Dynamics Of Seedlings In Subtropical Evergreen And Deciduous Broad-leaved Mixed Forest Of Central China

Seedling is the most important stage during the life history of plant,and is also the most vulnerable stage of natural forest regeneration.The survival of seedlings will affect the number and regeneration rate of the plant population,and determine the position of the tree population in community succession after seedling establishment.Based on a 5-year continuous monitoring data of 405 plots,135 seedling stations in the 25 ha Badagongshan forest dynamics plot,we analyzed species composition,quantity characteristics,recruitment/mortality and so on.We also examined the relative importance of biotic and abiotic factors with Generalized Linear Mixed Models(GLMMs)using the survival data for 3554 seedlings of 128 species.The main results are as following:(1)During the survey,a total of 13972 individual seedlings were recorded ·Species richness of Lauraceae was the highest,and the prevailing family at see.dling stage was still dominant at its adult stage.The seedlings have been found in 405 seedling plots,but distribution of seedling species was uneven.Species richness per plot ranged from one to 31,and most plots from 5 to 17 species.The total number of seedling species was steady during the five years,but the distribution of seedling species in the plot significantly decreased.Fifteen species had more than 200 seedlings totally,accounting for 71%of total seedlings while 14 species only had one seedling.(2)Among the 5644 seedlings of 110 species recorded,16 species had more than 100 seedlings totally,and 41 species did not have new seedlings.Seedlings emerged in May were more than in August.Among the 10569 dead seedling of 117 species,the mortality rate of 15 species was 100%while all seedling of 34 species survived.Although the total number of seedlings decreased by 59.2%across the five years,it showed a declining tendency then stable.(3)With GLMM,we found at the community level,focal seedling survival was significantly negatively correlated with conspecific neighbor density indicating the effects of negative density-dependence(NDD)in this plot at seedling stage.As for age class,the survival of seedlings<4 years old was significantly negatively correlated with conspecific neighbor density;for seedlings>4 years old,the importance of negative density dependence was exceeded by environmental factors.Compared with the evergreen species,the survival rate of deciduous species was more sensitive to conspecific neighbor density.At species level,the effects of biotic and abiotic factors on seedlings differed among species.For instance,Machilus ichangensis was positively related to canopy openness.However,seedling survival of Symplocos anomala was significantly negatively correlated with conspecific neighbor density,heterospecific adults basal area,canopy openness;while significantly positively related to heterospecific seedling neighbor density and elevation.