Abstract
Modern pollen-rain studies are crucial for the calibration and interpretation of fossil pollen records. In East Africa, numerous pollen records provide important insights into the impact of human populations and climate change on tropical ecosystems. However, the confident use of fossil pollen data to reconstruct vegetation and climate dynamics requires well-founded knowledge regarding the relationship between pollen deposition and modern-day vegetation, which is still deficient for large parts of the African continent and non-existent for the tropical East African Mountains. In this study, we investigated the relationship between vegetation and modern pollen-rain along the elevational gradient of Kilimanjaro. We apply multivariate data analysis to assess the relationship between vegetation and modern pollen-rain and quantify the representativeness of forest zones. We further assessed the taxonomic level needed for differentiation between forest zones based on the modern pollen-rain assemblage, biodiversity patterns and pollen and spore drift. In the montane vegetation of Kilimanjaro, it is sufficient to analyse the pollen-rain on plant family level in order to derive the forest zone of the surrounding vegetation. Along this elevational gradient, pollen and spore dispersal is strongly influenced by regional wind patterns, but their deposition reflects the diversity patterns of the surrounding vegetation. This study represents the first statistical analysis of pollen vegetation relationship along an elevational gradient in Africa. Hence, this paper improves confidence in interpretation of palynological records from the tropical East African Mountains and may refine past climate reconstructions for a more accurate comparison of data and modelling.
Highlights
Modern pollen analogues are essential tools for palaeoecological reconstructions (Birks and Birks, 1980; Huntley et al, 2011)
We address the following questions: (1) how are the different plant taxa represented in the modern pollen-rain and why? (2) which taxonomic level is necessary to distinguish between the different forest zones observed in the vegetation? (3) are the biodiversity patterns of the modern vegetation reflected in the pollen-rain? and (4) what pollen drift effects do we observe by investigating and quantifying the modern pollen-rain–vegetation relationship along an elevational gradient on the southern slope of Kilimanjaro between 1900 and 3200 m a.s.l
The non-metric multidimensional scaling (NMDS) of the modern pollen-rain data (Figure 2) provides information on the differences between individual pollen traps and between different vegetation plots derived from the modern pollen-rain data based on identified pollen types and at family level
Summary
Modern pollen analogues are essential tools for palaeoecological reconstructions (Birks and Birks, 1980; Huntley et al, 2011). Only few of such calibration studies, which quantitatively relate pollen with altitude and climatic parameters, exist. Modern pollen calibration studies along latitudinal and longitudinal gradients in Africa demonstrate that pollen spectra within one particular vegetation zone are more similar to one another than these pollen spectra are to pollen samples from other vegetation zones (Gajewski et al, 2002); a good latitudinal correspondence exists between the distribution patterns of pollen in marine surface sediments and the occurrence of the source plants on the adjacent continent (Dupont and Wyputta, 2003; Hooghiemstra et al, 2006). Pollen-rain vegetation relationships along steep climatic gradients in the Neotropics show that pollen spectra closely reflect the vegetation composition of Amazonian montane forests (Urrego et al, 2011; Weng et al, 2004). Niemann et al (2010) show that a high number of pollen and spore taxa are characteristic for one vegetation type, and that they reflect the altitudinal distribution of genera and families in the modern vegetation
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