| Alsophila spinulosa,a mesozoic ancient relic species under the second-grade state protection,is a kind of survival plant tracing from the end of Cretaceous Periods and the forepart glacier of the Tertiary Period.As one of the oldest living fossil in the word,it has been of great value for study on geologic climate and origin and evolution of plant,exploration of the mysteries of biological evolution,and insurance of the sustainable use of genetic species ecosystem.Alsophila spinulosa and its habitat are the protection objects of Chishui Alsophila National Nature Reserve of Guizhou.This Alsophila spinulosa population is one of the populations with the most abundance and the largest distribution.However,in recent years due to human factors,and other species such as Phyllostachys heterocycla and Alsophila spinulosa in space,water,sunlight and other aspects of competition,Alsophila spinulosa breeding and survival are more and more difficult,with a large number of Alsophila spinulata being damaged to different degree.The study chooses the site-Chishui Alsophila National Nature Reserve.Based on the field investigation,Alsophila spinulosa population and characteristics were studied systematically and comprehensively by adopting quantitative ecology methods,including community structure and composition,associated flora,species diversity,niche breath and niche overlapping of dominant population,age structures and interspecific relationship etc.The existing literature and other parts of our country have also been studied to investigate into the Alsophila spinulosa community,apart from analysis of the similarities and differences between different parts of the sign for community and its regularity.Finally,the status of Alsophila spinulosa was summarized to optimize the structure of Alsophila spinulosa community and prevent the decline of Alsophila spinulata population.1?Ecological and floristic methods were used to study the species diversity,floristic elements,life form spectrum and community structure.The results show that:(1)A total of 122 species,96 genera and 60 families were found in the community,among which 17 fern species belong to 14 genera and 12 families,2 gymnosperms belong to 2 genera and 2 families,and 103 angiosperms belong to 80 genera and 46 families;(2)The families and genera floristic composition is complex with various types.Tthe floristic characteristics were mainly influenced by pantropic,followed by temperate,which reflected its transitional characteristic.(3)The main life form distribution was phanerophytes,about 57.38% of which reflected that the phanerophytes lifeforms are the dominant in mid-subtropical forest.((4)Vertical stratification is obvious,trees with the heightbetween 4 m and 12 m had the highest proportion about 76.64%,shrubs with the height between 2 m and 3 m had the highest proportion of 69.78%,and herbs with the height between 0 m ~0.2 m had the highest proportion,so the level is obvious.(5)Phyllostachysheterocycla cv.pubescens and Alsophila spinulosa were the dominant tree species;Alsophila spinulosa was the dominant species of shrub layer;Dryopteris erythrosora and Selaginella uncinat were the main herbs.The result of species richness analysis was tree layer < shrub layer < herb layer.Diversity index and uniforimity analysis shown aggregated distribution for tree layer and its relatively simple composition.The distribution forms of shrub and herb layers were uniform with low abundance.2?The niche breadth and niche overlapping of dominant population of Alsophila spinulata communities were studied by using Shannon-Weaver index and Portraits' s methods.The results were as follows:(1)In the tree layer,niche breadths of Phyllostachys heterocycla were broader than other species,with Levins(LB)and Hurlbert(HB)values being 6.675 and 0.709,followed by Alsophila spinulata and Mallotus barbatu,with LB and HB values being 4.917 and 0.490,4.640 and 0.455,respectively,but that of Lasianthus chinensis and Vernicia fordii were narrower;15 species counterparts,about 21.8%,had niche overlap values larger than 0.5,33 species counterparts,about 78.2%,had niche overlap values smaller than 0.5,and 1 speies counterparts had no niche overlap,accounting for 1.82%.(2)In the shrub layer,Alsophila spinulata as dominant species,accounting for significant status had maximum niche breadths,it's LB and HB values were 7.651 and 0.709,respectively,in addition to Alsophila spinulosa,the other species of niche breadth no big difference,HB are between 0.248-0.446;17 species counterparts,about 30.9%,had niche overlap values larger than 0.5,38 species counterparts,accounting for 69.1%,had niche overlap values smaller than 0.5,and 2 speies counterparts had no niche overlap,accounting for 3.6%.(3)The niche overlap values among the population with the same or similar environment requirements and similar biological properties were also big,but there is no relationship between niche breadth and niche overlap of dominant species.3?Field data comes from servey of Alsophila spinulata populations,including the population life table and the theory of survival analysis,the static life table of Alsophila spinulata population Chishui Alsophila National Nature Reserve of Guizhou province was compiled by applying the “spatial sequence replacement temporal sequence” and the “Piecewise smooth technology”,The mortality rate curve,Killing power curve,survival rate curve,and survival function curve were also analyzed to reveal the population's quantitative dynamics.The results were: there was a fluctuation in the structure of Alsophila spinulata population,and population age structure was characterized with less amount of old trees,more middle aged individuals and short of young saplings;The survival curve of the population to type of Deevey?,the mortality rate curve and killing power curve in the lifespan had similar variation trend,all with the peaks in 1th and 10 th age class periods;The survival rate of the population decreased monotonically,whereas the cumulative mortality rate was in adverse,By 4 survival function curve that the Alsophila spinulata population grew little in early period and stably in middle period,but declined at last.Individual seedling shortage is the important cause of the endangered Alsophila spinulata.4?Combined with the existing literature,this study and previous studies are conducted from different perspectives-time and space.Results show that:(1)In the time dimension,this study is more consistent with the Tu Yulin study in 1990,indicating that the distribution type of the study area has obvious tropical floristic nature;The study of life is more abundant,has the hemicryptophyte and geophyte,show bringing layer species composition more abundant characteristics.Compared with the study of Zhou Congsheng in 2005,the Alsophila population has changed from growth to recession mainly due to a large number of tourists within the scenic spots,resulting in Alsophila spinulosa growth environment changes,and Alsophila spinulosa community is near a large number of bamboo,so that the growth and development of Alsophila spinulosa was inhibited.(2)In the spatial dimension,this study is consistent with the study of species composition,floristic,niche and population dynamics in Chongqing Miaotougou,Sichuan Wutongqiao,Sichuan Rongxian and Xinchun;the associated plant life as well as the differences of species diversity is more obviou,indicating signs of habitat differences. |
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