| Tiankeng is a kind of negative landform geologic wonder discovered in the Karst area recently. The plant invasion starts at the beginning of Karst tiankeng development, and with the tiankeng growing and aging, the plant communities also experience settlement, adaption, competition, and eventually they formed stable plant community, which are named the Karst tiankeng plant community. In different Karst tiankeng development stage, we collected field investigation data by the the typical sampling method and the space-for-time substitution. The quantitative ecology methods including species importance value,two-way indicator species analysis (TWINSPAN), detrended correspondence analysis(DCA), diversity indices and niche breadth were used to deal with the field data. The plant community species composition, structure and succession tendency in different tiankeng development stages were studied. Meanwhile we analyzed the dynamic changes of species diversity and niche breadth on community succession process. According to the above results, we can reveal the plant community building and succession pattern in the process of tiankeng development. The15tiankeng had been investigated and recorded411species belonging to131families and269genera. There are29sample plots madding by the29communities and the total area of sample plots is about23200square meters, the total work is420man-day.The results are as follows:(1) The classification of communities in different development stages tiankengThe form of young tiankeng is similar to a inverse’funnel’, with fewer sunlight, wet air, thin soil and bare rock. Normally, species lived in the young tiankeng communities are sciophiles, and most of them are herbs. There are10formations in the young tiankeng, such as Form. Elatostema brachyodontum Dryopteris varia. The form of middle aged tiankeng is similar to a’shaft’, with more sunlight, wet air and thickening soil. Species lived in the middle aged tiankeng plant communities are shade tolerant plants, most of them are trees. There are9formations in the middle tiankeng, such as Form. Manglietia aromatica+Neolitsea confertifolia. The form of old tiankeng is similar to a’funnel’, with enough sunlight, dry bottom and lat terrain. Species lived in the old Karst tiankeng communities are heliophiles, most of them are trees. There are9formations in the old tiankeng, such as Form. Choerospondias axillaris+Handeliodendron bodinieri.(2) The vertical structures of communities in development stages tiankengLichens and mosses live in palisades and rocks in the young Karst tiankeng. Community structure is as simple as a herbs layer. In middle Karst tiankeng, species increased and the community structures became complex composed by tree, shrub, herb layer and interlayer plants. The canopy coverage of tree layer is20%-90%with2-3sublayers. The height of shrub layer and herb is continuation. The structure of plant communities in old Karst tiankeng is composed by tree, shrub and herb layer, with rare interlayer plants. The canopy coverage of tree layer is45%-95%. The height of shrub layer is much taller than herb layer.(3) The species composition of communities in different development stages tiankengThere are105vascular plant species recorded in the young Karst tiankeng sample areas, belonging to50genera and78families. The dominant families are Urticaceae(3/8), Dryopteridaceae(4/7), Asteraceae(5/6), Pteridaceae(1/5), etc. There are246vascular plant species recorded in the middle Karst tiankeng sample areas, belonging to246genera and92families. The dominant families are Lauraceae(8/13), Urticaceae(4/12),Rosaceae(8/9), Araliaceae(6/7), etc. There are206vascular plant species recorded in the old Karst tiankeng sample areas, belonging to155genera,78families. The dominant families are Lauraceae(7/12), Rosaceae(9/10), Urticaceae(6/10), Fagaceae (3/5), ect.(4) The life form spectrum of community in different development stages tiankengThe vegetation in young Karst tiankeng is a community which composes mainly by herb species whose life form spectrum is58.06%. The vegetation in middle aged and old Karst tiankeng is a community which composes mainly by tree species whose life form spectrum is44.33%and38.40%, respectively. The ratio of evergreen species(ES) to deciduous(DS) in the tree layer of middle Karst tiankeng is (ES/DS=)1.97:1, and the ratio ES/DS of the individual number is1.71:1. The ratio of ES/DS in old Karst tiankeng is1.05:1, and the ratio ES/DS of the individual number is1.33:1. The deciduous synusia increases in old Karst tiankeng compared with middle Karst tiankeng.(5) The influences of slope position on Karst tiankeng plant communityWith fewer sunlight, wet humidity and thick humus soil in lower postion of the palisades, the vegetation is a complex structure with liana and shade tolerance species. The community’s species richness is52, and the Shannon-Winer index3.62. With more sunlight, dry humidity and thin soil in higher postion of the palisades, the community structure is relatively simple with heliophilous tree species, lack of liana and shade tolerance species. The community’s species richness is28, and the Shannon-Winer index1.83. (6) The influences of slope orientation on Karst tiankeng communityOn sunny slope with more sunlight, the species richness in the tree layer is22and the Shannon-Winer index is2.93, the species richness in the shrub layer is15and the Shannon-Winer index is2.49, the species richness in the herb layer is17and the Shannon-Winer index is2.66.On shady slope with fewer sunlight, the species richness in the tree layer is18and the Shannon-Winer index is2.73, the species richness in the shrub layer is14and the Shannon-Winer index is2.46, the species richness in the herb layer is11and the Shannon-Winer index is2.32.The richness and Shannon-Winer index in every layer of community in sunny slope are higher than those in shady slope.(7) The dynamic changes in the succession process of Karst tiankeng communityThe species diversity in the succession process is the highest in middle aged Karst tiankeng, and the lowest in young Karst tiankeng.The shady tolerant species are gradually replaced by the heliophilous species from young to old Karst tiankeng. The niche breadth of shady tolerant species decreases, for instance, from0.35to0.17for Schefflera minutislellata, and from0.35to0.18for Tetrapanax papyrifer. The niche breadth of heliophilous species, however, increases, for instance, from0.27to0.30for Alangium chinense, and from0.11to0.32Choerospondias axillaris.(8) The succession series of Karst tiankeng communityThere are5stages in the succession series of Karst tianekng community. The series is that pioneer speciesâ†'sciophiles species settlementâ†'shurbs competitionâ†'mesophyte and heliophilous constructive speciesâ†'climax community with evergreen-deciduous plant. |
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