Novel insights into post-glacial vegetation change: functional and phylogenetic diversity in pollen records

QuestionHow do pollen-based functional and phylogenetic diversity help to explain post-glacial vegetation change in relation to climate and human influence? LocationEstonia and Latvia, NE Europe. MethodsWe used a data set of 1062 pollen samples from 20 sites covering the last 14500yrs to estimate plant richness, evenness, functional and phylogenetic diversity (community-weighted mean and mean pair-wise distance). We adjusted existing functional and phylogenetic diversity measures for the pollen data and tested the methods with a simulation study. The simulations showed that species-based and pollen-based diversity estimates were all significantly positively correlated. ResultsThe Late Glacial (14500-11650cal. yr BP) and the mid-Holocene (8000-4000cal. yr BP) periods showed contrasting values for most of the diversity components, and several diversity estimates were strongly associated with climate. The cold climate during the Late Glacial led to high phylogenetic diversity, and relatively low functional diversity. Climate warming during the transition from the Late Glacial to the Holocene was followed by a decrease in phylogenetic diversity but an increase in functional diversity based on plant height and seed weight. Increasing human impact in the late Holocene was associated with an increase in plant richness and decreases in functional diversity based on plant height and seed weight and in phylogenetic diversity of herbs. ConclusionsPollen-based functional and phylogenetic diversity provide novel insights into post-glacial vegetation change and its drivers. Both functional and phylogenetic diversity were closely related to climatic conditions, suggesting that trait differences play an important role in long-term community response to climate change. Our results indicate that human impact during the last two millennia has influenced functional and phylogenetic diversity negatively by suppressing plants with certain traits (functional convergence) and giving advantage to plants from certain phylogenetic lineages. We see great potential in the further development of functional and phylogenetic diversity methods for pollen data