藏北高原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,对藏北高原草地29个样点进行统计分析。结果显示:(1)TWINSPAN数量分类将藏北高寒草地群落划分成10种类型。(2)样点DCA排序第一轴基本反映了水分环境梯度,第二轴基本反映了热量梯度。(3)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优势群落与其环境资源之间的关系。(4)样点CCA排序表明,影响群落分布的首要环境因子是水分因子(年均降水量)和空间因子(经度),其次是热量因子(年均温度),CCA排序进一步阐明了群落分布决定于水分和温度等环境因子,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。

Quantitative classification and ordination of grassland communities on the Northern Tibetan Plateau

The relationship between vegetation and the environment is one of the fundamental questions in understanding plant species composition and community distribution along an environmental gradient. Understanding vegetation-environment correlations may help predict possible shifts in plant communities in response to climate and land use changes. There are 48 million hm² of natural grasslands on the Northern Tibetan Plateau, accounting for 59% of the total grassland area in the Tibet Autonomous Region. However, these alpine grasslands are threatened by global climate change and intense human activities in recent decades, and are now widely degraded. Quantitative classification and ordination are important methods in examining the internal classification of plant communities, characteristics of their associations, and in revealing the ecological relationships between vegetation and the environment. TWINSPAN classification and DCA,CCA ordination were used to conduct a classification and ordination of the plant communities of 29 plots in the northern Tibetan grassland. Our results indicate that: (1) Northern Tibetan alpine meadows are classified into 10 associations: Stipa purpurea+Festuca nitidula+Carex ivanovae; Stipa purpurea+Carex ivanovae; Stipa purpurea+Leontopodium nanum; Kobresia pygmaea; Kobresia pygmaea+Stipapur purea; Stipa purpurea; Stipa purpurea+Blysmus sinocompressus+Oxytropis; Stipa purpurea+Heteropappus semiprostratus+Astragalus puivinalis; Carex moorcroftii+Stipa purpurea+Rhodiola smithii; and Stipa glareosa+Stipa purpurea+Ajania khartensis; (2) The first axis of DCA basically reflected a moisture gradient, and the second axis indicated a thermal gradient; (3) Each community divided by TWINSPAN classification had its specific distribution and boundaries on the DCA ordination diagram, which indicated that DCA ordination can explain the relationships between the plots and environment; (4) CCA plots indicated that the primary environmental factors controlling the distribution of communities were rainfall (average annual rainfall) along longitude, followed by temperature (average annual temperature); CCA sorting further elaborated the relationship between plant community distribution and the environment, and indirectly supported the results of the TWINSPAN classification; (5) Quantitative analysis of 74 species by CCA indicated that the distribution pattern of species and plots in DCA was similar. The first axis of species CCA reflected water conditions of species distribution. Taken together, we conclude that the distribution patterns of plant species communities closely mirror each other. In general, the present study provides an ecological interpretation of the distribution of plant species communities along an environmental gradient on the Northern Tibetan Plateau.