| This paper focuses on Magnolia cylindrica, a rare and endangered endemic plant of China. Based on the field investigation, M. cylindrica population and community characteristics were studied systematically and comprehensively by using quantitative ecology methods, including community structure characteristics, species diversity, population structure, distributional pattern, intraspecific and interspecific competition and niche breadth and niche overlapping of dominant populations etc. The aims of this study were to reveal its endangered condition and endangered reasons, promote some theory proof so as to protect the endangered species from damage, product plantation and utilize sustainable the resource. The main results are as follows:There were 60 species of vascular plants, belonging to 46 genera,30 families, among which pteridophyte had 2 families,2 genera and 3 species, monocotyledon had 1 family,3 genera and 4 species, and dicotyledon had 27 families,41 genera and 53 species in M. cylindrica communities. The flora of carpophyte genera in M. cylindrica communities was complicated. The ratio of tropical and temperate genera is respectively 37.778% and 62.222%, temperate distribution elements made significant dominant and had important function in flora composition. The phytogeographic components of the community had intermediate traits between temperate and tropical zones. The appearance of community was characterized by phanerophytes plants with mesophyll, single leaves and herbaceous leaf. The vertical structure of community is relatively complicated, which could be divided into tree layer, shrub layer and herb layer. Generally, the order of the magnitude of species diversity was:shrub layer>tree layer>herb layer. The richness index, species diversity index and evenness index in M. cylindrica community were low. M. cylindrica was dominant species accompanied with Cyclobalanopsis multinervis. Using the methods of plots and the technique of censusing every individual, all trees were indentified and measured in quadrats. Based on the DBH class frequency distribution patterns, the population age structure of different tree species were categorized into five regeneration types:Unimodal, Sporadic, Bimodal, Pyramid and Unibar type. According to the biological and ecological characteristics, the population regeneration types of every species were discussed. At the same time, the diagnosis of succession stage of this community was also given. Unimodal type species, such as Liquidamber formosana, Cornus controversa, Rhododendron fortunei, were shade intolerant, pioneer species or long-lived pioneer emergent trees which only regenerated on the bare ground following severe disturbances or in very large canopy gaps. Moreover., these species would disappear finally in the relatively stable community that at later succession stage. Sporadic type species, such as Rhododendron simiarum, Symplocos sumuntia, Cyclobalanopsis multinervis etc., were late seral stage species that could regenerate in large gaps and had intermediate shade-tolerance between pioneer species and dominant species of climax community. Inverse-J type species Cyclobalanopsis glauca and Cyclobalanopsis multinervis are shade tolerant, climax forest species that can regenerate through seedling bank and sprouting under the closed forest canopy. Pyramid type species, such as Illicium henryi, Camellia cuspidata, Cinnamomum chekiangense, Camellia chekiang-oleosa, Eurya japonica etc.,. and Unibar type species, such as Ardisia crenata, were the dominant species in tree upper layer and shrub layer of climax community. Succession stage of the M. cylindrica community was classified as a late seral stage that would develop into a climax community dominated by bimodal species. Based on the analysis above, protection measures were proposed. In allusion to the biological characteristics of different M. cylindrica populations, in site conservation should be taken as the most important management countermeasure for the forest in the future. The population structure of M. cylindrica was a spindle type. The age structure of the population of M. cylindrica was declining due to lack of seedlings. There are two regeneration models of M. cylindrica in forest:sexual and asexual reproduction, but the latter was the main mode. As to the distribution pattern of M. cylindrica, generally speaking, the M. cylindrica population was clump, but there are differences among various developmental stages:clump for saplings, random for adult trees and big trees. To increase accuracy, both methods of Greig-smith and Kershaw were used to analyse the pattern scale of the population of M. cylindrica. The pattern scale of all the populations was 16-32 m2. M. cylindrica presented a spatial population distribution whose aggregating intensity declined with increased altitude. The spatial distribution of the populations closely related to their biological and ecological characteristics and habitat conditions.The competition trees range could be effectively determined by the method of increasing the range gradually, and the sample with 7 m radius was the optimum range to study intraspecific and interspecific competition in M. cylindrica communities. The intraspecific competition was much higher than the interspecific competition. The relationship between competition intensity and growth of the tree of interest closely followed the following equation CI=AD-B. The competition intensity of M. cylindrica declined with increasing DBH, and the change was very small when the diameter of the objective tree reached 30 cm.The niche breadth and niche overlap of 19 main arbor populations in M. cylindrica forests were analyzed by a quantitative method. The result showed that the importance value and horizontal spatial niche breadth of M. cylindrica was the biggest, the horizontal spatial niche breadth of Cyclobalanopsis multinervis, Camellia chekiang-oleosa, Sapium japonicum, Photinia serrulata and Viburnum dilatatum was bigger than other species, the horizontal spatial niche breadth of Ilex polyneura, Pterostyrax corymbosus, Rhododendron latoucheae and Cornus hongkongensis was smaller than other species. There was a positive correlation between the horizontal spatial niche breadth and the importance value. The horizontal spatial niche overlap between the dominant species in M. cylindrica forests was small. The height niche breadth of M. cylindrica was smaller than that of C. multinervis, because the number of seedlings and saplings was small. The height niche overlap between M. cylindrica with Acer elegantulum was big, the reason for which was that they had similar height structure. The height niche overlap among C. chekiang-oleosa, C. cuspidate, Illicium henryi and Symplocos sumuntia was big. The reason for the phenomenon was that these species were distributed relatively even in each height class. The niche overlap values among the populations with the same or similar environment requirements and similar biological properties were also big. There is no relationship between niche breadth and niche overlap of dominant species. The niche of the major arbor species reflect succession patterns of forest communities, which would offer scientific theories for reserving of the endangered and rare plant M. cylindrica.From the generalization of the conclusion before, and the endangered mechanism of the M. cylindrica, found the reasons which lead to the M. cylindrica in the endangered condition are, restricted by its biological characteristics, strict habitat selection, negative interference and influences by human being, and seed damaged by animals. In the future, the in site conservation should be taken as the most important management for the forest, and the natural regeneration should be promoted. At the same time, the artificial population should be expanded. In future forest management and rehabilitation, the forest-tending area should be the one at which the highest aggregating intensity will appear depending on forest habitats and ages. Otherwise, the study on the dynamic of seed to seedling should be strengthened.
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