摘要:林下草本层是人工林生态系统的基础功能层，对维护人工林生态系统的健康、稳定和功能具有重要意义。了解陕北"三北"防护林建设对林下草本群落特征的影响，并解析林下草本群落发育与林分结构和土壤养分变化的响应关系，对合理评估防护林建设工作和指导未来生态建设具有重要价值。为此，调查了陕北典型风沙区和黄土区不同造林阶段防护林下草本地上生物量和物种多样性的变化，并分析其与林分结构和土壤养分的关系。结果表明：（1）风沙区不同造林阶段人工林下草本平均地上生物量（23.64 g/m²）显著低于黄土区（44.53 g/m²）。随造林年限增加，风沙区林下草本地上生物量和物种多样性逐渐升高，而黄土区林下草本地上生物量和物种多样性则逐渐降低。（2）风沙区人工林土壤有效氮和有机碳随造林年限的增加逐渐升高，而黄土区人工林下土壤有效氮和有机碳则无明显变化趋势。（3）风沙区早期林下草本地上生物量和物种多样性升高主要得益于土壤养分的提升。而黄土区早期林下草本生物量和物种多样性降低主要是人工林郁闭度增加所致。风沙区防护林的建设促进了林下草本的发育，而黄土区早期人工林下草本出现退化现象。建议对风沙区进行防护林建设，而黄土区以自然恢复为主。



Abstract:Understory herbs make up a basic functional layer of plantation ecosystems, and have great significance for their health, stability, and function. Aboveground biomass and species diversity of understory herbs in plantations of different ages and their relationships with stand structure and soil nutrient availability were compared and evaluated in representative sandy and loess hilly areas on the Loess Plateau, which is important for the rational assessment of future shelterbelts and ecological restoration sites. The results showed that: (1) the understory herb average aboveground biomass in sandy area (23.64 g/m²) was significantly lower than that of loess hilly areas (44.53 g/m²). As the duration of afforestation efforts increased, the understory herb aboveground biomass and species diversity in the sandy areas increased consistently, while in loess hilly areas, they declined gradually. (2) Soil available nitrogen and organic carbon in sandy areas increased gradually as duration of afforestation efforts increased, while in the loess hilly areas, they showed no obvious trend. (3) The increase in understory herb aboveground biomass and species diversity of younger plantations in sandy areas was a direct benefit of improvements in soil nutrient levels. In contrast, the understory herb aboveground biomass and species diversity decline of young plantations in the loess hilly areas was mainly caused by increases in canopy density. The plantation restoration efforts in sandy areas promoted the development of understory herbs. However, the understory herb layers of young plantations in loess hilly areas were severely degraded. These findings imply that shelterbelt construction is necessary for sandy areas, while natural restoration is more suitable for loess hilly areas.





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