Community Structure Characteristics And Short-term Dynamic Of Rhododendron Simii Shrubland At Daweishan

Structure, composition and population spatial patterns of a specific plant community has generally been the focal thesis of the vegetation ecology. The research results provides a reliable basis for the vegetation restoration, effective utilization of resources, vegetation ecology process reveal and forest sustainable development, it also provide a theoretical basis for biodiversity conservation. Shrubland is one of the three largest land natural ecosystem that juxtaposed with forest, grassland which plays an important role on the vegetation succession, biodiversity protection and maintaining ecological balance. Therefore, This paper studies the rhododendron simsii shrubland community structure characteristics, the spatial pattern and short-term dynamic by analyzing the flora, species composition and community structure and distribution pattern of woody plants, short-term changes of species composition and structure, etc, to provide basic information for further research on scrub vegetation ecology.Based on the data of 2012 collected from 6 representative plots (15×15m) of Rhododendron simsii shrubland at Dawei shan, Hunan province, this study aimed to analysis community species composition, community structure and distribution patterns of woody species in Rhododendron simsii shrubland. Distribution patterns and aggregate intensity of 14 common woody plants were analysed by variance/mean ratio, t-test, negative binomial parameter, clustered index, mean crowding index, poly block index, diffusion index, Green’s index and Cassic index. We have analyzed the community short-term dynamic changes including community species composition, the change of base diameter and height, deaths, broken tip, etc. by using the data of 2012 and 2013. The main research results are as follows:(1) There were 36 families,50 genera and 58 vascular plant species including 19 woody pants and 39 herbaceous species in the community without woody vines species. Community composition at the seed plant generic level, was dominanted by the temperate floristic elements, affected strongly with tropical and subtropical flora. The physiognomy was short and the vertical structure of community was distinct with obvious shrub and herb layers. Most individuals of shrub species were concentrated in 1～2m height class. The shrubland was one type of montane mesophilius deciduous broad-leaved thicket, belonging to temperate deciduous broad-leaved thicket formation group. The results of life form spectrum implied the cold climatic condition for the higher percentage of phaenerophyte and hemicryptophytes. There were obviously dominant species in the community which had a high stability and uniformity. The analysis of height and basic area classes of shrub layer indicated mid-size individuals of species had conservative life strategies in this community.(2) 85.7% of 14 common woody species (e.g. Rhododendron simsii、Symplocos. hunanensis、Ilex szechwanensis) were distributed aggregately in Rhododendron simsii shrubland and their aggregate intensity decreased with population density; the aggregate intensity of non-dominant species (e.g. Viburnum foetidum var. rectangulatum, Weigela japonica var. sinica and Rhododendron latoucheae) was larger than dominant species (e.g. Rhododendron simsii and Symplocos. Hunanensis); The main driving factors of Rhododendron simsii shrubland’s spatial patterns were the adaptabilities of species to humid microthermal climate at the top of the mountain, biological characteristics (e.g. seed dispersal, spruting abilites and shade-tolerant) and disturbance.(3)The aspection stages of Rhododendron simsii shrubland at Daweishan is obviously, community dynamic analysis shows that the Rhododendron simsii shrubland of woody plant species did not change, still keep 19 species, The total number of individuals are reduced from 6499 to 6383, the 116 individuals reduced mainly are Rhododendron simsii and Symplocos hunanensis. the individual number of non-dominant species has not changed. The size-class and height structure of all species and Rhododendron simsii still remain basiclly stable and unimodal type structure, it shows that community structure is also stable. The size-class and height structure of Rhododendron simsii and Ilex szechwanensis is gradually becoming a unimodal type,and the population of regeneration are suffering to certain obstacles; The individual number of Rhododendron simsii. Symplocos hunanensis,Ilex szechwanensis and all species in small size-class have obvious drop, and then the individual number of large size-class have increased.119 individuals of woody plants died in the community, self-thinning and unself-thinning phenomenon is the main cause of plant individual death in community.172 woody plants of top breakage were found in the community, crowded and interlaced individual growth with cold, windy climate conditions on top of the mountain is the main causes of top breakage.(4)The analysis of the community structure, spatial patterns and short-term dynamic shows that:Due to not too long enclosed time, Rhododendron simsii shrubland is still in the succession of the former or the middle, and the community is not stable.The Rhododendron simsii shrubland in Daweishan will succession towards zhongshan evergreen and deciduous broad-leaved mixed forest when to extend the time of enclosed.