阿拉善高原荒漠植被组成分布特征及其环境解释 Ⅰ.典型荒漠植被分布格局的环境解释

阿拉善高原是亚洲中部荒漠亚区的一个植物地理区域,特殊的地理位置和严酷的气候条件形成了该区独特的植被组成。目前由于气候的干暖化、黑河断流、森林草原的过度开采利用以及人口的激增等,给当地的农牧业发展、生态环境的可持续发展和利用带来严重障碍。如何有效地管理和利用当地的草场资源是当地政府和科研人员面临的首要问题。通过分析环境因子和植被分布的相互关系,来确定影响该区草场资源分布的主要环境因子。通过对52个样地的植被调查资料进行分析,发现所调查到的70种植物包括16个科和46个属,其中一年生植物占7.1%,灌木和小灌木占52.9%。种数最多的4个科是豆科(Leguminosae)、蓼科(Polygonaceae)、禾本科(Gramine-ae)和菊科(Compositae),分别占到总种数的20.0%、15.7%、14.3%和14.3%。高位芽和地面芽是主要的生活型,这代表了沙漠植物典型的生活型谱。采用二歧双向指示种分析(TWINSPAN),将所调查植被分为6个类型,每个植被类型及相应的土壤特征代表了特定的地理单元。此外采用除趋势分析(DCA)和典范对应分析(CCA)方法研究了植被分布和环境变量二者的关系。环境因子主要有29个:其中包括18个土壤因子、8个气候因子和3个地理位置因子。DCA和CCA分析的结果一致,都表明植被分布和环境因子之间相关性较强。其中,CCA的第一轴主要代表了土壤有机质、全氮、沙黏粒含量、海拔、Kira湿度指数以及相对湿度,而CCA第二轴主要和Cl-、K+、Mg2+和电导率相关。这两轴在解释植物-环境关系的过程中累积贡献率达到60%,说明前两轴代表的环境因子是决定该区荒漠植被分布的主要因子。这一结果阐明了阿拉善干旱荒漠区植被分布的独特性,以及与关键环境因子之间的作用机制,这为该区域荒漠草场的恢复和管理提供了一定理论基础。

Environmental Effects on Distribution and Composition of Desert Vegetations in Alxa Plateau:Ⅰ. Environmental effects on the distribution patterns of vegetation in Alxa Plateau

This study aims to provide an analysis of vegetation and environment relationship in the Alxa Plateau of Inner Mongolia,China. Seventy species representing 46 genera and 16 families are collected. The largest families are Leguminosae,Polygonaceae,Gramineae and Compositae,representing 20.0%,15.7%,14.3% and 14.3% of the total flora,respectively. Phanerophytes and hemicryptophytes are the most abundant life form. Classification of the vegetation is conducted by using two-way indicator species analysis (Twinspan) techniques. There are six vegetation groups,each group and its soil characteristics can be linked to a specific geomorphologic unit. Ordination techniques as detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) are used to examine the relationship between vegetation and environmental parameters. Analysis with DCA gave results similar to CCA,suggesting that there is a relatively strong correspondence between vegetation and environmental factors. CCA axis 1 is highly associated with organic matter,total nitrogen,silt and clay content,elevation,Kira moisture index and relative humidity,and CCA axis 2 shows significant correlation with chlorine,calcium ion,magnesium ion and electrolytic conductivity. The first two canonical axes can explain the 60% causes of the species-environment relationship in the study sites,implying that the environmental factors expressed by these two axes are the key determining the distribution of desert vegetation in study area. Understanding relationships between environmental variables and vegetation distribution in this area helps us to apply these findings in management,reclamation,and development of arid and semi-arid grassland ecosystems.