Pollen richness is not equivalent to plant species richness:

Because climate variables have varied in the past with respect to one another palaeoecological records of species richness could improve models of species richness and help with future biodiversity modeling. Fossil pollen has been used as a proxy for past plant richness but the relationship between pollen and the parent plat community is affected by the low taxonomic resolution of pollen and taphonomic processes (pollen production, transport, deposition and preservation), which may degrade the degree to which pollen accurately represents vegetation communities.

By combining pollen data from modern lake sediments (n = 546; n = 167 in British Columbia, Canada) in the Pacific Northwest and a detailed data base (n = 16 071) of plant presence across British Columbia we were able to test whether pollen richness can act as a proxy for regional patterns of plant richness. Ultimately, we find that palynological richness cannot be considered a reliable proxy for inferring plant richness in British Columbia, even though changes in richness have been reported in the literature.