Is the age of plant communities predicted by the age, stability and soil composition of the underlying landscapes? An investigation of OCBILs

Old, climatically buffered, infertile landscapes (OCBILs) have been hypothesized to harbour an elevated number of persistent plant lineages and are predicted to occur across different parts of the globe, interspersed with other types of landscapes. We tested whether the mean age of a plant community is associated with occurrence on OCBILs, as predicted by climatic stability and poor soil environments. Using digitized occurrence data for seed plants occurring in Australia (7033 species), sub-Saharan Africa (3990 species) and South America (44 482 species), regions that comprise commonly investigated OCBILs (Southwestern Australian Floristic Region, Greater Cape Floristic Region and campos rupestres), and phylogenies pruned to match the species occurrences, we tested for associations between environmental data (current climate, soil composition, elevation and climatic stability) and two novel metrics developed here that capture the age of a community (mean tip length and mean node height). Our results indicate that plant community ages are influenced by a combination of multiple environmental predictors that vary globally; we did not find statistically strong associations between the environments of OCBIL areas and community age, in contrast to the prediction for these landscapes. The Cape Floristic Region was the only OCBIL that showed a significant, although not strong, overlap with old communities.

Methods
This dataset was collected from two main sources, GBIF and iDigBio. We downloaded occurrences for all plant species within South America, Australia and Sub-Saharan Africa. The data was processed using python and R scripts available at https://github.com/biotaphy/projects/tree/master/OCBILS/code. You can also find further information, with detailed explanations about the data download and processing at https://biotaphy.github.io/projects/ocbils.