Pollen–vegetation relationships in the central Caspian (Hyrcanian) forests of northern Iran

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We studied pollen–vegetation relationships along an altitudinal transect in the Caspian (Hyrcanian) forests of northern Iran. We collected surface samples from 20 plots of 400 or 625m2 in the major forest communities and compared pollen percentages of the most abundant plant taxa with the vegetation abundances (cover and basal areas) in the pollen plots and in areas of different radii (100, 250, 500 and 1000m) around the pollen plots using both linear regression and qualitative methods. The results show that anemophilous taxa (i.e. Quercus, Fagus, and Carpinus) in general produce more pollen relative to entomophilous taxa (i.e. Acer, Parrotia, Diospyros, and Hedera). Taxa with light pollen grains, such as Quercus and Carpinus, show large positive intercepts in linear regression analysis, while heavier pollen grains or those possessing a patterned exine, such as Diospyros, Parrotia, Acer, and Hedera show small or even negative intercepts. Larger intercepts indicate that a higher proportion of pollen in the samples arrives from outside the area covered by the vegetation analysis. Our findings indicate that light pollen grains are deposited more slowly than heavy pollen grains. Dissimilarity matrices using the Bray–Curtis index showed that the overall relationship between species composition of vegetation plots and pollen assemblages is better for the areas with 100m radius than for the pollen plots.