4.1.1. Analysis of Annual Change Features of the ECLU
From
Figure 3, the radial Banker–Charnes–Cooper (BCC) model is more efficient than the non-radial SBM model, and the result of the SBM model without considering the internal undesired output is higher than that of the SBM-Undesirable model considering the internal undesirable output, which indicates that the non-radial model can overcome the shortcomings of the radial model, and that not considering the internal undesirable output leads to the overestimation of the eco-efficiency. At the same time, in the case of considering internal undesirable output, the efficiency value of SBM-Undesirable model is smaller than that of EBM model, which indicates that EBM model integrates the advantages of radial and non-radial functions, and it has a better comparative advantage in eco-efficiency measurement. Therefore, this paper adopts a non-directed, scale-reward invariant, Super-EBM model to measure the ECLU in 71 counties in the region around Beijing-Tianjin from 2005 to 2020.
As shown in
Figure 4, the overall state of the ECLU in the research area from 2005 to 2020 expanded from 0.388 in 2005 to 0.727 in 2020, with a rate of rise of 87.37%, but a sharp decline in 2017, mainly impressed by natural calamities such as abnormally high temperature and low precipitation leading to drought, with an overall average value of only 0.55. The ECLU in the region around Beijing and Tianjin still has much room to rise. In the future process of cultivated land use, more importance needs to be attached to the rational invest and resource use of arable to guarantee the sustainable use of cultivated land.
As shown in
Figure 4 and
Figure 5, the ECLU in the research area is consistent with the overall trend, but there are disparities among the cities, and the disparities is more obvious over time. In the light of the average value, the ECLU in Chengde, Cangzhou and Tangshan was relatively high, 0.609, 0.603 and 0.571, respectively, which is due to the obvious advantages of local transportation location, developed advanced technology, more investment in agricultural machinery, and strong awareness of ecological protection of farmers. And Langfang, which borders Beijing and Tianjin, has the most stable development and is comparable to the overall average in terms of the ECLU, but its unique location advantage has not been fully utilized. Zhangjiakou and Baoding are lower, with the ECLU values of 0.476 and 0.517, mainly because Zhangjiakou and the western part of Baoding are mostly mountainous areas, with poor quality cultivated land and poor agricultural infrastructure. From one year to another, the ECLU of Chengde and Zhangjiakou has changed significantly. The ECLU in Chengde declined significantly in 2009, mainly due to the impact of drought, which led to a 50.2% reduction in grain production and thus a sharp decrease in the ECLU. In 2012, the ECLU value rose sharply, which depended on the total power of agricultural machinery increased by 5.9% compared with the previous year, and agricultural production conditions were greatly improved. The ECLU of Zhangjiakou fluctuated greatly from 2005 to 2010, the main reason for the decline in 2007 was the decrease in agricultural output value, which was 13.3% lower than the previous year, and the significant decrease in 2009 was due to the sudden decrease in grain production caused by the drought.
As shown in
Figure 6, from a county perspective, the average value of eco-efficiency in all counties did not reach an effective state. Relatively speaking, the counties (cities and districts) with overall high ECLU are Rongcheng County of Baoding, Longhua County of Chengde and Pingquan City, Yutian County and Caofeidian District of Tangshan, Dachang Hui Autonomous County of Langfang, Renqiu City, Cang County and Qing County of Cangzhou, with mean efficiency values reaching 0.7 or more, of which 33.33% are in Cangzhou City, followed by Chengde City and Tangshan City, and one county each in Baoding and Langfang. The reason for that is that the high ECLU of the three counties in Cangzhou City is related to their topography and location, as all three counties are in the plain area, and Renqiu City, Cangzhou County, and Qing County are bordered by Xiong’an New Area, Cangzhou City, and Tianjin City, respectively, so they are more likely to be exposed to advanced agricultural farming technology and ideology in comparison. While Rongcheng, which has the highest efficiency mean, is located in Baoding, which was designated as Xiong’an New Area in 2016, and the scale and mechanization of land are constantly improving, and the awareness of environmental protection is advancing with the times to improve the ECLU. However, there are 29 counties with an average efficiency of less than 0.5, including Yangyuan County, Yu County and Quyang County, with 34.48% in Baoding and 24.14% in Zhangjiakou, which are mainly located around the Taihang Mountains, with high terrain, relatively poor soil, and poor agricultural irrigation conditions, so there is greater space.
Four periods of the ECLU data in 2005, 2010, 2015, and 2020 in the region around Beijing and Tianjin were selected for analysis, and the data were visualized using ArcGIS 10.7. The natural interruption point method was used and considering that an efficiency of 1 is an effective decision-making unit, each county unit was divided into five classes according to (0, 0.5], (0.5, 0.6], (0.6, 0.7], (0.7, 1.0], and (1.0, 1.1] into five classes, as shown in
Figure 7.
Study on the temporal features of the ECLU in each county. In general, the number of zones increased, except the number of inefficiency zones gradually decreased. 59 of 71 counties were in the inefficiency zone in 2005, accounting for 83.1%, but only 2 counties, Longhua County and Caofeidian District, were effective decision-making units, i.e., high efficiency zones, whose percentage was only 2.82%, indicating that the space distribution of efficiency values in the research area was relatively homogeneous at this time, and there is a large potential for development. As the promotion of the construction of ecological civilization, the ECLU in several counties (cities and districts) in the region around Beijing and Tianjin increased to different degrees from 2005 to 2020. 2010 saw a slight improvement in ECLU, but more than two-thirds of the counties were still in the inefficiency zone. In 2015, the ECLU was further improved, and the number of inefficient zones accounted for about one-third, and more than 40% of the areas were medium-high efficiency zones. In 2020, the ECLU has improved significantly, with only 6 counties in the inefficiency zone, mainly in southwest Zhangjiakou, southwest Baoding and eastern Cangzhou, and those 6 counties have been in the low efficiency zone for 16 years, with poor resource endowment being the fundamental reason for their low ECLU. The number of counties in the lower, medium and higher efficiency area are 12, 22 and 18 respectively, but the overall ECLU of the western area of the region around Beijing-Tianjin is low. 13 counties (cities and districts), including Qian’an City, Rongcheng County, Guyuan County, Pingquan City and Cang County, have efficiency values greater than 1, i.e., they are in an effective state, indicating that these 13 counties attach more importance to the rational use of resources and have a stronger sense of ecological protection. While the ECLU values of Longhua County and Caofeidian District have dropped from the high efficiency area in 2005 to the higher efficiency area. The efficiency value decreases significantly, which is mainly due to the increase of redundancy in essential productive factors such as pesticides, films and chemical fertilizers.
4.1.2. Study on the spatial distribution features of the ECLU
From the distribution of the ECLU by county in 2020, the distribution of low and lower efficiency zones is concentrated, mainly distributed in the western part of the region around Beijing and Tianjin with Zhangjiakou City and the western of Baoding City as the main part. Although the ECLU improved during the research time, the growth of the ECLU was slow, which was caused by the barren quality of cultivated land in the area, the high altitude, and the insufficient agricultural water supply. The low ECLU in Yanshan and Haixing counties in the southeastern part of Cangzhou City is mainly due to the extensive distribution of saline land, which leads to the low output rate of cultivated land and thus inhibits the ECLU. The distribution of medium efficiency zones is relatively scattered. The higher efficiency zones and high efficiency zones, although involved in all municipalities, are mainly distributed in Cangzhou in the immediate south of Tianjin and Tangshan in the north, which are mainly related to their location advantages and topographic conditions, which are flat and suitable for large-scale cultivation. And Tianjin, as a municipality directly under the central government, is an important transportation hub, with obvious radiation effects on the surrounding counties, and is in the coastal zone, with relatively advanced production concepts and planting techniques are introduced, so the use of cultivated land is more scientific and rationalized, thus enhancing the ECLU.