Ecological Study Of Fraxinus Griffithii Populations On The Karst Hills Of Guilin

Fraxinus griffithii is a species belonging to genus Fracinus in family Oleaceae. In china, Fraxinus griffithii distributes mainly in Guilin, Lingui, Lingchuan, etc. and is a species endemic to the north of Guangxi. Fraxinus griffithii distributes mainly on karst hills, and ofen acts as constructive species or dominant species in a forest community. It has a vital role in improving the vegetation succession direction and habitat conditions of karst forest. However, it hasn't been found any reports about the study of population ecology of Fraxinus griffithii on karst hills, it is therefore urgent to systematically grasp the ecological characteristics of Fraxinus griffithii populations, which are help not only to discusses the classificatory level and zonal character of Fraxinus griffithii community, but also to provide the theory basis for protecting and reasonably using the karst forest resources in Guilin.In this paper, environment conditions, size structure, distribution pattern, interspecies relationship, niche, etc. of Fraxinus griffithii populations on the karst hills of Guilin were analyzed, and the results are as follows:(1) There were 52 species of vascular plants belonging to 50 genera and 38 families in Fraxinus griffithii community. Among them, there were 5 species of pterido- phyta belonging to 5 genera and 5 families, 1 species of gymnosperms belonging to 1 genera and 1 families, 40 species of angiosperm belonging to 38 genera and 32 famil- ies (6 species of monocotyledoneae belonging to 6 genera and 4 families, 40 species of dicotyledoneae belonging to 38 genera and 28 families). The flora of seed plants was classified into 11 areal-types, and tropical floristic elements dominated in the community, which involved 22 genera accounting 47.8 % of the total genera. The community physiognomy was characterized by the decid- uous broad leaved Me. Phanerophyt- es,microphylls,Compoundleaf and Coriaceous. The community vertical structure could be subdivided into three layers: tree, shrub and herb layer. All the three layers had low species diversity.(2) The tree height of Fraxinus griffithii population ranged mostly from 8~14m, TH index of majority individuals is low. The diameter at breast height mainly distributes upon 10cm, especially , 10~20 cm big tree has a great proportion, it is consistent with the influence to tree height; TC index isn't high as TH index. The quantity of the crowns 2~5m in width is more. Being influenced largely by density, competition of individuals for space etc., the crown structure is more difference, but in the all, TCD is limited. Individuals with medium size of tree height, diameter at breast height and crown dominate in the community, and small trees unceasingly supply through self- renewal process. Therefore, the population has the self- renewal ability, which will be advantageous to increase the complexity and stability of community structure.(3) The distribution pattern of most Fraxinus griffithii populations was random, while that of a few populations was clumped in the scale below 2m. These phenomena were closely related to the biological characteristics, especially seed dispersal, of Fraxinus griffithii.(4) Positive spatial correlations were found mainly between Fraxinus griffithii and Radermachera sinica, and between Fraxinus griffithii and Cladrastis platycarpa., the correlations weren't statistically significant mostly, it also was found naganative spatial correlation between these species pairs, and the correlations is singnificant or approaches to singnificant. It declarations that in the Fraxinus griffithii community, the interspecific competition is larger , and also shows the translating characteristics of this community.(5) Most populations in Fraxinus griffithii community had wider niche breadth, and the larger the important value of populations , the wider of their niche. Fraxinus griffithii population had the largest niche breadth, indicating that Fraxinus griffithii population dominates in the community, and it decides the structure, spatial distribution pattern and dynamic change of the community. The interspecific relationship was complex in the community, and it has certain sharing to the resources. The dominant species are very similar in utilizing the resources, the niche similar proportion ranged mostly from 0.4 to 0.6. In the community, the wider the niche breadth, the higher the niche overlap value, because of their similarity in utilizing the resources. The overlap value of Fraxinus griffithii and Cladrastis platycarpa was largest, indicating that there was intense competition between them. So the niche similar proportion and niche overlap value of population may more or less indicates the ecological characteristics of subtropical evergreen, broad-leaved forest。.