石羊河下游白刺灌丛演替过程中群落结构及数量特征

白刺灌丛(Nitraria tangutorum Bobr.)是在石羊河下游存活面积最大的天然植被类型,研究不同演替阶段白刺灌丛群落的结构和数量特征可为该区白刺群落保护与恢复提供科学依据.根据白刺灌丛生长及其生境状况,在石羊河下游选择了初期发育、稳定、衰退、严重衰退的群落,研究了各演替过程中各阶段的群落物种组成、生活型谱,群落盖度、群落物种多样性及各演替阶段群落的相似性特征.结果表明,从初期发育阶段到稳定阶段的群落物种数量明显减少,而从稳定阶段至严重衰退阶段的演替过程中群落物种是逐渐增加的.在整个演替过程中,1年生植物所占比例逐渐增加,至严重衰退阶段时1年生植物所占的比重高达80％.不同演替阶段群落盖度最高、最低值出现的月份也不相同,5-10月群落盖度的平均值为稳定阶段＞初期发育阶段＞衰败阶段＞严重衰败阶段.各演替阶段多样性Simpson、Shannon-Wiener指数以及Pielou均匀度指数5-10月均呈现波动变化特征,Simpson、Shannon-Wiener指数大小顺序均表现为初期发育阶段＞严重衰退阶段＞衰退阶段＞稳定阶段,而均匀度Pielou指数为衰退阶段＞严重衰退阶段＞稳定阶段＞初期发育阶段.各演替阶段群落之间的相似性均较低,演替序列越相近,相似性系数越高.

Analysis on community structure and quantitative characteristics of Nitraria tangutorum nebkhas at different succession stage in lower reaches of Shiyang River

Nitraria tangutorum occupy the largest area among all natural vegetation in the lower reaches of the Shiyang River.The plant is tolerant to high-temperature, drought, salts, wind-erosion and sand burial, so it has been highly regarded as a sand fixation plant.The formation and development of N. tangutorum nebkhas is also the result of interaction between vegetation and environment in the process of community succession.The research on the structure and quantitative characteristics of N. tangutorum communities in different succession stages can provide a scientific basis for its conservation and restoration. Based on growth and habitats, N.tangutorum communities at different succession stages: early development, stable equilibrium, deterioration, and serious deterioration, were selected to look into species composition, life form spectrum, coverage, species diversity and community similarities. The results demonstrated that the species composition of the plant community was relatively simple. There were 29 plant species, belonging to 25 genuses and 11 families. Zygophyllaceae and Chenopodiaceae showed up in all succession processes. Gramineae dominated the early development stage, whereas Chenopodiaceae was predominant in the stable equilibrium. At the deterioration stage, species of Zygophyllaceae were prevailing after N. tangutorum community came to deterioration. Chenopodiaceae was dominant again when the succession was at the serious deterioration phase. The number of species abated significantly from the early development to the stage of stability, whereas that increased gradually from the stable equilibrium to deterioration and serious deterioration. Throughout the succession process, the proportion of annuals was increasing by degrees, from about 26% at the early development to 80% at the serious deterioration stage. So, the degradation succession of desert plants was a course of gradual increase of annual plants. The proportion of phaenerophyte was gradually increasing from the early development to the deterioration stage, and decreasing at the stage of serious deterioration. Chamaephytes had larger quantities at the early development stage, were decreasing at the stable equilibrium stage, and disappeared at the deterioration stage. Hemicryptophyte were prevailing at the early development stage, decreasing at the stable equilibrium phase, and disappeared at the deterioration period, even only 1 species of hemicryptophyte existing at the serious deterioration phase. There was no cryptophytes in all succession processes. The annual variations of community coverage at different succession stages were various and the maximum and minimum values of the community coverage at different succession stages occurred in various months. The mean community covering rates in May to October was in the order stable equilibrium, early development, deterioration, serious deterioration. With respect to community diversity at different stages, the Simpson index, the Shannon-Weiner index, and the Pielou evenness index showed fluctuation. The Simpson and Shannon-Wiener indexes rank the stages in the order of early development, severe decline, decline, and stability. Meanwhile, the pielou index ranked as follows: recession, serious recession, stability, and early development. The species composition of N. tangutorum communities in different succession stages was various with a level of similarities. Coefficients of similarity between communities at the stages of deterioration and serious deterioration were lightly similar, and those between other communities were dissimilar. The closer the successional series, the higher the similarity coefficients.