Patterns of modern pollen and plant richness across northern Europe

Sedimentary pollenoffers excellent opportunities to reconstruct vegetation changes over past millennia. Number of different pollentaxa or pollenrichness is used to characterise past plant richness. To improve the interpretation of sedimentary pollenrichness, it is essential to understand the relationship between pollenand plant richness in contemporary landscapes. This study presents a regional-scale comparison of pollenand plant richness from northern Europe and evaluates the importance of environmental variables on pollenand plant richness. We use a pollendataset of 511 lake-surface pollensamples ranging through temperate, boreal and tundrabiomes. To characterise plant diversity, we use a dataset formulated from the two largest plant atlases available in Europe. We compare pollenand plant richness estimates in different groups of taxa (wind-pollinated vs. non-wind-pollinated, trees and shrubs vs. herbs and grasses) and test their relationships with climate and landscape variables. Pollenrichness is significantly positively correlated with plant richness (r = 0.53). The pollenplant richness correlation improves (r = 0.63) when high pollenproducers are downweighted prior to estimating richness minimising the influence of pollenproduction on the pollenrichness estimate. This suggests that methods accommodating pollen-production differences in richness estimates deserve further attention and should become more widely used in Quaternary pollendiversity studies. The highest correlations are found between pollenand plant richness of trees and shrubs (r = 0.83) and of wind-pollinated taxa (r = 0.75) suggesting that these are the best measures of broad-scale plant richness over several thousands of square kilometres. Mean annual temperature is the strongest predictor of both pollenand plant richness. Landscape openness is positively associated with pollenrichness but not with plant richness. Pollenrichness values from extremely open and/or cold areas where pollenproduction is low should be interpreted with caution because low local pollenproduction increases the proportion of extra-regional pollen. Synthesis. Our results confirm that pollendata can provide insights into past plant richness changes in northern Europe, and with careful consideration of pollen-production differences and spatial scale represented, pollendata make it possible to investigate vegetation diversity trends over long time-scales and under changing climatic and habitat conditions.