In recent years, the problem of ecosystem degradation caused by human activities has become increasingly serious. Vegetation restoration is a key means to solve this problem, which has increased. To address the suitability and structural optimization of vegetation restoration in the Loess Plateau (China), the MaxEnt model was used to quantify the impacts of environmental and human activities on the planting suitability of vegetation restoration species at the raster scale. Three layers of trees, shrubs, and herbs with 12 common vegetation restoration species were selected. The factor index system was constructed by combining climatic, ecological, and socio-economic data, and the MaxEnt model predicted land suitability. It was found that human activities significantly increased the unsuitable planting area. This especially affected Robinia pseudoacacia in the tree layer and Amorpha fruticosa in the shrub layer. High and medium suitable areas were mainly sparsely populated areas with close water sources. Through maximum suitability optimization, it was identified that the overall spatial distribution of the three layers in the study area was relatively consistent, and the structural dominance of trees + shrubs + herbs and single herbs in the vertical structure was obvious; these were concentrated in the southwestern and northeastern parts of the study area, respectively. In addition, organic content (OC) and distance from the road to woodland (RW) were the dominant factors affecting land suitability, with a contribution rate of more than 50% and up to 80%. These results provide a scientific basis for optimizing planting structures. They are of significant theoretical and practical significance in guiding vegetation restoration work.

Artificial afforestation is considered as one of the key ecological restoration measures. The early large-scale, single-species afforestation method is considered detrimental to the environment. However, there is still a lack of empirical research on the differences in understory biodiversity between monoculture and mixed forests, as well as the response mechanisms of understory plants to environmental factors. We compared the differences in understory plant diversity in different types of plantations and analyzed the differences in understory species composition and the impact of understory plants on local scales (soil organic matter, soil-available phosphorus, and distance from the road) and landscape scales (patch density, landscape fragmentation, and patch diversity) and environmental variable response mechanisms in a mountainous area. Our findings revealed that there was no significant difference in overall understory plant diversity between monoculture and mixed forests, but the perennial species and native species in the mixed forest were significantly higher than those in the monoculture. In monoculture plots, the disparity in species composition was more pronounced compared to that observed in mixed plots. Soil organic matter had a positive effect on understory plant diversity, and soil available phosphorus and distance from the road significantly affected plant diversity in monoculture forests but had no effect in mixed forests. Landscape-scale environmental factors have no effect on understory species diversity. The findings of the current study emphasize the disparities in the plant species composition between mixed and monoculture forest plantations, as well as their respective reactions to environmental factors.

In recent years, the problem of ecosystem degradation caused by human activities has become increasingly serious. Vegetation restoration is a key means to solve this problem, which has increased. To address the suitability and structural optimization of vegetation restoration in the Loess Plateau, the MaxEnt model was used to quantify the impacts of environmental and human activities on the planting suitability of vegetation restoration species at the raster scale. Three layers of trees, shrubs, and herbs with 12 common vegetation restoration species were selected. The factor index system was constructed by combining climatic, ecological, and socio-economic data, and the MaxEnt model predicted land suitability. It was found that human activities significantly increased the unsuitable planting area. This especially affected Robinia pseudoacacia in the tree layer and Amorpha fruticosa in the shrub layer. Highly suitable and moderately suitable areas were mainly located in sparsely populated areas with close water sources. Through maximum suitability optimization, it was identified that the overall spatial distribution of the three layers in the study area was relatively consistent, and the structural dominance of trees + shrubs + herbs and single herbs in the vertical structure was obvious, which were concentrated in the southwestern and northeastern parts of the study area, respectively. In addition, organic content (OC) and distance from the road to woodland (RW) were the dominant factors affecting land suitability, with a contribution rate of more than 50% and up to 80%. These results provide a scientific basis for optimizing planting structures. They are of significant theoretical and practical significance in guiding vegetation restoration work.