Study On Communtity Structure Of Deciduous Broad-leaf Forests And Their Plant Sexual System Diversity In Dalaoling, Hubei Province

In order to understand forest community structure and plant sexual system distribution pattern of subtropical deciduous broad-leaf forests, on the basis of typical quadrat survey, data collected in the four deciduous broad-leaf forests survey are analyzed and studied from the community biodiversity, physiognomy and structure, the relationship of plant sexual system distribution pattern and species richness, living habit, plant reproductive organs characteristics,etc. The following results have been obtained in the research.1. Species diversity is high in deciduous broad-leaf forests of Dalaoling Nature Reserve. The families and the genera with a variety of species are the common component, but the families and the genera with only one species take the dominant position in the community. There are the more same families and the less same species between quadrats of the same community, which is related to the degrees of difference of the microenvironment between the different quadrats. Meanwhile the age structures of constructive species and dominant species are different between communities. The plant growth season has the characteristics of warm and wet, but long ice and snow time in the winter, spring with mild drought for a short time, which determines by the physiognomy which is composed by phanerophytes with medium-sized, careless qualitative, non-entire simple leaf.2. The vertical structure of deciduous broad-leaf forests is simple and layered obvious. All can be divided into the tree layer, the shrub layer and the herb layer from the top to the bottom. The tree layer can be divided into three sub planes. The constructive species located in the first sub plane has an absolute advantage with the biggest important value in the whole community. The associated tree species and the dominant species are significantly different different from each other. Except for some real shrub, trees seeding also became the major component of the shrub layer. Species diversity is significantly different in the herb layer of every community, but Gramineae and Cyperaceae possess certain proportion.The species of different living habits have the different distribution pattern along altitudinal gradients, namely the change rule of the different life-form species and species diversity variation are not similarly with the elevation changes. The difference is linked to not only its microenvironment, community's canopy density and the density of tree layer, but the characteristics of the constructive species. Generally speaking, species distribution hasn't obvious uniformity. 3. Through the analysis of co-occurrence of the plant species between different quadrats, the rule of the species diversity with altitude change was revealed. For species of different life-forms or all the species as a while, co-occurrence of the plant species is the highest between the same vegetation types, while it is significantly downtrend with the increase of elevation difference. Between different communities, the ecological microenvironment similarity determines the values of co-occurrence of the plant species.4. Sexual system distribution pattern is closely linked to species richness and the life habits in deciduous broad-leaf forests of Dalaoling Nature Reserve. Hermaphroditism is always the highest proportion in all quadrats, followed by monoecious plants, dioecious plants minimum percentage. The amount and the proportion of hermaphroditic species in quadrats are related to the amount of species of seed plants. Along with the amount of species of seed plants increased, the proportion of hermaphroditism is significantly rising trend. Herb species increases can make the increase of hermaphroditic proportion, while the increase of woody plants can make the increase of dioecious proportion in communities. The dioecious proportion of Dalaoling nature reserve is significantly lower than that of the tropical flora in the tree layer. Dioecious plants can live better in the stress environment.5. In Dalaoling deciduous broad-leaf forests, plant sexual systems are significantly associated with plant reproductive organs and living habits. Small inconspicuous flowers are prevalent with diclinous sexual systems generally. Meanwhile inflorescence is the existence form of unisexual flowers, only a few plants are solitary flowers which exist only in hermaphroditic species. In addition, sexual systems are significantly associated with fruit types. Monoecious species produce proportionately more dry fruits and less fleshy fruit. In contrast, dioecious species produce proportionately more fleshy fruit and less dry fruits. However, there is no significant association between sexual systems and fruit types. The proportion of dry fruits is higher than that of fleshy fruit in the community.The proportion of hermaphroditic species is lower in the tree layer than in the herb layer. Monoecy have the highest proportion in the tree layer, while herb species include proportionately less dioecy than wood species.6. The important values of three sexual systems are different in the tree layer, the shrub layer and the herb layer. The most important sexual system is the consistent with that of the constructive species in the tree layer. Hermaphroditism is the most important sexual system in the shrub layer and the herb layer, followed by monoecious plants. Dioecious plants have the minimum important value in the shrub layer and the herb layer.