Factors influencing changing AP/NAP ratios in NW-Europe during the late-glacial period

Abstract

In Quaternary deposits from the cool-temperate zone of the N. hemisphere, the changing ratios of arboreal and non-arboreal pollen are often considered as being indicative for mean summer temperatures. Detailed studies of Late-Glacial deposits in NW-Europe have shown that - apart from time needed for migration from the refugia - some other factors than temperature alone may have influenced the lack of trees during the first half of the Late-Glacial period. Such inter-related factors were: Oligotrophic conditions, a low biomass production, the initial absence, and the subsequently low content of humus in soils, and a fast process of mineralisation of the scarce plant remains as a consequence of relatively high temperatures. Also, soil covering crusts and toxic substances produced by Cyanobacteria initially may have delayed and hampered development of a dense herbaceous vegetation cover and the immigration of trees. A decline of summer temperatures during the Bolling-AIIerad interstadial may have triggered soil conditions that were more favourable for tree growth.