摘要
对于本次间冰期以来黄土高原是否存在大面积森林植被的问题一直存在争议，本文通过对渭南、宝鸡和兰州剖面的植物硅酸体记录研究表明，末次间冰期以来，在黄土高原南部，主要发育草原和森林草原的植被类型，只有在气候最适宜期年降水量超过800mm以上，才可能有短期的森林植被发育。在黄土高原源区发育森林植被所需要的降水量要比基岩山地高250mm以上。
There are two kinds of views concerning whether there was an extensive naturalforest in the Loess Plateau since Late Pleistocene. Some researchers assert that nonatural forest has occurred on the plateau surface for at least the last 600 000a, andherb plants have been the dominant vegetation community. Forest vegetation isconsidered to be present only in a few comparatively short bine intervals in thesouthern part of the Loess Plateau during the last 100 000a. Other researchers suggested an extensive natural forest developed during historical Period, which coveredalmost three-fifth area of the plateau. The present lack of forest growth on the plateauwas explained as due to human activities. Actually, interpretation of the nearalvegetation succession on the Loess Plateau since the Late Pleistocene is of specialimportance in loess-based pale0-climatological studies as it usually serves as the basisfor interpreting environmental changes. It also provides the basic information forestimating the human impact on environmental changes.This paper presents a new result of phytolith analysis from three loess sections ofthe Late Pleistocene to characterize the natural vegetation succession in the southernpart of the Loess Plateau,especially the plain areas, through the comparison with thedistribution of modem phytolith pattern using mathematic methods.Weinan and Baoji loess-paleosol sequences are located in the southern parts of theLoess Plateau, both in the warm temperate zone with broad-leaved deciduous forestgrowth. Lanzhou loess section, in the western part of the plateau, is located in thesemi-arid temperate zone with dry steppe vegetation nowdays. In this study, Phytolithassemblege of 156 samples has been analyzed for the Weinan section, 59 samples forthe Baoji section, and 57 samples for the Lanzhou section. A great quantity ofphytoliths have been found in almost all samples. Based on the variations of phytolithassociahons in the three studied sites, 6 phytolith zones were identified for both theWeinan and Baoji sections, and 4 zones for the Lanzhou section. In order to clarifythe relationship between phytolith associations and vegetation communihes, 153 modemphytolith associations from the surface soils have been used to determine thevegetation communities related to climatic conditions. In so doing, 15 groups ofphytolith associations have been recognized, corresponding to 15 vegetationcommunities with specific climatic regimes. Using mathematic discriminant methods(Bayes' step discriminant method, the shortest distance method and para-equilibrationmethod), the authors are able to distinguish the phytolith associations from loess strataand funther relate them with corresponding vegetation communities.The results obtained show that 1) An extreme dry desert and steppe vegetationcommunity developed in the Guangzhong region of the southern pod of the LoessPlateau during the deposition period of loess L2. At the optimum period of S1developmenta broad-leaved deciduous forest and temporary forest-steppe vegetationoccurred in the Weinan area, while a forest-steppe vegetation in Baoji area waspunctuated by a few comparatively short intervals of broad-leaved deciduous forest 2)During the formation of Malan Loess (L1), in the western part of the loess Plateau adesert steppe covered the Lanzhou region, and temporary steppe and dry steppedeveloped in warmer periods. In the southern part of the Loess Plateau, typical steppeor dry steppe dominated the Weinan and Baoji areas. In the colder periods the drysteppe and desert steppe appeared, while in warmer periods forest-steppe and broad-leaved deciduous forests developed. In the Holocene, a steppe vegetation occurred inthe Lanzhou area, and a forest-steppe existed in the Guangzhong area with the broad-leaved deciduous forest growing temporarily. Thus, steppe and forest-steppe were thedominant vegetation community in the southern part of the Loess Plateau since theLate Pleistocene. Temporary forest vegetation occured only at the optimum periodswithin annual mean precipitation perhaps over 8
出处
《第四纪研究》
CAS
CSCD
北大核心
1999年第4期336-349,共14页
Quaternary Sciences
基金
国家自然科学基金!49771078
中国科学院"九五"重大项目!KZ951-A1-402
