Phytoliths and the Late Quaternary vegetation history of West Africa

植物岩（=植物硅体）是一种有价值的古生态学工具，是花粉和植物宏观化石的补充。沉积物中的植物岩研究可以结合和校准不同的信号，而其他植物代用物是可用的。草花粉仅在科水平上可识别，而草短细胞植物岩（GSCP）多样性高，可区分现代和古代草地。这在非洲尤其重要，因为稀树草原和草原覆盖了非洲大陆的大部分地区。拟议项目的主要目标是通过研究现代植物和土壤中的植物岩组合，以及已经发表了其他植物代用物（花粉、木炭）的晚第四纪湖泊和河流序列，对西非植被史作出创新贡献。在西非，古植物岩研究中的三个主要问题值得关注，并将在该项目中考虑：1)区分草地群落，2)评估木本植物覆盖（森林-稀树草原问题），3)检测人类影响。该研究分为三个互补的工作包：WP 1)我们将沿着从萨赫勒到几内亚地区400-1300毫米的降水梯度研究现代土壤植物岩组合。在布基纳法索，主要目标是在不同稀树草原植被群落的植物岩光谱中分离气候、土壤和人为信号。在贝宁，我们将研究廊道林和半落叶林的土壤植物岩，以便更好地区分森林类型。为了描述草原、稀树草原和森林群落，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）。我们的工作组首先描述的Commelinaceae植物岩将有助于检测和量化人类的影响。在对现代组合进行统计评估的基础上，我们将测试新的植物岩指数，并在第二步将其应用于化石样品。WP 2)我们将重建全新世和晚更新世草原的发展及其与气候波动的关系，并对萨赫勒地区和苏丹地区3个确定年代的古生态序列（Lake Tilla和Manga grass /尼日利亚；Ounjougou /马里）进行研究。我们还将测试人类的影响，主要是农业，是否如考古证据所表明的那样，在全新世晚期的萨赫勒和苏丹组合中可以检测到。对于Lac s<s:1> /贝宁的序列，主要问题是如何在植物岩记录中表示4500 cal BP左右从森林到稀树草原的明显转变，如花粉图中所示。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的植物标本室材料，以确定潜在的诊断形态

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