人工林目前存在结构单一、土壤退化、生物多样性降低等人类普遍关注的生态问题。马尾松(Pinus massoniana)是长江上游低山丘陵区退耕还林的主要人工林树种。研究采伐林窗对植物物种组成和更新的影响，对马尾松低效人工林的改造，提升其生态服务功能具有重要的意义。该文以采伐39年生的马尾松人工林形成的7种不同大小的林窗为研究对象，分析了不同季节林窗内的植物生活型组成及多样性变化。结果表明：1)马尾松人工林林下植物以高位芽植物居多，其次是地面、地下芽植物，一年生植物较少而缺少地上芽植物。在林窗形成初期，林窗的高位芽植物比例明显低于林下，大林窗的高位芽植物比例稍高于小林窗，地下芽和一年生植物的比例低于小林窗。2)林下的物种丰富度和物种多样性指数显著低于大林窗。不同林窗下植物的丰富度指数、优势度指数、多样性指数也存在显著差异。3)夏季林窗下植物多样性最高，其次是秋季，春季多样性最低。1225-1600 m2的大林窗能够促进马尾松人工林植物多样性恢复和植被更新。
Aims Pinus massoniana is the major plantation tree species in the low hilly lands of the upper Yangtze river valley for commercial purpose. The large areas of plantations have caused serious ecological problems such as biodiversity decline and soil degradation. Our objectives were to study the dynamics of species composition and plant diversity in forest gaps, to test the hypothesis that forest gaps facilitate the regeneration and plant diversity in P. massoniana plantations, and to determine the size of forest gaps that harbors the most complex compositional structure and the greatest plant diversity. <br> Methods We selected 39-year-old P. massoniana plantations with seven different gap sizes in the study, and used combination of systematic and representative sampling approaches. In the spring, summer, and autumn of 2013, sampling plots of the dimension 5 m × 5 m were laid out in the center of the forest gaps and under the canopy, and plants within each plot were surveyed for determination of their diversity and compositional structure. <br> Important findings The understory of P. massoniana plantations were dominated by phanerophyte plants, fol-lowed by hemicryptophytes, geophytes, and therophyte plants. The phanerophyte plants were more abundant un-der the canopy than in forest gaps. The large gaps had more phanerophyte plants, while the geophytes and thero-phyte plants were less frequent under the canopy than in the small gaps. The species richness and diversity were significantly lower under the canopy than in the large forest gaps. Moreover, species richness, dominance, and diversity differed significantly among the forest gaps of different sizes. Seasonally, the highest diversity occurred in summer, followed by autumn, with the spring having the lowest diversity. The greatest diversity was found in the forest gaps of the size 1 225-1 600 m2, which could be the optimal gap size for facilitating plant diversity and regeneration of vegetation in P. massoniana plantations.