As the main abandoned land in coal mining area, coal gangue hill has been studied and practiced in vegetation restoration and ecological reconstruction for more than ten years in China. At present, more than a dozen coal gangue hills have been afforested in China, and good results and preliminary experience have been achieved in some mining areas. However, due to the complexity of the site conditions of coal gangue hill, there are still many technical problems to be solved urgently, especially the research on greening and ecological reconstruction of spontaneous combustion coal gangue hill is less. On the other hand, China has a vast territory, and the natural conditions vary greatly from place to place, and the sources and characteristics of coal gangue in various mining areas are also different. The research results of vegetation restoration technology have their own emphases, mainly focusing on the research of single technical measures (site condition analysis, plant species selection, soil preparation and matrix improvement technology, survival or growth of young forests), and the lack of scientific and effective vegetation restoration and ecological reconstruction technology model leads to poor comparability and popularization, which affects the coal gangue hill.

Based on the theory of restoration ecology, the theory and technical framework of forest cultivation, the practical experience of vegetation restoration in spontaneous combustion coal gangue hill in China and the successful case of afforestation in Yangquan, Shanxi Province, the technical model of vegetation restoration and ecological reconstruction in spontaneous combustion coal gangue hill (Figure 6- 1) is put forward, which consists of six vegetation restoration engineering technologies.

1. Site condition analysis and evaluation technology

Through the measurement and analysis of various site factors, the limiting factors of vegetation restoration were found out, and the dominant factors were determined, which provided the basis for plant species selection and site condition improvement.

2. Choose the right plant species

By analyzing the biological characteristics of plant species, especially the physiological and ecological characteristics of plants, taking native plant species as the main object, we can choose suitable plant species to achieve the purpose of "adapting trees in the right place" or "adapting trees in the right place".

3. Plastic soil preparation, fire prevention and site improvement technology

Through reasonable soil preparation and scientific matrix improvement methods, the purpose of "extinguishing fire, reducing temperature, storing water to preserve moisture and increasing fertilizer" can be achieved, creating a good environment for vegetation restoration.

4. Drought-resistant and barren-tolerant comprehensive planting techniques

Through reasonable plant cultivation methods and drought-resistant planting techniques, the survival rate and preservation rate can be improved, and then the goal of vegetation restoration and stable growth can be promoted.

5. Reasonable community composition and density control technology.

By determining the reasonable planting density and plant composition type, the restored plant community structure is reasonable and stable.

6. Plant community management and tending technology

Through soil management and vegetation management measures, the goal of "reasonable structure, stable function, high yield and high efficiency" of plant ecosystem is achieved.

Figure 6- 1 Block diagram of vegetation restoration and ecological reconstruction technology in spontaneous combustion coal gangue hill

The above technical measures are complementary, interrelated and indispensable. In the process of ecological reconstruction of spontaneous combustion coal gangue hill, scientific construction and cultivation can be carried out according to the above six technical measures, and a plant ecosystem with stable structure and function can be established in coal gangue hill to realize the ecological reconstruction of coal gangue hill, which is also the ultimate goal of any degraded ecosystem restoration and reconstruction.

Second, the greening scheme of coal gangue hill

Spontaneous combustion coal gangue hill is an artificial "landform" formed by mining waste. Its topography, surface composition and physical and chemical properties are not conducive to the growth and succession of vegetation, and the ecological problems encountered by vegetation are superimposed. For example, the general coal gangue hill is high in temperature, acidic, poisoned by toxic substances such as heavy metals, and lacks organic matter and nutrients such as nitrogen, phosphorus and potassium. Therefore, the ecological reconstruction project of coal gangue hill must be supplemented by other special engineering technical measures and implementation procedures in addition to conventional plant cultivation technical measures to ensure the success of vegetation restoration and ecological reconstruction project of spontaneous combustion coal gangue hill.

The vegetation restoration project of spontaneous combustion coal gangue hill includes three stages and nine steps, which is referred to as "three stages and nine steps" (Figure 6-2).

Figure 6-2 Project Procedure for Vegetation Restoration in Spontaneous Combustion Coal Gangue Mountain

1. Preliminary investigation and analysis of coal gangue hill

Vegetation restoration in spontaneous combustion coal gangue hill is limited by the environment and site conditions of spontaneous combustion coal gangue hill, so it is necessary to investigate and analyze the environmental conditions of coal gangue hill, including the following three aspects:

(1) Environmental investigation of spontaneous combustion coal gangue hill. Including ecological environment investigation and regional environmental investigation of coal gangue hill. Investigate the ecological environment of coal gangue hill, including spontaneous combustion, temperature, soil, hydrology and nutrients. The regional environmental investigation should comprehensively investigate the ecological, social and economic conditions of the area where the coal gangue hill is located, and provide information for the ecological reconstruction target planning of the coal gangue hill.

(2) Analysis and evaluation of environmental conditions of coal gangue hill. The site condition analysis of coal gangue hill is mainly carried out from the aspects of soil, hydrology, pH value and nutrient status of weathered layer of coal gangue hill. According to the lithologic characteristics of coal gangue hill, some need to analyze its metal toxicity and harmful substance content. Therefore, the suitability of coal gangue hill as a living environment for plants was evaluated. Through the analysis of the regional environmental conditions of coal gangue hill, the expected goal of ecological reconstruction of coal gangue hill is determined and evaluated.

(3) Analysis and determination of the dominant factors of vegetation restoration in coal gangue hill. Through the analysis and evaluation of the site conditions and environmental conditions of coal gangue hill, the main factors limiting the survival and growth of vegetation in coal gangue hill are understood and determined, which provides a basis for the selection of plant varieties and site improvement measures in coal gangue hill.

2. Ecological reconstruction engineering and technology

On the basis of fully understanding the environmental conditions of coal gangue hill, the ecological reconstruction goal of coal gangue hill is planned, suitable tree species are selected, and appropriate measures such as site improvement and plant planting are taken to realize the vegetation restoration of coal gangue hill. To monitor and evaluate the vegetation of coal gangue hill, strengthen the management of vegetation restoration process, and realize the ecological reconstruction goal of coal gangue hill.

(1) Determination of ecological reconstruction goals

According to the ecological environment and regional environmental conditions of coal gangue hill, the ecological reconstruction objectives of coal gangue hill are determined, namely, forestry utilization objectives, agriculture and animal husbandry utilization objectives, scenic tourism utilization objectives and comprehensive utilization objectives. The goal of ecological reconstruction must be coordinated with the regional ecological environment and social and economic development.

(2) Tree species planning and site improvement

According to the site conditions and environmental conditions of the mining area, planning and selecting suitable tree species and site improvement measures is the key to the success of vegetation restoration. Tree species planning should adhere to the principle of "suitable land and suitable trees" and consider the long-term utilization goal of tree species selection. The selection of tree species is mainly native tree species, which can appropriately increase the domesticated exotic tree species that can adapt to the environment of coal gangue hill, increase the diversity of tree species, and create a multi-layer vegetation community system with reasonable allocation of trees, shrubs and grass. Site improvement uses physical, chemical and biological methods to improve the physical structure, nutritional structure and chemical properties of soil to meet the requirements of plant survival and growth.

(3) Scientific plant configuration and planting management technology

The goal of vegetation restoration in spontaneous combustion coal gangue hill is to rebuild the self-sustaining and stable ecosystem of coal gangue hill. Therefore, the plant configuration of coal gangue hill should adopt the form of community configuration, and the density, structure and composition of vegetation community should be determined according to the environmental conditions of coal gangue hill. The composition of the community should also consider the combination of trees, shrubs and grasses and the diversity of tree species, so as to lay the foundation for the stability of the plant community. Vegetation planting should combine the site conditions and site improvement methods of coal gangue hill and adopt appropriate planting techniques. Drought-resistant afforestation methods should also be considered in water-deficient areas. The key point of vegetation restoration management in spontaneous combustion coal gangue mountain is to strengthen the management of water, fertilizer and heat. After the initial results of vegetation restoration in coal gangue hill, the control efforts have been strengthened. With the growth of vegetation, the management intensity can be appropriately reduced according to the actual situation to promote the self-succession of plant ecosystem.

(4) Monitoring and evaluating vegetation restoration in time.

After the initial success of vegetation restoration, the restored vegetation may be degraded for many reasons. Through monitoring and evaluation, we can find out the causes of vegetation degradation as soon as possible and take appropriate measures to maintain the restored vegetation. Through monitoring and evaluation, it can also be found in time that the self-succession of restored vegetation has not developed in the direction of planning and design due to the invasion of native tree species or other species. At this time, we can create a desired ecological restoration system in the direction of planning and design by introducing the desired tree species.

Monitoring and evaluating the established ecological restoration system can also evaluate the environmental and ecological benefits of vegetation restoration, deeply study the process and mechanism of ecological restoration, and provide theoretical support for popularizing and developing vegetation restoration technology.

3. Benefit accounting and popularization and application

The main purpose of vegetation restoration in coal gangue hill is to restore and protect the ecological environment of mining area and realize environmental, social and economic benefits. Through the benefit accounting of vegetation restoration in coal gangue hill, we can understand the input-output relationship of vegetation restoration in coal gangue hill, and then adjust the vegetation restoration model in coal gangue hill to make it more optimized and more suitable for the actual situation of coal gangue hill, so as to obtain higher benefits. Popularize and apply the high-benefit ecological reconstruction model of coal gangue hill to improve the ecological environment of coal gangue hill and mining area.