Studies On Community Characters, Population Structure And Adaptability Of The Endangered Plant Juniperus Rigida Sieb. Et Zucc.

Juniperus rigida Sieb. et Zucc. is a useful plant species in many ways, such as soil and water conservation, environment improvement and so on. But because of the human doing, it has been listed to the endangered plant species in Shaanxi province. With the helps of various statistical analyses we studied the composition, species diversity and liaison between species in the communities, as well as the niche, distribution pattern, modular structure of the populations. The result shows as following:There are 62 species of 49 genera in 24 families of higher plants in the Juniperus rigida communities. In terms of genus geographical elements, many of them are distributed in temperate zones. According to Raunkiaer's statistics of life-form, the life-form hemicryptophyte of this community numbers first, and the nanophanerophyte second. The features of the community leaf is mainly microphyll, simple, herbaceous and unentire.The vertical structure of community is relatively simple which can be divided into tree layer, shrub layer and herb layer as well as few number of interstratum plants.In terms of genus geographical elements, many of them are distributed in temperate zones. According to Raunkiaer's statistics of life-form, the life-form hemicryptophyte of this community numbers first, and the nanophanerophyte second. The features of the community leaf is mainly microphyll, simple, herbaceous and unentire.The vertical structure of community is relatively simple which can be divided into tree layer, shrub layer and herb layer as well as few number of interstratum plants. The species diversity index of different layers shows: herb layer>shrub layer>tree layer.In the communities studied, the total related differences VR of shrub layer and this of herb layer are 8.06, 17.68, the test statistics W are from 3.85 to 36.42 and 11.59 to 32.67, which indicates a notable positive correlation among species. From the test of the interspecific relatedness among species in the communities we know that in the shrub layer there 6 species pairs of inapparent positive correlation. In the herb layer there are 95 species pairs of positive correlation, 72 species pairs of negative correlation and 4 species pairs of no correlation, among those species pairs there are 8 species pairs of notably positive correlation, 7 species pairs of notably negative correlation and 2 species pairs of extremely positive correlation. In the communities we studied 4 populations in the shrub layer and 19 populations in the herb layer. The order of the value about niche breadth in shrub layer from large to small is: Rosa hugonis> Juniperus rigida> Berberis brachypoda> Spiraea trilobata> Lespedeza davurica, the order in herb layer from large to small is: Polygala tenuifolia>Pennisetum flaccidum>Heteropappus altaicus>Artemisia capillaris>Thymus mongolicus>Cynanchum komarovii>Artemisia gmelinii>Stipa bungeana>Oxytropis gracillima>Bupleurum chinensis>Geranium dahuricum = Ixeris sonchifolia>Gypsophila licentiana>Allium senescens>Artemisia annua>Patrinia scabra>Dracocephalum heterophyllum>Carex lanceolata>Suaeda glauca. With the help of Pianka's niche overlap we further studied the niche overlap among different species in the sampled communities, the value of the niche overlap in the shrub layer are small, but in the herb layer are large, the niche overlap among the species with the same or similar environment requirements are greater.From our study we can find that the numbers of Juniperus rigida population was very limited. The population is of declining type. Its survival curve could be left-skewed type. The discipline of mortality ratio showed the similar dynamics to that of the hazard ratio.With the helps of various spatial distribution patterns statistical analyses, we can see that: the distribution pattern was clustering. From sapling to grown up tree, the clustering degree was decreasing, while the big tree had random distribution. Also from our investigation, we could see the human disturbance would affect the distribution pattern of Juniperus rigida population.The structure of branch modular population influenced the whole crown of trees. The angle of branch are form 30°to 90°, the value order of the angle is: first branch>the second>the third; the value order of the length is: first branch>the second>the third; the number order of the branch is: the second branch>the first>the third.The length and angle of branch are minished with the situation of the branch's raising.Little seedlings from germination observed in the populations of Juniperus rigida. The main reproduction of the species is vegetative reproduction.