits for the city;
(4) Systematization, manifested in three aspects. First of all, there is an exchange of quality and quantity between different types of water (seawater, atmospheric precipitation, surface water, groundwater and wastewater). Second, the water resources inside and outside the city are usually in the same water resources system, and there is a close hydraulic connection between them. Third, the different links in the process of urban water resources development and utilization (such as water intake, water supply, water use and drainage) are an organic whole.
(5) finiteness, characterized by limited water resources and limited development and utilization of urban water resources;
(6) Vulnerability is manifested in two aspects. First of all, water resources are easily polluted because of the large number, wide area and high intensity of pollution sources in urban areas. Second, it is easy to be destroyed, especially groundwater. When the exploitation exceeds the supply, the quality and quantity of water resources will be out of balance, which will also lead to a series of environmental geological problems.
(7) Regeneration means that the utilization of urban water resources is not one-off, but has the characteristics of multi-purpose and recycling;
(8) Commerciality, because in the development and utilization of urban water resources, the government and water supply departments have invested manpower and material resources and paid a lot of socially necessary labor, and the value of water resources has been realized through exchange, creating economic benefits for all kinds of water users. Therefore, urban water resources are both public and commercial.
3.2 The meaning of water resources constraints
Water resource constraint refers to the shortage of water resources needed for economic and social development, which restricts development. Its manifestations are: first, the shortage of water resources faced by economic and social development in the short term; The second is the potential constraint of water supply on long-term development. With the rapid economic growth and increasing population in China, the demand for water resources is rising, and the growth mode of extensive economic has not been effectively changed. In particular, some industries with high resource consumption, blind investment and low-level repeated construction are more serious, with low water resources utilization efficiency and serious pollution waste, which makes the contradiction between supply and demand of water resources increasingly acute.
The restriction of water resources on social and economic development is reflected in the following aspects: First, water resources are the source of life and an indispensable material condition for maintaining life, and the existence of water plays a decisive role in people's lifestyle. Second, water resources constraints restrict the scale and growth rate of economic development. The total water resource constraint determines the scale and growth rate of long-term economic development, while the resource constraint caused by water shortage will inhibit short-term economic development and often become the "bottleneck" of short-term economic development. Thirdly, the characteristics or imbalance of water resources in time and space structure in China have formed structural constraints of water resources. Economic development structure is a model of economic development, or an economic development model is a dynamic description of economic development structure. Water resource constraints limit the choice of economic development model, and certain water resource constraints determine certain economic development model.
3.3 constraints of water resources on urban sustainable development
Through the above analysis, this paper holds that the constraints of water resources on urban sustainable development are various and multi-angle, mainly manifested in functional constraints, ecological constraints, economic constraints and institutional constraints. Some of these constraints are naturally formed and need to be improved through artificial adjustment, and some are caused by unreasonable production and lifestyle in the process of urban development. This constraint needs to be improved by improving people's ideology and innovating related supporting systems.
Functional limitations. Since ancient times, water has existed with cities. For example, except for a few military towns, almost all cities in the world are built by rivers, lakes and beaches, especially those engaged in commodity trading activities. Water resources are limited, and their distribution in time, space and region is extremely uneven. Different regions and cities have different regional characteristics and advantages due to different historical and geographical positions. Therefore, the planning and exertion of urban functions are restricted. To alleviate this constraint, it is generally necessary to make artificial adjustments, such as the Luanhe River Diversion Project in Tianjin, the Heihe River Diversion Project in Xi, the Yellow River Diversion Project in Beijing and the famous South-to-North Water Transfer Project.
Ecological constraints. This restriction is mainly manifested in the deterioration of urban water environment with the development of the city. In the development and utilization of water resources, many cities in China only pay attention to the pursuit of economic benefits and water conservancy benefits, without protecting and improving the water environment, resulting in a series of ecological problems. It has caused ecological obstacles to the further development of the city in the future. Ecological constraints are both long-term and difficult to repair. That is, once the urban water resources are destroyed, its impact will not be reflected in a short time, and its impact will be long-term and it will take a long time to control the water body.
Economic restrictions. The influence of water resources on urban economy is an indirect binding force. As an indispensable urban infrastructure, urban water resources always determine the quality and survival of a city. To a certain extent, the quality of water environment has become one of the standards to measure the civilization and advanced degree of a city. At the same time, investment in water environment restricts government behavior economically. Once the urban water environment is destroyed, it will inevitably affect the infrastructure environment of urban production and life. This will have a restrictive impact on the hard environment of urban investment, and to some extent affect the rapid and sustainable development of urban economy.
Institutional constraints. Institutional constraints are mainly manifested in the constraints of urban managers on urban sustainable development due to the defects of the water resources development and utilization system itself. Any kind of urban water resources development system is established according to the objective situation at that time, in order to complete a specific stage goal, which has certain timeliness. However, the development and change of objective things are independent of people's subjective will, and the passage of time will greatly change the conditions for the existence of some things. So is the urban water resources development system. If it is not adjusted according to the change of objective conditions, it will inevitably lead to institutional defects and then lead to decision-making mistakes. We must accelerate institutional innovation, guide urban water system planning and the formulation of relevant technical, economic and investment policies, and promote a virtuous circle of urban development.
4 under the constraints of water resources to improve the ability of urban sustainable development countermeasures
According to the basic national conditions of water shortage in China, in order to improve the sustainable development ability of cities in the future and build a resource-saving society, we must choose a water resources combination model different from developed countries, that is, a non-traditional modernization road. The key lies in promoting water conservation, eliminating water waste, changing traditional production methods, reducing water consumption, improving water utilization rate, productivity and water carrying capacity, thus alleviating the contradiction between supply and demand.
First of all, it is necessary to raise the awareness of the whole nation about resource hardship and saving, establish the concept of saving resources in the whole society, cultivate the social fashion of saving resources for the whole people and create a good environment for saving resources for the whole people. It is necessary to promote resource conservation to the height of the basic national policy, incorporate the goal of building a resource-saving society into the national economic and social development plan, establish an index system that comprehensively reflects Scientific Outlook on Development's outlook on political achievements, such as economic development, social progress, resource utilization and environmental protection, build a "green economy" assessment index system, realize the unity of "political achievements index" and "green index", and completely change the one-sided pursuit of growth. [3]
Secondly, the city government should firmly establish Scientific Outlook on Development, change the way of overdraft resources development, adjust the economic structure and urban layout, and take the road of circular economy with China characteristics. Fundamentally solve the sharp contradiction between economic growth and water resources and environment encountered in the process of urban development. According to the requirements of Scientific Outlook on Development, we should give priority to the protection and conservation of water resources, fully consider the carrying capacity of water resources, and dialectically understand the relationship between water resources and economic development. Increase the rational development of water resources and strive to improve the effective supply level. Adjust the energy structure, choose clean energy as much as possible, and establish a "low consumption and high efficiency" social and economic structure.
Third, for some cities, water shortage has affected the sustainable development of urban economy. While consuming the original small amount of water resources in the city, in order to solve the problem of insufficient water resources, we should actively open up new water sources. At present, it is mainly alleviated by cross-regional water transfer projects. However, when reasonably transferring water across regions, we should take the principle of maintaining the balance of regional water resources system, and fully realize that this cross-regional water transfer project can not fundamentally solve the problem of urban water shortage. Excessive water transfer is essentially an unbalanced transfer behavior of water resources system in different places, which will be accompanied by a large environmental effect in the water transfer area.
Finally, to realize the sustainable development of the city, the key is to speed up the innovation of the management system of urban water resources development. The key is to attach importance to the application of economic operation mechanism in water resources management, mainly relying on relevant economic policies formulated by government departments as economic levers to indirectly regulate and influence water activities such as development, utilization and protection of water resources. [4] So as to promote the sustainable utilization of water resources and ensure the sustainable development of cities.
As a valuable natural resource, once the land resource is degraded, it is difficult to recover in a short time, and its utilization is also very difficult. Only when the utilization does not exceed the carrying capacity of land can the sustainable utilization of land resources be realized. Due to economic development, land resources are facing increasing pressure. When this pressure exceeds the carrying capacity of land resources, it leads to the occurrence of land degradation. As the foundation of terrestrial ecosystem, the degradation of land resources is manifested in the reduction of soil fertility, biodiversity and backward economic development. At present, the basic method to control land degradation in the world is still the biological method based on ecological theory. However, the research of restoring land degradation and rebuilding ecosystem needs long-term and well-designed experiments. The importance of the ecotone between oasis and desert is not only that it is the protective barrier of oasis, but also plays a great role in the development of oasis economy. By reviewing a large number of studies at home and abroad, the methods used in long-term experiments in different regions are discussed. The restoration and ecological reconstruction of degraded land involving human factors can achieve obvious results in a short period of time. The causes of land degradation are not only natural factors such as land resources and natural environment characteristics, but also some social and economic factors. Therefore, the restoration of degraded land and the success of ecological reconstruction need a method that comprehensively considers natural, social and economic factors.
Sustainable development of land resources;
As a valuable natural resource, once the land resource is degraded, it is difficult to recover in a short time, and its utilization is also very difficult. Only when the utilization does not exceed the carrying capacity of land can the sustainable utilization of land resources be realized. Due to economic development, land resources are facing increasing pressure. When this pressure exceeds the carrying capacity of land resources, it leads to the occurrence of land degradation. As the foundation of terrestrial ecosystem, the degradation of land resources is manifested in the reduction of soil fertility, biodiversity and backward economic development. At present, the basic method to control land degradation in the world is still the biological method based on ecological theory. However, the research of restoring land degradation and rebuilding ecosystem needs long-term and well-designed experiments. The importance of the ecotone between oasis and desert is not only that it is the protective barrier of oasis, but also plays a great role in the development of oasis economy. By reviewing a large number of studies at home and abroad, the methods used in long-term experiments in different regions are discussed. The restoration and ecological reconstruction of degraded land involving human factors can achieve obvious results in a short period of time. The causes of land degradation are not only natural factors such as land resources and natural environment characteristics, but also some social and economic factors. Therefore, the restoration of degraded land and the success of ecological reconstruction need a method that comprehensively considers natural, social and economic factors.
Key words: ecological reconstruction of land degradation oasis-desert ecotone
1. Introduction
At present, land degradation has become a serious global problem, which has aroused widespread concern. The International Convention to Combat Desertification signed by all countries in the world in 1992 defines desert as: land degradation, including desertification, salinization, grassland degradation and soil erosion. From the United Nations Conference on Desertification in Nairobi in 1977 to the World Conference on Environment and Development in Rio de Janeiro in 1992, and then to the signing of the United Nations Convention to Combat Desertification in Paris in 1994, desertification has always been an environmental and social issue of great concern to governments and scientists all over the world. China is one of the countries most seriously affected by desertification, and the prevention and control of desertification has also been included in China 2 1 Century Agenda by our government, which is one of the key environmental problems to be solved in implementing the sustainable development strategy. The total area of desertification in different areas of China is 2.622 million square kilometers, accounting for 27.3% of the national territory. Among these areas, 1 148000 square kilometers are distributed in arid areas, accounting for 43.8% of the total desertification area, and it is still expanding at a relatively fast speed [1].
In arid areas, mountains, oases and deserts are regional ecological landscape unit systems linked by surface and underground water sources. In this system, the oasis unit was formed in geological period, and its vegetation ecological type is mainly composed of hidden wet plant communities, while the desert unit is composed of obvious xerophyte and super xerophyte communities, and the ecological type between them is composed of mesophyte communities. The sustainability of the ecological ecotone outside the artificial oasis is the fundamental guarantee to realize the sustainable development inside the oasis. Some research results show that [3-7], compared with oasis and desert ecosystem, the ecotone between oasis and desert has a strong "ecological gradient" due to the difference of environmental conditions such as water source, and is easily disturbed by the change of water source. Since the historical period, the main objects of human large-scale land development are almost all natural oases, so that natural oases almost no longer exist, and this transitional zone has become the object of further development and utilization (reclamation, grazing and firewood cutting). Under certain water source conditions, due to the changes of vegetation ecological factors (water quantity, water level, salt content and soil physical and chemical properties) caused by human activities such as water and soil resources utilization and natural forces, the reverse succession of plant communities and land desertification will inevitably occur in the transitional zone. At present, the most common desertification areas in arid areas are almost all in the oasis-desert ecotone. Such as the southern edge of Gurbantunggut Desert in Junggar Basin and the oasis edge of Hexi Corridor.
2. Regional characteristics:
Relying on the blocking of water vapor by tall mountains, there is basically a complete natural band spectrum in arid areas [8], and water factor is the key factor to control the distribution of natural band spectrum. When water is relatively concentrated in some areas for some reasons, such as rivers and springs overflowing, these areas form oases. With the decrease of water content, the vegetation type of oasis changes from recessive wet plant type to dominant xerophyte type and super xerophyte type, and the transition zone between them is the so-called oasis-desert transition zone. Under natural conditions, after long-term evolution, the ecosystem in this area is in a stable climatological climax system that adapts to the climate. Functionally, the ecotone between oasis and desert can not only be used as a pasture for grazing livestock and wild animals, but also increase the roughness of the underlying surface, inhibit the development of desertification and protect the oasis from sandstorms. At the same time, the oasis-desert ecotone is also the interface area where energy, material and information exchange between oasis ecosystem and desert ecosystem is the most frequent. Habitat is fragile and sensitive, and its desertification status is a direct reflection and concentrated expression of external interference conditions such as human activity intensity and natural climate change. This research has always been the key field of desertification-related research in arid areas.
Gurbantunggut Desert is located in Zhungeer Basin, which is a fixed and semi-fixed desert. Although the desert vegetation here is sparse and the natural productivity is very low, it plays an important role in fixing sand dunes. After the 1950s and 1960s, the Production and Construction Corps established many state-owned farms in the oasis and oasis-desert ecotone on the edge of the desert. Taking the northern foot of Tianshan Mountain and the southern edge of Gurbantunggut as examples, it only accounts for 8.67% of the total land area, but the gross industrial and agricultural output value accounts for 5 1.26% of the total industrial output value, while the gross industrial output value accounts for 70.24% of the total industrial output value, which is the highest level of industrial and agricultural production in Xinjiang [9]. Due to excessive human activities, the natural environment, especially the natural vegetation, in the oasis-desert transitional zone in this area has been seriously damaged. According to the research in Xia [10], in the 1950s, fixed and semi-fixed sand dunes occupied most of the desert, but in the 1980s, along the junction of desert and oasis (transitional zone), 500 kilometers of strip-shaped movable sand dunes appeared, affecting 20 counties and state farms. In Mosuo Bay Reclamation Area, mobile sand dunes, ranging in width from 5 to 20 kilometers, appear in many places, which has become a serious environmental problem in this area today.
Another phenomenon that widely exists in arid areas and is aggravated by human activities is soil salinization. Due to the unreasonable utilization of water resources, soil salinization caused by the rise of groundwater level is the most prone problem in the development of irrigated agriculture. Because of strong evaporation and less precipitation in arid areas, soil is more prone to salinization due to unreasonable irrigation, which is the primary problem of agriculture and soil research in Xinjiang. For the ecotone between oasis and desert, due to unreasonable management, soil fertility is seriously reduced after reclamation, and salinization is forced to abandon farming, which is widespread in many areas. Because the original vegetation has been destroyed and the soil structure has deteriorated due to salinization, it is difficult for new vegetation to grow again, which has become a new source of sandstorms and aggravated the deterioration of the natural environment. Since 1970s, Li Shugang and Wang studied the typical types and characteristics of desert alkaline earth distributed in Junggar Basin, and discussed the chemical characteristics [1 1], clay minerals [12] and humus characteristics [13] of desert alkaline earth. Their monograph [14] focuses on the formation, types, characteristics and improvement of desert alkaline earth, and systematically classifies desert alkaline earth. Understanding and management of desert alkaline earth is also an important part of oasis-desert transition zone management.
Oasis-desert transition zone is in a special position in arid area. On the one hand, limited by harsh natural conditions, the ecosystem in the coverage area is extremely fragile. On the other hand, various human activities, such as chopping wood, grazing and land reclamation, are mainly negative, and the intensity of destruction is far greater than that of protection. Huang Peiyou [15] pointed out the phenomenon of landscape differentiation caused by development for the first time through a long-term study on the relationship between vegetation and desert environment, and put forward the process of transforming from a single landscape to an oasis, an oasis out-of-bounds area and a desert that maintains its natural state. The scope of this forbidden area is basically the same as that of the oasis-desert transition zone mentioned above. Due to the strong influence of human activities (overgrazing, logging, land reclamation, etc.). ), vegetation decline, ecosystem collapse, fixed dune activation and other phenomena occur from time to time in this area. There are some researchers [16]. According to this view, the causes and scope of the forbidden area were studied, and it was concluded that excessive logging and grazing were the main reasons for the serious degradation of vegetation. According to the range of human activities, it is defined as 40-60 km, especially 0-40 km zone on the outer edge of oasis. Pan Xiaoling [17] proposed that this vegetation zone (oasis-desert ecotone) has changed from a real transition zone to a fault zone, and this area has also changed from a barrier to maintain oasis stability to an alien invasion that threatens the existence of oasis.
3. Overview of the study:
Vegetation degradation in oasis-desert ecotone is firstly carried out under the background of arid environment. Due to harsh natural conditions. Such as drought and little rain, poor soil and high salt content, although the vegetation in this area can exist in the form of top-level ecosystem with little influence from human activities. However, due to the lack of plant species, low coverage and simple type structure, the structural function, input and output of matter and energy of the ecosystem are in a very unstable state, and the balance is easily broken. The reasons leading to the degradation of oasis-desert ecotone can be roughly divided into human factors and natural factors.
In recent years, all kinds of studies on the influence of natural factors have focused on abnormal global changes, especially the trend of climate development in the middle latitudes towards warming and drying. For example, Wang Tao and others [18] think that the development of global climate, especially in mid-latitude areas, is a big ecological background conducive to the development of desertification. Gao Shangyu et al. [19] pointed out that the aggravation of sandstorm disaster in China is caused by large-scale development of sediment yield under the background of climate warming, and the future development of sandstorm disaster in China mainly depends on the temporal and spatial distribution of falling water, the change of wind in sand area and the adjustment of land use pattern under the background of climate warming. Through the study of sandstorm disaster in China, Shi et al. think that the serious sandstorm is aggravated year by year because of the expansion of desertification land under the background of dry and warm climate. Dong Guangrong and others [2 1] have studied the climate fluctuation in northern Xinjiang since 1950s, and the general trend is towards drought. Through the summary of the above research, it can be considered that the current global climate change, especially the trend of climate development in mid-latitude areas, provides a great background for the degradation of oasis-desert ecotone in arid areas.
Oasis is a hidden landscape developed in arid areas, and global climate change is the basic factor to control its existence and development. However, in recent 50 years, the scale of oasis has expanded rapidly, and the oasis-desert ecotone has been seriously degraded, and human factors have played a major role, which is the consensus reached by many researchers at present. The study of historical documents on the southern edge of Gurbantunggut Desert shows that [22] when there is little human influence, the vegetation in this area is very lush. The northern route of the ancient Silk Road, also known as the Tang Dynasty Road, which can still be seen now, shows that there used to be a green corridor in this area. The investigation in the early days of the founding of the People's Republic of China also showed that there was a large area of natural Haloxylon ammodendron in this area [23]. Even now, in some well-protected areas, such as the east of Fubei Farm and the north of Tang Chao Road, there are still 220,000 mu of Haloxylon ammodendron forest, and the vegetation coverage rate is above 30%.
Considering human factors, the definition of soil degradation proposed by Bridges [24] may better describe the land degradation in the oasis-desert ecotone: the reduction of soil's current or future ability to support life caused by human beings. Therefore, the restoration of land productivity and the renewal of vegetation are the core issues in this area. Because the degradation of oasis-desert ecotone has become a serious problem, the local government and people have made considerable efforts to this end. Recently, with the development of economy, coal has gradually replaced firewood, and people cut down shrubs as fuel less and less. The environmental awareness of the government and the masses has been greatly enhanced, and most of the oasis-desert ecotone has been closed or relatively closed. The natural ecosystem is recovering, but the recovery speed is extremely slow due to bad conditions. However, there is another potential in this respect.