干旱荒漠区斑块状植被格局及其生态水文效应研究

In the vast majority of arid lands in China, the need for large-scale programs aimed at restoring the ecosystem structure, composition and function has never been more pressing, revegetation is one of most successful measures to stabilize desert sand dunes. There is a paradox exists between the extensive revegetation processes and the restricted vegetation carrying capacity of arid lands due to the scarcity of soil moisture. In light of this, we choose the typical transitional zone between desert steppe and steppified desert at the southeast edge of the Tengger Desert, based on the experimental and numerical methods, to study the (1) composition and patterns of patchy vegetation, (2) influence of vegetation patches which consists of different dominant floristic compositions including woody plants (shrubs and dwarf shrubs), herbaceous plants and cryptogams on hydrologic cycle, (3) hydrologic cycle and its transformation relations among vegetation patches of mosaic in different sizes, (4) characteristics of the spatial distribution of soil moisture and its linkage between vegetation patches and bare patches, in order to explore the characteristics of water cycle and water balance that controlling vegetation pattern. Moreover, we are aiming at constructing such a model that can, under the influence of vegetation pattern, reflect the influence of ecosystem variations on the biological processes of water cycle in vegetation processes including the proportions of dominant floristic compositions forming the vegetation patches. A better understanding of the hydrologic effects on vegetation patches, by developing fundamental theories for reasonably regulating the composition of the patchy vegetation and the water cycling in arid regions, and, in theoretically, by solving the key scientific issue regarding interactions and feedbacks among water cycle and vegetation patterns in the revegetation processes of arid regions, with a mean annaul precipitation of less than 200 mm, are expected to provide a successful model for the establishment of artificial eco-protection system and to reach a sustainable ecosystem management in arid desert areas.

干旱荒漠区以不连续的植被斑块和裸地斑块镶嵌分布为主要特征，形成了独特的斑块状景观格局，水循环与斑块格局的耦联是维系干旱荒漠生态系统稳定演替的关键因素。本项目以观测试验与模拟分析相结合的研究方法，调查植被斑块的植物群落学特征、裸地与植被斑块镶嵌分布的结构特征（包括斑块类型指数、形状指数、面积比例、斑块分离度等），测定不同类型斑块的土壤水文物理特征参数并分析其空间变异性，表征裸地与植被斑块镶嵌分布对地表径流的截持与再分布过程，阐明裸地与植被斑块土壤水分空间变异性及其与土壤水文参数空间变异的内在联系，量化不同斑块对水循环的调控能力并揭示驱动斑块状植被格局形成的水循环机制，探明植被斑块变化的生态水文效应，建立水循环与斑块格局的耦联关系。本研究对揭示斑块植被格局的维持机制具有重要科学意义，对发展干旱区植被斑块与水文相互关系的生态水文学理论具有促进作用，对干旱区植被重建与生态功能恢复具有指导意义。

干旱区水与植被的反馈作用将水文和生态过程联系起来。水分在植被－土壤系统的再分布，是决定植被格局形成和演变的重要因素。土壤水分呈斑块分布比均匀分布更有利于提高生态系统生产力；反过来，植被格局亦影响水循环。荒漠植被景观具有高度的空间异质性，呈不连续斑块状分布格局，斑块内植株密集，植被盖度高，斑块周围植株稀疏，盖度较低甚至是裸地斑块。在不同时空尺度上，斑块状植被格局对驱动生态过程具有重要作用，对维持荒漠生态系统的稳定性及多样性具有重要的生态学意义。斑块格局具有动态变化的特点，包括众多原有斑块的不断破碎和新斑块的重新形成。植被斑块的破碎化使裸地不断增加，加剧了土壤及养分的流失，新的植被斑块的形成则可以使土壤和养分再次固定下来。.本项目选择腾格里沙漠东南缘荒漠草原向草原化荒漠过渡区，针对不连续的植被斑块和裸地斑块镶嵌分布格局，详细调查植被斑块的物种组成、空间分布状况，模拟分析斑块植被格局的跃变特征，基于早期信号理论检测其对斑块植被格局跃变的预警能力。利用张力计试验原位分析不同优势植物种（主要包括灌木、草本和隐花植物）构成的植被斑块对降水再分布的影响，定量研究植被和裸地斑块土壤水文物理参数及空间变异性，建立了裸地和植被斑块土壤水分与土壤水文物理参数空间变异的联系，辨析了不同斑块对水循环的调控作用，揭示了驱动斑块状植被格局形成的水循环机制，探明了植被斑块变化的生态水文效应，理论上回答了在降水不足200mm的干旱区驱动生态过程的关键生态水文学问题。在项目实施期间，发表研究论文23篇，其中SCI刊物收录论文17篇，论文总被他引73次，其中SCI收录刊物他引46次。本项目揭示的斑块状植被格局及其水文效应，不仅具有生态水文学理论意义，而且为干旱区人工生态防护体系建设及生态系统可持续管理提供重要依据。