Holocene treeline shifts and monsoon variability in the Hengduan Mountains (southeastern Tibetan Plateau), implications from palynological investigations
Holocene treeline shifts and monsoon variability in the Hengduan Mountains (southeastern Tibetan Plateau), implications from palynological investigations
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DOI：
10.1016/j.palaeo.2009.12.001
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发表时间：
2010-02-01
影响因子：
3
通讯作者：
Zhang, Chengjun
中科院分区：
文献类型：
--
作者：
Kramer, Annette;Herzschuh, Ulrike;Zhang, Chengjun
通过对纳伦湖沉积岩芯上部8.45m的孢粉和木炭含量的分析，研究了青藏高原东南部自更新世-全新世过渡(11.7cal KYR BP)以来的植被、气候和人类活动的变化。花粉指示类群、花粉总数、生物作用和多变量分析的应用帮助重建了全新世的环境条件。此外，还对青藏高原东南部及其前陆的表层样品进行了分析，以探讨现代花粉组合与植被的关系。现代植被通过花粉指示类型记录在表层花粉组合中，尽管沉积物中也含有花粉光谱，这被认为是TP东南边缘陡峭的海拔梯度的结果，从较低的植被带输送的区外花粉。不同植被带与现代采样点温度的关系被用来推断全新世记录的定量温度趋势。全新世初期森林的扩展标志着向更温暖条件的转变。从10.7到类似4.4卡的KYR BP，在纳冷湖发现了疏松-白桦林，可能反映了比现在更强的夏季风。温度范围重建表明，当时的气温比现在高出2-3摄氏度，树线位置比现在高出400-600米。气候严重恶化，气温比以前低约1-2摄氏度，8.1至7.2卡路里BP之间的撤退森林记录了这一点。森林后退，而亚高山杜鹃灌木在纳冷湖周围蔓延，表明在4.4卡基尔BP之后，气温比全新世早期和中期水平低1-2摄氏度。森林减少4.4卡KYR BP被认为反映了气候条件，因为在此期间发现的低浓度木炭颗粒排除了人为火灾作为森林撤退的原因。然而，放牧指标表明，自3.4 KYR BP以来，人类对纳冷湖周围的环境产生了影响。因此，我们认为3.4卡KYR BP的树线快速移动部分是由人类活动造成的，部分是由气候条件造成的。(C)2009爱思唯尔B.V.保留所有权利。
The upper 8.45 m of a sediment core from Lake Naleng were analysed for its pollen and charcoal content to detect vegetation, climate, and human activity changes on the southeastern Tibetan Plateau (TP) since the Pleistocene-Holocene transition (11.7 cal kyr BP). The application of pollen indicator taxa, pollen sums, biomisation, and multivariate analysis helped to reconstruct environmental conditions during the Holocene. Furthermore, 64 surface samples from the southeastern TP and its foreland were analysed to investigate the relationship between modern pollen assemblages and vegetation. The modern vegetation was recorded in the surface pollen assemblages by pollen indicator types, although sediments also contain pollen spectra extra-regional pollen transported from lower vegetation belts, which is seen as a consequence of steep elevation gradients at the southeastern margin of the TP. The relation between different vegetation belts and temperature from the modern sample sites was used to infer quantitative temperature trends for the Holocene record.Spreading of forests at the beginning of the Holocene marks the transition to warmer conditions. From 10.7 to similar to 4.4 cal kyr BP open Abies-Betula forests were found at Lake Naleng probably reflecting a stronger-than-present summer monsoon. Temperature range reconstructions suggest a temperature that was about 2-3 degrees C warmer and a treeline position that was 400-600 m higher than today. A severe climate deterioration with temperatures about 1-2 degrees C colder than before is documented by a retreating forest between 8.1 and 7.2 cal kyr BP. Forests retreated while subalpine Rhododendron shrubs spread around Lake Naleng indicating colder conditions with temperatures 1-2 degrees C below early and mid Holocene level after 4.4 cal kyr BP. The forest decline at 4.4 cal kyr BP is considered to reflect climatic conditions as low concentrations of charcoal particles found in this period exclude human-induced fires as reason for the forest retreat. However, grazing indicators imply human influence on the environment since 3.4 cal kyr BP around Lake Naleng. We therefore consider the rapid treeline shift seen at 3.4 cal kyr BP as partly generated by human activity and partly by climatic conditions. (C) 2009 Elsevier B.V. All rights reserved.