关键词: 次生针阔混交林, 广义线性混合模型, 乔木幼苗存活, 生物邻体, 生境

Abstract:

Objective: This study aimed to explore the relative importance of negative density dependence and habitat filtering on tree seedling survivalin community, age class and species, so as to provide theoretical basis for the mechanisms of seedling regeneration and species diversity maintenance in a temperate forest. Method: During 2016 to 2018, 209 seedling census stations were monitored in the secondary mixed conifer and broad-leaved forest plot in Jiaohe, Jilin Province, northeast China. We used generalized linear mixed models including zero, biotic, habitat, and full model to assess the relative importance of the habitat factors and biotic neighborhood variables on tree seedling survival at the levels of community, age classes and species. Result: From 2016 to 2018, a total of 3 970 tree seedlings belonged to 13 genera, 10 families and 19 species were recorded. In order of the important values, the top five seedling species were Fraxinus mandschurica, Tilia amurensis, Acer mono, Pinus koraiensis, and Acer mandshuricum. At the end of the census year, 2 644 seedlings had died, with a survival rate of 33.4%. At the community level, the survival of seedlings was significantly correlated with both biotic neighborhoods and habitat factors. Specifically, the survival of seedlings was positively correlated with the number of heterospecific seedling neighbors, the soil available potassium and total phosphorus(P < 0.05). The response of seedling survival to biotic neighborhoods and habitat factors varied among different age groups. The survival of annual seedlings was positively correlated with their conspecificand heterospecific seedling neighbors(P < 0.05, P < 0.01, respectively), but negatively correlated with heterospecific adult neighbors(P < 0.05). For perennial seedlings, however, there is no significant correlation between the seedling survival and the biotic neighborhoods. Nevertheless, we found a significant positive correlation between perennial seedling survival and habitat factors(P < 0.05), such as soil available potassium and total phosphorusty. Individual species-level analyses indicated that the optimal seedling survival models varied among species. We also found that the response of seedling survival to biotic neighborhoods and habitat factors varied widely among species. Specifically, the Fraxinus mandshurica seedlings survival was positively correlated with heterospecific seedling neighbors(P < 0.05). The survival of Acer mono seedlings was negatively correlated with conspecific adult neighbors(P < 0.05). Tilia amurensis had a higher survival rate in habitats with higher soil available potassium. Pinus koraiensis seedlings, however, preferred to soil with lower available nitrogen and phosphorus. Conclusion: We provided strong evidence that both density dependence and habitat filtering affect tree seedling survival and their relative importance varied with age classes and seedling species. The survival of annual seedlings was mainly affected by biotic neighbors, however the effect of habitat factors was more significant on the survival of perennial seedlings. Our result indicated that the effect of negative density dependence was verified in our forest plot. Among the habitat factors, soil nutrient had a significant effect on seedling survival.According to the differences of biotic neighborhood and habitat effects on seedling survival among species and age classes, corresponding forest managements are needed in seedling raising and replantation of the main tree species.

Key words: secondary mixed conifer and broad-leaved forest, generalized mixed linear model, survival of arbor seedlings, biotic neighborhood, habitat