Analysis On The Distribution Status And Characteristics Of Xishui Rhododendron In Xishui National Nature Reserve, Guizho

In order to explore the population status of Rhododendron xishuiense,an new plant plant in Xishui National Nature Reserve,Guizhou,reveal the dynamics and endangered causes of its population and strengthen its protection,13 transects were set up in the reserve to investigate the distribution of Rhododendron xishuiense.The sample plot survey of Rhododendron xishuiense distribution community was carried out.The population structure of Rhododendron xishuiense distribution community was analyzed by using Wu Zhengyi’s floristic division standard,Raunkiear life form system statistical method,Gleason richness index,Simpson diversity index,Shannon Wiener diversity index and Pielou evenness index.Space method instead of time order was used in the research.The population age structure,the static life table,survival curve,mortality curve,disappearance rate curve and four survival functions are prepared to analyze the dynamic characteristics of Rhododendron xishuiense population.The spatial pattern and population niche of dominant species in Rhododendron xishuiense distribution community are analyzed by Ripley point pattern method,Levins and Shannon Wiener niche breadth index and pianka niche overlap index.The main research results are as follows:The structure analysis of the distribution community of Rhododendron xishuiense shows that:（1）there are 65 species of vascular plants in 27 families,42 genera,including 62 species of seed plants in 24 families,39 genera and 3 species of ferns in 3 families and 3 genera;（2）In the life form statistics of the community,the species of high bud is the largest,56 species in total,accounting for 86.15%among all species,followed by aboveground bud plants,aboveground bud plants and underground bud plants;（3）Among the diversity indexes,the tree layer>shrub layer>herb layer is exhibited,and the tree layer index occupies an absolute dominant position.in the communityThe results of the study on the population dynamics of Rhododendron xishuiense showed that:（1）the age structure date of the population is presented a"pyramid"diagram,and the number of individual seedlings of the population is larger than that of the whole population;（2）the fitting result of population survival curve emerges as Deevey II type,and the number of individuals is decreasing with the increase of their age.The mortality and disappearance rate reaches a high peak at the fourth age level,and even there is a lack of survival individuals of Rhododendron xishuiense at the fourth age level as well;（3）According to the study,the population survival rate are declining,the cumulative mortality and death density are rising,and the risk rate curve first increased and then decreased.Its survival status of the population showed a depression in the whole growing period.the reduction rate is fast in the early stage,slow in the middle stage and slow in the late stage;（4）Regardless of the external disturbance,the dynamic index of quantity change of Rhododendron xishuiense population V_pi=34.37%>0.Considering the influence of external disturbance,V_pi’=3.4%>0,this population shows an expanding growth in distribution.The analysis of spatial distribution pattern of Rhododendron xishuiense population and dominant population of community species showed that:（1）from the perspective of small scale,the seedlings,young trees,medium trees of Rhododendron xishuiense and its population showed a random distribution in space;（2）the dominant species of Rhododendron glabra in arbor layer also showed a random distribution;Manglietia chingii,Lithocarpus brevicaudatus and Machilus microcarpa usually showed an aggregation distribution in scale range,and the dominant species of Rhododendron in shrub layer showed an aggregation distribution among all the individuals;（3）by observing at different growing stages,the spatial position of Rhododendron xishuiense develops in a certain diffusion ability.The reproduction mode and seed diffusion ability are the main reasons affecting the species distribution pattern of the community.The niche analysis of the dominant populations of Rhododendron xishuiense population and community species showed that:（1）the niche width B_i（2.83）and B_a（1.07）of Rhododendron xishuiense are the largest in the tree layer,with a stronger adaptability in resource utilization and environment,but the niche overlap value（both greater than 0.70）is relatively high,and the number of overlapping species accounts for 100%,which is suffering a strong competition from other species;（2）In the shrub layer,the niche width B_i（3.24）and B_a（1.27）of Rhododendron xishuiense are second only to Rhododendron.However,due to the resource constraints,its degree of dominance is not obvious.In conclusion,the distribution range of Rhododendron xishuiense population is narrow,the species diversity of the distribution community is high,and there are relatively many seedlings,which shows a growth type,but the total population is very small and subject to strong competition.It is suggested to take appropriate measures to promote the growth of seedlings and young trees,so that middle-aged individuals can be effectively supplemented,so as to ensure the sustainable growth of the population.