Spatial pattern analysis of dominant tree species saplings in spruce-fir coniferous and broadleaved mixed forests based on Ripley L function

Objective The structure and dynamics of dominant tree species saplings determine the structure and growth dynamics of future stand. Investigating the spatial distribution patterns and interspecies associations of dominant tree seedlings is of significant theoretical and practical importance for the restoration of forest ecosystems and the prediction of forest succession dynamics.

Method This study focused on five dominant tree species in a 1-hectare mixed coniferous and broadleaved forest plot in the Jingouling Forest Farm, Wangqing County, Jilin Province of northeastern China. The spatial correlations between five kinds of saplings and the intraspecific spatial correlations between saplings and juveniles and adults were analyzed by univariate Ripley L and bivariate Ripley L functions.

Result A total of 471 saplings were investigated in the plot, and the quantity size was as follows: Abies nephrolepis (357) > Picea jezoensis var. komarovii (47) > Tilia amurensis (23) > Acer pictum subsp. mono (22) > Pinus koraiensis (14). Abies nephrolepis occupied an absolute advantage. The spatial patterns of Abies nephrolepis, Picea jezoensis var. komarovii and Tilia amurensis saplings with the increase of scale conformed to the aggregation-uniform-random distribution pattern; the scales of aggregated distribution of Pinus koraiensis were 14−21 m, 31−36 m and 39−50 m, and other scales were random. Acer pictum subsp. mono distributed randomly in 0−50 m and distributed aggregately at few scales (23−38 m). The interspecific relationships between saplings were mostly positively correlated with the significant indigenous space (0−36 m), uncorrelated on the 36−42 m scale, and only saplings of Abies nephrolepis were negatively correlated with the significant indigenous space on a large scale (42−50 m), indicating that the five saplings maintained a good relationship of mutual benefit and symbiosis. The intraspecific correlation was mainly spatial positive correlation, and there was a significant negative correlation between saplings and adult trees in large scale (42−50 m).

Conclusion The spatial distribution and associations of saplings in this forest stand are primarily influenced by seed dispersal limitations and environmental heterogeneity at the horizontal structure level. Saplings predominantly exhibit an aggregated distribution at smaller scales. In the vertical structure, the main forest layer provides a significant “shelter effect” for the saplings. There exists a beneficial symbiotic relationship both within and between the five sapling species. Therefore, in the restoration of natural mixed secondary forest of spruce and fir, it is feasible to conduct seeding of these saplings at a small scale of 0−36 m, based on forest management needs. The degree of aggregation should prioritize fir, followed by spruce, and then pine, to enhance the survival rate of saplings and promote their nature regeneration.