木论喀斯特森林木本植物多样性垂直格局

Altitudinal pattern of woody plant species diversity in the karst forest in Mulun,China

基于木论国家级自然保护区内西南坡一条垂直样带16个样方的调查资料,运用丰富度指数、物种多样性指数和均匀度指数对木论喀斯特森林木本植物多样性的垂直格局进行研究。结果表明:(1)在16个样方中共记录植株5089个,分属48科90属120种。(2)喀斯特森林木本植物群落具有明显的垂直分布格局,采用等级聚类和非度量多维标度排序方法可将植物群落沿海拔梯度划分为3个类型,分别是:下坡位以小果厚壳桂(Cryptocarya austrokweichouensis)和灰岩棒柄花(Cleidion bracteosum)为主要优势种的群落;中坡位以长管越南茜(Rubovietnamia aristata)和罗伞(Brassaiopsis glomerulata)为主要优势种的群落;上坡位以化香树(Platycarya strobilacea)和密花树(Rapanea neriifolia)为主要优势种的群落。沿海拔梯度升高,水热组合发生变化,地带性植被以及群落内的建群种和优势种都发生了变化。(3)物种生活型方面,常绿树种所占的比例高于落叶阔叶树种,针叶树种仅出现在山顶。(4)沿海拔梯度物种丰富度及α多样性指数中的Shannon-Wiener指数曲线均符合单峰格局,峰值出现在坡腰位置。(5)β多样性指数起伏较大,总体上β多样性随着海拔的升高呈递减的趋势。

Variation in species diversity along ecological gradients is the main focus in recent biodiversity studies. Among multiple interacting resource gradients,altitude gradient may be a decisive factor determining spatial patterns of species diversity. Forest community classification,ordination,and species diversity patterns along altitudinal gradients can reveal relationships between species distribution and environmental factors,and provide an important basis for understanding the function of mountain ecosystems. For studying the species diversity along ecological gradients in karst ecosystems,we conducted a study in Mulun National Nature Reserve（ MNNR）,northwest of Huanjiang Maonan Autonomous County in Guangxi,China. This reserve and Maolan National Nature Reserve together possesses the largest and most typical karst forests in the world,and play an important role in plant biodiversity research due to their unique geography,climate,and vegetation conditions. The climax community in this region is an evergreen and deciduous broadleaf mixed forest on limestone in the central subtropical zone in MNNR. The area of this forest is 89. 69 km-2 with 94. 8% of vegetation coverage. The soil type is calcareous lithosols（ limestone soil）. Sixteen sample plots（20 m × 20 m） were established in a typical depression landscape between karst hills on a southwestern slope in MNNR. All woody plants [DBH（ diameter at breast height） ≥ 1 cm]from the 16 plots were investigated. We analyzed the pattern of woody plant species diversity along an altitudinal gradient in MNNR by measuring the indices of species richness,diversity,and evenness. The results showed that：（1） there were 5089 individuals in the studied plots,which belonged to 120 species,48 families and 90 genera;（2）there was a distinct altitudinal pattern of woody plant species in the karst forest communities. Hierarchical cluster analysis and Non-metric Multidimensional Scaling analysis showed that the forest communities could be classified into three types,including those in lower slope,middle slope and upper slope respectively. In the lower slope,the dominant species were Cryptocarya austrokweichouensis and Cleidion bracteosumare; in the middle slope,the dominant species were Rubovietnamia aristata and Brassaiopsis glomerulata; Platycarya strobilacea and Rapanea neriifoliaare were the dominant species in the upper slope. As the altitude increases,the temperature and moisture also changed. Aridity and low temperature respectively limited plant growth at low and high altitude; the precipitation and sunshine were plentiful in middle elevations,which supports a high diversity of plant species;（3） among the woody species,there was a greater proportion of evergreen species than deciduous broadleaf species. In addition,coniferous species only grew on the top of the mountain;（ 4） Species richness and the Shannon-Wiener index,along the altitudinal gradient,exhibited a pattern of unimodal distribution,with the peak appearing in the mid slope;（5） the β diversity index fluctuated considerably,and decreased with rising elevation in the ecosystem. Our results will be useful for developing strategies of vegetation restoration in the karst region.