Ecological Study Of Cinnamomum Burmannii Populations On The Karst Hills Of Guilin

Cinnamomum burmannii is a evergreen broad-leaved tree species belonging to genus Cinnamomum in family Lauraceae. Through field sampling investigation and quantitative analysis, environmental condition, size structure, age structure, distribution pattern, niche, interspecific relationship etc. of C. burmannii populations were systematically analyzed in this paper. The results are as follows:1. 11 plots were conducted in different C. burmannii communities. The results show that 94 species of vascular plants belonging to 83 genera of 54 families were found. Among them, 8 genera of 8 families were ferns, 2 genera of 2 families were gymnosperms, and 44 genera of 73 families were angiosperm. The families with only one species and the genera with a few species dominated. The number of families with one species was 34, accounting for 62.96% of the total families, the number of genera with one species was 71, accounting for 86.59%. The flora of 75 seed plants founded in the communities was classified into 11 areal-types and 2 subtypes, of which tropical elements had 40 genera, accounting for 58.82%, temperate elements had 28 genera, accounting for 41.18%, and tropical floristic elements dominated in the community. Community physiognomy was characterized mainly by evergreen broad-leaved mesophaenerophytes with small-sized, single, leathery and entire leaves. The vertical structure of the community was quite simple, consisting of tree layer, shrub layer and herb layer. Classification of C. burmannii communities was conducted by Two-way Indicator Species Analysis(TWINSPAN), The results shows that C. burmannii communities could be divided into five associations:Ⅰ.Ass.Cinnamomum burmannii - Albizzia kalkora - Arthraxon hispidus;Ⅱ.Ass.Cinnamomum burmannii - Osmanthus fordii + Mallotus philippinensis - Ophiopogon japonicus;Ⅲ.Ass.Cinnamomum burmannii - Osmanthus fordii - Ophiopogon japonicas + Carex lanceolata;Ⅳ.Ass.Cinnamomum burmannii - Osmanthus fordii - Ophiopogon japonicus + Carex lanceolata;Ⅴ.Ass.Cinnamomum burmannii - Cladrastis wilsonii + Osmanthus fordii - Pteris ensiformis + Pseudocyclosorusk subochthodes. Species diversity was analyzed by various kinds of diversity indices such as the Patrick's richness index (R), Simpson index (D), Shannon-Wiener index (H) and Pielou's evenness index(E). In the five associations, species diversity indices of associationⅢandⅤwere higher than those of others, and the indices of associationⅣwere relatively lower. Influenced by habitat conditions and human disturbance, species diversity was different among the association types.2. The heights of individuals of C. burmannii population ranged mostly from 2 to 8m. Structure differentiation analysis show that most tree height were moderate differentiation, indicating that there were no obvious structure differentiation between neighboring individuals. The height contour chart of C. burmannii populations not only showed the height arrangement status of individuals of C. burmannii population, but also reflected difference of different C. burmannii populations in height structure. In the overall, saplings and small trees of C. burmannii population dominated in the community, middle tree has the certain distribution, while the big tree are less.3. The DBHs of individuals of the C. burmannii population ranged mostly from 2 to 6cm.Most DBHs were belonging to moderate differentiation, but the differentiation degree was not obvious. Individuals with smaller DBHs dominated in 11 plots. It has found that most C. burmannii populations consisted mainly of young trees, and there was remarkable relationship between DBHs and heights.4. Influenced largely by habitat conditions, density, competition of individuals for space etc, the crown diameter of most individuals ranged mostly from 1~4m, while a few ranged from 5~7m. Crown of C. burmannii population showed moderate differentiation There was remarkable relationship between crown radius and DBH, and between height and crown radius. Crown radius significantly increased along with the increasing of DBH, while height significantly increased along with the increasing of crown radius.5. There was a linear relationship between age and stem diameter of C. burmannii population. Young-aged individuals were more, while middle-aged and old individuals were less. The age structures could be classified into two types: growing and stable. The survival curves had two types: Deevey II and DeeveyⅢ. Habitat condition and the human disturbance were the major factors affecting the age structure and the dynamic of C. burmannii population. It may be concluded that the protection and fostering management of C. burmannii community should be reinforced, and the human disturbance should be reduced.6. Based on the data collected from 6 plots, ie Q1 to Q6, the distribution pattern of C. burmannii populations in Karst hills of Guilin were analyzed with method of point pattern analysis. The results show that C. burmannii populations were clumping distribution at most scales in plots Q1 and Q5, random distribution at most scales in plots Q2 and Q3, and exhibited clumping distribution at small scales and random distribution at most scales in plots Q4 and Q6. The main factors affecting the distribution pattern of C. burmannii population were habitat condition, reproduction characteristics, intraspecific and interspecific competition, and heterogeneity of microenvironments. It has been found that the method of point pattern analysis could clearly exhibit the distribution pattern characteristics of C. burmannii population at different spatial scales, and therefore, this method is suitable to be used to study the ecological characteristics of karst forest populations.7. The niche breadths and overlaps of 12 main tree populations and 13 main shrub populations of C. burmannii community on Karst hills of Guilin were measured and analyzed by using Levins and Pianka formulas. The results show that in tree layer, the niche breadths of some species such as C.burmannii, Osmanthus fordii and Phaseolus vulgaris were higher, being respectively 10.051, 6.935 and 5.695, while those of the species such as Cinnamomum camphora and Pinus massoniana Lamb were lower. Overlap between Cl. platycarpa and Melia azedarach, O. fordii and Cladrastis wilsonii, Cl. Wilsonii and Ligustrum lucidum.were lager. In shrub layer, the niche breadths of the saplings of C. burmannii, O. fordii and Mallotus philippinensis were higher, being respectively 10.493, 7.099 and 4.949, while those of Albizzia kalkora and Acanthopanax trifoliatus were smaller. Overlaps between Alchornea trewioides and Cl. wilsonii Takeda sapling, C. burmannii sapling and O. fordii sapling, C.burmannii sapling and M. philippinensis sapling, and O. fordii sapling and Sageretia rugosa were lager. The species with higher niche breadth in tree layer and in shrub layer have wider ecological amplitude, and they can adapt to more kinds of environment whereas they are the constructive or accompanying species of the community. The niche overlaps among the species with the same or similar environment requirements were larger, and those between the species with broad niche breadth and other species were also lager.8. Based on the data collected from field investigations, the interspecific relationships of 12 tree layer species and 13 shrub layer main species of C. burmannii community on Karst hills of Guilin were analyzed by usingχ2 test and Spearman's rank correlation coefficient. The results show that: (1) In tree layer, based onχ~2 test (p<0.05), one species-pairs showed significant positive association, and one species-pairs showed significant negative association. Based on Spearman's rank coefficients, 3 species-pairs were significant or very significant positive correlation, and 4 species-pairs had significant or very significant negative correlation. In shrub layer, based onχ2 test (p<0.05), one species-pairs showed significant positive association. Based on Spearman's rank coefficients, 8 species-pairs were significant or very significant positive correlation, and 2species-pairs had significant or very significant negative correlation. On the whole, species-pairs that present significant or very significant association was few in number, most species were not closely related with each other and independently distributed.(2)The species with similar in biological features or in ecological adaptability to the habitat or with higher degree of niche overlap tended to be positively related, while those with different biological features and different adaptability to the habitat or existing inter-competitions tended to be negatively related.(3)The main factors that significantly affect the fluctuation of interspecific relationships in C. burmannii community were the complexity and diversity of habitats of Karst hills, human disturbance, etc.