Data Sheet 1_Stand structure influences understory plant diversity through soil factors: three afforestation types of Masson’s pine in the upper Yangtze River, China.docx

PurposeIn general, mixed forests have the potential to enhance understory plant diversity. However, the effects of stand spatial structure formed by different types of mixed afforestation on understory plants communities are still not clear.
MethodsTo answer these questions, we examined the stand spatial structure’s impact on soil (nitrogen, phosphrous, potassium, etc.) and understory plant communities (diversity indexes, ecological niche width and resource overlap of shrub and herb) in three types of Pinus massoniana afforestation: a monoculture (MPF), a mixed forest with Cunninghamia lanceolata (MCLMF), and a mixed forest with Liquidambar formosana (MLMF).
ResultsMCLMF substantially increased diversity and ecological niche width for understory shrubs and herbs, steered understory plants toward resource utilization generalism. MLMF enhanced shrub diversity by reducing dominant species ratios. In terms of stand structure, MCLMF significantly increased the opening degree (O), mingling index (M), and competition index (CI), while MLMF decreased CI but increased M. Redundancy analysis indicated that the opening degree explained 52.47% of the variation in shrub diversity and 42.51% in herb diversity, and CI explained 24.57% of the shrub diversity variation. Soil pH, total nitrogen, and available potassium were significantly enhanced after mixed afforestation. The indices O, CI, and M indirectly affect the diversity of understory plants through soil properties, such as temperature, moisture, available nutrients (e.g., nitrogen, phosphorous, and potassium), organic carbon, and pH.
ConclusionsStand spatial structure significantly shapes understory plant community structure through soil mediation, demonstrating its role in enhancing artificial forest quality and stability in ecologically sensitive areas.

研究背景 总体而言，混交林具备提升林下植物多样性的潜力，但不同混交造林模式所形成的林分空间结构（stand spatial structure）对林下植物群落的影响机制仍未明确。
研究方法 为解答上述科学问题，本研究以3种马尾松（Pinus massoniana）人工林为研究对象，分别为纯林（monoculture，MPF）、杉木（Cunninghamia lanceolata）混交林（MCLMF）以及枫香（Liquidambar formosana）混交林（MLMF），探究林分空间结构对土壤（氮、磷、钾等）及林下植物群落（灌木与草本的多样性指数、生态位宽度与资源重叠度）的影响。
研究结果 杉木混交林（MCLMF）可显著提升林下灌木与草本的多样性及生态位宽度，引导林下植物向资源泛化利用方向发展；枫香混交林（MLMF）则通过降低优势种占比提升了灌木多样性。在林分结构特征方面，杉木混交林（MCLMF）显著提升了林分开张度（opening degree，O）、混交度（mingling index，M）与竞争指数（competition index，CI），而枫香混交林（MLMF）则降低了竞争指数（CI）并提升了混交度（M）。冗余分析（redundancy analysis）结果显示，林分开张度（O）可解释52.47%的灌木多样性变异与42.51%的草本多样性变异，竞争指数（CI）可解释24.57%的灌木多样性变异。混交造林后，土壤pH值、全氮与速效钾含量均得到显著提升。林分开张度（O）、竞争指数（CI）与混交度（M）可通过土壤温度、含水量、速效养分（如氮、磷、钾）、有机碳与pH值等土壤理化性质间接影响林下植物多样性。
研究结论 林分空间结构可通过土壤介导作用显著塑造林下植物群落结构，证实其在提升生态敏感区域人工林质量与稳定性方面的重要作用。