毛乌素沙地油蒿灌丛空间自组织格局及其生态水文响应机制

The human activities are enhancing in the arid and semi-arid region, we expect that the ecological environment can be improved through vegetation restoration, but it induced some negative ecological problems to exacerbate the regional water contradiction, such as the soil dry layers, water level dropping and reducing the runoff, and this is mainly because there did not consider the relationship of vegetation spatial pattern and ecohydrological processes in the vegetation restoration.Artemisia ordosica is an important species that fixed the sands in Mu Us sandy land. Understanding the ecohydrological response mechanism of spatial pattern of vegetation is a very important and key scientific problem for vegetation restoration in the area. By field observation, the project will analyze the characteristics of vegetation spatial self-organized pattern. And then the vegetation transpiration and soil moisture dynamics will be observed by field fixed observation and modeling to explore the relationship of shrub spatial pattern and ecohydrological processes, such as soil moisture and transpiration. The project will reveal the spatial self-organized pattern of Artemisia ordosica shrub and its ecohydrological response mechanism, and couple the relationships of vegetation spatial pattern and ecohydrological processes and validate the ecohydrological model and understand profoundly the mechanism of spatial pattern and ecohydrological processes. Based the Brook90 ecohydrological model, the project will simulate and evaluate the characteristics of soil moisture and evapotranspiration under the different vegetation spatial pattern scenarios to guide water resource regulation and vegetation restoration, such as the spatial distribution and densities in the vegetation restoration.

干旱半干旱区人类活动在增强，希望通过植被恢复改善生态环境，但却产生了土壤干化、地下水位下降等负面生态效应，这主要是由于植被恢复过程中没有考虑植被空间格局与生态水文的关系。油蒿是毛乌素沙地最重要的固沙植物，弄清其植被空间格局的生态水文响应机制是该地区植被恢复的基础和核心科学问题。项目针对毛乌素沙地油蒿灌丛生态系统，通过野外调查，分析油蒿灌丛空间自组织格局特征，利用定位观测和模型模拟等手段，分析油蒿灌丛植被蒸腾耗水和土壤水分动态，探索油蒿灌丛空间格局与土壤水、蒸腾耗水等生态水文过程的关系，揭示毛乌素沙地油蒿灌丛空间自组织格局特征及其生态水文响应机制，耦合植被空间格局与植物蒸腾和土壤水的关系，构建并验证生态水文模型，优化和修正模型参数，深刻理解油蒿灌丛空间格局对植被耗水与土壤水的作用机制，并基于改进的Brook90模型，模拟并评估植被空间格局变化的生态水文特征，指导植被恢复与水资源的合理调控。

毛乌素沙地是一个脆弱的自然、经济、社会的复合生态系统，以灌木为主的植被恢复重建是该区域具有代表性的生态工程，植被恢复改善生态环境过程中产生了土壤干化、地下水位下降等负面生态效应，这主要是由于植被恢复过程中没有考虑植被空间格局及其与生态水文的关系。本研究针对毛乌素沙地油蒿灌丛生态系统中植被分布类型，选取了多个油蒿灌丛样地，植被种类包括油蒿、柠条、油蒿+柠条、油蒿+紫花苜蓿及油蒿+草木樨，通过野外调查，基于点格局分析方法，对毛乌素沙地主要灌木空间分布格局及其空间关联性进行研究，并对油蒿灌丛存活-死亡状况及开花-未开花状况的空间格局进行分析，探究与之相关的潜在生态过程；结合研究区降水和土壤水分监测数据，对研究区降水特点及降水事件下固定沙地、半固定沙地和流动沙地三种类型土壤水分的响应进行了对比分析。研究发现毛乌素沙地中，油蒿、柠条、紫花苜蓿、草木樨在小尺度上主要呈现显著的聚集分布的空间格局，随着空间尺度的增加，聚集尺度不断减小，逐渐呈现出随机分布的空间特征，柠条和油蒿可以较好地共存于毛乌素沙地中，而紫花苜蓿、草木樨分别与油蒿可能存在竞争关系，导致油蒿种群的死亡；半固定沙地油蒿种群存活状态明显优于固定沙地，半固定沙地存活和死亡油蒿之间不存在竞争，固定沙地存活油蒿和死亡油蒿两者之间表现为高度竞争的关系。半固定沙地油蒿种群开花状态也好于固定沙地，半固定沙地开花与未开花油蒿之间互相促进，固定沙地开花与未开花油蒿种群则互相竞争；对研究区降水及三种类型沙地土壤水分分析表明降水以小于10mm的小降水事件为主，大降水量事件的降水占据全年降水总量的较大比例。降水后，土壤水分的补充受到降水模式（降水量、降水历时和降水强度）、土壤理化特性及初始含水量等因素的综合影响。

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