4.1 Ecological source identification
When determining the optimal study scale, based on the ecological source, different particle size grid plots were generated from 30 m to 1500 m using the landscape pattern index at different granularity levels calculated by Fragstats (Fig. 4.). The number of patches and the landscape division index decreased with granularity, and the composition number stabilized after 600 m. For patch cohesion, as the granularity increased slightly, the condensation size decreased sharply after more than 600 m, indicating a strong connectivity for the landscape granularity level of 600 m, which was also applicable to other indexes. As the key point of each landscape index, 600 m can be used as an appropriate reference for the size selection of ecological sources. Due to the limited radiation range of fine fragment patches, patches with habitat areas greater than 2 km2 were selected as the ecological source in combination with relevant references.
After calculation, the habitat quality of the Dawen River basin is shown in Fig. 4. The average value was 0.1967, and the area above the average value accounted for 57.95%. The overall habitat quality of the Dawen River basin was at a low level. The value area was concentrated in the southeast and northwest of the research area, with a large area, and was connected into pieces that were mainly located in Taishan District, Dongping County, Daiyue District and Xintai City. The land use types were mainly woodland and grassland. The low-value area was concentrated in the central and southern urban land, with small areas, and mainly located in Feicheng city and Ningyang County, accounting for 8.89% of the total area.
The study identified 49 source plots (Fig. 5.), including its national forest park, Dongpinghu, Baifang, Mount Tai, with an area of 262.25 km2, for 2.73% of the total area (9602.68 km2). These areas included woodlands, wetlands and water areas, among which water bodies were the main ecological source type, accounting for 76.66% of the total source area. Dongping County has the largest ecological source area of 139.91 km2. For the Dawen River basin, the relatively typical ecological land type that can form is the wetland and water bodies, which are currently less affected by human beings and can form a relatively typical protection area.
a Number of patches b Landscape division index c Landscape shape index
d Shannon's evenness index e Contagion index f Proportion of like adjacency
Figure 5. Habitat quality identification and selection of final ecological sources
4.2 Construction of comprehensive resistance surface
Based on the data in Table 2, the resistance value was measured, and then the comprehensive resistance surface was constructed (Fig. 6). The area with a large comprehensive resistance value was basically located in the urban area with intensive manual activities and around the roads. Although farmland has better-growing vegetation, due to the influence of human agricultural activities and artificial control around it, especially the highly intensive utilization mode, the resistance value directly increased. The maximum resistance of the entire greater basin was 449.50, the minimum resistance was 1.00, and the average resistance was 140.51. The resistance value distribution was relatively fragmented, similar to the basic resistance surface of land use type. After the superposition of the factor resistance data, the internal resistance value will vary; specifically, except for the high-value area that is concentrated in the central city and northwest, the rest are scattered.
4.3 Key ecological corridor identification
Ecological corridors are the basic architecture (Li et al.,2019) for maintaining regional ecological security by connecting different sources, increasing regional landscape connectivity and maximizing ecological benefits. There are 75 ecological corridors identified in the Dawen River basin, of which there 47 key corridors with a length of 643,812 m and potential corridors with a length 550,766 m. The overlap of some critical and potential corridors in specific sections was excluded (Fig. 7), totaling 1963.04 km.
Among them, the ecological sources in the northern and central parts were mainly connected by short corridors with lengths within 10 km, showing fine fragmentation characteristics, accounting for 32.80% of the total key corridors, and the regional corridors overlapped, which is a manifestation of frequent species movement. The northwest and southeast were far separated from the ecological sources. From the northwest to southeast, it was gradually complex and gridded, and the connectivity was gradually enhanced, forming a systematic ecological security pattern composed of sources and corridors.
Based on the circuit principle, key ecological corridors and potential corridors were identified, and "pinch points" and "barrier points" were identified. Ecological factors such as mountains, water, forests, fields, and lakes should be coordinated, and ecological zoning should be carried out. The landscape ecological security pattern of the Dawen River basin was reconstructed in points, lines and layers, and a resource optimization strategy was proposed for the landscape ecological security pattern. This approach was of positive significance to maintain the systematic and ecological integrity of the river basin and build the Dawen River-Dongping Lake Collaborative Development Community.
4.4 Key point identification and protection recommendations
This study was based on the circuit principle, and 32 pinch points were identified, most of which were in the ecological conservation section, indicating that protected pinch point areas could significantly improve landscape connectivity. The land use types of pinch points are mainly water areas. Specifically, there were 5 in Dongping County, 2 in Feicheng city, 2 in Daiyue District, and 2 in Taishan District (Table 3).
The study identified 19 "barrier points" (Fig. 9.), mainly for construction land, roads and rural settlements (Table 2). Specifically, there were 5 in Dongping County, 2 in Feicheng city, 2 in Daiyue District, and 2 in Taishan District (Table 3). Since such areas of human activities are often relatively dense, most of the spatial distribution was mostly located at the connection of ecological sources and ecological corridors, which were the key positions of communication. Therefore, there is still much room for improvement of the Dawen River regional landscape connectivity.
Table 3
Regional distribution table of "pinch points" and "obstacle points"
FID * | NAME | Pinch point | FID * | NAME | Barrier point |
1 | Daiyue District | 12 | 1 | Daiyue District | 7 |
2 | Dongping County | 2 | 2 | Dongping County | 3 |
3 | Feicheng City | 1 | 3 | Feicheng City | 2 |
4 | Liangshan County | 3 | 4 | Liangshan County | 1 |
5 | Ningyang County | 3 | 5 | Ningyang County | 2 |
6 | Taiqian County | 1 | 6 | Taishan District | 1 |
7 | Taishan District | 2 | 7 | Xintai City | 3 |
8 | Wenshang County | 2 | | | |
9 | Xintai City | 6 | | | |
Table 4
Key areas of protection and restoration of the Dawen River basin
| Status Type | Region | Existing problem |
"Pinch points" to be protected | Rivers | Dongping County | Industrial development is extensive, low-quality, inefficient, and the ecological overdraft problem is serious. Affected by water conservancy project coercion and human agricultural activities, the water conservation capacity has decreased. Coastal pollution discharge problem is serious, and rivers gradually shrink and narrow. |
| Feicheng City |
| Daiyue District |
| Taishan District |
| Woodland Construction Land | Taishan District | Falling forest coverage, forest network fragmentation has increased. Lower biodiversity, putting pressure on the ecological environment and reducing connectivity between habitats. |
| Xintai City |
| Feicheng County |
Barrier points" to be | Xintai City | Changing the original flow direction and speed of water bodies can partially hinder the migration path of aquatic and terrestrial organisms. Ecological community structure has received obvious influence, decreased original river regulation and storage capacity, and frequent flood disasters |
addressed | Feicheng City |
| Dongping County |
| Taishan District |
| Road land | Daiyue District | During the development, protective forests, wetlands and woodlands are damaged and isolated on both sides of the highway. |
| Taishan District |
| Rural settlements and paddy fields | Dongping County | Intensive human activities, the use of modern agricultural technology gradually rice farming from mixed planting to single planting, and the destruction of habitat connectivity in some mechanized planting areas. |
| Feicheng City |
| Xintai City |
| Daiyue District |
For the "key points" regional problems (Table 4), relevant protection measures are put forward in combination with the actual situation of the region. In view of the river pinch points, restoring the river buffer zone, planting ecological protective forests along the coastline, strengthening wetland construction along the river, and improving wetland water conservation are important. Attention should be paid to river pollution control, the control of industrial pollution sources along the line should be strengthened, and the construction of urban sewage centralized treatment facilities should be sped up. Efficient and green pollution-free fertilizer should be promoted, and the development mode of combining industry, sightseeing, ecological functions and agriculture should be implemented. We should establish a scientific research mechanism for pollution prevention and control, monitor on time, and grasp the dynamics of water environmental pollution in real time. In view of the woodland pinch points, attention should be given to returning farmland to forest and grassland and strengthening the construction of woodland on both sides of the river. Permanent basic farmland, towns, villages and mining rights that have been allocated into the core reserve areas are gradually withdrawn in a gradual and orderly manner. Having been transferred into the general control area the gradual exit in an orderly manner will affect the ecological function. Those that do not cause obvious impacts can be properly handled by measures such as adjusting the scope of general control areas according to laws and regulations to realize the overall protection of the natural ecosystem. Natural conservation sites and nature parks should be strengthened to maintain and protect the biodiversity of forest systems.
In view of the regional problems of "barrier points", combined with the actual situation of the analysis area, the "barrier point" area cannot be directly removed because of some traffic arteries and areas with important living functions; thus, targeted repair measures are proposed. Some functional backward earth and rock dams can be removed, the overflow dams and reservoirs are reserved for diversion and flood control, and vegetation protection along the coast is increased. We should establish a joint scheduling mechanism for the ecological water flow of important reservoirs and river sluice dams, vigorously implement wetland water diversion and water replenishment and saline-alkali land management projects, improve the connectivity of rivers, lakes and reservoirs, and improve the ecological function of wetlands.
Light insulation facilities have been built on both sides to avoid interference from certain light and noise to biological living habits. Biological channels were built in obstacle areas on both sides of important roads, and warning signs were set up to ensure the smooth movement of animals. The landscape design on both sides of the expressway should be done to reduce the slope protection damage to vegetation, and plant greening should also be adopted in the central isolation belt to maintain the diversity of landscape diversity. Village joint construction in rural settlements and paddy fields should be promoted, and the intensive use of land should be improved. By enriching planting varieties, local advantageous tree species can be chosen to avoid reducing biodiversity due to single planting and to improve the quality of the forest network. The use of chemical fertilizers and pesticides should be reduced under the condition of ensuring the proper yield and stabilizing the soil properties. Necessary ditches and channels should be cut, the connectivity and systematic nature of water ecological corridors should be increased, and flood regulation and storage capacity should be improved.
4.5 Ecological protection zoning and management countermeasures
The ecological security structure of the Dawen River basin was established based on natural resources observation and survey data. The area was classified into 4 regions according to habitat quality and regional comprehensive protection requirements. The scope of improvement areas was determined based on BarrierMapper tools, and it was divided into two levels by natural breakpoints based on the improvement coefficient. The higher improvement coefficient is the primary improvement area (0.05 < IS ≤ 0.15), which is the key area of ecological recovery; the lower secondary improvement coefficient is (0.00 < IS ≤ 0.05); and the rest is the development area.
Table 5
Statistical table of zoning situation and area of all districts and cities
Area | Core Improvement Area | Secondary improvement area | Ecological protection Zone | Ecological source | Total |
Daiyue District | 2,553 | 17,422 | 17,931 | 5,683 | 43,589 |
Dongping County | 905 | 3,749 | 1,173 | 13,878 | 19,730 |
Feicheng City | 303 | 199 | 2,627 | 654 | 3,783 |
Liangshan County | 825 | 1,781 | 410 | 557 | 3,573 |
Ningyang County | 600 | 2,875 | 571 | 935 | 4,981 |
Taishan District | 245 | 1,600 | 5,214 | 1,228 | 8,287 |
Wenchuan County | 42 | 1,708 | 236 | 158 | 2,144 |
Xintai City | 1,213 | 4,305 | 5,609 | 3,080 | 14,208 |
Total: | 6,689 | 33,646 | 33,851 | 26,225 | 100,437 |
The ecological conservation area is 6689 km2, accounting for 6.66% of the total area, mainly composed of large areas of high-level habitats. The land type is mainly woodland, wetland and water, and a small amount is garden land. The ecological corridor of this section focuses on wetland ecological protection. High vegetation coverage and rich biodiversity are important for the conservation and maintenance of biological species and their habitat, which can give priority to endangered development through their own powerful regulatory function.
The ecological improvement area of 33,646 km2 is 33.50% of the total area, mainly sandwiched by "barrier points" and ecological corridor composition. The ecological corridor of the development area highlights the construction of the urban wetland park and the urban Dawen River landscape belt. The core ecological source current intensity of "one mountain and one lake" was the strongest, with the species movement density (current intensity) gradually enhanced from eastern Dongping County to Taishan District in the northeast (Fig. 11.).
4.6 Ecological restoration of the typical areas
Based on model analysis and field research data statistics, the landscape ecological security pattern of the Dawen River basin was optimized and subdivided. Along the Dawen River, Dongping Lake protection area (Zone A), Yunwei Jie village-Yangjiazhuang (Zone B), national forest park (Zone C), Daiyue-Tai district (Zone D) and independent protection area (Zone E) were classified from east to west.
Zone A takes Dongping Lake conservation as the center point and vigorously carries out nine major actions, such as net lake clearance, dining ship bans, and the construction of an ecological isolation belt around the lake. A wetland water system should be built on the back side of the lake, a variety of trees, shrubs and aquatic plants should be chosen for planting, and a green ecological road should be built on the side of the lake to create conditions for cultural tourism and leisure activities. Zone B is mainly development management, and the number of obstacles in the area is high, with governance along the Yellow River as the work center. It is recommended to clear ditches and branches, restore depressions, promote the circulation of water systems, and establish a joint dispatching mechanism for the ecological water volume of important reservoirs and rivers and dams. It is also recommended to vigorously implement wetland water diversion and water treatment projects and saline-alkali land treatment projects. The connectivity of rivers and lakes (reservoirs) and the ecological function of wetlands should be improved. It is recommended to strengthen the protection and management of key ecological functional areas in the river basin, enhance the function of water conservation and soil conservation, and comprehensively protect and restore wetland resources.
Zone C mainly focuses on conservation work. The area focuses on the protection of forest resources, establishes forest resource protection bases, implements closed management, and focuses on the protection of animal and plant resources in the area. It is recommended to divide the full gradient plant sealing area of land and sea, effectively protect and restore the natural plant communities in the area, maximize and protect the wild plant resources in the area, and enhance the richness of native plants. Additionally, the construction of a biodiversity dynamic monitoring network platform that relies on domestic professional colleges and scientific research institutions is recommended to build an "integrated monitoring network of sea, land and air", a comprehensive monitoring and research of water, gas, soil, life and other elements of the protection areas to enhance the scientific and technological support ability of the nature reserves. Zone D is mainly for prevention and control work. The transformation from "extensive" to "ecological" should be accelerated, industrial ecological and ecological industrialization should be improved, and the ecological industry should be strengthened. It is recommended to promote the extension of the industrial chain, plan the industrial layout of "a group of five parks", and promote the upgrading of traditional industries and the "two-wheel drive" of emerging industries. Zone E is mainly for protection. When this area is near Yimeng Mountain, the exploitation of diamond and other geological relic resources should be strictly controlled, and the engineering scale should be near the site. At the same time, Yimeng geological relic resources should be jointly developed, and the comprehensive value of Yimeng geological relic resources should be fully excavated. It is recommended to develop cultural products and tourism services of geological relic resources, form industrial groups related to geological relic resources, and improve the development level of geological relic resources to further promote the development of the local economy.