Spruce representation in zonal woodlands may be overestimated when using pollen spectra from peatlands

Abstract

The proportion of taxa in a pollen spectrum may not correspond to their proportion in vegetation. Quantitative reconstruction models therefore consider pollen productivities or fall speeds. We argue that azonal presence of spruce, an otherwise zonal tree species, in wetlands may confound the pollen-inferred reconstructions of vegetation cover as well. Based on a large database of vegetation plots from the Western Carpathians, we demonstrate that spruce is the tree species which most frequently colonizes peatlands, more so than alder, whose effect on local pollen spectra has been frequently admitted. Using 73 sequences we further demonstrated significantly greater pollen percentages of spruce of about 20–25% when the sediments contain spruce macrofossils. Finally, we compared the proportions of spruce and beech in modern surface pollen spectra with their real proportions in the surrounding landscape where beech acts as zonal tree. We found that even a small patch of spruce alters the proportion of spruce to beech. By contrast in an open fen we observed pollen spectrum corresponding well with the real proportions of spruce and beech. All these results suggest, contrary to the premises of current models of pollen-based quantitative reconstructions in Central Europe, that fossil pollen counts from wetlands did not underestimate the representation of spruce. Instead, its representation may even be overestimated where it occurred within or in close vicinity of a wetland. We appeal to palynologists to consider macrofossils or stomata in interpretations, and to adjust quantitative reconstruction models for sites that have experienced a woodland history.