Selection of sample plot for ecological security evaluation of land resources

8. 1. 1 Overview of the evaluation area

According to the research results of ecological security of sustainable land use at home and abroad, it can be found that there are two main types of ecological security evaluation area selection: vector evaluation unit based on surface and grid evaluation unit based on point.

The regional evaluation unit takes vector bin as the information carrier of evaluation, which is convenient for obtaining data, especially socio-economic data, and the evaluation conclusion is also convenient for application to environmental management. The main types of regional evaluation units are administrative units, small watersheds and landscape units.

(1) administrative unit: administrative unit is widely used in regional ecological security assessment with the scale of country, province, city and county. Social and economic indicators are all counted according to administrative unit, and statistical data are easy to obtain. The conclusions obtained are convenient for determining and comparing the ecological protection and construction achievements of administrative units.

(2) Watershed unit: The assessment of regional ecological security based on small watersheds is mainly based on the geomorphological differentiation of regional ecosystems and the ecological spatial pattern formed by hydrological processes in small watersheds. Because the small watershed is an independent geomorphic unit, the ecosystem in the watershed has ecological integrity from upstream to downstream, which is of great significance to the regional ecological security evaluation aimed at protecting and restoring the aquatic ecosystem.

(3) Landscape unit: The landscape is composed of inlaid land units, which is a natural and social composite regional ecosystem with a certain spatial structure, consisting of matrix, blocks embedded in the matrix and corridors that linearly connect the ecosystems in the landscape. The lower unit that constitutes the landscape is the land unit, and the upper unit is the basic unit of ecological division that constitutes geographical differentiation. Therefore, it is the intermediate link between ecological regionalization and land use planning, and the regional ecological security evaluation based on landscape is of great significance for the division of ecological functional areas and regional ecological protection.

Point evaluation unit takes grid unit as information carrier and evaluation unit. Because the grid cells have the meaning of "precise position" in space, the evaluation results have the meaning of "real space". However, the evaluation conclusion cannot be directly compared between regions, and it is not regional in environmental management and cannot be directly applied.

8. 1.2 principle of evaluation area division

Evaluation area is the basis of research, and the number and representativeness of regional selection directly affect the accuracy of ecological security evaluation results, so the principles of comprehensive analysis, dominance and operability should be followed in the process of selection and division.

8. 1.2. 1 principle of comprehensive analysis

Ecological security system is a multi-level and multi-factor complex system. As a basic evaluation area, the evaluation of such a complex system should have strong comprehensive analysis ability, which can not only reflect the current situation of ecological security, but also show the existing ecological problems, provide decision-making basis for ensuring the ecological security of land resources and realize the goal of sustainable utilization of regional land resources.

8. 1.2.2 Leading principle

There are many areas that affect ecological security, and the number of selected areas and the selection of representative areas will directly affect the accuracy of the research results, so the representative areas must be optimized when selecting evaluation areas.

8. 1.2.3 operability principle

The selection of evaluation area should fully consider the difficulty of data acquisition to ensure the accuracy and reliability of data. As far as possible, the area with complete statistical data, existing norms and standards, relevant planning data and investigation data of relevant departments will be regarded as the evaluation area. This not only ensures that it can fully reflect the present situation of ecological security of land resources and the various connotations of its changing trend, but also facilitates operation.

8. 1.3 evaluation sample selection results

According to the respective characteristics of vector area evaluation unit and grid point evaluation unit, combined with the actual situation of Henan Province, this study adopts the administrative unit in vector area evaluation unit as the comprehensive evaluation and analysis unit, and the specific operation is mainly realized through database function and GIS technology.

Using GIS technology and the polygon overlay analysis method of MAPGIS software, the evaluation area is selected and divided. Polygon overlay analysis refers to overlaying data files of two or more groups of polygon elements in the same area and scale, establishing polygons with multiple attributes according to the intersection of the two groups of polygons, or making statistical analysis on the attribute characteristics within the polygon range. Its essence is to superimpose two or more layers of elements (plane or linear) to produce a new element layer. The new element layer integrates the properties of the original two or more layers of elements.

The spatial analysis base map of this study adopts the Land Eco-environmental Suitability Zoning Map and Natural Economic Zoning Map in the basic research of the revision of the overall land use planning in Henan Province. When selecting the ecological security assessment area of land resources, a new ecological security assessment zoning map is formed by superimposing the land ecological environment suitability zoning map and the natural economic zoning map with MAPGIS software. In order to eliminate the influence of such special value individuals or extreme value individuals on the evaluation results, a reasonable and scientific ecological security evaluation zoning map is determined by comprehensively considering the landform conditions, water resources distribution and social and economic development level. Finally, in different regions, according to the principle of homogeneity and uniqueness, select representative sample points in counties (cities, districts) to carry out ecological security evaluation of sustainable use of land resources.

The revised ecological security assessment zoning map is divided into five regions: Taihang Mountain hilly region, Qinling-Funiu Mountain hilly region, Tongbai-Dabie Mountain hilly region, Nanyang Basin region and Huanghuai Plain region, and 34 sampling points (regions) are selected.

8. 1.3. 1 Taihang Mountain Hilly Area

Taihang Mountain is located in the northwest of Henan Province, including Anyang City (Linzhou and Anyang County), Hebi City (urban area and Qixian County), Xinxiang City (Huixian County, Weihui County and Huojia County), Jiaozuo City (Xiuwu County, Aibo County and Qinyang City) and Jiyuan City. This area is the distribution area of Taihang Mountain range, which is composed of arc mountains protruding in the southeast, low hills in the east and piedmont plains. The landform in this area belongs to the steep slope of Zhongshan, with an altitude of 1 0,000 ~10,500m. The mountain is steep, the slope steps are steep, the cliffs are extremely developed, and the gully cutting depth reaches 50 ~ 200m m. Due to the high terrain, the average temperature is about 65438 03℃, which is one of the longest cold periods in Henan Province. The northern part of this area belongs to Haihe River Basin, where Anyang River, Qihe River and Tanghe River all originate. The west belongs to the Yellow River Basin, where tributaries of the Yellow River, such as Qinhe River and Mang River, originate. The annual precipitation is about 700mm, most of which is concentrated in summer, and there are many heavy rains, which are easy to cause flash floods, landslides on hillsides and serious soil erosion. The low hills in the east of this area are generally 400 ~ 800 m above sea level, with steep slopes and gentle slopes. There are some fault basins between Zhongshan and low mountains, about 300 meters above sea level. The ground in the basins is flat and the soil layer is deep.

According to the characteristics of topography, temperature, water and soil conditions in this area, from the perspective of sustainable ecological security of land use, with the goal of strengthening the prevention and control of soil erosion in mountainous hills, and considering the homogeneity of sample selection, the selected sample points are Linzhou City, huixian city City, Xiuwu County and Jiyuan City in turn. 8. 1.3.2 Qinling-Funiu Mountain Hilly Area

Qinling-Funiu Mountain hilly area includes hills, Xiaoqinling, Xiong 'er Mountain, Waifangshan and Funiu Mountain. Generally, the altitude is 1000 ~ 2500 m, and gradually decreases to the low mountains and hills in the east and southeast. Due to the steep terrain, there is little cultivated land, but the area of woodland and barren hills is large. The climate in this area is complex and varies greatly from place to place. Luanchuan, Lushan and Nanzhao have more precipitation, 800 ~ 900 mm; Lushi area is less, only about 600mm, and more than 50% of the annual precipitation is concentrated in summer, with high precipitation intensity and heavy rain, which is easy to form floods. Due to the complexity of the ecosystem, there are great differences from place to place. In Yima, Mianchi and Shanxian counties in the north, exposed bedrock and land subsidence caused by mineral development have caused serious soil erosion and water pollution and frequent geological disasters. Lingbao, Lushi, Luoning, Luanchuan and Songxian in central China are prone to soil erosion and geological disasters due to high vegetation coverage, high biodiversity, complex terrain and shallow mine development. In the mountain valley area between Xiong 'er Mountain, Xiaoshan Mountain and Funiu Mountain in Lushi County, the closed conditions of natural terrain have created a stable ecological environment, but the cultivated land resources are relatively scarce. There are many rivers in Xichuan, Xixia, Neixiang and Nanzhao counties in the south, which belong to the source of Huaihe River basin and the source of main tributaries in the middle and lower reaches of Hanshui River in the Yangtze River basin. Danjiangkou Reservoir is the source of the Middle Route of South-to-North Water Transfer Project, an important water conservation area and soil and water conservation area, with extremely rich vegetation and high sensitivity to biodiversity protection. However, there are low-grade building stones and craft stones, which have certain damage to the ecology.

The ecological characteristics of this area are obvious. From the perspective of sustainable ecological security of land use, considering the homogeneity and regionality of sample selection, the sample points selected from the north, middle and south of the region are yima city, Mianchi County, Shaanxi County, Lushi, Luanchuan, Songxian County, Xichuan and Xixia in turn. 8. 1.3.3 Tongbai-Dabie Mountain Hilly Area

Tongbai-Dabie Mountain hilly area is located in the south of Huaihe River and east of Nanyang Basin, including most of Tongbai Mountain, northern Dabie Mountain and the hilly area on the east side of Nanyang Basin. Most areas are hilly, and Zhongshan, with an altitude of 1000 meters, is distributed on the southern edge. Due to the erosion and cutting of flowing water, the terrain is relatively broken and low, especially in hilly areas, most of which are 300 ~ 600 m above sea level. The valley between mountains is wide, the slope is gentle and the water diversion is convenient. Some Zhongshan mountains are steep, with little cultivated land except the valley bottom and valleys, but rich in plant resources. This area is located in the northern part of the North Subtropical Zone with a mild climate. It is the region with the richest water and heat resources in the province, with many rivers, rich water energy resources and high soil potential fertility. Unreasonable land development, exploitation of some mineral resources and excessive hunting of wild animals are the main reasons leading to soil erosion, accelerated extinction of species, decreased vegetation coverage and soil desertification, which are the ecological security problems to be solved urgently in this area.

The problem of ecological security in this area is obvious. From the perspective of sustainable ecological security of land use, it is considered that the selection of sample points should have the characteristics of reflecting the ecological problems in this area, and the selected sample points are Biyang, Xinxian, Shangcheng and Xinyang City.

8. 1.3.4 Nanyang basin area

Nanyang basin, located in the southwest of Henan province, is a part of Nanxiang basin. The west, north and east sides of the basin are surrounded by Funiu Mountain and Tongbai Mountain, and the middle part is the accumulation plain. The terrain is inclined to the south, with the gradient from 1: 3000 to 1: 5000, and the elevation reduced from 200m to 80m. This area belongs to the northern edge of the north subtropical zone, with mild climate and abundant heat resources. Cold air in the basin is not easy to invade, and crops have good wintering conditions and little cold damage. The annual precipitation is about 900mm, 50% of which is concentrated in summer, with heavy rainfall and frequent floods; There is little rain in spring and summer, and droughts often occur. This area has superior climatic conditions, abundant water resources and huge land production potential, and is the main producing area of grain crops and cash crops in Henan Province. The soil is mainly yellow brown soil and black soil in Jiang Sha, which is a harmful factor for agricultural development because of its heavy texture, poor structure and poor farming performance.

From the perspective of sustainable ecological security of land use, soil improvement should be done well in this area, and the selected sample sites are dengzhou city and zhenping county.

8. 1.3.5 Huanghuai Plain

Huanghuai Plain consists of Huaihe Plain and Yellow River alluvial plain, in which Huaihe Plain is located in the south of Sha Ying, north of Huaihe River, west of Yushan Mountain and east of provincial boundary. Flat terrain, with an altitude of 40 ~ 50m, is the lowest place in the province. The terrain inclines from northwest to southeast, and there are many ups and downs on the plain, especially along the river. The western part of the whole plain is slightly higher and the hills are lower; The eastern part is low-lying, mostly shallow depressions and lacustrine depressions. The winding rivers and poor drainage are prone to floods, especially on both sides of the Hongru River, which is the most serious area in Henan Province. This area is located in the south of warm temperate zone, with semi-humid climate and sufficient heat, and the annual precipitation is 800 ~ 900 mm, which is the most abundant rainfall area in Henan Province. There are many rivers, rich groundwater and good water quality in the area, which is an important grain, cotton and oil producing area in Henan Province. However, the scale of industrial production in this area is large, the water environmental capacity is limited, the industrial pollution discharge is large, and the water environmental quality seriously exceeds the standard, which poses a great threat to ecological security. Industry should carry out technological transformation and strictly control sewage discharge.

The alluvial plain of the Yellow River is located in the northeast of Henan Province, bordering the mountainous area of western Henan, hilly area of loess tableland and hilly area of Taihang Mountain in the west, with Shaying River in the south and provincial boundaries in the east and north, belonging to the upper part of the alluvial delta of the Yellow River, and the Yellow River passes through the central part of the plain. Due to sediment deposition, the riverbed is generally 3 ~ 7m higher than the flat land on both banks, and some river sections can reach more than 10m, making it a suspended river on the ground. The Yellow River Plain is flat and open, and only because of the flood diversion of the historical breach of the Yellow River has some low and undulating micro-landforms formed. In addition, there are sand dunes, sandy land and inter-hill depressions with different areas in different sections, as well as the old Yellow River channel and ancient He Qian depressions distributed in strips. The region has a semi-arid and semi-humid climate, with an annual average temperature of 13 ~ 14℃ and abundant heat resources. The annual precipitation is mostly 600 ~ 700 mm, and the temperature and rainfall tend to decrease from south to north. The Yellow River is rich in water and good in water quality, which is the main source of water diversion and irrigation. Most of the groundwater in the plain is good in water quality, shallow in burial, abundant in water and easy to exploit, so it is a good irrigation water. This area is an important part of the economic belt along the Yellow River and the Central Plains urban agglomeration, with excellent traffic conditions, urban and industrial construction taking shape, and a good foundation for industrial and agricultural development. However, natural disasters such as drought, flood, sandstorm and salinity are serious, and the air and water environment are seriously polluted. Therefore, land desertification should be prevented in the alluvial fan area of crevasse, soil salinization should be prevented in the Beihewa area, and air and water pollution should be prevented at the same time. Industrial development should be adjusted, and controlling the total amount of pollution discharge is the key to solve the ecological security problem of sustainable utilization of land resources.

According to the natural and unique ecological environment conditions in this area, from the perspective of sustainable ecological security of land use, the selected sample sites are xinmi city, gongyi city, Neihuang, Yanjin, lankao county, hua county, Fengqiu, Yucheng, Xiayi, Yongcheng, Xixian, Zhengyang, Xincai, Baofeng, Lushan and Yexian.

A total of 34 sampling points (regions) were selected as evaluation sample regions (Table 8. 1). See Figure 8. 1 for the regional and sample distribution of land resources ecological security assessment in Henan Province.

Table 8. 1 sample area for ecological security assessment of land resources

Figure 8. 1 Distribution map of sample price area and evaluation area