Ecological Study Of Excentrodendron Hsienmu Community In North Tropical Karst Seasonal Rainforest

The Excentrodendron hsienmu is one of the constructive species in the primary karst seasonal rainforest. In order to illustrate the distribution law of E. hsienmu populations in difference growth stages,and to clarify the correlation among the distribution of E. hsienmu population,other populations as well as the geomorphological features of karst cluster-peak depression region, we chose a typical forest plot (4ha) where the E. hsienmu population growing as our study area in the north tropical karst seasonal rainforest. We investigated all woody plants whose diameter at breast height greater than lcm in the plot, and record the plants’ species name, spatial coordinates, and growth conditions. We measured elevation on the each one of the4angles within each small quadrat(10*10m2), and calculated the topographical factors including mean elevation, slope, convexity and aspect in the400small quadrats.The spatial factors can be used by the spatial coordinates(x,y) of each small quadrat,as well as the xy,x2,x2y,y2,y2x,x3,y3.Based on above data, we analysised the vegetation type, floristic composition and the age structure of E. hsienmu population in the plot. The correlation among the distribution characteristics of the E. hsienmu population and othe population as well as the topographic factors was discussed by using canonical correspondence analysis and trend surface analysis. Based on the generalized additive models,we analyzed the variation of the number characteristics of the E. hsienmu populations in different life history in different topographic gradient. The results showed that:1. Species Composition And Floristic CharacteristicsA200m×200m forest plot was established on a hillside where the E. hsienmu population growing in a karst cluster-peak depression area. There are18898genotype individuals (25603individuals with branch), belonging to179species,128genera and52families. the floristic composition is consistent with its geographical position in the study area. The floristic characteristics of the community belong to tropical plant flora,including some north temperate types, east asia and north America disjuncted types. It is obvious that the floristic composition also has a certain transition in the plot, and is consistent with the location in the northern fringe of tropic.The statistics of Relative abundance, Relative frequency, Relative dominance, and important value showed that the distribution characteristics of different types of plants are different. Among the top10dominant species based on important value in the plot, Excentrodendron hsienmu, Diplodiscus trichosperma species have large diameter at breast height, but general distribution range and general abundance; Cleistanthus sumatranus, Vitex kwangsiensis, Sterculia monosperma, Memecylon scutellatum species have large abundance, comparatively wide distribution range, comparatively large diameter at breast height; Drypetes congestiflora, Garcinia paucinervis, Hydnocarpus hainanensis species have wide distribution range, but general abundance and general diameter at breast height; Canthium dicoccum species have large diameter at breast height and large abundance, but narrow distribution range。2. Age Structure Of E. hsienmu PopulationBased on previous analytical wood data of E. hsienmu specie, we obtained the E. hsienmu species’regression equation between age and diameter at breast height:Age=1.28*DBH+56; equation basically accord with the relationship between age and diameter in the primary E. hsienmu community(age from5to45years) of karst areas. And can predict the relations between age and diameter of E. hsienmu species to a certain extent beyond the scope of ages from5to45years.The size-class structure of E. hsienmu specie showed invent "j" distribution. The composition of each age-class structure is complete. Survival curve is in line with the negative power function.hence, the E. hsienmu population is in good growth trend in our study areas.3. The Degree Of Community Structure Explained By The Environmental FactorsThe more complex of the Vegetation’s structure and distribution, the lower of the degree of the environment’s explaination.Residuals analysis beween the difference dominance of species and the terrain, space factor shows that:â‘ the terrain, space factor can explain the amount of species importance value in the community better, while the amount of the smaller species of important value in the community can be explained is low.â‘¡space factor which have the large amount of information on vegetation can explain the distribution of vegetatior better, and basically consists of the amount of information of the terrain factor.â‘¢the degree of environmental factors’explaination on vegetation distribution and structure was decided by the complexity of the vegetation itself. the more complex environment, the lower degree can be explained by the environment.Hence, the Distribution of dominant species in community are influenced by the environmental factors more significant,such as E. hsienmu, D. trichosperma, C. sumatranus. 4. Spatial Variation Of The Community StructureThe study area is located in the karst seasonal rainforest areas, including the different parts of the karst peak and depression. with increasing altitude, the terrain gradually changes in the plot:â‘ moist, flat, hypertrophy of depression.â†'â‘¡water moderate soil, slope and soil moderate peak slope.â†'â‘¢drought, complex terrain, bare rock peak. This study results show that there is a strong correlation detween the distribution of plant species and topography in the plot, and the distributions in different species are greater difference.Some of the species’ distribution are influenced by a strong spatial autocorrelation in the specific area. This may be related to the distribution of some other environmental factors or soil chemical elements in the plot.5. Habitat Associations Of E. Hsienmu Population in the different life historyThe distribution of E. hsienmu population in the different life history are quite discrepancies, and the restrictive effect of E. hsienmu population on the terrain are different. based on the generalized additive model,we make a regression analysis between the population characteristics of E. hsienmu in different diameter classes and topographic factors. The results show that the distribution of E. hsienmu population in different diameter classes are discrepancies in the study area. the limitations of The E. hsienmu saplings on the topography is relatively small, so its distribution is quiet broad. With the increasing diameter class, the three limitation factors including elevation, slope and convexity are gradually rising. Finally, the large-diameter class trees are almost concentrated at the place where mean elevation is280m, slope is45°and convexity is2m. While the response of E. hsienmu in different diameter classes to aspect is randomness. The E. hsienmu shows strong dominance in the southeast and northwest aspect, what’s more, it shows weak dominance in the northeast and southwest aspect in the study area.