摘要
景观格局和生态过程之间的相互关系是景观生态学的核心问题之一,其二者相互关系根据特定的景观格局和生态过程又包含众多方面,干旱地区植被景观格局与水生态过程则为其中之一。干旱地区水分缺乏,以荒漠植被为主,具有蒸发量大、降水稀少的气候环境特征。干旱区内,水分因素在生态系统中占主导地位,植被景观格局在很大程度上随着水分环境的变化而相应演变。干旱地区植被景观格局与水生态过程的研究对干旱地区生态系统的保护和恢复具有重要意义。
黑河流域是我国西北地区第二大内陆流域,位于河西走廊中部,发源于祁连山脉,最终注入内蒙古额济纳旗,且在额济纳旗内孕育了额济纳天然绿洲。由于自上世纪60年代以来,黑河流域中游用水过度,使得进入额济纳天然绿洲的水量锐减,造成了一系列的生态环境问题。因此从2001年开始在黑河流域启动了分水工程,保证进入额济纳天然绿洲的水量,以促进绿洲内生态环境的恢复。
本文主要以黑河下游额济纳天然绿洲为研究对象,基于研究区2001-2009年MODIS影像、三个年份(1987、2001、2009)TM/ETM+影像以及2002年和2009年的实地植被样方调查,分别进行NDVI指数、景观格局指数和植被样方数据分析;并结合研究区内地表水、地下水数据,从多个层面和角度分析分水后研究区内水分环境动态变化对植被景观格局演变的影响,为干旱地区生态系统的保护和恢复提供参考。
主要结果表明:
①地表水是干旱地区植被生长所需水分的主要来源,能够通过下渗转化成地下水,直接影响植被生长及植被景观格局的演变;
②地表径流量和植被覆盖度之间具有正相关关系,地表以地表水为主导,地表径流量增加会引起植被覆盖度的增加,反之亦然,植被覆盖度会响应当年以及往年的地表径流量变化,且具有时滞性;
③地下水位的上升使得研究区内植被生长状况得到改善,植被密度、生长高度、盖度均有一定幅度提升,物种丰富度增加,且草本植物受地下水位影响最为明显;
④地下水位上升使得研究区整体景观格局趋于复杂化、多样化、均匀化,基质景观类型(戈壁滩)在景观中优势度降低,植被景观格局破碎化程度提高、趋于复杂化。
One of the core issues in landscape ecology is the relationships between the landscape pattern and hydro-ecological process, which contains many fields on the basis of specific pattern and process. The relationships between the dynamic vegetation landscape pattern changing characteristics and hydro-ecological process in arid regions are studied in the research into the correlation of vegetation landscape pattern and hydro-ecological process in arid regions. Due to climate featured by great amount of evaporation and scarce rainfall, arid regions are constantly in short of water and mainly covered by the desert vegetation; hence the hydro-ecological process dominating the ecological system as well as the changing of vegetation landscape pattern. To the arid region, the study of correlation between vegetation landscape pattern and hydro-ecological process is of great importance to the protection and restoration of the ecological system.
The Hei River is the second largest inland river in the northwest of China, which is located in Hexi Corridor, originated in Qilian mountains and flows into Ejina Banner of Inner Mongolia and gives birth to the Ejina natural oasis. Since the 1960s, as the overusing of water in the middle Hei River, the amount of water fall into Ejina natural oasis decreased markedly which lead to a series of ecological and environmental problems. Under these circumstances, the project of water distribution was launched in 2001 to promote the ecological system restoration of the oasis. This paper takes the Ejina natural oasis as the research subject. Adopting the remote sensing techniques and on-the-spot survey of vegetation quadrat, the NDVI index, landscape pattern index and data of vegetation quadrat are studied. Based on the surface water, underground water data, the correlation between vegetation pattern changing and dynamic changes of water ecological process are studied, in order to provide reference for the protection and restoration of the ecological system. The findings are as follows:
①Surface water is the main source of water for vegetation growth in arid regions, since it is transformed into underground water through the infiltration to affects vegetation growth directly.
②There is a positive correlation between the surface water and the coverage of vegetation which is dominated by the surface water. The increasing of the runoff will lead to the rising of the vegetation coverage and vice verse. Vegetation coverage will respond to the changes of surface water with a time lag.
③The vegetation growth condition was improved with the rising of underground water level:the vegetation density, growth height, coverage have certain improvements, species richness is increased and the change of herbaceous is most obvious.
④The landscape pattern of the subject area tends to be complex, diverse and uniform with the rising of underground water level. The dominance of the matrix landscape type (desert) is reduced, while the fragmentation of vegetation landscape pattern improves.
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