Statistically significant minimum pollen count in Quaternary pollen analysis; the case of pollen-rich lake sediments

The statistical reliability of a pollen count in representing the true composition of modern and fossil pollen assemblages depends on the minimum number of pollen grains counted. In palynological literature this number varies between <150 and >1000, but very few studies have probed the question using robust statistical approaches. Here, we use the Pearson-Brown Prophecy formula and apply it to different fossil pollen counts from two large lake systems in Iran to calculate the minimum terrestrial and total pollen count necessary to obtain a reliable representativity of pollen assemblages. Our results surprisingly show that a pollen count of <150 is sufficient to achieve a reliability of 0.90 with no additional significant information obtained when counting more pollen. If the upland vegetation reconstruction is important, then terrestrial pollen counts as low as 67 could be sufficient. It seems that the statistically significant pollen counts are site-specific and vary between different environments and even within the same type of environment. We suggest that this value should be calculated for each pollen site so that the pollen analysts can more efficiently manage their time when counting pollen slides.