Abstract:

Aims: This study selected dominant tree species from natural coniferous-broadleaf mixed forests in Northeast China to analyze the differential characteristics of factors influencing spatial distribution patterns among species with different sexual systems, and to investigate the impact of reproductive cost variations on plant adaptation to environmental specificity.

Methods: Four dominant tree species Pinus koraiensis, Tilia amurensis, Juglans mandshurica, and Fraxinus mandshurica from the natural coniferous-broadleaf mixed forest in Jiaohe City, Jilin Province, were selected as research subjects. The diameter at breast height (DBH), tree height, and crown width of them were measured in July 2019. The gender of all reproductive individuals of Juglans mandshurica and Fraxinus mandshurica in the plots were identified by observing reproductive organs through a telescope in May 2024. All relevant and environmental data from the plot were integrated into four datasets: tree sizes, environmental conditions, crowding index, and distribution patterns of plants. With the datasets, we analyzed the spatial distribution patterns of four tree species, and respectively constructed partial least squares path modeling (PLS-PM) for different sexual systems and different genders within the same sexual system, to evaluate the impact of environmental conditions, crowding index, and tree size on their distribution, and to compare the results for different sexual systems and different genders to explore their response differences.

Results: The findings demonstrated that all four tree species are aggregated within a radius (r) of less than 60 m. The monomorphic species Tilia amurensis and Pinus koraiensis exhibited positive correlations between crowding index, tree size, and spatial aggregation. Furthermore, crowding index positively influenced tree size. Howover, environmental conditions had different effects on the two species: it was positively related to the size of T. amurensis but negatively related to the size and crowding index of P. koraiensis. In the heterodichogamous species J. mandshurica, the different mating types showed considerable differences. The only similarity was that crowding index was negatively correlated with the degree of aggregation in spatial distribution. In the protogynous group, tree size was negatively correlated with the degree of aggregation in spatial distribution, and increased crowding index had a positive effect on tree size. The protandrous group showed the opposite patterns in these aspects, and environmental conditions also showed a significant negative correlation with tree size. For the dioecious species F. mandshurica, tree size and environmental conditions were positively correlated with the degree of aggregation in spatial distribution, whereas crowding index showed a negative correlation. Environmental conditions and crowding index negatively affected tree size, while environmental conditions were positively correlated with crowding index.

Conclusion: Plants with different sexual systems respond differently to environment changes, population crowding, and individual plant size in terms of distribution trends. In addition, plant exhibiting gender dimorphism or transitioning to gender dimorphism showed similar responses when performing the same reproductive functions, but distinct sexual specializations emerged where reproductive functions differed. This research further validates the sexual specialization hypothesis and its applicability across different sexual systems. Greater divergence in male and female functions within the same species leads to more distinct sexual specialization.

Key words: sexual system, spatial pattern, gender differences, differential response, ecological correlations