Characteristics of desert flora and vegetation in lower reach of Shiyang River论Basin

石羊河下游位于干草原向荒漠过渡区域,有天然种子植物23个科,73个属,123个种,不仅有典型的戈壁荒漠成分,也渗入一些草原化荒漠植物种类.其荒漠植被特征更明显,群落层片结构简单,群丛建群种的74.4%是灌木和半灌木,构成了灌木、半灌木旱生群落;1年生草本植物随季节性降雨可形成＂灌草丛＂,成为荒漠植被的重要组成部分.在植物地理区系成分上,温带成分属占优势,其中地中海至中亚分布型及其变型最多,其次为北温带分布及其变型.整个区域内植物的分布集中在生境较适宜的区域,空间结构的成群性高,但在小区域内植物种的分布则较单一.植被可划分为4个植被型,5个植被亚型,13个群系组,23个群系,38个群丛.地域性植被以绿洲为中心,成环状分布,可分为3个带.

Characteristics of desert flora and vegetation in lower reach of Shiyang River Basin

The lower reach of Shiyang River Basin(LSRB) is located at the transition area from steppe to desert.There are 23 families,73 genus and 123 species of spermatophyte,which are not only the elements of desert and Gobi,but also the steppe-desert species.The LSRB has an obvious characteristic of desert vegetation.The structure of synusia is simple,and 74.4% of association constructive species are shrub or semi-shrub,which composes of shrubbery or semi-shrubbery xerophytic community.The annul herb accounts for a few rate,but makes up "shrubbery-herb association" and acts as an important element of desert vegetation.In the floristic composition,the component of Temperature Zone is dominant,with superior to the species of Mediterranean Sea to Central Asia and their variants,and the second to the species of North Temperate Zone and their variants.The plants centralize in more adaptive habitats,with an obviously clumped distribution in whole area,but the species distribute simply at a small area.The vegetation can be classified into 4 vegetation types,5 vegetation subtypes,13 formation groups,23 formations,and 38 associations.The zonal vegetation distributes circularly with oases,and can be divided into three belts.Such a circular distribution of vegetation in LSRB is quite common in arid zone.