Abstract:

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.

Key words: forest structure, vertical structure, β diversity, β diversity partitioning, biodiversity, stratification, community assembly