The openess of the present-day landscape reflected in pollen assemblages from surface sediments in lakes : a first step towards a quantitative approach for the reconstruction of ancient cultural landscapes in south Sweden

Abstract: Summary: The aim of this study was to analyse how the composition and in particular the openess of the present-day landscape is reflected in pollen assemblages from surface sediment in lakes. The study is a continuation of an earlier pilot study including thirteen sites and a first step in an attempt to find a method of quantifying ancient cultural landscape in terms of surface areas from fossil pollen records using the modern analogue approach. Surface sediments from twenty two small lakes (0.5-20 ha) located mainly in the forest region of south Sweden were collected and analysed for pollen. The composition of the landscape surrounding the lakes within a 1000 m and 500 m radius was mapped using aerial photos. Despite the large variation in openess of the landscape mapped the variation of the relationship AP/NAP was low. This contrasts with the results of the pilot study in which the sites were selected mainly in the agricultural region of south Sweden and the variation of the relationship AP/NAP was higher. The pollen and landscape data were analysed using numerical ordination techniques, PCA and RDA. Despite the fact that the compositional gradient of the pollen assemblages was small it was possible to detect a pattern of variation and to analyse to what extent landscape data could explain the pollen data. The two dominant pollen taxa Betula and Pinus are uncorrelated to relevant landscape units such as coniferous forest and deciduous forest. This implies that these taxa are primarily of regional origin and can not be directly related to the local landscape around the lakes. Gramineae, Cerealia, Filipendula and Salix are positively correlated to cultivated land within both radius. Quercus and Fagus have a positive correlation with deciduous forest within 1000 m radius but not within 500 m radius. Therefore, it is suggested that the landscape units cultivated land and deciduous forest within 1000 m radius are reasonably well reflected in the pollen assemblages and that this radius is a good approximation of the relevant pollen source area of such sites. An important conclusion of this work is also that the performance of the modern analogue approach is improved if the modern data set is collected in the same vegetation region as the fossil pollen record used for reconstruction of past landscapes.