Study On Patterns Of Forest Vegetation And Its Maintenance Mechanism In Karst Peak-cluster-depression Region

Karst peak-cluster-depression mainly lies in the south slope of karst region in southwest of China.Karst mixed evergreen and deciduous broadleaf forest is an azonal climax community in the area,which is mostly in Mulun National Nature Reserve and Maolan National Nature Reserve.The other forest in the area degenerates in varying degrees due to human activities. Based on the observation,investigation and analysis items in the dynamics sample plots and supplementary plots of forests in karst cluster-peak-depression areas,the paper analyzed the pattern and its maintenance mechanism of woody plants(DBH≥1 cm),which would provide important theoretical guide to quick vegetation recovery and ecological restoration in karst cluster-peak-depression area in southwest of China.The main results are as followed.(1) There were abundant woody plant species in forests in karst cluster-peak-depression area. In the succession from manmade forest,to secondary forest,to primary forest,species and families increased notably,the predominance of species and families reduced,the composition of evergreen increased gradually and that of deciduous decreased gradually.The variation suggested that the forest vegetation develop towards diverse life forms and reasonable forest structure,and the ecosystems gain more equilibrium.(2) Both semivariagram analysis and Kriging analysis showed that there were three patches of manmade forest,enclosing area and primary vegetation in the 2 hm2 dynamic sample plot of Mulun mixed evergreen and deciduous broadleaf forest in karst cluster-peak-depression area.Scaling effects suggested that the sampling area should be more than 10 hm² and sampling interval of 10 m be feasible,and the interval should increase with the extent of sampling size,aimed to study spatial heterogeneity in the area.(3) The vegetation diversity index and structural index except Simpson index and evenness in the three typical forests in karst cluster-peak-depressions fit different theoretical models of semivariagram.All of these index in Mulun primary forest performed strong spatial autocorrelation and large range,while those in Mulian secondary forest and Guzhou manmade forest performed medium or strong spatial autocorrelation,and with small and less range.The trend of fractal D was in the accordance of range.(4) The results of PCA demonstrated that topography was in the leading factors in the three forests,and other leading factors were different in different forest types.Cluster analysis devised Mulun primary forest,Mulian secondary forest,and Guzhou manmade forest into 5,4, and 4 groups at the gravitative level of 30,respectively.Classical correlation analysis showed that the relationships between vegetation,soil,and topography were in a less close trend with the process of primary forest,to secondary forest,to manmade forest.(5) The vegetation communities in the Mulun primary forest were in the gradual succession from primary forest to secondary forest from the left to fight of the 1^st axis of DCCA(i.e., along the gradient of decrease of topography factors,content of Fe₂O₃,MnO,and Al₂O₃,and increase of pH,CaO and TN).Those in Mulian secondary forest were in the gradual succession from secondary forest type to communities with pioneer species and grass from the left to right of the 1^st axis of DCCA(i.e.,along the gradient of decrease of topography factors, and the increase of Fe₂O₃,MnO,and pH).The forest communities in Guzhou manmade forest were in the gradual succession from secondary forest type to manmade forest types from the left to fight of the 1^st axis of DCCA(i.e.,along the gradient of main nutrients and soil water).(6) Fraction of species abundance variation explained by soil environmental variables in Mulun primary forest,Mulian secondary forest,and Guzhou manmade forest was 32.59%, 30.82%,and 31.38%,respectively.Fraction of species abundance variation explained by topography variables in the three forests was 18.79%,17.64%and 13.21%.The unexplained vegetation variation was large,which hinted that random factors including interaction among creatures and human disturbance took in an important role in the three forests except niche differentiation theory.(7) With the succession from grass,to grass and shrub,to shrub,to liana and shrub,to climax community,The community height,hiomass,diversity,content of soil organic matter, main soil nutrients,CEC,SiO₂,Fe₂O₃,and Al₂O₃ increased,and the pH and content of CaO and MgO decreased.(8) Different disturbance types showed various affections on natural vegetative restoration, among them,tillage after whole slope burned caused the worst impact where rocky desertification was the consequence,followed by depastufing after whole slope burned.While cutting was selective disturbance,the vegetative restoration in the area with combination of cutting,depasturing and slope foot burning was relatively fast,however,it was even better in the area with combination of cutting and slope foot burning.(9) A new model was established to simulate the complex degradation process of vulnerable karst ecosystem based on local human activities,natural environment and economic development by using interruption degrees,community types,service and function of ecosystems,land degradation and poverty as indicators.A controlling model was also established to prevent rocky desertification. @...