ObjectiveThis paper aims to explore the seedling regeneration status of a mixed conifer-broadleaf forest in Jiaohe, Jilin Province of northeastern China, and to provide a better guidance and theoretical basis for scientific and reasonable management.

MethodBased on 4 ha thinning sample land in Jiaohe, Jilin Province, with the seedlings of all tree species in 100 seedling plots (2 m × 2 m) as the research object, we compared the species composition, quantity characteristics and monthly dynamics according to the seedling monitoring data from early June to early August in 2018. We used single factor anova to analyze the effect of thinning on undergrowth seedling regeneration.

Result(1) A total of 948 seedlings were found, belonging to 10 families, 12 genus and 19 species. The species richness of the control, light, moderate and heavy thinning plots were 8, 13, 14 and 16, the Simpson ’s diversity index, Shannon-Weiner index and Pielou index of the seedlings were significantly increased after thinning. (2) The number of seedlings in the sample plot varied greatly under different thinning intensities, and the number of seedlings in the light thinning plot and the heavy thinning plot was significantly higher than control and the moderate thinning plot. After thinning, the number of seedlings in different age grades and height grades tended to be evenly distributed. With the increase of thinning intensity, the proportion of the number of seedlings in older age grades and higher height grades gradually increased. (3) The mortality rate of seedlings reduced and the supplementation rate increased after thinning and it had difference under different thinning intensities. The mortality rate of seedlings in heavy thinning sample plots was lower, while the supplementation rate in light and moderate thinning sample plots was higher.

ConclusionThinning affected the regeneration of undergrowth seedlings. The species diversity index was significantly increased after thinning. From the seedling number under the forest, the regeneration status was better under light and heavy thinning intensities. From the seedling growth under the forest, the distribution of seedling age grade and height grade was more uniform and the seedling growth was better.