Phylogenetic diversity and clustering in modern vegetation communities reflects habitat formation and age during the late Cenozoic in New Zealand

Abstract Phylogenetic diversity analyses were used to interpret the timing and assembly of vegetation communities in temperate New Zealand. A data set comprising 1638 permanent vegetation plots provided plant-distributional data, and a plastid rbcL phylogenetic tree provided phylogenetic metrics. Mean crown age, standardized effect size of mean pairwise distance and standardized effect size of mean nearest taxon distance were analysed in relation to taxonomic groups (angiosperms, gymnosperms and pteridophytes), life form (woody angiosperms, non-woody angiosperms) and temperature and precipitation using generalized additive models. Angiosperms in South Island have a younger crown age than those in most North Island sites, and phylogenetic clustering is prevalent throughout. Angiosperms and pteridophytes from drier and cooler open-habitat communities in central and eastern South Island have younger crown ages and phylogenetic clustering compared to wetter and warmer closed-habitat communities of western South Island and North Island, with older crown ages and phylogenetic over-dispersion. Phylogenetic clustering is consistent with species-rich radiations that have diversified into newly available niches during the late Miocene to Plio-Pleistocene. Pteridophytes displayed less phylogenetic relatedness than angiosperms, reflecting their older crown ages. These findings are consistent with a view that northern New Zealand retained older lineages of subtropical origin during glaciations, whereas novel habitats in cool, dry climates in southern New Zealand facilitated more recent radiations. These results emphasize the strong legacy of history in the modern-day composition of plant communities.