Vegetation, climate and fire-dynamics in East Africa inferred from the Maundi crater pollen record from Mt Kilimanjaro during the last glacial–interglacial cycle
Vegetation, climate and fire-dynamics in East Africa inferred from the Maundi crater pollen record from Mt Kilimanjaro during the last glacial–interglacial cycle
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DOI：
10.1016/j.quascirev.2012.02.003
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发表时间：
2012-04
影响因子：
4
通讯作者：
L. Schüler;A. Hemp;W. Zech;H. Behling
中科院分区：
文献类型：
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作者：
L. Schüler;A. Hemp;W. Zech;H. Behling
位于乞力马扎罗山东南坡海拔2780米的芒迪陨石坑的花粉、木炭和沉积学记录是赤道东非最长的陆地记录之一，使人们对最后一次冰川早期的植被和气候动态有了有趣的洞察。我们的沉积物记录有可靠的年代学，直到42年。年龄深度模型的外推，以及与热带东非其他古记录的匹配，表明记录底部的总年龄约为90亿年前。在末次冰期，植被带的分布和组成发生了变化，这些植被带分为高山稀树草原、亚山林地、山地森林、橡胶带和高山植被。末次冰期早期以大量的禾本科和菊科花粉为特征，表明该冰期气候干燥但稳定。根据在70ka BP左右沉积的样品中没有花粉颗粒的情况，我们假设发生了明显的干旱时期。在LGM(末次冰盛期)之前，记录到了较高的类群多样性，表明森林和灌木植被的分布，从而指示了一个更湿润的时期。在记录的时间跨度内，分类群多样性稳步增加。植被带的下沉表明末次冰期期间的干燥和寒冷条件，似乎对许多分类群有害，特别是森林植被；然而，末次冰期早期似乎明显比末次盛冰期更干燥。在去冰期和全新世期间，大多数分类群(最重要的是AlChemilla、Araliaceae、Dodonea、Hagenia、Ilex、Myrine、Moraceae、Piperaceae)的重现表明了向湿润条件的转变。全新世期间蕨类植物的增加和草本植物的减少也表明湿度增加。火对红壤带和林线的发育和抬升起到了重要的控制作用。在全新世期间，没有观察到茂迪陨石坑周围的人为影响增加，因为既没有记录到更高的火灾活动，也没有记录到嗜水植物的扩散。这份花粉档案揭示了上层植被带(橡胶带和山地林区)至少1100米的变化，但强调了乞力马扎罗山作为类似于东弧山脉的山地森林物种的冰川避难所的作用。
The pollen, charcoal and sedimentological record from the Maundi crater, located at 2780 m elevation on the south-eastern slope of Mt Kilimanjaro, is one of the longest terrestrial records in equatorial East Africa, giving an interesting insight into the vegetation and climate dynamics back to the early last Glacial period. Our sediment record has a reliable chronology until 42 ka BP. An extrapolation of the age-depth model, as well as matching with other palaeo-records from tropical East Africa, suggest a total age of about 90 ka BP at the bottom of the record. During the last Glacial the distribution as well as the composition of the vegetation belts classified as colline savanna, submontane woodland, montane forest, ericaceous belt, and alpine vegetation changed. The early last Glacial is characterized by high amounts of Poaceae and Asteraceae pollen suggesting a climatically dry but stable phase. Based on the absence of pollen grains in samples deposited around 70 ka BP, we assume the occurrence of distinct drought periods. During the pre-LGM (Last Glacial Maximum) a higher taxa diversity of the ericaceous and montane zone is recorded and suggests a spread of forest and shrub vegetation, thus indicating a more humid period. The taxa diversity increases steadily during the recorded time span. The decent of vegetation zones indicate dry and cold conditions during the LGM and seem to have been detrimental for many taxa, especially those of the forest vegetation; however, the early last Glacial seems to have been markedly drier than the LGM. The reappearance of most of the taxa (most importantly Alchemilla, Araliaceae, Dodonea, Hagenia, Ilex, Myrsine, Moraceae, Piperaceae) during the deglacial and Holocene period suggest a shift into humid conditions. An increase in ferns and the decrease in grasses during the Holocene also indicate increasing humidity. Fire played an important role in controlling the development and elevation of the ericaceous zone and the tree line. During the Holocene no increased anthropogenic impact around the Maundi crater can be observed, since neither higher fire activity nor a spread of hemerophilic plants is recorded. This pollen archive reveals shifts in the upper vegetation zones (ericaceous zone and montane forest zone) of at least 1100 m but underlines the role of Mt Kilimanjaro as a glacial refuge for montane forest species similar to that of the Eastern Arc Mountains.