鼎湖山南亚热带常绿阔叶林是北回归线附近保存较完好的地带性植被，是在南亚热带季风湿润型气候条件下发育的植被类型，具有热带向亚热带的过渡性质，群落结构相对复杂，组成种类相对丰富。参照巴拿马巴洛科罗拉多岛（Barro Colorado Island, BCI） 50 hm2热带雨林样地的技术规范，采用中国森林生物多样性监测网络的统一调查研究方法，于2005年在鼎湖山南亚热带常绿阔叶林建立了20 hm2 固定监测样地，调查并鉴定了样方内胸径 （Diameter at breast height， DBH）大于1 cm的木本植物。首次调查结果表明，群落内共有木本植物210种，71 617个活的个体，分属于56科119属。从乔木区系的组成及其特点可以看出，其南亚热带的区系成分占绝对优势，并呈现出由亚热带向热带过渡的趋势。群落垂直结构复杂，地上成层现象较明显，乔木可分为3层，其中重要值最大的锥（Castanopsis chinensis）、木荷（Schima superba）和黄杞（Engelhardtia roxburghiana）均是乔木上层的优势种；中层是群落的主要层，由厚壳桂（Cryptocarya chinensis）、黄叶树（Xanthophyllum hainanense）和华润楠（Machilus chinensis）等中生和耐阴树种组成；下层成分较复杂，物种多样性高，不同地段的物种组成差异较大。样地内物种十分丰富，种-面积曲线拟合显示其物种数量接近于BCI。稀有种比例极高，有110种，占总物种数的52.38%，其中有45%的稀有种源于物种本身的特性，有20%源于区系交汇，人为或自然干扰造成的稀有种占30%以上。样地中所有个体的径级分布(以1 cm等级排列)明显呈倒“J"形，表示群落稳定与正常生长状态。根据对优势种径级结构的分布分析，将各树种的径级结构归纳为4种类型：1）峰型（中径级个体储备型），此类物种为乔木上层优势种；2）倒“J"型 （正常型），此类物种为乔木中层的优势种；3）类倒“J"型（偏正常型），此类物种占据乔木的中、下层； 4）“L”型（灌木型），此类物种分布于乔木下层和灌木层。点格局分析得出优势种在各个层上的绝大部分尺度都是聚集分布的，而不同径级的空间分布随物种的不同而呈现出明显的差异性，点格局显示了优势种在相同径级的分布（特别是DBH=10～40 cm）具有一定的空间互补性。对大径级（DBH＞40 cm）的504个个体进行空间分布格局分析，结果表明，所有这些个体随机分布于整个样地，但不同的物种在空间分布上存在一定的规律。
Aims Lower subtropical evergreen broadleaved forest in Dinghushan is one of typical vegetations in Southern China. Its vegetation is protected very well. Because of its geographical location, the composition of its flora is transitional between the subtropical and tropical. A 20 hm2 permanent plot of 400 m × 500 m was established in 2005 for long-term monitoring of the biodiversity in t he forest. Methods The plot was established following the field protocol of the 50 hm2 plot in Barro Colorado Island (BCI) in Panama. All free-standing trees with diameter at breast height (DBH) at least one centimeter were mapped and identified to species. Important findings There are 71 617 individuals, belonging to 210 species, 119 genera and 56 families. Its floristic composition is transitional between the sub tropical and tropical. The vertical structure of the forest is clear. There are five layers from the top of the canopy to the ground floor, three tree layers (upper, middle and low), one shrub layer and one herb layer, respectively. Based on important value, Castanopsis chinensis, Schima superba and Engelhardtia roxburghiana are the three most dominant species in the upper layer. There are many shade-tolerant and intermediate light-demanding species, such as Cryptocarya chinensis, Xanthophyllum hainanense , Machilus chinensis in mid-layer. Species in low layer are rich and complex, which composition varies a lot. The species-area curve indicates that there is high diversity in the forest and the number of species is close to BCI. There is high proportion of rare species represented by <20 individuals which account for 52.38% of the total number of species. Among these rare species 45% of them lead to be rare by species characteristics, 20% by the floristic transitional nature of the plot, while the rest by disturbances. Size distribution of all individuals shows an invert J-shape, which indicates that the community is in a stable and normal growth status. Size distributions of the dominant species are classified into four types based on their size-class frequencies, unimodal in the top layer, inverse J-shape in middle layer, close to inverse J-shape in middle and low layer, and L-shape in low and shrub layer. Dominant species in different layers are aggregated by the spatial pattern analysis and the spatial patterns of these species in different layers vary with size-classes. However, spatial patterns of them also show complementary within the same size classes, especially in 10-40 cm DBH. The individuals with DBH＞ 40 cm are randomly distributed.
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