鼎湖山南亚热带常绿阔叶林群落垂直结构及其物种多样性特征

Vertical structure and its biodiversity in a subtropical evergreen broad-leaved forest at Dinghushan in Guangdong Province, China

群落结构在森林生态系统中具有重要作用,其构建机制一直是森林生态学的研究核心。群落结构不仅包括水平方向上的物种分布格局,还包括垂直方向上的物种分层结构。本文基于鼎湖山南亚热带常绿阔叶林塔吊样地,利用林冠塔吊和测高杆精准测量样地内每个个体(胸径大于1cm)的树高,并划分群落的垂直层次,研究了每层的群落多样性特征(α多样性)和林层间的群落多样性变化特征(β多样性)。结果表明:(1)样地群落垂直层次由下至上分为5层:灌木层、亚冠层、林冠下层、林冠中层和林冠上层。(2)随林层向上,物种丰富度、多度和Shannon-Wiener指数均下降,Pielou均匀度指数在林冠下层最大。(3)利用POD法计算并分解β多样性,发现随林层向上,β多样性在灌木层与其他各层间呈递增趋势,在相邻林层间呈单峰型,不同林层间的物种组成差异主要由丰富度差异造成。但在林冠下层与林冠中层间丰富度差异较小,物种替换组分增大,可能与林冠下层所处特殊位置有关。(4)各林层内微环境从灌木层向上,趋于高温、强光照和低空气相对湿度,但林冠下层平均日光强最低。综上,鼎湖山南亚热带常绿阔叶林林冠下层可能存在强烈的环境筛选作用,且光照可能是影响群落垂直结构形成的限制因子。

Community structure plays a fundamental role in forest ecosystems as one of the basic mechanisms underlying community assembly. Community structure includes both horizontal and vertical structure. We stratified the vertical structure of a lower subtropical evergreen broad-leaved forest at Dinghushan in Guangdong Province, China by surveying each individual with DBH ≥ 1 cm via a canopy crane, and then explored α diversity within each layer, as well as β diversity between layers. We found that:(1) The vertical structure of the forest was stratified into five layers;from bottom to top, the shrub, sub-canopy, lower canopy, middle canopy, and upper canopy correspond to the traditionally defined vertical levels of a forest community.(2) Layer α diversity decreased with height, and the Pielou evenness index was largest in the lower canopy.(3) The β diversity of layers relative to the shrub layer increased with height. Using the POD framework, the differences between layer community compositions were mainly attributed to differences in species richness. However, the lower canopy showed increased species replacement and decreased richness difference relative to the middle canopy layer when compared with other neighbouring layers.(4) Air temperature, light intensity and relative humidity increased with layer height, and the most dramatic change in light occurred in the middle canopy. These microenvironmental features may play an important role in the formation of vertical hierarchy in the forest, with light intensity as the largest factor.