A global review of functional vegetation paleoecology and the integration of plant traits with fossil pollen

Understanding long-term changes in vegetation functional composition is essential for interpreting ecosystem responses to environmental change. However, most trait-based ecological studies focus on contemporary ecosystems, overlooking the long-term dynamics that can be revealed through paleoecological archives. Functional vegetation paleoecology addresses this gap by linking plant functional information with fossil pollen records, providing a means to investigate past ecosystem properties and vegetation dynamics over millennial timescales. Despite growing interest in this approach, its methodological development and current applications have not been comprehensively assessed. Here, we present a systematic review and quantitative synthesis of 62 case studies published between 1996 and 2025, examining publication trends, spatial and temporal coverage, sources of pollen and functional information, and methods used to link them. Our results reveal a gradual shift from approaches based primarily on plant functional types (PFTs) and biome classifications towards the use of quantitative plant functional traits. However, the field remains geographically uneven, with most studies concentrated in the Northern Hemisphere, and predominantly focuses on the Holocene. We also identify substantial methodological heterogeneity, particularly in how functional information is assigned to fossil pollen types. Most studies rely on specialised linking tables, while only a small proportion use probabilistic approaches to account for taxonomic uncertainty. This uncertainty represents a major challenge, as individual pollen types may encompass multiple plant taxa with different functional characteristics. We argue that future progress requires reproducible methodological frameworks that explicitly account for uncertainty in pollen-plant relationships and trait estimates, alongside greater use of global datasets and validation against modern vegetation. Addressing these challenges will help advance functional vegetation paleoecology towards a more robust quantitative framework for understanding long-term ecosystem dynamics.