青藏高原全新世植被的时空分布

Temporal-Spatial Distribution of the Holocene Vegetation in the Tibetan Plateau

根据青藏高原 30个点湖泊的孢粉记录综合研究显示 :在进入全新世之前 (12kaBP以前 )除最东南部外 ,高原从东到西均发育为荒漠草原植被 .全新世早期 (12～ 9.0kaBP)高原东南部 (10 4°～ 98°E)为落叶阔叶林 /针阔叶混交林 ,季风已进入本区 ,气温比前期上升 2～ 4°C ,降水波动于 35 0～ 5 5 0mm之间 .中部 (98°～ 92°E)为草甸或灌丛草甸 ,再向西至 80°E左右为草原植被 ,气候寒冷干燥 ,平均气温比现在低 4.5～ 5 .5℃ .最西部 10 .5～ 9.9kaBP出现相当于欧洲新仙女木气候倒转事件 .全新世中期 (9.0～ 3.2kaBP)高原由东向西古植被依次发育为针阔混交林或硬叶阔叶林 (10 4°～ 98°E)→针阔混交林 (98°～ 80°E)→灌丛草甸→草原 (92°～ 80°E) .中期气候比早晚期温暖湿润 ,东南部 1月份气温高于现在 3℃ ,年降水量比现今多 2 5 0mm以上 .中西部气候温暖湿润 ,出现高湖面期 ,年均温高出现在 5℃以上 ;全新世晚期 (3.2kaBP以后 )由东向西古植被依次为硬叶阔叶林→针阔混交林→草甸→草原→荒漠 ,气温降水呈非线性下降 ,越向西下降幅度越大 .东南部 1月份气温比中期下降 4～ 4.5℃ ,年降水少 35 0mm ,东北部最冷月气温比中期下降 8℃左右 .中西部严重干旱 ,湖面降低 。

On the basis of pollen records in the lake cores from 30 sites in the Tibetan Plateau, the temporal-spatial distribution of vegetation, climatic changes and the South Asian monsoon development in the plateau in the Holocene are studied. During the early Holocene (12 ～ 9 ka BP), mixed conifer and deciduous broad leaved forest and mixed deciduous broad leaved forest dominated the vegetation in the east of the plateau (104°～ 98° E). At that time the South Asian monsoon was stronger, with mean annual temperature 2 ～ 4 ℃ higher than that prior to the Holocene and annual precipitation raging from 350 to 550 mm. In the middle of the plateau (98 °～ 92 ° E), meadows or shrub meadows appeared, with annual temperature 4 ～ 4.5 ℃ lower than that of present. Farther west about 80° E, there was a steppe vegetation landscape, which indicated a cold and dry climate.During the middle Holocene (after 9 ～ 3.2 ka BP), from the east to the west of the plateau, the paleo vegetations were, sequentially, mixed conifer and deciduous broad leaved forest or sclerophyllous broad leaved forest conifer (104 °～ 98° E) and mixed deciduous broad leaved forest (98°～ 92° E) or shrub, meadow and steppe (92°～ 80° E). The climate was warmer and wetter than that of the early Holocene. In the southeast, the January temperature was 3 ℃ higher than that of present and the annual precipitation was 250 mm more than that of present. In the northeast, the middle and the south of the plateau, the January temperature was 5 ℃ higher than that of present; and in the west it was 4 ℃ higher than that of present. During the late Holocene (after 3.2 ka BP), from east to west, the paleo vegetations were, sequentially, sclerophyllous broad leaved forest mixed conifer, deciduous broad leaved forest, meadow, steppe and desert. Drop of temperature and precipitation was nonlinear. The January temperature and the July temperature of the southeast were 4 ～ 4.5 ℃ and 3 ～ 3.5 ℃ lower than that of the middle Holocene, respectively, and annual precipitation was 350 mm lower. In the northeast, the forest shrank back and the coldest month temperature was about 8 ℃ lower than that of the middle Holocene. Lake water descended obviously in the west, indicating a very dry climate. Above all, the timing of vegetation and climatic changes supported the result of global climatic-model experiments that suggested a strengthened monsoon system during early to middle Holocene followed by a weakened monsoon system. The South Asian monsoon became stronger from 11 ka BP to 7 ka BP and weakened gradually from 7 ka BP to the present..