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The phylogenetic structure of global conifer diversity and conifer richness hotspots

Abstract

Conifers play an important role in ecosystems around the world, particularly in Northern Hemisphere forests, and they have received considerable attention in conservation biology, biogeography, and evolutionary biology. The wealth of phylogenetic, ecological, and geographic data available for conifers makes them an ideal group to investigate a variety of macroevolutionary and macroecological processes, and here we use them to understand how regions of high species richness may form. We use a richly sampled conifer phylogeny (90% of the 615 living species species) combined with geographic range data for every conifer species to quantify the phylogenetic structure of conifer floras around the world. Our results suggest that hotspots of high species richness are consistently found in mountainous areas, but their exact phylogenetic structure varies immensely in relation to regional phylogenetic structure and climate. Hotspots in drier areas consist primarily of young species, while those in wetter or milder climates often harbor more deep-branching and relictutal lineages. Regardless of climate, some hotspots appear to simply represent accumulations of broadly occurring species, while others harbor active diversification and contain a high proportion of endemic species. Overall, conifers show the diverse ways in which high species richness assemblages may form, and our results also highlight the importance of mild, wet, and stable habitats for the preservation of woody plant lineages through time.