A step further towards quantitative reconstruction of past vegetation in Fennoscandian boreal forests: Pollen productivity estimates for six dominant taxa

Abstract

Pollen productivity estimates (PPE) are needed for producing quantitative reconstructions of the past landscapes by means of modelling. This study aims to provide estimates of relative pollen productivity for the two main tree species ( Pinus sylvestris L. and Betula sp .), for Cyperaceae and Gramineae, and the dominant dwarf shrubs ( Empetrum, Vaccinium sp .) of northern boreal forest vegetation in Finnish Lapland. A set of 24 moss samples were collected and their pollen content analysed, and detailed vegetation analyses were carried out within a 10.5 m radius around the samples. Vegetation further away, up to 10 km from the sites, was analysed from the Finnish Land Survey data. Vegetation proportions were calculated from the remotely sensed data using the program PolFlow, and distance weighting was applied using the program ERV_v6. The distance weighted vegetation data from the field survey and the Land Survey data were combined, and analysed with the pollen data using the ERV model. The resulting PPEs were evaluated by simulating pollen loadings with the POLLSCAPE model for an independent set of eight moss samples from the same area, using the obtained PPEs. The estimated pollen loadings and the observed pollen loadings were compared using paired samples t-tests. The PPEs obtained for the two major tree species are in keeping with expectations: PPE for Pinus is 8.4 (reference taxon Gramineae = 1) and for Betula 4.6. For Cyperaceae (0.002), Empetrum (0.07), and Vaccinium (0.01) the PPEs are very low and, according to paired samples t-test of the predicted and actual pollen loading, not reliable for Cyperaceae and Gramineae. The radius of the relevant source area of pollen (RSAP) is estimated to be ca. 1000 m. The pollen productivity estimates of the species, especially Pinus and Betula, are different in the northern boreal forest than in previously studied areas, such as southern Sweden. This has great implications for quantitative interpretations of fossil pollen records from the region.