Objective  The study aims at determining the development stages of natural spruce-fir and broadleaved mixed forest so as to provide theoretical basis and technical support for its management according to stage.

Method  One hundred and seventy-two permanent sample plots of spruce-fir-broadleaved mixed forest in Jilin Province were selected for initial classification based on the TWINSPAN two-way indicator species quantitative classification analysis techniques. The growth, species diversity and stand structure of spruce-fir mixed forest were compared and analyzed to determine the development stage.

Result The result indicated that the spruce-fir-broadleaved mixed forests could be divided into three groups (group 1:spruce-birch mixed forest; group 2:fir-softwood-broadleaved mixed forest; group 3:Korean pine-spruce-hardwood-broadleaved mixed forest) by TWINSPAN. In general, the diameter of all stands showed an inversed J-shape distribution. The height structure development of stand showed a trends related with tree species characteristics. There were differences in stand factors and periodic annual increment among these groups. The stand average diameter, mean height, dominant height, dominant diameter and volume all ranked by ascending order as group 2, group 1 and group 3; the periodic annual increment ranked by ascending order as group 3, group 2 and group 1. The species richness ranked by descending order as group 2, group 3 and group 1. The species dominance of groups 2 and 3 were lower than that of the group 1.

Conclusion  According to the above classification and characteristics analysis, the development stage of spruce-fir-broadleaved mixed forest was determined as fir-softwood-broadleaved mixed forest, spruce-birch mixed forest, Korean pine-spruce-hard-broadleaved mixed forest. This method might be suitable for other natural forests.