Phytoliths and the Late Quaternary vegetation history of West Africa

植物硅体是一种有价值的古生态工具，是对花粉和植物大型化石的补充。对沉积物的植硅体研究可以结合和校准不同的信号，而其他植物学替代品也是可用的。草类花粉只能在家族水平上识别，但利用高度多样性的草类短细胞植硅体(GSCP)可以区分现代草原和古代草原。这在非洲尤其重要，那里的稀树草原和草原覆盖了非洲大陆最大的部分。拟议项目的主要目标是通过研究现代植物和土壤以及已发表其他植物学指标(花粉、木炭)的晚第四纪湖泊和河流序列中的植硅体组合，对西非植被历史作出创新贡献。在西非，古植硅体研究中的三个主要问题值得关注，并将被该项目考虑：1)区分草原群落，2)评估木本植物覆盖情况(森林-稀树草原问题)，3)检测人类影响。这项研究分为三个互补的工作包：WP 1)我们将研究从萨赫勒到几内亚地带400-1300毫米降水梯度上的现代土壤植硅体组合。在布基纳法索，主要目标是在不同稀树草原植被群落的植硅体光谱中分离气候、土壤和人为信号。在贝宁，我们将研究走廊和半落叶森林的土壤植硅体，以更好地区分森林类型。为了描述草原、稀树草原和森林群落的特征，我们将使用最近开发的GSCP分类系统和木本植物的详细形态特征(见WP3)。我们工作组最先描述的盆栽植物将有助于检测和量化人类的影响。基于对现代组合的统计评估，我们将测试新的植硅体指数，以便在第二步将其应用于化石样本。WP2)我们将重建萨赫勒和苏丹带(提拉湖和芒加草原/尼日利亚；奥恩朱古/马里)三个成熟的古生态序列的全新世和晚更新世草原的发育及其与气候波动的关系。我们还将测试考古证据表明，人类影响，主要是农业，是否可以在全新世晚期的萨赫勒和苏丹组合中检测到。对于Lac SéLé/贝宁的序列，主要问题是如何在植硅体记录中表现出从森林到稀树草原的明显转变，如花粉图所示，大约4500卡BP。为了更好地解释现代和古代沉积物中木本植物的信号，我们将研究现代乔木和灌木中的植物标本，以确定潜在的诊断形态类型。

Phytoliths (= plant silica bodies) are a valuable palaeoecological tool and complementary to pollen and plant macro-fossils. Phytolith studies on sediments for which other botanical proxies are available allow for combining and calibrating the different signals. While grass pollen is only identifiable to family level, with the highly diverse grass short cell phytoliths (GSCP) modern and ancient grasslands can be differentiated. This is especially important in Africa where savannas and grasslands cover the largest part of the continent. The major objective of the proposed project is an innovative contribution to the vegetation history of West Africa through the study of phytolith assemblages in modern plants and soils, and in Late Quaternary lake and fluvial sequences for which other botanical proxies (pollen, wood charcoal) have already been published. In West Africa, three major issues in palaeo-phytolith research merit attention and will be considered by the project: 1) distinguishing grassland communities, 2) assessment of the woody plant cover (forest-savanna question), 3) detecting human impact. The research is organized into three complementary work packages: WP 1) We will study modern soil phytolith assemblages along a precipitation gradient of 400-1300 mm from the Sahel to the Guinean zone. In Burkina Faso, the major objective is the separation of climatic, edaphic and anthropogenic signals in the phytolith spectra of different savanna vegetation communities. In Benin, we will study the soil phytoliths of gallery and semi-deciduous forests for a better discrimination of forest types. For characterizing the grassland, savanna and forest communities, we will use a recently developed GSCP classification system and detailed morphotypes characteristic for woody plants (see WP3). Commelinaceae phytoliths, first described by our working group, will help to detect and quantify human impact. Based on the statistical evaluation of the modern assemblages, we will test new phytolith indices to apply them, in a second step, to the fossil samples. WP 2) We will reconstruct the development of Holocene and Late Pleistocene grasslands and their correlation with climatic fluctuations for three well-dated palaeoecological sequences of the Sahelian and the Sudanian zone (Lake Tilla and Manga Grasslands / Nigeria; Ounjougou / Mali). We will also test if human impact, mainly agriculture, is detectable in the Late Holocene Sahelian and Sudanian assemblages, as suggested by archaeological evidence. For the sequence of Lac Sélé / Benin the major question is how the distinct shift from forest to savanna around 4500 cal BP, as visible in the pollen diagram, is represented in the phytolith record. WP 3) For a better interpretation of the signal for woody plants in the modern and ancient sediments, we will study herbarium material from modern trees and shrubs to identify potentially diagnostic morphotypes