Floristic composition, structure, and spatial patterns are the fundamental characteristics that reflect species assembly in forests. Species assembly in a forest result from stand development processes [1,2] that are driven by immigration through various means of propagule dispersal [3] and extinction; these are due to species response to environmental conditions [4] and biotic interactions, such as competition, erbivores,  and  predation  [5].  Understanding  the  underlying  processes  of  species  assembly  in  a  forest could  provide  useful  information  for  predicting  stand  dynamics  and  for  forest  management  and biodiversity conservation. In general, two approaches may be followed to analyze the processes that affect species assembly. One is a dynamic approach where the factors affecting changes in species richness are nvestigated  using  data  collected  from  the  forests  at  different  successional  stages  [1].  Another  is  a statistical approach where the factors are inferred from the existing stand structure and spatial pattern using the  data  collected  in  a  plot  [6].  For  example,  spatial  patterns  (aggregation,  random,  and  regular)  are usually used to interpret species assembly and coexistence [7,8]. It is assumed that aggregation spatial patterns are a common phenomenon for conspecific trees in order to reduce competitive exclusion and promote a more diverse coexistence of species [9]. Many factors, including functional traits (e.g., growth form,  shade  tolerance,  and  dispersal  modes),  life  history  strategy  [10],  regeneration  strategy  [11], disturbances [12], and habitat heterogeneity [13], lead to aggregated distribution.Some evidence  has  indicated  that  habitat  heterogeneity  plays  an  important  role  in  regulating  the distribution  of  species  [14].  Previous  studies  reported  that  species  distribution  was  correlated  with variations  in  topography  or  soil  in  tropical  [15],  subtropical  [16–18],  and  temperate  forests  [19]. However, habitat associations of the majority of species were inconsistent with life stages or vertical layers in tropical and temperate forests  [20,21]. Topography  and soil variables significantly  affected species  assembly  in  China’s  subtropics  [16,17],  but  their  relative  contribution  to  entire  stands  and dominant species among vertical layers is poorly understood. Evergreen  broadleaved  forests  in  subtropical  areas  of  China  are  climax  vegetation  with  diverse species,  high  stability,  and  productivity  [22].  The  favorable  climate  results  in  diverse  evergreen broadleaved  forests  [12].  However,  primary  evergreen  broadleaved  forests  had  almost  disappeared
until  now  and  their  total  area  was  less  than  5%  of  the  original  area  as  a  result  of  clearance  for plantations  and  the  conversion  into  secondary vegetation, due  to  sustained  human  disturbance  and  a timber-centric forestry policy over past decades [23]. Recently, China has changed its forestry policy from timber production to ecosystem services [24]. Close-to-nature forest management occurred just
as  a  practical  approach  to  over  exploitation  and  degradation  in  fragile  mountain  landscapes.  The general  aim  of  close-to-nature  management  was  to  formulate  diversely  structured  and  uneven-aged forests  on  a  finer  scale  [25].  For  Chinese  subtropical  areas,  remnants  of  those  surviving  original evergreen broadleaved forests are considered as templates of sustainable management for natural forest
development.  Although  numerous  studies  related  to  species  diversity  and  coexistence  have  beenconducted in old-growth forests at remote mountain locations [26,27], information remains limited on floristic  composition,  stand  structure,  and  spatial  pattern,  as  well  as  on  the  driving  mechanisms  of species assembly in subtropical areas of China.