云贵高原抚仙湖近13300年的花粉/炭屑记录

POLLEN/CHARCOAL RECORD OVER THE PAST 13 300 YEARS FROM FUXIAN LAKE IN THE YUNNAN-GUIZHOU PLATEAU

抚仙湖是云贵高原著名的断陷深水湖,其沉积物蕴藏着流域地质历史时期丰富的环境信息。对钻取自该湖的900cm湖泊沉积物岩芯进行花粉/炭屑分析及花粉数据的主成分分析表明,抚仙湖流域的植被、气候与火灾在过去的13 300年经历了5个阶段的变化:(1)13 300—10 400cal.a BP,植被以松林为主,伴有山地暗针叶林和常绿阔叶林,表明该时期气候较为冷湿,森林火灾多发,在后期随着温度和湿度的降低,森林火灾愈加频繁。(2)10 400—5 700cal.a BP,松林收缩,常绿阔叶林扩张,出现一定数量的落叶阔叶林,显示该时期气候偏暖偏干;此阶段早期随着气候变暖变干森林火灾的发生延续上阶段高发的状态,直到9 500cal.a BP后随着湿度的增加森林火灾明显减少。(3)5 700—1 800cal.a BP,松林变化较小,常绿/落叶阔叶林比重增大,首次出现了暖热性的枫香林,显示该时期暖湿的气候特征,火灾发生频率低。(4)1 800—500cal.a BP,松林扩张,阔叶林收缩,本阶段后期草本植被比重开始增加,显示该时期气候相对冷干,森林火灾发生频率较高。(5)500cal.a BP至今,松林收缩,落叶阔叶树种增多,草本植物花粉明显增多,显示该时期气候温凉偏干,森林火灾发生频率降低。

Fuxian lake on sediments Lake is a well-known rift deep-water the Yunnan-Guizhou Plateau. Its contain abundant environmental information in its drainage region during geologic times. Pollen/charcoal analysis on 46 samples from a 900 cm core of this lake provides a history of vegetation, climate, and forest fire in its drainage region during the last 13 300 years. The results of pollen/charcoal analysis and principal component analysis on pollen data show five-stage vegetation succession, climate change, and forest fire. 1） 13 300--10 400 cal. a BP, the vegetation was dominated by pine forests, accompanied by dark coniferous forests and evergreen broadleaved forests, indicating cold and wet conditions; high frequent forest fires occurred in this stage, and especially more fires appeared as the humidity decreased in its late period. 2） 10 400--5 700 cal. a BP, the shrinkage in pine forest, expansion in evergreen broadleaved forest, and appearance of deciduous broadleaved forest indicated relatively warm and dry conditions; forest fires occurred frequently like the previous stage as climatic conditions became warm and dry at the early period of this stage until 9 500 cal. a BP, when relative humidity increased and forest fires decreased obviously. 3） 5 700-1 800 cal. a BP, the pine and evergreen broadleaved forests still dominated, but Liquidambar forests favoring warm and hot climate first appeared, showing warm and wet conditions; the occurrence frequency of forest fire was low. 4） 1 800-500 cal. a BP, the expansion of pine forest and the shrinkage of deciduous broadleaved forest with an increase of upland herbaceous plants indicated relatively cold and dry conditions; forest fires were more than the preceding stage but less than the first stage. 5） 500 cal. a BP to the present, the shrinkage of pine forests and a significant increase of upland herbs showed cool and dry conditions, and suggested increasing human activities.