A Study On The Population Ecology Of Camellia Pingguoensis Var. Terminalis

Camellia pingguoensis var. terminalis is an endangered plant species which is endemic to Evergreen monsoon rain forests in Guangxi limestone hills. Currently only distributed in the confined region in the south and south-west of Tiandeng county. The community acreage is about 2.38 hm2 with only 1729 individual Camellia pingguoensis var. terminalis plants. Plant taxonomy and various ecology statistical methods are applied to the analysis of the distributional patterns, habitat preservation characteristics, biological characteristics, population structure and dynamics, species diversity of its communities, and the modular population characteristics of Camellia pingguoensis var. terminalis. The study has the following conclusions:⑴Camellia pingguoensis var. terminalis population mainly depends on B.hsienmu+C. saxatile(P1), Z.insignis+B.hsienmu(P2), L.ramiflora+P.calcarea(P3) and H.serratus+C.saichikii (P4) communities for survival. It constitutes a dominant species or one of codominant specieses in shrub layer. At the level of community, L.ramiflora+P.calcarea community is the highest one in both species richness and diversity index, and the habitat of this community is the most fitting one. Z.insignis+B.hsienmu community, which has been suffering from the most serious disafforestation, has the highest species diversity in the shrub layer and the lowest in the tree layer. H.serratus+C.saichikii community, which is distributed in the highest altitude, has the highest evenness in the shrub layer and herb layer. B.hsienmu+C.saxatile community with the most abundancy of naked rock has the lowest evenness in the tree layer. Vertically, the species richness in all communities is of the order: shrub layer> tree layer> herb layer. The diversity index in B.hsienmu+C.saxatile and Z.insignis+B.hsienmu communities is of the order: the shrub layer> herb layer> tree layer. In L.ramiflora+P.calcarea and H.serratus+C.saichikii communities, the order is the tree layer> herb layer> shrub layer. As for species evenness, the order is tree layer>herb layer>shrub layer.⑵The height distribution of Camellia pingguoensis var. terminalis population is mainly between 0.5~2.5m. The basal diameter distribution of adult plants is mainly between 1.5~5cm. The largest basal stem size of Camellia pingguoensis var. terminalis in the plot sampling is 13.85cm. According to its life history, its diameter class can be divided into seven grades: ClassⅠandⅡa re for seedlings and tree saplings; ClassⅢ,ⅣandⅤwith 1.5 ~5cm basal diameter are for middle age plants, ClassⅥandⅦwith diameter greater than 5cm are for older plants. The age order of four Camellia pingguoensis var. terminalis populations is that P2 < P1< P4 < P3. The type of size structure of C. pingguoensis var. terminalis population in B.hsienmu+C.saxatile(P1)community is regarded as stability type. The type of C. pingguoensis var. terminalis population in Z.insignis+ B.hsienmu(P2)community is regarded as transition from stability to recession-type. The type in L.ramiflora+P.calcarea community(P3) is belonged to a stable type. The type in H.serratus+C.saichikii community is an increasing type. Cubic regression equation is more suitable for the development trend of Camellia pingguoensis var. terminalis forecast models than the traditional power regression equation.⑶The population pattern of Camellia pingguoensis var. terminalis turns out to be a clear clump distribution at different sampling scales of 9m2, 16 m2, 25 m2, 36 m2 and 100m2. At the sampling scale of 9m2,it is shown that the degree of clumping is the highest. Regarding the degree of clumping of four different communities, the order is P2>P3>P1>P4. The distribution pattern analysis over various development stages of Camellia pingguoensis var. terminalis shows that:the clustering degree of size ClassⅠseedlings and size ClassⅡsaplings are high; from size ClassⅢindividuals to grown-up trees, the clustering degree begins to decrease; and among size ClassⅣmedian trees and above, the clustering tends to be even or in a random distribution. Size ClassⅣindividuals are affected outstandingly by the environmental resistance.⑷The studies of Camellia pingguoensis var. terminalis architecture and branching pattern show:In its different growth phases, there are significant differences in crown architectures. Seedlings, tree saplings of Camellia pingguoensis var. terminalis generally rise fast in height and slow in crown-width. In adult tree stages, the growth of height slows down,and ClassⅦold trees are slightly bald with rapidly expanding crown-width. The correlation between the average number of basal trunks and the individual cut rate is significant. The ClassⅣindividuals cut rate is the highest, and the average number of basal trunks achieves the peak value accordingly. In different communities, there are some differences in crown architectures. In L.ramiflora+P.calcarea communities with optimal general environmental conditions, the module indexes of C. pingguoensis var. terminalis are higher than those in other communities, for example, a higher bifurcation ratio, taller individuals and the best high-growth. In H.serratus+C.saichikii community of high altitude and high shading intensities, C. pingguoensis var. terminalis has outspread crown shape, smaller height and optimal crown-width growth. In the B.hsienmu+C.saxatile community with higher temperature, less rainfall and the highest rate of rock outcrops, the module indexes are lower than those in P3, P4 communities. In Z.insignis+B.hsienmu community of the lowest shading intensities, which has been suffering from the most serious disafforestation, the various module indexes are the lowest, and the individuals are scrubby, thin and weak with thick and tight branches at all levels. The average branching angles are around 30°while mostly about 50°in other communities. The branch of C. pingguoensis var. terminalis are generally of 5~9 levels. The statistical analysis of P3 community with of the most levels (9 levels) of branch shows: In different branch classes, the branching pattern varies. The branches of Class 1~3 rise fast in length, and they are mainly nutritional branches above 0.5cm long. The branches above Class 3 are mainly reproductive branches. The average branching angles of Class 1~9 branches generally range from 50°to 30°. The total average branching number of Class 1~3 primary branches with a strong ability of sprouting are remarkably higher than Class 6~9 senior branches.⑸The reproductive module studies show:The flowering duration of C. pingguoensis var. terminalis population usually lasts from September to December, and the fruit phase is from December to May next year. But it is not every year that flower and fruit would continuously happen in a population. Flowering start dates are earlier in the population with low shading intensities and in low altitude than in the population with opposite conditions. At the same time, the flowering intensity is also lower and the life span of each flower is also shorter. The reproductive branches is mostly distributed in the sun shined upper lever of crown with basal diameter ranging from 1.5 to 10cm, especially between 2.5 to 5cm. Unfortunately the diameter of Class 1 branch that has been cut most frequently is just fall in this range, so that human interferences would have significantly malignant effects on the quantity and spatial distribution of reproductive modules.C. pingguoensis var. terminalis can produce flowers and fruits atⅢ~Ⅶdiameter class. The fruit amount and percentage of abortive flower increase accordingly with aging, while the fruit-set ratio and percentage of abortive fruit decrease with aging. Percentages of abortive flower in different plots are all as high as 58%. The difference between fruit amount and flower amount is very significant. The percentages of abortive fruit of each diameter class in Z.insignis+B.hsienmu and L.ramiflora+P.calcarea communities are about 40~60%, and inB.hsienmu+C.saxatile and H.serratus+C.saichikii communities are 20~30% around. C. pingguoensis var. terminalis population has a low fruit-set ratio, and has a reproductive mechanism of "mass flowering, few fruiting". The short of nutritional supply, the low pollinator efficiency seem to be the most likely explanations for this mechanism. Moreover, the interference of wildlife has an important impact too. The growth and reproduction characteristics of C. pingguoensis var. terminalis generally show the K-selection ecological adaptation strategies.The number of reproductive modules of C. pingguoensis var. terminalis is the highest in L.ramiflora+P.calcarea community, which has the higher abortive percentage of reproductive module and the lower reproductive efficiency. This number is the lowest in Z.insignis+ B.hsienmu community, which has the highest abortive percentage of reproductive module and the lowest reproductive efficiency although its flowering rate and reproductive investment are the highest. In B.hsienmu+C.saxatile community, the number is median, but its abortive percentage of reproductive module is the lowest and reproductive efficiency is the highest. In H.serratus+C.saichikii community, the number is lower, which has the lower percentage of abortive fruit and higher reproductive efficiency.⑹Camellia pingguoensis var. terminalis population grow well in typical evergreen monsoon rainforest communities with stable structure, high humidity, clear layers, and 60%~90% shading intensities. The main restrictive factors of their growth are illumination and human interference.⑺The key reasons leading to the endangering of Camellia pingguoensis var. terminalis are most probably the direct human interference, the habitat fragmentation, the breeding characteristics of itself, and its special habitat.