Composition, diversity, structure and function of modern plant communities are strongly related to the current environment, but they may also depend on past eco-evolutionary dynamics. For example, climate change can exert a strong influence on lineage diversification and niche evolution, and thus have long-lasting effects on species pools and local assemblages. Integrating such long-term dynamics with short-term ecological processes in a common analytical framework is a major challenge of integrative biodiversity science. Phylogenetically informed diversity measures and palaeo-environmental models are important elements in this framework. Here, we integrate both types of data in order to explore the determinants of forest tree diversity using the conifers as a model group. Conifers are an old, diverse (ca. 650 spp. in 6 families) and widespread group of woody plants of high ecological and economic importance. They are better studied than most other globally distributed groups of forest trees, allowing integrative studies with high phylogenetic and spatial resolution. We analyse phylogenetic diversity, assemblage structure, and diversification rates for regional conifer assemblages throughout the natural range of the group (269 TDWG3 “botanical countries”) to infer the effects of current and past climate . To explore the effects of taxonomic and spatial scale, we deconstruct the overall pattern into families and perform a fine-scale analysis for one particular lineage (the genus Pinus, 111 spp.). In particular, we address the hypothesis that long-term palaeo-climatic stability has a major effect on forest tree assemblages, requiring us to interpret and analyse the diversity and function of modern forest ecosystems on much larger timescales than is usually done. Together, those analyses will allow an integrated view of the ecological and evolutionary processes underlying the diversity and structure of conifer assemblages worldwide .