拉萨河谷草地群落的数量分类与排序

采用TWINSPAN数量分类和DCA、CCA排序的方法,对拉萨河谷草地23个样点进行统计分析。结果显示:(1)TWINSPAN数量分类将拉萨河谷草地群落划分成8种类型,拉萨河谷的草地群落分布呈现明显的垂直地带性分布格局。(2)TWINSPAN分类所划分的各群落在DCA排序图上都有各自的分布范围和界限,说明DCA排序能较好的反应各群落与其环境资源之间的关系,同时,TWINSPAN的分类结果也在排序图上得到较好的印证。(3)样点DCA排序的第一轴基本反映了海拔高度的变化梯度,第二轴基本反映了坡向的变化。(4)样点CCA排序表明,影响群落分布的主要环境因子是海拔,其次是坡向。CCA排序进一步阐明了拉萨河谷草地群落分布决定于海拔和坡向等环境因子,并间接验证了TWINSPAN的分类结果。(5)物种CCA排序和TWINSPAN分类结果表明:植物群落中物种的分布格局与植物群落类型的分布格局存在一定的相似性,物种的分布格局在很大程度上影响着群落的分布格局。

Quantitative classification and ordination of grassland communities in Lhasa River Valley

Alpine grasslands on the Qinghai-Tibetan Plateau play an important role in safeguarding the economic sustainability of local animal husbandry. However, these alpine grasslands have been degraded due to increased human disturbance and changing climate in the past few decades. Quantitative classification and ordination are necessary to reveal how alpine grasslands respond to the changing environments. In this study, the Two-way indicator species analysis (TWINSPAN) was used to classify 23 plots of alpine grassland communities in the Lhasa River Valley. Canonical correspondence analysis (CCA) and detrended canonical correspondence analysis (DCA) were used to clarify the geographical distribution patterns of these alpine grassland communities. Our results indicate that:(1) Alpine meadows in the study area can be classified into 8 subtypes:Elymus nutans + Tripogon bromoides; Carex moorcroftii; Kobresia pygmaea + Carex moorcroftii; Potentilla fruticose + Kobresia pygmaea; Rhododendron primuliflorum + Kobresia pygmaea; Rhododendron primuliflorum + Rhododendron nivale + Kobresia pygmaea; Rhododendron nivale + Kobresia pygmaea; and Kobresia pygmaea. (2) Each subtype identified by TWINSPAN had a specific distribution and boundaries on the DCA ordination diagram, suggesting that DCA ordination can explain the relationship between community composition and environmental factors, (3) The first and second axes of DCA reflected the influences of plot elevation and aspect, respectively, (4) CCA ordination also confirmed that altitude, followed by aspect, was the primary environmental factor controlling the distribution of alpine grassland communities, (5) The CCA of species and TWINSPAN of community subtypes were similar, indicating that the distribution patterns of the grassland community were largely affected by the species distribution pattern. Quantitative analysis is suggested to examine and assess the relative contributions of anthropogenic and natural factors to changes in the Tibetan alpine grasslands in the future.