| Woody seedlings are an important part of the forest ecosystem,which affect the regeneration and succession process of forest ecosystems,and play an important role in the maintenance of community diversity.However,in the past,the studies of woody seedlings were often limited to a single plot,and there were few studies on the cross-sites,which tended to underestimated the diversity of seedlings.This study was conducted in April and May 2017 in the Xishuangbanna area,investigating the seedlings of five tropical seasonal rainforest dynamic monitoring plots,and measuring seedlings height,canopy openness,herb coverage.The differences in seedling diversity and composition,the effects of canopy opening and herbage coverage on the diversity of understory seedlings were discussed.The results show that:(1)A total of 6366 woody seedlings were investigated in five plots,belonging to 291 species.Among them,the highest number of seedling species is 188 in 55 plot,and the lowest is 116 in Bubeng plot.The Simpson index of the five plots is 0.92 to 0.96,the Shannon-Wiener index is 3.65 to 4.07,and the Pielou evenness index is 0.77 to 0.82.The species richness and diversity of the seedlings under the tropical seasonal rain forest are higher than those of other forest types,and have strong renewability.It is an important reason that tropical seasonal rainforest can be evolved into a variety of forest communities.(2)The top 10 species with the highest importance value in the five plots contributed to the majority of seedlings,Individual species that are scarce contribute most of the species richness.Species is belong to the top 10 of the important value in a plot,but it may belong to a rare species in another plot.The important values of woody seedlings changed among different groups,so that woody seedlings could monitor forest ecosystem dynamics well.(3)The number of species surveyed a single plot accounted for only 39.73% to 64.38% of the total species that surveyed in five plots.There was a significant difference in the average abundance and average richness of seedlings among plots(p<0.05).The average abundance and average richness of seedlings in the 55 plot were significantly higher than those in other plots,while those in the Bubeng plot were significantly lower than those in other plots.The Jaccard similarity coefficient of woody seedlings in each plot was 0.32 to 0.45,and the dominant seedlings are also different among the plots.The survey results showed that the community type can affect the diversity and composition of woody seedlings.In the study of the seedlings composition and species diversity in Xishuangbanna tropical seasonal rain forest,it is difficult to explain the seedling diversity and composition in a single plot.(4)Among the five plots,With the increase of the height,the number of seedlings decreased.At the same time,species richness also decreased with the increase of height,but the trend of decline was less than species abundance.This shows that inter-specific and intra-specific competition among individuals is an important cause of seedlings death,especially the interaction between seedlings of the same species.(5)The canopy density of tropical seasonal rain forests is high.There is no significant relationship between diversity index and canopy openness in the five plots,indicating that the diversity of seedlings in this region is affected by other factors.Only the Bubeng plot,the diversity index of woody seedlings decreased with the increase of herbage coverage,and there is a significant negative correlation(p<0.05).The above findings indicate that: the woody seedlings composition and species diversity of different communities in Xishuangbanna tropical seasonal rain forest are different,and the reasons for the differences need to be further studied from the tree composition,soil,climate and topography,etc.,to deepen the understanding of Xishuangbanna tropical seasonal rainforest dynamics. |
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