Objective  Plant diversity protection and good forest structure are important targets for natural forest protection. It is helpful to improve plant diversity based on stand structure adjustment to clarify the effects of stand size, community characteristics and vertical structure of arbor, shrub and herb on its change.

  Method  In this paper, from August to September of 2016, the individual size characteristics, community characteristics and plant diversity characteristics of arbor, shrub, herb and regeneration layer were investigated in China northernmost Shuanghe National Nature Reserve in the cold temperate zone of China, and redundant analysis and variance partitioning analysis were conducted to decouple the complex association and possible factors responsible for diversity variations.

  Result  (1) A total of 9 tree species were found in the study area, with over 80% of white birch (Betula platyphylla) and larch (Larix gmelinii) in total number;19 shrub species were found and bilberry (Vaccinium vitis-idaea) accounted for 93% of the total shrubs. There were 74 herbaceous plants, and the most dominant was Deyeuxia langsdorffii (15%); pioneer tree species of Betula platyphylla was the most abundant in the regeneration layer (60%). (2) The diameter and height of trees were only half of those in 1970s. The species richness, diversity and evenness of Shuanghe National Nature Reserve all showed as herb layer > tree layer > shrub layer, and evenness index was 0.53−0.73, with very lower richness in the regeneration layer. The diversity of trees and herbs was about 50% higher than that in the central Daxing’anling at Huzhong Nature Reserve. (3) Redundancy ordination and variance partitioning found that community characteristics and herb characteristics had the greatest interpretation power for diversity variation, and the regenerated tree height showed the most statistical significant indicating function (P < 0.05).

  Conclusion  Shuanghe National Nature Reserve has a rather high richness of arbor and herb plants in this area, but it still needs a long time to recover the forest quality related to tree size. Adjusting the stand structure should be an effective way to approach species diversity conservation via the plant species succession.