中文摘要：

对现有11年生马尾松（Pinus massoniana）人工林通过均匀间伐、抚育修枝,结合冠层分析仪测定郁闭度,形成郁闭度约为0.9、0.8、0.7、0.6、0.5的5个梯度林分,研究不同郁闭度林下植物组成及多样性特征,结果表明：（1）各郁闭度林下植物物种重要值分配较为平均,灌木中枹栎（Quercus serrate）、毛桐（Mallotus barbatus）、黄牛奶（Symplocos laurina）较高,草本中铁芒萁（Dicranopteris dichotoma）、金星蕨（Parathelypteris glanduligera）、狗脊蕨（Woodwardia japonila）、山菅兰（Dianella ensifolia）较高,在各郁闭度都占主要优势.（2）随郁闭度减小,林下植物物种数、Margalef丰富度指数、Simpson优势度指数、Shannon-wiener多样性指数都有增大趋势,但多在0.6或0.5郁闭度较0.9郁闭度才有显著增加,在0.5郁闭度灌木物种数又有减小;各郁闭度林下灌木、草本Pielou均匀度指数差异都不显著,5个郁闭度林分草本Alatato均匀度指数差异较小,灌木Alatato均匀度指数在0.6郁闭度中最高,0.5郁闭度较0.6郁闭度又相对降低.（3）各郁闭度林下植物生活型都是以高位芽为主,占比均为50%-60%,在0.6、0.7郁闭度中出现了地上芽植物,0.6、0.5郁闭度中出现了一年生植物、大型高位芽植物,地下芽植物百分比在0.5郁闭度有明显升高.（4）0.9郁闭度林分分别与其他各郁闭度林下植物群落相似系数都较低,0.5、0.6、0.7郁闭度之间群落相似系数相近且较高,都超过70%,在0.7、0.6郁闭度左右物种类别有稳定的趋势,0.5与0.8郁闭度林分群落相似系数又有下降,又有许多新物种更新.综合而言,随郁闭度减小,林下植物物种数、生活型层次和多样性指数都呈增大趋势,在0.6郁闭度中各项指标表现最优,更小郁闭度可能会导致林下植物物种数、均匀度和多样性相对减小,不利于林地地力维持.

英文摘要：

This study investigated the species composition and diversity of understory vegetation of Pinus massoniana plantations. The plantations were of five canopy density gradients as about 0.9, 0.8, 0.7, 0.6, 0.5, respectively. The investigation used methods including uniform thinning, pruning, and canopy analysis system （CI-110）. The results showed comparatively even important values of understory vegetation in P. massoniana plantations with different canopy densities; Quercus serrate, Mallotus barbatus and Symplocos laurina were the dominant shrubs, Dicranopteris dichotoma, Parathelypteris glanduligera, Woodwardiajaponila, Dianella ensifolia were the dominant herbages. With the decrease of canopy density, the species number, Margalef richness index, Simpson diversity index and Shannon-wiener diversity index of understory vegetation showed an increasing trend, while the shrub species number reduced at the canopy density of 0.5. The Pielou evenness index of shrub and herbage and the Alatato evenness index of herbage showed no significant difference in P. massoniana plantations with different canopy densities, but the Alatato evenness index of shrubs was highest at 0.6; the Alatato evenness index of shrubs at 0.5 canopy density was lower than 0.6. The understory vegetation was mainly Phanerophytes （50%-60%）; Chamaephytes appeared at 0.6 and 0.7 canopy coverage densities; Pherophytes and Meso-phanerophytes appeared at 0.5 and 0.6 canopy coverage densities; the percentage of geophytes at 0.5 was obviously higher than others. The understory vegetation of P. massoniana plantations of 0.9 canopy coverage density had lower coefficient of community similarity with others, which was similar among the understory vegetation in P. massoniana plantations with 0.5, 0.6 and 0.7 canopy coverage density. The coefficient of the vegetation community similarity between 0.5 and 0.8 was relatively low. In general, with the decrease of canopy density, the species diversity index and the number of species and life forms of understory