Combining taxonomic, functional and phylogenetic diversity metrics to explain spatiotemporal variation in mountaintop flora

Abstract

Questions Accounting for multiple facets of biodiversity can help to shed light on community assembly of mountaintop flora across space and time, but this approach has rarely been applied. Here we addressed the following questions: (a) Is the filtering effect of elevation on taxonomic diversity of mountaintop plant communities also mirrored in their functional and phylogenetic structure? (b) Can environmental changes over time interact with, and thus change, elevational patterns in mountaintop plant diversity? Location Dovrefjell, central Norway Methods The floristic composition of four mountaintops, spread across an elevational gradient from tree line to the uppermost margins of vascular plant life, was surveyed every seven years between 2001–2022. Six metrics of taxonomic, functional and phylogenetic richness and diversity were calculated for each mountaintop and survey. With these data, we assessed how richness and diversity metrics varied over space (across the elevational gradient) and over time (between surveys). Results All richness and diversity metrics decreased towards higher elevations, except phylogenetic diversity which showed a marked increase with elevation. Taxonomic richness did not change significantly over time, while functional and phylogenetic richness increased between 2001–2022. No significant temporal trend in taxonomic, functional and phylogenetic diversity was detected. Conclusions Different metrics of taxonomic, functional and phylogenetic diversity can show divergent spatial and temporal trends. Future environmental changes may give rise to functionally or phylogenetically novel communities that cannot be predicted from trends in species richness alone. We therefore encourage researchers to look beyond species richness and consider multiple facets of biodiversity when analysing the impact of environmental change on mountaintop flora.