es about nodes and corridor, including the core protection, maintenance upgrading, and potential complementary, which will effectively control and guide on land-use in Anqing City.
3.1. Ecological Land-Use Variety
The woodland is mainly distributed in the Dabie Mountain in the northwest and Dalong Mountain in 2005.
The area of woodland in Anqing was mainly distributed in the Dabie Mountains and Dalong Mountain, which accounts for 18.29% of the total land area of the city in 2017. The distribution was mainly affected by the project of returning
Table 1. Ecological resistance values for different land types.
farmland to forests. At the same time, some woodland was mainly distributed in the southeastern city, partly converted into construction land.
The distribution of grassland in the downtown area of the west. But based on the conversion for woodland and cultivated land, although a relative low rate, the percentage of grassland in Anqing City was increased at a high speed in 10 years in order to maintain a good urban landscape structure and ecological security. Due to the development of animal husbandry and large-scale farming, grassland began to spread from the western region to the east. Because of the high production, water area also increased significantly in 2017. The extra land mainly came from the cultivated land in the southeast, converted by water land. In 2005, the garden was mainly distributed in the northwest area of the Dabie Mountains. By 2017, suitable area in Anqing City is about 3.42 km2 at a high rate, accounting from the forestry in the northwest region. Viewing Table 2 and Figure 2 for specific quantitative results (Table 2; Figure 2).
Figure 2. Schematic diagram of land use change in Anqing from 2005 to 2017.
Table 2. Anqing ecological land transfer matrix from 2005 to 2017.
In Figure 2: Maintaining cultivated land; 2: Construction land-cultivated land; 3: Forest land-cultivated land; 4: Pasture-cultivated land; 5: Water-cultivated land; 6: Unutilized land-cultivated land; 7: Garden-cultivated land; - construction land; 9: maintenance of construction land; 10: forest land - construction land; 11: pasture grass - construction land; 12: water area - construction land; 13: unused land - construction land; 14: garden land - construction land; Cultivated land-forest land; 16: Construction land-forest land; 17: Maintaining forest land; 18: Pasture-forest land; 19: Water area-forest land; 20: Unutilized land-forest land; 21: Garden-forest land; 22: Cultivated land-grazing land; 23: construction land - pasture; 24: woodland - pasture; 25: water - pasture; 26: unused land - pasture; 27: garden - pasture; 28: cultivated land - water; 29: construction land - water ; 30: forest land - waters; 31: water conservation; 32: unused land - waters; 33: gardens - waters; 34: cultivated land - unused land; 35: construction land - unused land; 36: woodland - unused land 37: Waters - Unutilized land; 38: Maintain unused land; 39: Cultivated land - Garden; 40: Construction land - Garden; 41: Woodland - Garden; 42: Pasture - Garden; 43: Water - Garden ; 44: unused land - garden; 45: keep the garden.
3.2. Construction of Ecological Security Pattern
An ecological safety pattern applies the above method of landscape elements, using MCR (the minimum cumulative resistance model method) in 2005 and 2017 (Figure 3). We found that the ecological security pattern of Anqing City is divided into 3 sub-networks, including northwest, southeast and northeast, which have complex and close connection inside the network but fragile link outside the network.
The core corridors with low correlation source were loosely distributed in 2005, at the same time, the northwest Dabie Mountains and northeast Dalong Mountain only extended in potential corridors without tangible corridors. The
Figure 3. Anqing security structure chart, (a) in 2005; (b) in 2017.
core corridors were mainly concentrated in the southwest area. In addition, the distribution of corridors was relatively dense with high correlation sources due to the increasing number of points in 2017. The ecological part of other regions was steady increased, which has formed an effective connection in the northeast, except for the northeastern region .
3.3. Ecological Land-Use Impact on Security Pattern
We superimposed 2005 and 2017 ecological security pattern and found that both the nodes and core corridors were all increased in 3 regions. Two new corridors have been added to the northwest, so the links to the Southwest are closer. Four new strategic nodes are mainly distributed in the area where arable land is converted into forest land. The areas (Dabie Mountains) were regarded the most stable zone in Anqing safety landscape system. The southeast area is the most densely distributed area of strategic points and core corridors. It is also a concentrated area of lakes and rivers. Comparing with the outside critical points and core corridors in the southwest area in 2005, the distribution in 2017 have paid more attention to the internal lakes and rivers network. The reason for the phenomenon is that many arable lands have conserved into forest and water, promoted by the policy of returning farmland to forest and fisher. Therefore, the connectivity and permeability of the ecological security pattern have been greatly enhanced. However, the northeast area with northwest and southeast was a relative fragile area, with fewer critical points and core corridors, especially in the downtown area of Anqing City. That is mainly caused by the conversion of forest and water to construction land. The district has become the most unstable area of ecological security (Figure 4).
3.4. Guidance of Ecological Security Pattern
According to the decade trend, we conclude 3 types of critical nodes and
Figure 4. Diagram of ecological land use variety in Anqing from 2005 to 2017.
corridors, including the core protection type, maintenance upgrade type, potential supplementary type, superimposing the ecological land and ecological security pattern in Anqing City. Based on it, it will be the great significance to the ecological security pattern by effective control and guidance (Figure 5) .
The core protection type mainly refers to the nodes and corridors that play a prominent role in the whole network . The area most distributed in the critical links of the Dabie Mountains, Longgan Lake, Bohu Lake and the Yangtze River, emphasizing the structural integrity of the plaque according to the principle of no declining ecological functions.
Maintenance upgrade mainly refers to nodes and corridors, threaten by land-use changes. The network is always distributed inside the major ecological nodes, which emphasize ecological maintenance and promote the control and guidance of ecological protection and restoration in ecological improvement.
The potential supplementary type mainly refers to the potential corridor. The network is distributed in the area where the regional connection is blank, which focuses on the continuity of ecological space and the ecological treatment of
Figure 5. Schematic diagram of control and guidance of ecological security pattern in Anqing in 2017.
related construction. We should follow the principle of both mainly ecological supplement and minor construction, allowing construction activities based on the ecological functions .
4. Conclusions and Discussions
According to the 2005 and 2017 overlapping analysis of ecological land-use in Anqing City, we inferred the ecological land-use variety in the past two years. Based on ecological sensitivity and ecological interference evaluation analysis, we concluded ecological safety evaluation results as the following.
• Among 4 types of ecological land, grassland, waters and gardens all have increased, with the largest area of water growth. But only the area of forest has decreased from 2005 to 2017.
• There are several land-use about the forest and construction land, conversed by cultivated land. Due to the small base number and conversion, the area always locates in the Dabie Mountain and Fu Mountain, affected by returning farmland to forest. Based on it, the urban expansion construction land mainly distributed in the downtown in the southeast of Anqing.
• Through ecological safety assessment, the high-security zone is distributed in the northwest forestland, the higher-security zone is distributed in the southwest river and lake. Besides, the low-security zone and the lower-security zone are distributed in the southern Yangtze River plain.
• From 2005 to 2017, the strategic nodes and core corridors in 3 districts all increased. The connection between northwest area and southwest area has become closer. We pay more attention to the network link between southeast area and internal lakes and rivers. The northeast area is affected by the conversion of forest and water to construction land. There are partly declining strategic nodes and cores.
• Through the comparison of the strategic nodes and corridors from 2005 to 2017, we concluded 3 types, including the core protection type, maintenance upgrade type and potential supplementary type. The ecological land in the core protection area emphasizes the structural integrity of the plaque. We should strictly control it according to the principle of no declining the ecological function. Maintaining the ecological land in the enhanced area emphasizes ecological maintenance and promotes the control and guidance of ecological protection and restoration in the ecological improvement area . The principle of ecologically potential supplemented areas is supplementary construction and ecological supplements, allowing construction activities according to the direction of ecological function protection.
The ecological security pattern is a network pattern, playing an important role in guarding human life and economic development . For urban land, the protection of ecological land and the expansion of constructed land are co-existent processes. Ecological land refers to the land-use type that mainly provides ecosystem services and usually includes farmland, woodland, and water bodies. The dynamic change in ecological land area is the main driver of changes in urban ecosystem services. Putting forward the concept of suitable ecological land helps in the calculation of the spatial range of ecological land needed to meet the minimum requirements of a healthy urban environment as well as facilitates urban planners to solve the conflicts between urban development and protection of ecological land in order to maintain a stable urban ecosystem. Studies on the ecological land use and ecological security pattern of Anqing in 2005 and 2017 can reflect significant changes in the ecological security pattern in Anqing City, both the strength of the connectivity and balance of ecological security pattern in city area and fragile in downtown area. In the future, the construction of ecological security pattern in Anqing should be combined with urban and rural planning and land-use planning to build the overall ecological security pattern from the perspective of city area. In addition, we should firstly strengthen the control of ecological land management about core protection type, and secondly maintain ecological guidance about enhanced restoration type, and finally preserve spatial continuity and ecological treatment about potential supplemental types.
In addition, it should be noted that there are some defects in this study, for example, when we use the MCRM to select landscape type and construct the ecological land security pattern, a large number of studies have limitations in the choice of single factors. It is critical to consider multi factors, including the social economic level, environmental pollution level and so on. These factors affect the ecological security man-made element. Besides, the control and guidance of ecological security pattern need further design integrating with specific urban and rural planning and land-use policy. The improvement of ecological security requires overall strategic and policy and transformation of land use nature and function, requiring the coordination of ecology and economy. As long as improving the scientific use of land, we can exert greater ecological and economic benefits at the same time.
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