坝上地区不同年代退耕还林生境的草本层植物多样性及影响因子

退耕还林是坝上地区重要的生态修复工程，其生态效益日益受到广泛关注，但针对林下植物多样性保护功能的研究还较少，虽然草本层植被是森林生态系统服务功能的重要指标之一。为评估不同年代退耕还林生境的生物多样性，调查了20世纪70年代至21世纪初共4个年代退耕还林生境的草本层植物多样性，并与弃耕生境及自然林生境进行了对比。为进一步分析林下草本层植物多样性的影响因子，还分析了乔灌层植被、土壤理化性质与林下草本植物多样性的关系。结果显示，不同年代退耕还林的林下草本植物多样性未有显著差异，且均显著低于弃耕生境与自然林生境。草本层物种丰富度对土壤碱解氮含量、灌木层丰富度、灌木层密度具有显著的正响应，Simpson多样性主要与乔木层林木密度呈显著负相关。研究表明，不同年代退耕还林后的林下草本层植物多样性保护功能低于预期，而改善林分空间结构与建设模式可能利于提升其生物多样性保护功能。未来植被修复中需充分权衡生态系统不同服务功能之间的关系，因地制宜，宜林则林，宜草则草，重视自然恢复与多元化生态修复方式，以实现更好生态效益。

Herb diversity and its impact factors in different periods from 1970s to 2000s of the returning farmland to forest project in the Bashang Area of North China

Returning farmland to forest (RFTF) project is one of the most critical ecological restoration projects in Bashang area, and its ecological service value has been paid more and more attention. Although the herb layer of the artificial forest was a vital indicator to biodiversity conservation and ecosystem services, the relevant researches were much less than expected in this area. We surveyed herb diversities of these forests that were planted in four different periods from 1970s to 2000s of the returning farmland to forest project. Then, the herb diversity of returning farmland to forest habitat was compared with that in abandoned farmland and the natural forests. The effect of the soil character, tree and shrub layer on herb diversity was also analyzed. The results showed that there was no significant difference of herb diversity among different periods of RFTF projects. While all of them were significantly lower than that in the abandoned farmland and the natural forests species richness of herb layers was significantly and positively responded to the content of soil alkali-hydrolyzable nitrogen species richness and densities of shrub. The Simpson diversity of herb layer was negatively responded to the densities of tree. The research revealed that the herb diversities of RFTF habitats might be lower than that we expected, improving vertical spatial structures and construction mode might be helpful to increase the herb diversity level. In order to preferably realize ecological benefits of future ecological restoration projects in Bashang area, it needs to weigh the different relationships of ecological ecosystem service functions, choose ecological restoration methods based on local conditions, and emphasize the importance to natural restoration and diverse restoration methods.