Effects Of Local Biotic Neighbors And Habitat Heterogeneity On Seedling Survival In Spruce-fir Valley Forest Of Xiaoxing’an Mountains,China

Seedlings are vulnerable to many biotic and abiotic agents,and the dynamics of seedlings are critical to species distribution and coexistence,thus examining the causes of seedling dynamics can help understand mechanisms of species coexistence.The research was conducted on a 9.12 ha spruce-fir valley forest dynamic plot in Liangshui,Heilongjiang Province,China.We examined the species composition,seedling community structure and the relative importance of biotic neighborhood(conspecific and heterospecific)processes and habitat heterogeneity(topography and soil properties)using survival data for 6,256 seedlings over 4 years spruce-fir valley forest of Xiaoxing’an Mountains,China.(1)We documented 33 species with 6,256 individuals,belongs to 12 families and 27 genera,including gymnosperms of 1 families 3 genera 4 species and angiosperms of 11 families 24 genera 29 species;The seedling height distribution showed reversed "J",and the height distribution of mortality seedlings between 2011-2015 showed reversed "J" as well;The numbers of 5 tree species which height ≤ 1.5 m are sufficient,reflecting good regeneration of these seedlings.(2)We found significant conspecific negative density dependence(CNDD)effects on seedling survival,the probability of seedling survival decreased when seedlings were surrounded by high density of conspecific individuals,especially for dominant species Abies nephrolepis and Picea koraiensis.We also found significant phylogenetic negative density dependence(PNDD),the probability of seedling survival decreased when seedlings were surrounded by more closely phylogenetically related species,especially for groups of tree,deciduous and shade-intolerant,as well as Pinus koraiensis and Betula platyphylla.However,the habitat heterogeneity played a more important role in seedlings survival of shrub group and Acer ukurunduense.(3)Despite of the significance of CNDD,PNDD,and habitat heterogeneity on seedling survival,large proportions of the total variance were not accounted for by the studied variables,suggesting the needs to examine the influences of other factors such as pests,diseases,herbivores,forest structure,species functional traits,and microclimatic conditions on seedling survival in the future.