荒漠绿洲过渡带沙拐枣种群结构及动态特征

Structure and dynamic characteristics of Calligonum mongolicum population in the desert-oasis ecotone

沙拐枣(Calligonum mongolicum)作为黑河中游荒漠绿洲过渡带的一种主要固沙植物种,它对于维护荒漠绿洲过渡带生态系统的稳定性起到了至关重要的作用。通过样地调查和数据统计,绘制了沙拐枣种群的径级结构图,在此基础上编制了种群的特定时间生命表,分析了存活曲线、死亡率曲线等重要参数,并运用时间序列模型预测种群数量动态,以揭示荒漠绿洲过渡带沙拐枣种群的结构及动态特征。结果表明:沙拐枣种群属于增长型,Vpi'=0.0233,表明该种群趋近于稳定型,但沙拐枣种群Ⅰ、Ⅱ龄级个体数目少于Ⅲ龄级的个体数目;存活曲线趋于Deevey-Ⅱ,各龄级种群有相近的死亡率;时间序列预测分析表明,在未来2、4、6、8个龄级时间后沙拐枣老龄个体逐渐增多,幼龄株数则有所降低,种群稳定性长期维持困难,因此,适当的人工辅助恢复和现有植株及生境的保护是保持沙拐枣种群自然更新和种群恢复的关键。

The desert-oasis highly sensitive to climate years. The changes ecotone is an ecological transitional zone between desert and oasis ecosystems, and it is also change. The importance of the desert-oasis ecotone has received increasing attention in recent in plant populations and in community dynamics due to environmental disturbances reflect the interaction mechanism between the ecotone and climate change to climate change. Population structure reflects not , providing a foundation for understanding and predicting plant responses only population dynamics and plant development, but also reflects the relationship among the population, its environment and each plant＇s position in the population; thus, comprehensive studies of population structure can reveal population size, survival conditions, and habitat suitability, and, when combined with analyses of ecological requirements, survival rates, and reproduction rates, also allow the evaluation of past population disturbances and predictions of future behavior. Thus, they are invaluable in understanding how populations adapt to environmental condition and will prove essential in protecting and regulating endangered plants. The shrub Calligonum mongolicum （Polygonaceae） is one of the most important sand-binding plants in the desert-oasis ecotone of the middle reaches of the Heihe River Basin in Gansu Province, China; it plays an important role in the stability of the desert-oasis ecotone. To elucidate the population structure and population dynamics of C. mongolicum, we surveyed and analyzed the size and structure of a natural C. mongolicum population in the field. Based on these data, we estimated the survival curve,mortality curve, and life expectancy of the plants, as well as other population parameters. Population dynamics were predicted by a time-sequence model. The aims of our study were to 1 ） provide references for the regulation and protection of C. mongolicum and 2） formulate strategies for enhancing its reproduction and restoring populations. The results showed that： 1 ） The age structure of the C. mongolicum population was a pyramid, with the size classes Ⅰ -Ⅲ comprising 89.98% of the total population, but there were fewer individuals in classes Ⅰ and Ⅱ than in class Ⅲ. Using the quantization method of population dynamics, we found that the C. mongolicum population was of the growing type, with a dynamic index of population size structure of Vpi= 0.0233 under random disturbance, which showed that its population tend to be stable in this desert-oasis ecotone and that it was very sensitive to environmental disturbance. 2） The stationary life table of the C. mongolicum population indicated that the number of survivors, l, at age x years （lx） decreased as size class increased ; the observed life expectancies, e, at age x years （ex） were highest in size classes Ⅰ and Ⅱ then decreased. The survival curve of the C. mongolicum population showed that it approached a Deevey-Ⅱ type, and the mortality rate in different size classes was similar. 3） The time sequence model predicted that the number of individuals in size class IV would increase in the coming 2, 4, 6 and 8 age classes, but the numbers in size classes Ⅱ and Ⅲ would decrease. Therefore, if appropriate action is not taken to protect and foster these plants, C. mongolicum populations will inevitably decline from a lack of recruitment of young individuals. Therefore, we encourage appropriate vegetation restoration by humans and the protection of their habitat as crucial strategies to renew the natural C. mongolicum populations.