Time-space evolution of the goods export network of the Belt and Road countries: The view of weighted complex network

1 Introduction

Promoted by differentiated resource endowment and highly complementary industrial structure, the export of goods among the Belt and Road countries grows rapidly. In 2003, the total exports volume 82 sample Belt and Road countries is $750.7 billion US dollars, which rapidly climbs to $3,305.9 US dollars in 2018 with a 2.2 times growth rate compared with that of global exportation volume in the same period. The total trade volume of internal goods export network accounts for 17.6% of global exportation volume in 2018, up from 10.1% in 2003 [2]. The development of exports network of the Belt and Road countries helps undeveloped countries to get rid of the manufacturing-return predicament caused by European and American countries’ “reindustrialization” strategy [3]. Therefore, it is of greatly practical significance to study the time space evolution of goods export network of the Belt and Road countries.With the rise of network analysis methods, scholars have analyzed the topological structure characteristics and evolution laws of trade networks, pointing out that global trade networks have the characteristics of scale-free, heterogeneity, and like a small world [1].

And some scholars find out that a few countries having strong connections in the network are more clustered [4, 7], thus the network presents a layer structure of “core-semi edge-edge” [6, 8]. Since the launch of the Belt and Road Initiative, many domestic scholars start to utilize network analysis method to study the trade behaviors under the Belt and Road Initiative. Zou and Liu (2016) find out that China is the most important core country in the sub-trade network in the sub-trade network consisting of China and Southeast Asian countries by utilizing cohesive subgroup and core-edge models [9, 11]. Liu, Xu, and Zhang (2019) find out that the trade network of the Belt and Road countries is mainly composed of central and eastern trade blocks along with Asian trade block by using block model. Yang, Du, and Ma (2018) study the topological features and spatial structure of the network and finds out that trade network of the Belt and Road countries has characteristics including small world, scale-free, and “core-edge” and the like [12]. Besides, some scholars also analyze the network structures of high-end manufacturing, steel [10], agricultural products [13], transportation, oil and other subdivided products under the Belt and Road Initiative.

However, most studies are based on undirected topological networks. Topological network is an abstract representing the real network, thus cannot accurately reflect the difference of trading capabilities between countries. Moreover, excessively high threshold setting of topological networks may lead to some small trading countries to be ignored, while excessively low threshold setting fails to distinguish each country’s trading capability [14]. In addition, most studies use the total volume of bilateral trade to measure the trading relationship between two countries, on which the undirected network based cannot show the trade flow relationship between two countries. While merely studying exports, the ability of countries to export commodities, technologies and other heterogeneous resources can be further investigated. Therefore, this paper uses each country’s bilateral exportation data to construct a weighted complex network of goods flows of the Belt and Road countries. Based on the systematic investigation of the overall scale and structure evolution of the network, each country’s centrality status in the network is measured by weighted centrality and PageRank index, and changes of each country’s influence is measured by Hubbell influence index. Finally, the spatial clustering relationships and the correlation relationships among each block can be revealed by utilizing block model. The above studies are helpful to clarify the evolutionary mechanism of the goods export network under the Belt and Road Initiative, identify each country’s role in the network and trade incidence relations among each block, and provide empirical support for the relevant theoretical studies such as division of production network and south-south cooperation to a certain extent.

2 The construction and analysis methods of the goods export network under the Belt and Road Initiative

3 The whole scale and structure evolution of exports network under the Belt and Road Initiative

With continuous expansion of the scale of the economic and trade cooperation of the Belt and Road Initiative, the characteristics of spatial unbalanced development in the goods export network becomes more and more obvious, and the network presents a “core-edge” layer structure (see Fig. 1).

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Fig. 1

The evolution of export of goods network under the Belt and Road Initiative.

(In the same year, the larger the legend of the node, the darker the color of the legend, indicating the larger the export volume of the country. The thicker the line between the nodes, the greater the export volume between the two countries. However, the node legend size, color depth and line thickness in different years are not equal to the proportion of actual export volume.)

In 2003, a network structure was established with China, Italy, South Korea, Singapore and Russia as core, and Malaysia, Austria, Thailand and Indonesia as second-tier core in the exports network under the Belt and Road Initiative. In the network, 682 relations with an export value of more than US $100 million have been established, of which China and Italy have established relationships with an export value of more than US $100 million with more than half of the sample countries. The calculated modularity value is 0.369, showing that the community in goods export network under the Belt and Road Initiative is obviously divided. As research shows: the goods export network under the Belt and Road Initiative has primary formed intra-European and CIS trade network with Italy, Russia and other countries as the main body, the Asia-Pacific intra-trade network with China, South Korea, Singapore, Malaysia, Thailand and Indonesia as the main body, as well as the West Asia and Africa intra-trade networks and the Central and South America intra-trade networks whose trade volume are relatively small. China, Italy, South Korea, Singapore and Russia are not only the hubs of the sub-level trade network, but also the hubs of goods exports under the Belt and Road Initiative. China, Italy, South Korea, Singapore and Russia, the trade values (node strength) these five countries export to other countries in the network are 98.237, 78.714, 74.665, 74.160 and 71.220 billion US dollars respectively, and they contribute the greatest weight in the network (see Table 1 for more detailed information).

In 2008, the scale of the exports network under the Belt and Road Initiative significantly expanded. The relations with export value greater than $100 million US dollars were 1144, and the total export value within the network increased to $2323.794 billion US dollars as well. The increase of node degree and node strength are far much greater than the other countries, with a more obvious centrality status, while Russia, South Korea, Italy and Singapore have become the core of the second echelon. Judging from the evolution of the community structure of the goods export network under the Belt and Road Initiative, the value of modularity has risen to 0.370, indicating that the community differentiation is more obvious. Research shows that the network has further evolved into three internal trade networks of Europe and CIS, Asia Pacific and Africa, among which the internal trade of Europe and CIS network and Asia-Pacific network are the most prominent. The former’s internal trade volume accounted for 37.92% of the total intra-regional trade under the Belt and Road Initiative from 36.80% in 2003, while the latter’s proportion increased to 40.78% from 37.36% in 2003. In addition to the significant increase in intra-network trade in subnetworks, the proportion of trade between European and CIS networks and Asia-Pacific networks has also increased. At that time, the bilateral exports of South Korea and China, Russia’s exports to Italy and Singapore’s exports to Malaysia and Indonesia constituted the greatest weighted advantages (see Table 1 for more detailed information).

Due to the international financial crisis, in 2013 the increasing speed of the scale of goods export network under the Belt and Road Initiative declined significantly. The number of relations with export value greater than $100 million US dollars increased slightly to 1,300, and the total export value increased to $3019.268 billion US dollars. Among the core countries, China, South Korea and Singapore bucked the trend and further strengthened their centrality status with a relatively high node strength. However, the centrality status of Russia and Italy declined slightly due to the decrease of trade value. Judging from the evolution of the community structure of the goods export network under the Belt and Road Initiative, the value of modularity has dropped to 0.334, indicating that the degree of community differentiation of the network has decreased, but the value of modularity is still relatively high, indicating that the community differentiation of the network is still obvious. Research shows that the network can be divided into three intra-trade networks: Europe and CIS, Asia Pacific, and Africa. At this stage, the proportion of intra-trade of Europe and CIS dropped sharply to 28.66%, while the proportion of intra-trade in Asia-Pacific increased to 48.66%, and the proportion of trade between Europe and CIS networks and Asia-Pacific networks changed little. The results of this change were also vividly reflected in the edge weight ranking in the network: among the top ten weighted edges, except for the edge of China and Russia, the rest are all the edges of the Asia-Pacific countries (see Table 1 for more detailed information).

In 2018, affected by the global economic downturn and anti-globalization, the scale growth rate of export of goods network under the Belt and Road Initiative continued to slow down. The number of bilateral relations with trade volume exceeding 100 million US dollars has gradually increased to 1,366, and the total export volume has increased to 3305.936 billion US dollars. Among the core countries, China went up against the trend and its node strength rose to 805.983 billion US dollars. In terms of node strength, South Korea and Russia are far below China and are in the second tier of core countries, while Singapore and Italy fell into third-tier. The top ten weighted edges were mainly the edges between the Asia-Pacific countries, of which, China accounts for half. By far, the pattern of the network has evolved from multi-core in 2003 to one extreme (China) and multi-core (South Korea, Singapore, Russia and Italy) in 2018. In this stage, the value of modularity continues to drop to 0.316, indicating that the degree of differentiation of communities in the goods export network under the Belt and Road Initiative is further decreased, but the value of modularity is still relatively high, indicating that the differentiation of network associations is still obvious. Research shows that the network is still dominated by Europe and CIS and Asia-Pacific. The proportion of intra-European and CIS trade has further dropped to 26.59%, while the proportion of intra-Asia-Pacific network trade has risen to 51.05%. The top 15 sides are mainly the links in the Asia-Pacific intra-trade network, of which China issued 8 sides, compared with 3 sides in 2013 (see Table 1 for more detailed information).

The results of block model show that the network was divided into four blocks in 2003 : 1. The European block mainly consisting of 23 European countries such as Austria and Czech; 2. The former Soviet Union block consisting of 15 countries such as Russia and Ukraine; 3. The West-Asian and African countries consisting of 22 countries such as South Africa and the United Arab Emirates; 4. The Asia-Pacific block mainly consisting of 22 Asia-Pacific countries such as China, South Korea and Chile. The European block and the former Soviet Union block’s internal trade value is far smaller than external trade value, thus considered as isolated block; The exports of Asia-Pacific mainly focus on the internal block, thus seen as internal block (see Table 5).

In 2018, the composition, relations and types of the four blocks have some changes. To be specific, eight countries have left the European block, and new joint countries are Italy, Slovakia and Cyprus joined; Six countries have left the former Soviet Union block, with Turkey and Malta as new entrants; Seven countries left the West-Asian and African block, then Egypt, Lebanon and other ten countries joined; Four countries in the Asia-Pacific block left, with nine new entrants such as Russia and South Africa. The trade matrix and density matrix in Table 6 show that both internal and external relations of the four blocks have become much closer. Among them, the types of the former Soviet Union block, West-Asian, African block and Asia-Pacific black remain unchanged, while the difference between the huge improvement on internal trade relations and external relations of the European block is not significant, thus its block type converted from external type to balanced type.

In this paper, the values of the density matrix which are greater than the overall network density in the same year are assigned to 1, otherwise 0, and the correlation diagram of each block is drawn (see Fig. 2). It can be seen that the Asia-Pacific block is the hub of the entire network. In 2003, the internal trade relations of the Asia-Pacific block accounted for 39.05% of the total volume of internal trade relations in the network, which further increased to 49.71% in 2018. The Asia-Pacific Group has not only established close internal trade relations, but also has strong export capacity. In 2003, imports from the Asia-Pacific Group, the former Soviet Union Group, the West Asia Group and the African Group in the European Group accounted for 15.74%, 17.56% and 51.25% of the total imports respectively. This proportion increased to 31.09%, 55.23% and 56.82% respectively in 2018, indicating that the Asia-Pacific block has a leading advantage of importing in the network, which can boost the commodity flow throughout the entire network. The European block is the second-tier core block after the Asia-Pacific block in the network. However, the exports of the European block are mainly concentrated among the countries within the block, and the exports to the former Soviet Union block and the West Asia-Asia-Africa block are relatively small. The scale of trade between the former Soviet Union and the West Asia-Asia-Africa block has increased significantly. The West Asia-Asia-Africa block not only has significant internal trade relations, but also has close trade relations with the Asia-Pacific block. However, there is still a huge gap between these two blocks and the European block and the Asia-Pacific block.

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Fig. 2

The incidence relation of the four blocks of export of goods network on the Belt and Road.

(The circular arrow in Fig. 2 indicates that the export relation density among countries within the block is greater than the overall network density, that is, the export relation within the block is significant. The straight arrow indicates that the relation density of blocks’ exports to other blocks is greater than the overall density of the network, that is, the relation between blocks’ exports to other blocks is significant.)

Based on the above studies, we find that: 1. There is a “core-edge” layer structure in the export of goods network of the Belt and Road. Further, among the core countries, the centrality position of China, South Korea, Singapore has been significantly enhanced, while the centrality position of Russia and Italy has been slightly declined, thus the pattern of the network transformed from multi-core to one extreme and multi-core; 2. The weighted centrality and PageRank index of China, South Korea, Russia, Singapore and Italy always rank the top five, which indicates that these five countries are in the absolute center of controlling position in the network, and playing the roles of “engine” and “bridge”; 3. China, South Korea, Russia, Singapore and Italy are the countries having the most influential power. From the perspective of evolution, the influence of China is on the rise, and that of South Korea remains constant, while that of Russia, Singapore and Italy are on the decline; 4. The leading edge of Asia-Pacific block in the network has been increasing over the years. Not only has the internal trade volume increased to the half of the total trade volume of the entire network, but also its trade export to other three blocks have been significantly increased. The total trade value within the European block have been increased greatly, and its block type has transformed from external type to balanced type. The trade scale of the former Soviet Union block and West-Asian and African blocks have been improved significantly, but still a gap compared with the European block and the Asia-Pacific block.

The above conclusions have the following implications: First, strengthen China’s trade relations with the core countries in the network and other second-tier core countries. We should attach importance to cooperation with countries with high central status and great influence, and use the relationship between core countries and peripheral countries to enhance China’s control in the entire network. Second, promote the integration between the European production network and the exports network under the Belt and Road Initiative. European countries and the Belt and Road Initiative countries have complementary factors, endowment structure and differentiated industrial structures. Through bilateral or multilateral agreements and other methods to make European countries blend into the exports network under the Belt and Road Initiative, which is not only helpful for less developed countries to absorb technology spillover from European countries, but also expand external markets for countries in the network, thus reducing the damage to the domestic economy caused by the continuous economic downturn. And the third is to taking advantage of China’s central superiority in the network, actively construct the value circulation of the exports network under the Belt and Road Initiative. China uses its functions of “engine” and “bridge” in the network to help backward countries improve their technological level and promote their status of international division of labor, so that they can reap more benefits of division of labor in the value division of export network.