Biogeography and evolutionary patterns of temperate deciduous forests in the Northern Hemisphere

Temperate deciduous forests of North America, west Eurasia, and east Eurasia share a common origin but were later separated by major geographic barriers. Here, we examine their diverging biodiversity and evolutionary patterns by analyzing floristic richness, phylogenetic turnover, and community evolutionary distinctiveness (CED). We analyzed ~ 9600 vegetation plots across the Northern Hemisphere to calculate species rarefaction curves, within- and between-region phylogenetic turnover, and CED to assess the presence of evolutionarily isolated lineages within communities. We then modeled CED as a function of present-day and last glacial maximum (LGM) macro-environmental factors using boosted regression trees (BRTs). East Eurasian forests had the highest floristic richness, especially among woody species, while west Eurasia featured the richest herbaceous component. Within-region phylogenetic turnover was lowest in east Eurasia, followed by North America and west Eurasia. Between-region phylogenetic turnover was highest between west Eurasia and east Eurasia, and lowest for North America–east Eurasia. North America ranked highest in CED, followed by east Eurasia and west Eurasia. The BRTs revealed contrasting effects of the current and LGM climate on CED across regions. Present precipitation seasonality had a striking negative impact on CED in east Eurasia, whereas temperature seasonality had a strong negative effect in west Eurasia. East Eurasia’s exceptional woody, gymnosperm, and fern diversity may reflect the region’s long-term climatic and geological stability, which has allowed the persistence and diversification of ancient lineages. Meanwhile, the pronounced evolutionary distinctiveness of North American forests may be linked to more intense climatic and tectonic shifts over both Quaternary and deeper timescales. These findings highlight the unique evolutionary legacies of the temperate deciduous biome and call for future research that expands geographic and climatic coverage to capture the full diversity of temperate deciduous forests worldwide.