杉木林改造成乡土阔叶林对林下植物物种组成和多样性的影响

把杉木林改造成乡土阔叶林，不仅能提供高价值木材，而且能够提升生态系统服务功能，是我国目前改造退化针叶林最常见的经营模式之一，但这些改变对其林下植物物种组成和多样性的影响及机制我们尚知之甚少。以南亚热带杉木林采伐迹地上重新种植的杉木林、红锥林和米老排林为研究对象，调查研究其灌木层和草本层植物物种组成和多样性，结果表明：（1）和杉木林相比，改造后的红锥林和米老排林灌木层的植物物种丰富度和多样性均呈极显著降低（P<0.01），但其草本层植物只有物种丰富度极显著降低（P<0.01），多样性均无显著变化（P>0.05）；（2）主成分分析（PCA）表明改造后的林分灌木层和草本层的植物物种组成发生明显的变化，冗余分析（RDA）确定导致林分灌木层植物物种组成发生变化的主要原因是杉木林改造成红锥林和米老排林后的冠层透光率、土壤碳氮比、土壤含水量和凋落物碳氮比的显著变化，而冠层透光率和土壤碳氮比的显著变化是导致其林下草本层植物物种组成发生明显变异的主要因子；（3）方差分解结果显示微地形、乔木特性和土壤理化性质的独立效应对灌木层和草本层植物物种组成的影响高于它们的交互效应。该研究为科学经营管理人工林和提高人工林生态系统多功能性提供科学依据。

Effects of understory plant species composition and diversity under transforming Chinese fir into precious indigenous broadleaf plantations

Transforming Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) forest into precious indigenous broadleaf forest can not only provide high-value wood, but also enhance ecosystem service function, which is one of the most promising management measures of transforming the degraded coniferous forest in China. These transformations can alter the canopy structure community and the physicochemical properties of soil which caused by the quantity and quality of the litterfall. However, the impacts and mechanisms of broadleaf transformation on the species composition and diversity of undergrowth plant are still poorly understood. In this research, the replanted Chinese fir forest, Castanopsis hystrix forest and Mytilaria laosensis forest on the cutting-blank of the Chinese fir forest in south subtropics of China were studied. And its plant species composition and diversity in the shrub and herb layers were investigated. Our observations confirm that:(1) compared with Chinese fir, the richness and diversity of plant species in shrub layer of reconstructive C. hystrix forest and M. laosensis forest were extremely significant declined (P<0.01), while only the richness in herb layer extreme decreased significantly (P<0.01), and the diversity of the three forest types did not change distinctly (P >0.05). (2) Principal component analysis (PCA) showed that the composition of plant species in the shrub layer and herb layer of the transformed stand changed significantly. Redundancy analysis (RDA) determined that the main reason for the changes of the plant species composition in shrub layer was the obvious change of the canopy light transmittance, C/N ratio of soil, soil water content and C/N ratio of litterfall after the transformation of Chinese fir forest into C. hystrix forest and M. laosensis forest. The marked changes of canopy light transmittance and C/N ratio of soil were the main factors which led to the significant variation of plant species composition in the herbaceous layer under the forest types. (3) The variance partitioning showed that the independent effects of microtopography, tree features and soil physical-chemical proprieties had higher effects on plant species composition of shrub layer and herb layer than their interaction effects. Therefore, it is important to adjust the density and improve the canopy structure of the forests appropriately, and ultimately provide more opportunities for the invasion, settlement, reproduction and regeneration of more understory plant species when transforming Chinese fir into precious indigenous broadleaf forest. This study provides scientific basis for the operating management and improving of the multi-functional ecosystem of the plantation forests in subtropical China.