[Competition among dominant tree species in a natural spruce-fir forest in Changbai Mountain]

Dominant tree species are the main species in different layers of mixed-species forests. Examining competitive relationships among dominant tree species is important for proper management of mixedwood forests. In this study, we established a 100 m×100 m plot of uniform condition on Jingouling Forest Farm, Wangqing County, Jilin Province. The dominant tree species of the young forest community were first determined through dominance index analysis approach and the competitive relationships among dominant tree species were then examined using tree competition index that described intra- and inter-specific competition from the above and sides of individual tree crown. The results indicated three dominant tree species in this mixed-species community were Abies nephrolepis, Picea koraiensis and Pinus koraiensis. A. nephrolepis, Picea koraiensis, Pinus koraiensis, Betula costata, Tilia amurensis, Acer tegmentosum and Betula platyphylla were the main competitors of the dominant tree species, while A. nephrolepis was the major competitor for all three dominant tree species (1412.48), followed by Picea koraiensis (439.17) and Pinus koraiensis (245.28), they all had side squeeze effect (64.9%, 65.2% and 66.0% of the total competition for the three dominant tree species, respectively). The level of side and above competition decreased with individual tree DBH (diameter at breast height); the percentage of side competition was nearly equal to that of above competition in small trees and increased with tree size, reaching nearly 100% in large canopy trees. For the three dominant tree species, the side and above competition of three dominant tree species mainly came from A. nephrolepis, Picea koraiensis, Pinus koraiensis, T. amurensis, B. costata, A. tegmentosum and B. platyphylla, and the inter-specific competition was more intense than intra-specific competition (58.4%, 87.1%, 83.7% of the total competition for the three dominant species), both of which decreased with the increase of individual tree DBH.