Abstract: Species diversity is a crucial component of biodiversity. Changes in species diversity during forest succession directly affect ecosystem function and stability. Therefore, it is of significant importance to investigate the changes in species diversity and their influencing factors during forest succession for accurately predicting forest ecological processes and biodiversity patterns.The study focused on Betula platyphylla forest (early succession period), Betula platyphylla-Larix gmelinii mixed forest (middle succession period) and Larix gmelinii forest (late succession period) in the northern Da Hinggan Mountains as the research objects. The study employed a space instead of time to analyze the changes in species diversity during forest succession and explore the relationship between species diversity and envi-ronmental factors in cold temperate zone of China.The results demonstrated that: (1) Species richness and diversity significantly increased during forest succes-sion. Two indices including Margalef richness index and Shannon-Wiener index were 2.42 and 2.689 at the beginning of succession, and 5.90 and 3.432 at the end of succession. However, there was no significant dif-ference in the species Pielou evenness index. (2) During the forest succession process , the similarity of plant communities gradually decreased and the differences gradually increased.. The Jaccard index, Sorenson index and Bray-Curtis index all decreased. (3) During the forest succession process, soil pH, soil organic matter, total nitrogen, and total phosphorus significantly influnence the species diversity index. Specifically, total nitrogen and total phosphorus were the primary factors affecting species diversity in the pre-middle period of succession, while soil pH and soil organic matter were the dominate factors influencing species diversity in the later period of succession. (4) With the progression of succession, the influence of stand spatial structure on species diver-sity gradually increased. Angular scale and size ratio are the main spatial structure factors influencing species diversity during forest succession. Consequently, soil factors played a prominent role in species diversity during forest succession in the northern Da Hinggan Mountains, the driving effect of stand spatial structure on species diversity in the process of forest succession can not be ignored.

Key words: Da Hinggan Mountains, Secondary succession, Species diversity, Soil properties, Stand structure