The axis of the Yangtze River plays an important role in the national land development and is unique in the world. Building the Yangtze River Economic Belt is of exemplary significance not only to China, but also to the world. From the successful experience of macro-strategy of regional development in developed countries and domestic countries, effective institutional mechanisms and targeted supporting policies are the primary measures to promote the rapid development of key regions (Lu Dadao et al.,1999; Yang Guishan et al., 2007). Therefore, we should effectively establish the strategic position of the first-level axis of the Yangtze River Economic Belt from the aspects of national policies and institutional mechanisms.
Since the reform and opening up, regional policies have lacked consideration for the overall construction of the Yangtze River Economic Belt. Starting from the T-shaped strategy, the Yangtze River Economic Belt and the coastal areas are both the first-level axes of land development, and the two axes should be considered in the same important position. However, for a long time, from the perspective of the government, the Yangtze River Economic Belt has not been taken as the strategic arrangement of the first-level axis of land development, nor has it been issued with targeted regional development policies. Since the "Sixth Five-Year Plan", the state's policy on regional strategy has mostly considered the three major regions: the east, the west and the middle, which is consistent with the state's overall regional development strategy at the end of the 20th century, that is, giving priority to efficiency and supporting the eastern region to take the lead in development. Since the Ninth Five-Year Plan, the strategic focus of national development has gradually shifted to the central and western regions. However, due to the differences in factor endowments, the development gap between the eastern and western regions is getting wider and wider after the implementation of the policy of giving priority to the best. The government's regional policy pays attention to both advantageous areas and problem areas or special areas, such as poverty-stricken areas and ethnic minority areas, and lacks regional overall consideration and arrangement for the Yangtze River axis across the eastern, central and western regions. In fact, the Guiding Opinions issued by the State Council and the forthcoming Development Plan of the Yangtze River Economic Belt regard the Yangtze River Economic Belt as a policy area, and make overall plans for the integrated development of the economic belt from the government level and formulate corresponding regional policies.
3.2 Ensure the orderly development of the Yangtze River Economic Belt by constructing an efficient land spatial structure.
The "Thirteenth Five-Year Plan" period is not only an important period for the implementation of the national main functional area planning, but also an important opportunity for the Yangtze River Economic Belt to rebuild an efficient land space. There are 85 counties and cities in 9 provinces and 2 cities along the Yangtze River Economic Belt (Table 4), with a land area of 4.2× 104 km2, accounting for about 30% of the national optimal development area. There are 423 counties and cities in key development zones, with a land area of 46.3× 104 km2, which is more than 1/3 of the total area of key development zones at all levels in China. There are 365 counties and cities with a land area of 66.9× 104 km2, of which the area of major agricultural production areas in China is close to 1/3 of that of similar functional areas in China. There are 302 counties and cities in the ecological function zone, with a land area of 88.4× 104 km2.
In the future, we should build a national spatial pattern with clear functions and equal emphasis on development and protection with the help of the implementation of the main functional area planning (Fan Jie, 2006, 2007). The optimized and key development areas of the Yangtze River Economic Belt account for about 15% of the Yangtze River Economic Belt, mainly concentrated in the downstream and along the Yangtze River. Among them, the optimized development zone mainly undertakes key tasks such as high-end service industry agglomeration, manufacturing transformation and upgrading, and urbanization quality improvement in the future land space construction of the Yangtze River Economic Belt; The key development areas are the main areas for the future economic growth of the Yangtze River Economic Belt and the key areas for cultivating new urban agglomerations. Among them, the key development areas along the middle and upper reaches will play an important role in promoting the process of new industrialization and enhancing the ability of industry and population agglomeration. 90% of the main agricultural producing areas are national agricultural producing areas, almost all of which are distributed in the middle and upper reaches. In the future, on the one hand, we should give full play to the labor advantages of traditional agriculture and agricultural technology, establish a modern agricultural system, and provide superior agricultural products and agricultural technology services for the whole country; On the other hand, give full play to the advantages of diversified resources, establish a characteristic agricultural system, and provide diversified agricultural products and agricultural and rural leisure space for economic belt areas and urbanized areas. The key ecological functional areas account for more than 40% of the Yangtze River Economic Belt, of which more than 2/3 are at the national level and more than 2/3 are distributed in the upper reaches. The ecological function zone is located in the important subtropical mountain forest and wetland ecosystem in China. It is an important biodiversity protection and ecosystem diversity protection area in China, and also an important water conservation, soil and water conservation and rocky desertification prevention and control area in the Yangtze River basin.
3.3 Accelerate the improvement of comprehensive transportation capacity and support sustained and steady economic growth.
From the international experience, we can grasp two key issues in developing the river basin transportation capacity: one is the smoothness of waterway transportation, and the other is the convenience of land-water combined transportation (Liu, 20 13). In order to ensure the smooth navigation channel, according to the Comprehensive Three-dimensional Traffic Corridor Planning of the Yangtze River Economic Belt (20 14-2020), it is planned that the mileage of the Yangtze River high-grade waterway will reach 1.2× 104 km by 2020, accounting for 13.48% of its waterway mileage. In addition, the middle and lower reaches plan to extend the 12.5 m deepwater channel to Nanjing, the middle reaches plan to implement the waterway regulation project of Jingjiang reach, and the upper reaches plan to implement the waterway regulation project of Chongqing-Yibin section. At the same time, the engineering model tests and demonstration studies are carried out on Yichang-Anqing and Yibin-Shuifu waterways. Due to the large amount of sediment in the Yangtze River, shoals, branches and Jiang Xinzhou in the middle and lower reaches are widely distributed. On the one hand, the waterway regulation project will have a certain impact on the natural waterway, the direction of sediment migration and the stability of shoreline nodes (Qian Ning et al.,1987; Wang Chuansheng, 1999, 2010); On the other hand, waterway engineering maintenance costs a certain amount of money every year, so waterway regulation must be based on scientific model test and environmental impact assessment. According to the experience of developed countries, in addition to waterway regulation, the implementation of ship form standardization is also one of the measures to tap the potential of inland river shipping. Luo Shigang's (2006) research shows that the number of inland shipping vessels in developed countries is far less than that in China, but the average tonnage of each vessel is much larger than that of the Yangtze River. The average tonnage of ships in the trunk line of the Yangtze River is 750 t, among which the average tonnage of ships in Changhang Group is1360 t. Compared with developed countries, the average tonnage of inland ships in Germany is 1.395t, that in Russia is 1.383t, and that in the Mississippi River in the United States is1.350 t. Moreover, the inland ships in these countries have implemented standardized ship types, and the inland waterways have basically been channelized, and the transport indicators in terms of efficiency (including gate crossing efficiency), quality, energy saving and environmental protection are better than those of the Yangtze River inland transport ships. Therefore, at present, while waterway regulation, we should continue to speed up the process of ship type standardization suitable for the existing waterway of the Yangtze River and fully tap the potential of the existing waterway.
Therefore, we should take the implementation of the Comprehensive Three-dimensional Traffic Corridor Planning of the Yangtze River Economic Belt (20 14-2020) as an opportunity to further optimize the comprehensive traffic network pattern. According to preliminary statistics, the Yangtze River Port transfers about 5,000×104 t of goods by railway every year, which is less than 2% of the proportion of goods collection and distribution in the Yangtze River Port, far below the average proportion of 30% in developed countries. Among the ports of the Yangtze River trunk line, there are less than 10 ports that can transport molten iron, and only 65 berths are directly connected with the railway. At the same time, many ports lack the connection with expressway trunk lines, which makes a large number of hinterland logistics give up water transportation, which greatly affects the potential of Yangtze River shipping. At present, we should focus on Chongqing, Wuhan, Nanjing and other important land and water transportation hubs, organize an efficient collection and distribution system, and improve the convenience of land and water transportation; Accelerate the construction of connecting lines in important port areas such as Chongqing, Wuhan and Nanjing, promote the channel construction between ports and national new areas and coastal logistics parks, expand the hinterland of port collection and distribution by effectively solving the "last mile" problem, and enhance the comprehensive shipping service capacity.