拉萨河谷山地灌丛草地植物多样性监测方法的比较研究

生物多样性是西藏生态安全监测与评估的重要内容之一.在气候变暖和放牧干扰背景下沿海拔梯度探讨西藏拉萨河谷山地灌丛草地植物群落物种多样性的变化特征,对于该地区草地的保护与可持续利用具有重要意义.以拉萨市林周县白朗村沟域的山地灌丛草地为研究对象,采用常规样方法,重复样线法和Modified-Whittaker样地法3种方法进行系统调查,研究草地群落物种组成及其沿海拔梯度的变化特征.结果表明,1) 3种不同取样方法α多样性的物种丰富度均随海拔的升高呈先增加后降低的趋势,其中50 m样线法效果最好.2) 表征β多样性的Sorensen相似性指数和Bray-Curtis指数均随样地间海拔高差的增大而减小.3) 种-面积关系的截距c,斜率z随海拔的升高呈先增加后降低的趋势,与α,β多样性随海拔梯度的变化特征吻合一致.4) 依据种-面积关系研究结果,山地灌丛草地设置100 m²的样地可覆盖80%左右的植物物种.山地灌丛草地的α和β多样性指数沿海拔梯度均呈先增后减的变化特征,未来研究应注重植物多样性分布格局对山体气候梯度以及放牧干扰变化的响应和适应机制.

A comparative study of methods for monitoring plant diversity in montane shrub grassland in the Lhasa River Basin

Biodiversity is an important consideration in the monitoring and assessment of the ecological stability of rangelands in Tibet.Climate warming and grazing disturbance both threaten the stability of the Tibetan rangelands;hence,research into species succession,transition patterns and species diversity is important for the protection and utilization of grasslands in the region.A field survey was carried out to measure the commu-nity species composition and the species change along an altitudinal gradient in the Bailang village valley,Linz-hou County in the Lhasa River Basin.Three conventional sampling methods,random square quadrats,repeat sampling lines and the Modified- Whittaker plots,were compared in this study.Key results were:(1 )All three sampling methods indicated thatα-diversity initially increased and then decreased with increasing altitude, though the line transect method using three 50 m transects detected more species than the other two methods. (2)The Sorensen similarity index and the Bray-Curtis index ofβ-diversity decreased with increasing altitude. (3)The intercept c and slope z of the relationship between species and sampling area showed unimodal patterns with increasing altitude as also did species richness.(4)In order to cover 80% of local plant species,the mini-mum sampling area should be up to 100 m2 .Future research should focus on the factors determining biodiversi-ty distribution and community assembly in response to climate change and grazing disturbance.