| Restoration and reconstruction of degraded ecosystem has become one of the focused problems of modern ecology. The research on degraded ecosystem of karst concentrated mainly on individual ecology and natural restoration of degraded community, and some achievements in practical experience are obtained, with new theories of karst vegetation restoration produced. But the whole research lacked organic contact and conformity from the point of view of karst ecosystem, the degraded mechanism, characteristics, courses, indicators, evaluation index of vegetation restoration, restoration profits and technique measure etc are remained to be studied. In this paper, based on analyzing completely and systematically degraded mechanism, characteristics, processes, degraded index of ecosystem in karst mountain area, through a large amounts of typical plots to investigate the structure and function of the present artificial restoration community and natural restoration community, and using a method of time replaced by space for studying the succession of natural restoration community, to explore a systematic vegetation restoration technique, evaluation system, carbon cycle, comprehensive profits evaluation of vegetation restoration of degraded ecosystem in karst mountain area etc. This study not only enriched restoration ecology, but also provided scientific proof to vegetation restoration of degraded ecosystem in karst mountain area. The main study results were as following: (1)The degradation of ecosystem of typical karst mountain is mainly caused by two reasons: the first is natural reasons, including weather, lithology, geological structure movement and characteristics of topography-landform, the second is anthropogenic reasons, namely human disturbance and destruction, such as cut, herd, reclamation, fire etc. The human disturbance is the main factor to degradation of ecosystem. The vegetation degradation and the soil degradation are the main types of degraded ecosystem. The degraded course is substantively regressive succession of ecosystem, it includes sudden degradation course, leap degradation course, gradual degradation course, continual degradation course and complex of several courses, each of courses has different features because of different degraded degree and speed, but totally are the structure and function degrade. Through principal component analysis (PCA), it showed that the vegetation system was mainly presented by the height, biomass and amount of litter, and the soil system was mainly organic matter. (2)The ecological effect of different species in plantation restoration was different in karst mountain area. The height and diameter of breast-high (DBH) were Toona sinensis forest>Catalpa bungei forest>Cupoessus duclouxiana forest. The species numbers of shrub layer and biomass of herb layer were Cupoessus duclouxiana forest>Toona sinensis forest>Catalpa bungei forest; The nutrient elements contents of modules was also different in the different species, The N, P, K, Mg contents in leaves were Catalpa bungei>Toona sinensis>Cupoessus duclouxiana, its contents in branches and stems changed small, the Ca contents in leaves were Cupoessus duclouxiana>Toona sinensis> Catalpa bungei, in branches were Cupoessus duclouxiana>Catalpa bungei>Toona sinensis, in stems were Toona sinensi>Catalpa bungei>Cupoessus duclouxiana, the Mg contents in branches were Cupoessus duclouxiana>Catalpa bungei>Toona sinensi, in stems changed smaller, the thick ash contents in leaves and branches were similar with the Mg, in stems were similar with the Ca; The changes of the N, P, K, Ca, Mg and thick ash contents in litters were some high or low each other in three kinds of stands and its different aged stages; In the restored initial stages of three kinds of plantations, the soil physical and chemical characters improved in total, the soil matter and humus contents were lower, respectively about 5% and 1.5%, the CEC, exchangeable Ca, base gross, base saturation percentage, total N, total P, and available P contents were Catalpa bungei forest>Toona sinensis forest>Cupoessus duclouxiana forest, the total K contents were Toona sinensis forest>Cupoessus duclouxiana forest>Catalpa bungei forest, the hydrolytic N contents were Cupoessus duclouxiana forest>Catalpa bungei forest Toona sinensis forest, the available K contents were Toona sinensis forest>Catalpa bungei forest>Cupoessus duclouxiana forest. (3)The ecological effect of the different age stages restoration was also different with the same species in karst mountain area. In fifteen years old Toona sinensis, Catalpa bungei and Cupoessus duclouxiana, the height and amount of litter were significant difference, the DBH and dominance were most significant difference, and the biomass was not difference; The nutrient elements contents of modules was different in the same species, the leaves contents were N>K>Ca>P>Mg, the branches and stems contents were Ca>N>K>Mg>P in Toona sinensis, the leaves contents were K>N>Ca>P>Mg, the changes of the branches and stems contents were similar with those of Toona sinensis in Catalpa bungei, the leaves and branches contents were Ca>N>K>Mg>P, the stems contents were Mg>K>Ca>N>P in Cupoessus duclouxiana; In the nutrient elements contents of litters, ten years old and fifteen years old Toona sinensis contents were Ca>N>Mg>K>P, ten years old Catalpa bungei contents were Ca>N>Mg>P>K, fifteen years old that were N>Ca>K>Mg>P, five years old and fifteen years old Cupoessus duclouxiana contents were Ca>N>Mg>K>P, ten year old that were Ca>N>K>Mg>P, only the Ca contents were most significant difference, the N, P and K contents were not significant difference among three species at 15 years; The physical characters were not significant difference, in the chemical characters, only the total P contents were significant difference, the soil organic matter, total N, total K, humus and CEC contents were not difference among three species at 15 years. (4)In the selection of tree species, through a large area of planting experiment, the tree species of ecological forest for Karst area included the best adaptation tree species Robinia pseudoacacia(included three new breeds) and Choerospondias axillaries, the better adaptation tree species Betula luminifera, Pteroceltis tatarinowii and Toona sinensis, and the economic treespecies Prunus salicina and Prunus sp. are preliminary selected in karst mountain area of Puding county. (5)Taking the community height, biomass, amount of litter and dominance as property factor, the degraded communities of karst were divided into four types, namely herbaceous community, shrub-scrub community, secondary arbor community, primary arbor community by a method of combination of systematic clustering analysis and principal component analysis (PCA), and then degraded communities were divided into six stages, namely herbaceous stage, scrub-herbaceous stage, shrub-scrub stage, shrub-arbor stage, arbor stage and climax arbor stage with the division method of optimization. (6)The essence of natural restoration of vegetation is a progressive succession of community. The essential characters of community were different in different restoration stage in karst mountain area, and its role, function and law were also not similar. The study result showed that with natural restoration of degraded community development from lower stage to higher stage, the quantitative properties of communities changed, the height and diameter of communities increased gradually, its sudden change happened in which the shrub-arbor stage was replaced by arbor stage, the density was the highest in scrub-shrub stage, the lowest in climax arbor stage, the density of the former was 13.95 times than those of the latter. Species diversity, evenness, dominance were increased but ecological dominance was decreased. Biomass accumulated gradually, arbor layer biomass was dominant starting from shrub-arbor stage, and then it was increased, shrub layer biomass was dominant starting from herbaceous-scrub stage, to scrub-shrub stage was highest, later it was decreased gradually, herb layer biomass was decreased with the natural restoration process; The volume weight of soil, soil density, sandy grain and clay grain were decreased, but silt grain, total porosity and capillary porosity were increased, non-capillary porosity changed smaller, in a word, the physical characters of soil became good direction development; The soil organic matter, total humic acids, humic acid, fulvic acid, CEC, exchangeable Ca, total N, total P, hydrolytic N, available K were increased, exchangeable Mg was decreased, but total K and available P had no the obvious regulation variety, in conclusion, the change of soil chemical characters was benefit to growth and development of plant in total; In the nutrient elements contents of litters, the N, P, Ca were increased obviously, Mg was increased, but P was increased gradually, K had no the obvious regulation variety; In nine common tree species, the nutrient elements contents order of modules was leaves>branches>stems, the change of thick ash was similar, the nutrient elements contents were some high or low each other, had no regulation variety between tree species and modules. (7)The natural vegetation restoration of karst degraded communities was different in the different climate belt, the natural vegetation restoration of Libo county where belongs to middle subtropic monsoon humid climate was better than those of Puding county belongs to north subtropic monsoon humid climate. (8)The growth and development course of tree species in karst forest was the resultsadapted to ecological environment in karst mountain area, the mainly restoration succession mechanism of natural restoration in degraded karst forest were the difference of tree species adapted to water stress, light energy use especially weak light and reproduction regeneration strategy. (9)The roles of community biomass, litter amounts, soil organic matter, soil total porosity, community height and dominance on natural restoration degree of communities are analyzed by using a hierarchy analysis , and comprehensive index of natural restoration, namely restoration degree index (RDI) are calculated by coordinate comprehensive evaluation method, the results were as follow: the RDI in herbaceous stage was 0.0837, in scrub-herbaceous stage was 0.1188, in shrub-scrub stage was 0.1711, in shrub-arbor stage was 0.2828, in arbor stage was 0.6690 and in climax arbor stage was 0.8299. (10)The carbon storage study showed: In the initial stages of plantation establishment, the carbon storage of vegetation and litter were small, but existed the differences in different plantations, soil carbon storage was influenced by the soil organic matter, volume weight , thickness and area, carbon storage in soil under different plantations was mostly beyond 20 t/hm2. The carbon storage in vegetation increased from herbaceous stage to climax arbor stage, the soil carbon storage decreased gradually from herbaceous stage to shrub-arbor stage, then it increased slowly, finally it stabilized. The gross carbon storage of ecosystem in karst mountain area was 65.3913 t/hm2, which was mainly compose of the soil carbon (34.7297 t/hm2), secondly the vegetation carbon (27.4976 t/hm2), and the lowest litter carbon (3.1640 t/hm2); The gross carbon storage of karst ecosystem in different climate belts are Puding county with 76.8970 t/hm2, Libo county 62.8914 t/hm2, the carbon storage of the former was 14.0056 t/hm2 higher than those of the latter; The carbon storage of karst evergreen and deciduous broad-leaved forest was lower than those of nine vegetation types, namely temperate coniferous forest, warm temperate coniferous forest, coniferous forest, needle broad-leaved mixed forest, deciduous broad-leaved forest, sclerophyllous evergreen broad-leaved forest, evergreen broad-leaved forest, evergreen and deciduous broad-leaved forest and tropic forest in normal landform; The annual amount of CO2 fixed by fifteen years old Cupressus duclouxiana forest was 0.68 t/hm2 ,which profits converted into 204 Yuan, The annual amount of CO2 fixed by degraded karst forest was 3.78 t/hm2, which profits converted into 1134 Yuan. (11)The ways of the vegetation restoration for degraded ecosystem in typical Karst mountain area are mainly the ways of closing hill for afforestation, afforestation and artificially promoted natural regeneration; At the same time, the systematic technique of artificial vegetation restoration and natural restoration, the models of restoration and the process of restoration are described.
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