A 22 570-year record of vegetational and climatic change from Wenhai Lake in the Hengduan Mountains biodiversity hotspot, Yunnan, Southwest China

[摘要] The Hengduan Mountains, with their strong altitudinal vegetationzonation, form a biodiversity hotspot which offers the potential forcomparison between sites in order to understand how this zonation arose andhow it has responded to climate change and human impacts through time. Thispaper presents a 22 570-year pollen record of vegetational and climatic changebased on a core 320 cm in depth collected from Wenhai Lake on JadeDragon Snow Mountain, one of the highest peaks in the Hengduan Mountainsregion of Yunnan, Southwest China. From 22 570 to 21 140 cal yr BP, thevegetation was dominated by broad-leaved forest (comprising mainlyQuercus, Betula and Castanopsis), accompanied by needle-leaved forest (mainly Pinus and Abies), indicating arather cold and dry climate relative to the present followed by cold and wetconditions. In the period between 21 140 and 19 350 cal yr BP, thevegetation was still dominated by broad-leaved forest and needle-leavedforest as before but with a notable increase in Betula pollen and a sharp decreasein Quercus pollen, implying a relatively cold and dry climate with severalfluctuations in humidity. The period 19 350 to 17 930 cal yr BP was atransition stage from broad-leaved forest to needle-leaved forest, with adramatic decrease in Quercus pollen and a maximum reading for Abies pollen, reflectingthe coldest and driest climate since 22 570 cal yr BP. The expansion inneedle-leaved forest dominated by Pinus and Abies (22 570–17 930 cal yr BP) alongwith an increase of Betula might correspond to the Last Glacial Maximum (LGM; thestart of the LGM perhaps occurred prior to the basal age of the core).Between 17 930 and 9250 cal yr BP, needle-leaved forest declined andbroad-leaved forest began to increase at first, suggesting increases intemperature and humidity, while towards the end of the period, needle-leavedforest expanded and broad-leaved forest shrank, indicating a colder anddrier climate, possibly corresponding to the Younger Dryas. From 9250 cal yr BP to the present, the vegetation has been dominated by needle-leavedforest (comprising mainly Pinus, Abies and Tsuga), interspersed with broad-leaved Quercus andBetula, reflecting a significant decline in humidity from the early to lateHolocene. During this period, human activity likely increased in thisregion, with impacts on the vegetation such as a distinct decrease inPinus and Quercus pollen and an increase in Polygonaceae pollen in the upper 30 cm ofthe core. The marked decline in Quercus pollen compared with the early stage ofthis period, in particular, in the Wenhai core can be correlated with thatobserved in the Haligu core (situated about 2 km away) between 2400 cal yr BP and the present.

[学科分类] 地球化学与岩石