【摘要】 针对科尔沁沙地小叶锦鸡儿固沙林在持续高温干旱条件下出现稳定性波动的问题 ,选择 2、5、15、35 a人工群落和天然群落进行对比研究 ,探讨了人工小叶锦鸡儿防风固沙林物种多样性在 35 a间的变化以及对大气持续干旱的抵抗力和对外界干扰的恢复能力。流动沙丘固定后 ,固沙林内草本植物迅速侵入 ,其后则缓慢发展并处于相对稳定状态 ,植物种类数保持在 2 0～ 2 3种。但在人工固沙群落中 1年生植物在种类数和数量上始终处于优势地位 ,而天然群落则是多年生植物占优势。人工固沙群落物种多样性指数逐年提高 ,但明显低于天然群落。在受到大气持续高温干旱的干扰时 ,人工群落土壤条件极度恶化 ,出现了明显的干沙层 ,最深达 14 0 cm ,叶片含水量极度降低 ,植物生长停止。沙地植物群落对牲畜取食均具有一定的补偿的能力 ,在啃食较轻时表现为超补偿现象。通过建立数学模型分析 ,人工群落个体的补偿点和超补偿点明显低于天然群落。采用冗余理论对植物群落稳定性机制进行了论述 ,认为冗余结构的变化是导致群落稳定性变化的内在原因。对现有人工小叶锦鸡儿固沙林的稳定性进行了评价 ,并认为 15 a左右人工固沙林正处于相对稳定并缓慢发展状态。对于稳定的人工固沙群落应具备以下条件 :(1)适于当地环境条件 ;(2 )对外界?更多还原

【Abstract】 In north of China, the vegetation for wind protection and sand fixation was widely planted in last decades, playing an important ecological role in improving the agro-ecological systems in the region. Sustaining the desired functions of the plantations requires their stability of growth and development. Caragana microphylla, a species belonging to legume family, is a popularly adopted shrub for fixing moving sand dunes in Keerqin Desert, northern China. In the growing season of 1997, a severe drought lasted from May to July. Consequently, Caragana microphylla plantations were withered in numerous areas all over the western desert, providing us with an excellent opportunity to address the stability of Caragana microphylla plantations in comparison with natural ones. In Caragana microphylla plantations, the invasion and disappearance of plant species in response to the drought and grazing were investigated for describing the species dynamics and redundancy structure in the levels of community, population, and individual, respectively. The investigations indicate that herbaceous species invades into the plantations faster in the early development of the plantation and then the number of species fluctuates little. There are 20 herbaceous species at age of 15 and 23 at age of 35 in the plantations. In terms of the number of species, the Caragana microphylla plantations are dominated by annual species. Natural Caragana microphylla vegetation is, however, dominated by perennial species. Species diversity indexes in the plantations increase with age. These indexes in natural Caragana microphylla vegetations have the same trend, but significantly greater than those in the planted counterpart. In case of a continuous drought and high temperature, soil moisture content in the plantations decreases faster, forcing the dry layer of soil down to 140cm. With increasing in the transpiration of overabundant branches during the drought, the moisture content in leaves decrease so dramatically that the growth of plants halts. The experiment of removing branch shows that the plants in sandy land have the ability of compensation and overcompensation for grazing. Biomass of edible branches can be increased at low level of the removal and the compensation ability of branch decreases with the increase in height of the removal. The regression models describing the relationship between removal rate and branch growth are developed using the data in this experiment. The developed models show that compensation point on plants in the plantation is lower than that on plants in natural vegetation. Redundancy is an inherent feature of biological system and has a positive connection to compensation and stability of community. The degree of stability in a plantation relies on its quantity and structure of redundancy. The redundancy of the plantations is weakened as the result of high stand density, reducing the community’s resistance and resilience for disturbances. Therefore, the stand density is critical to the stability of the plantation. The planting design and management of the plantation should well define the appropriate stand densities for the Caragana microphylla plantations under different sit conditions. We conclude that vegetation for sand fixation would be stable if it could (1) adapt local environment conditions, (2) have some degree of resistance and resilience for disturbances, (3) normally grow and regenerate, and (4) have an integrated structure of population.更多还原