| Jatropha curcas, deciduous shrub or small tree, is classified as Jatropha in Euphobiaceae. In China, it is distributed mainly over some southern provinces. It often grows in Dry Hot Valley of Yuanmou in Yunnan province among those areas. It is one of the good plant species for soil and water conservation, as well as vegetation restoration in Dry Hot Valley in Yunnan. In recent years it has received much attention for its seeds, which can be processed to produce a environment-friendly clean biodiesel fuel.The natural regeneration population of Jatropha curcas and its community without severe anthropogenic disturbance was studied in Dry Hot Valley of Yuanmou in Yunnan. The population structure, distribution pattern of important species, species diversity, niche of important species, species correlation of important species and the ordination and cluster analysis based on the main woody plant in the community were analyzed by means of mathematic ecology on the basis of the field study. The objectives were to analyze the current survival status and ecological strategy of the population in respect of demography, to infer the comparatively vulnerable demographic stages of the population, to analyze the important factors affecting the population dynamics, to discover the member and the mathematic characteristics of the community as well as their main relevent factors, to discover the status of Jatropha curcas and the relationship between Jatropha curcas and the other important species in the community, to discover the resource utilization characteristic of the important spieces, and to discover the distribution characteristics of the main plant in the community and their main factors. The main results are as follows:1. The diameter structure diagram of the natural regeneration population of Jatropha curcas belonged to expansive type population pyramid. The static life table analysis indicated that the mortality was high both at the juvenile stage and in the transitional stage from the middle to the old. The shape of the survivorship curve was similar to that of Deevey type III curve. Survival analysis indicated that the survival condition of the population changed considerably in the earlier stage, and relatively slight in the later stage. The spectral analysis showed that the effect of the period was weak with the short of the period.2. In general, the total Jatropha curcas population followed clumped distribution pattern, so do each developmental stages in the study. Both most of important woody plants and most of important herb in the community followed clumped distribution pattern. Jatropha curcas population in each plot followed clumped distribution pattern. The distribution pattern differed in different developmental stages in different plot. The distribution pattern of the population generally transformed from aggregated distribution into random distribution with age, which often occurred at middle trees or old trees stage for the population. Pattern analysis by Greig-Smith method revealed that the scale of the spatial pattern varied among the populations from different plots, and the identified patch sizes were about50m2and100m2in this study.100m2or so was relatively frequent.3. Jatropha curcas and Heteropogon contortus was dominant species in woody plant and herb respectively. In general, species richness index, species diversity index and species evenness of the herb are higher than those of the woody plant respectively. There was a significantly negative correlation between species richness index of the community and slope aspect as well as between species richness index of the woody plant and slope aspect. There was a significantly negative correlation between Shannon-Wiener species diversity index of herb and the canopy cover of community. There was a significantly positive correlation between Shannon-Wiener species diversity index of herb and soil pH.4. In the woody plant of the community, Jatropha curcas, Dodonaea viscose, Rumex hastatus, Osyris wightiana, Osteomeles schwerinae and Rhamnus virgata were widely dispersed over the community. They had great ability to utilize resources and to compete. Any two species in the six woody species were very similar in resource utilization. The niche similarity indexes of the majority of the woody species were low, so were the niche overlap indexes. These indicated that the majority of the wood species differed greatly in the requirement for environment.In the herb of the community, Heteropogon contortus, Tridax procumbens, Cymbopogon distans, Eremopogon delavayi, Boerhavia diffusa, Atylosia scarabaeoides and Crotalaria medicaginea were widely dispersed over the community. They had great ability to utilize resources. Any two species in the seven herb species were very similar in resource utilization.. The niche similarity indexes of the majority of the herb species were low, so were the niche overlap indexes. These indicated that the majority of the herb species differed greatly in the requirement for environment. The interspecific competition in the community was not fierce. Most species could harmoniously coexist in the community relatively. This is one of the important reasons for the relatively persistence of the community.5. The overall interspecific correlation analysis showed that significant positive correlation exist both among the20woody species and among the20herb species. Spearman’s rank correlation coefficient analysis showed that the minority of the total woody species pairs showed significant correlation or highly significant correlation, so do the total herb species pairs. In the woody plant of the community,8,5,6and8species pairs showed significant positive correlations, highly significant positive correlations, significant negative correlations, and highly significant negative correlations respectively. In the herb of the community,2,4,3and3species pairs showed significant positive correlations, highly significant positive correlations, significant negative correlations, and highly significant negative correlations respectively. Most of the total woody plant species pairs did not show significant correlation, so do the herb species pairs. Most species did not closely correlated with other species. The numbers of species pairs with negative correlation were more than those with positive correlation both in the woody plant and in the herb. This indicated that the interspecific competition in most species was relatively weak in the community, which was one of the important reasons for the relatively persistence of the community.Most of the woody plant species pairs including Jatropha curcas showed negative correlation. There was a highly significant negative correlation both between Jatropha curcas and Albizia kalkora as well as between Jatropha curcas and Diospyros mollifolia. A small number of woody plant species pairs including Jatropha curcas showed positive correlation, but none of the positive correlation was significant.Most of the herb species pairs including Heteropogon contortus showed negative correlation. There was a significant negative correlation between Heteropogon contortus and Eremopogon delavayi. There was a highly significant negative correlation both between Heteropogon contortus and Ficus tikoua as well as between Heteropogon contortus and Rhynchosia volubilis. A small number of herb species pairs including Heteropogon contortus showed weak positive correlation, none of the positive correlation was significant.6. The results of Canonical Correspondence Analysis indicated that the correlations order of the community distribution with the environmental factors were bareness degree of rock, slope gradient, altitude, canopy cover and slope aspect in large to small. The majority of the plots lay in the sites with high altitude, high slope gradient and high canopy cover, so were the main woody plant. Jatropha curcas Linn., the constructive species in the community, appeared in the region near to the intersection of the first two coordinate axes of the CCA ordination plot, which indicated that the species adapted well to the environment. The result of the Two-way Cluster Analysis of the20main woody plant in the community and the plots was similar to that of the Canonical Correspondence Analysis. |
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