西藏色季拉山西坡种子植物多样性垂直分布

Species Diversity of Plant Communities along an Altitudinal Gradient on the West Slope of Sejila Mountains,Tibet

调查色季拉山西坡不同海拔梯度的植被,分析种子植物物种多样性的垂直分布格局及其原因。结果表明:色季拉山西坡共有植物288种,分属58科163属;从低海拔到高海拔植被依次为针叶林(3000～3200m)、暗针叶林(3300～4200m)、疏林及灌丛(4300～4400m)、高山草甸(4500～4800m);科数、属数、种数、灌木物种丰富度和草本物种丰富度随海拔梯度变化均呈双峰曲线,但乔木物种丰富度呈单峰曲线;Shannon-Wiener指数及Simpson指数均在海拔3300m处最大,β多样性指数在海拔3500m处最大,3个多样性指数均在海拔3700m处最低;种数/属数及属数/科数随海拔升高呈双峰曲线,种数/科数则随海拔升高而增大;立木株数随海拔的升高而降低,胸高断面积及最大胸径在海拔3900m处最高,最大树高则出现在海拔3600m处;物种丰富度与海拔及坡向具有显著的相关性(P<0.05),并可用不同的回归方程较好地描述,而与坡度、坡位及郁闭度无显著相关性(P>0.05)。

To explore patterns of plant diversity along altitudinal gradients on the west slope of Sejila Mountains,Tibetan,vegetation of different altitudinal gradients were investigated.Furthermore,we analyzed the reason of plant diversity patterns along altitudinal gradients.The results showed that there were 288 species,which belong to 58 families and 163 genera,on the west slope.There were four vegetation types,i.e.coniferous forest （3 000 ～ 3 200 m）,dark coniferous forest （3 300 ～ 4 200 m）,open forest or scrub （4 300 ～ 4 400 m）,and alpine meadow （4 400 ～ 4 800 m） from low to high elevation.The altitudinal pattern of family,genera,species,shrubs,and herb species richness showed a double-humped pattern,while trees richness first increased and then decreased with increasing elevation,peaking at the altitudes of 3 300 m.Maximum values of Shannon-Wiener index and Simpson index occurred at the altitudes of 3 300 m,while maximum β diversity occurred at the altitudes of 3 500 m,and three diversity indexes were all the lowest at the altitude of 3 700 m.The altitudinal patterns of the ratio of number of species /number of genera and number of genera / number of family also showed a double-humped pattern,but the ratio of number of species /number of family increased with increasing elevation.We also found that the number of stems decreased with increasing elevation,maximum values of basal area and maximum DBH occurred at the altitudes of 3 900 m,while it occurred at the altitudes of 3 600 m for maximum height.The correlation analysis between species richness and environments showed that species richness was negatively correlated with elevation,and was positively correlated with slope aspect.The relationships between species richness and altitude and slope aspect could be described by different regression equations.