Research advances in vegetation restoration and its ecological effects in earth-rock mountain areas of North China

Afforestation is a method for building a beautiful China, promoting the construction of ecological civilization, and improving the well-being of people's livelihood. It is a concrete measure to realize the green hills and mountains. The sparse vegetation, poor soil, severe climate, frequent disasters, and unreasonable production from human activities in the northern earth-rocky mountains have caused serious damage to the vegetation in the region, resulting in a series of ecological and environmental problems and forming large exposed areas of rocks, serious soil erosion. Vegetation recovery is the key to ecological restoration in this region. Here, we reviewed the current research status of vegetation restoration in the earth-rocky mountains of North China and the existing problems in current research, including allocation patterns and afforestation technology selection in vegetation restoration, environmental factors affecting vegetation restoration, and ecological effects of vegetation restoration. Further, we discussed the effects of allocating different tree species and afforestation techniques on the survival rate of afforestation. It was pointed out that the variant tree species and rational regulation of tree water use were keys to successful vegetation restoration in the earth-rocky mountains. We also discussed the effects of soil fertility, water, topography, and zonal differences on vegetation restoration, and the hydrological, soil and water conservation, soil environment, and biodiversity effects of vegetation restoration. We found that, in the process of vegetation restoration in the earth-rocky mountains, the vegetation and the environment interacted with and promoted each other; this, in turn, accelerated the restoration and upgrading of the regional ecosystem structure and function. At the same time, it was found that the researches on topographic effect of vegetation change in the earth-rocky mountains was relatively lacking, and the mechanism of soil nutrient impact on vegetation restoration was not yet clear. Finally, there were problems of unreasonable tree species selection, short research scale, limited data, and insufficient economic research on vegetation restoration in the process of vegetation restoration in the earth-rocky mountains. Our study proposed that more attention should be paid to selecting fine native tree species to plant in combination, establishing a long-term monitoring network for vegetation succession, monitoring and evaluating the comprehensive benefits of vegetation restoration, and clarifying the response mechanisms of vegetation to extreme climate; solving these issues was the next step in restoring vegetation research in the earth-rocky mountains.