Objective The object of this study is to determine which competition type, intraspecific or interspecific competition, was popular in typical natural mid-subtropical broad-leaved forest, and to determine how the vertical distribution of trees affect the competition, thereby to provide data for the protection and utilization of forest resources.

Method Five typical natural forest sample plots were investigated in Wanmulin Nature Reserve, Fujian Province. Hegyi's competition index was used to investigate two scenarios, without or with arbor-layer stratification.

Result The results showed that the competition intensity decreased largely with the increasing of sampling radius until the radius was more than 4 m so that 4 m is a suitable radius for analyzing competition among trees in the five communities. There were more than half of the species only occurred interspecific competition within a radius of 4 m in each plots. Interspecific competition intensity was generally stronger than intraspecific competition intensity for those tree species that were rebelling against both same species and different species, and more different species than same species in their competitors. The arbor layer could be divided into three layers of the five plots. On average, the higher the tree was, the farther the distance was from its competitors, there were more trees belonged to the third arbor layer among the competitors, and the competition pressure was lower for individual object tree with all of its competitors.

Conclusion Interspecific competition is popular in the five communities; both the competition pressure and the composition of competitors are closely related to vertical distribution of trees. More attention should be paid to the vertical distribution in the conservation and management of forest resources. There are none intensive interspecific or intraspecific competition occurred in dominant species of the five communities. There are four species, Castanopsis carlesii, Ilex qingyuanensis, Engelhardtia fenzlii, and Elaeocarpus decipiens, could occur intensive interspecific competition, but not specialized competitor was found and the four species mainly distribute in the second or third arbor layer together with their competitors. There are five species mainly distributing in the second or third arbor layer, Elaeocarpus sylvestris, Elaeocarpus chinensis, Randia cochinchinensis, Michelia skinneriana, and Symplocos glauc, could occur over-intraspecific-competition.