Applying a unified framework to compare taxonomic, functional and phylogenetic diversity in Holocene pollen records

1. Biodiversity is multifaceted, encompassing taxonomic, phylogenetic and functional dimensions of biological variation. Long‐term studies which compare these dimensions across a range of environments elucidate ecosystem dynamics and responses to environmental change. A recently developed quantitative framework allows measurement of taxonomic, phylogenetic and functional diversity in equivalent, abundance‐sensitive units, so that these three dimensions of diversity can be directly compared. This framework has been implemented for both alpha diversity (iNEXT.3D) and beta diversity (iNEXT.Beta3D).
2. We adapt this framework for application to pollen records, a major source of data on long‐term ecological change. To the best of our knowledge, this is the first application of the new framework to pollen records. We used the framework to compare dimensions of diversity during shifts in woodland extent and composition in northern Scotland, focusing on two sites with contrasting climatic and vegetation histories. These records capture responses to c. 8000 years of climatic and land‐use change.
3. We found that despite persistent woodland cover, the less exposed site exhibits large variations in taxonomic, phylogenetic and functional diversity and composition, including a decline across all dimensions of diversity since 1200 cal year BP. Since around 7500 cal year BP, the exposed site shows more stable biodiversity across all three dimensions. We attribute these differing dynamics to habitat heterogeneity at the less exposed site and slow ecological processes (e.g. peat expansion and regeneration failure in trees) at the exposed site. The results show that diversity responses to changing or persistent woodland cover varied across the three dimensions of diversity and also for rare, abundant and dominant groups. These responses are not detected through conventional analyses of taxonomic richness.
4. Synthesis. Evaluating long‐term diversity patterns in an integrated framework allows direct comparison of taxonomic, functional and phylogenetic diversity patterns, and generates insights of potential relevance to ecosystem management. Across multiple dimensions, changes in diversity and composition are evident despite woodland persistence, and long‐term site‐specific ecological processes strongly influence diversity dynamics. By applying the framework to pollen data, and demonstrating that this yields insights into long‐term diversity change, our work supports broader application of this method to palaeoecological records.