Challenges in using modern pollen analogs for Cenozoic paleoecology: examples from the European Neogene

Valentí Rull

The use of modern pollen analogs in paleoecology is well established in Quaternary studies; however, the reliability of this approach decreases with increasing geological age due to evolutionary changes. Establishing a definitive chronological boundary beyond which modern pollen analogs remain reliable is currently unfeasible. This limitation affects not only paleoenvironmental reconstructions based on the niche conservatism hypothesis for individual extant species, but also community- and biome-level reconstructions that assume compositional and environmental constancy over time. This paper discusses three case studies from the European Neogene—focusing on individual species, communities, and biomes—where the use of modern pollen analogs under the untested assumption of niche conservatism is common. These studies include: (1) quantitative paleoclimatic estimations using the climatic envelope of extant species, (2) comparisons between Middle Miocene European mangroves and present-day Middle-East mangrove communities, and (3) the use of Artemisia pollen as an indicator of dry steppe biomes. The main conclusion is that assuming species' niche conservatism and extrapolating this assumption to communities and biomes is unwarranted and may lead to unsupported conclusions. Therefore, empirical testing of species’ niche conservatism across the relevant time spans is essential. Alternative and complementary methods—such as the fossil community approach and the use of pollen-independent proxies (e.g., stable isotopes, biomarkers)—are strongly recommended.