| Seedlings are an important part of forest ecosystem and play a crucial role in the natural regeneration process of forest and the regulation of community structures.Different growth states of seedlings contributed greatly to the regeneration rate,population number,community composition,development,and stability of the whole forest community.The growth and survival of seedlings are also easily affected by many biological and abiotic factors in the community.At present,many researchers have conducted in-depth discussions on the factors affecting the survival of seedlings.Based on reviews of the current ecological literature on the seedling dynamics,the seedlings and the surrounding environmental factors were monitored in 870 1m*1 m small quadrats of 290 sample stations for 6 years,in the 60 hm~2 dynamic monitoring plot in Jianfengling tropical montane rain forest.All seedlings were classified into different types,including community level,life form,mycorrhizal type,and species level.The objective of this study is to understand the seedling composition and quantity dynamics,to analyze the distribution law of seedlings at the spatial scale,and to explore the biological and abiotic factors affecting the dynamic change of seedlings.It could provide an important scientific basis for further understanding of the biodiversity maintenance theory and its mechanism related to seedlings.The main results are listed as follows:(1)From 2013 to 2019,the total number of seedlings investigated in Jianfengling tropical montane rain forest varied from 6928 to 9426 each year.There were 60750 seedlings recorded in 290 stations,belonging to 234 species,149 genera and 66 families.The total number of recruit seedlings and dead seedlings was 6889 and 4391,respectively.Among them,there were28407 tree seedlings belonging to 135 species.The number of species and individuals of shrubs and liana seedlings were almost the same,with 18,318 shrubs seedlings belonging to 54species,and 13,766 liana seedlings belonging to 41 species,and only 259 individuals and 4species of herbaceous seedlings were recorded.At the level of mycorrhizal type,there were 58719 AM type seedlings belonging to 215species,1807 ECM type seedlings belonging to 16 species,and only 224 AM&ECM mixed type seedlings belonging to 3 species.The number of individuals of the first dominant 9 species was more than 1000,and the number of individuals of Glochidion coccineum was 951.The number of individuals of these ten dominant species accounted for 42.42%of total individuals of all seedlings.In terms of importance values,Psychotria asiaticas,Cryptocarya chinensis,Prismatomeris connata,Syzygium hancei,Symplocos adenophylla,Ardisia quinquegona and Gironniera subaequalis have importance values larger than 5,while Blastus cochinchinensis,Xanthophyllum hainanense and Glochidion coccineum were less than 5.In total,abundance,frequency and importance values of Psychotria asiatica and Cryptocarya chinensis were greatly larger than others,which indicated the two species are extensively distributed and dominant in the plot.For the rare species,the seedling density was less than 0.1 individual/m~2,and the importance value was less than 0.5.There were 147 rare species investigated,accounting for62.8%of the total number of seedlings.Among the 23 sample stations,there were no rare species.The number of stations with 1-4 rare species accounted for 73.8%of the total number of stations,and the number of stations having 3 rare species was the largest,up to 63 stations.Only one sample station had the largest number of rare species,up to 9 species.Four rare species only had 1 individual,which were Melastoma sanguineumdium,Distylium racemosum,Heynea trejaga var.pilosula and Cleyera obscurinervia.There were 12 rare species up to 7individuals which had the largest number of individuals.And 31 rare species only occurred in one station.(2)At the community level,the number of individuals investigated in 2019 increased by36.1%compared with that in 2013,which indicated that the survival rate of seedlings was relatively high.There are 1 to 6 individuals recruited to each station every year.In addition,the number of families and species also showed an increasing trend.The survival rates of tree,shrub and liana type seedlings were higher than that of herb type.The survival rates of AM and AM&ECM type seedlings were higher than that of ECM type seedlings.Among the top 10 dominant seedling species,the number of individuals of the 8 species showed an increasing trend except for Syzygium hancei and Blastus cochinchinensis seedlings.The survival rates of seedlings of Symplocos adenophylla,Ardisia quinquegona and Gironniera subaequalis was relatively high than the others,with most of the recruited individuals were survival.The number of individuals of rare species increased in total,accompanied by the increase of number of species of rare species.(3)The number of seedlings was affected by both biological factors and abiotic factors,which were different at different levels.Seedlings at different levels was affected by soil organic matter,pH values,water content,total nitrogen,total phosphorus,total potassium,available potassium,altitude and canopy openness.Among them,compared with tree and liana,the number of shrub seedlings is more likely to be affected by canopy openness.Compared with the dominant species,rare species is also more likely to be affected by canopy openness.At the community level,the number of seedlings were influenced by the density of conspecific seedlings.At the life form level,tree seedlings were affected by conspecific adults basal area,while the number of seedlings of shrub and liana were affected by the heterospecific basal area.At the mycorrhizal type level,AM&ECM and ECM seedlings were affected by the heterospecific adults basal area and the density of the heterospecific seedlings,respectively.At the species level,the seedlings of dominant species were influenced by the heterospecific adults basal area,and rare species seedlings were influenced by the density of the heterospecific seedlings.Through the analysis of variance partition,it was found that three kinds of habitat factors of soil,micro-environment and plant could well explain the change of seedling quantity at different levels except liana,with the explanatory rates above 50%(between 55.4%and 94.7%).However,for liana seedlings,the total effects of three kinds of habitat factors could only explained 6.8%.It indicated that there are some unknown factors may also affect the variation of seedling number in the plot. |
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