Phylogenomic analyses shed new light on the spatiotemporal evolution of global larches: Implications for the dynamics of boreal forests.

As the Earth warms, understanding the long-term dynamics of forest ecosystems is essential for guiding forest management and biodiversity conservation. Insights from past dynamics may provide valuable lessons for managing today's forests. Here, we investigated the spatiotemporal evolution of global larches to gain further insights into how boreal forests change over time. We first reconstructed a highly resolved and robust phylogeny of Larix covering all widely recognized species, using both transcriptome-based 1,301 orthologous genes (OGs) and plastid genomes. In sharp contrast to previous studies, an unexpected deep split between the circumboreal and Qinghai-Tibetan Plateau (QTP) larches was revealed in our study. Within each lineage, two geographically distinct clades were further resolved. Biogeographical analyses suggest that Larix might have an origin of Eocene in high-latitude uplands, and during the Miocene, all extant species have appeared. Cenozoic climate- and orogeny-triggered vicariance likely played a major role in the divergence of global larches. Our results also demonstrate that the proto-boreal forest biome may have a relatively old origin back to the early Miocene, and significant winnowing and species alteration would have occurred as the climate shifted to much colder and drier conditions during the Neogene. Ecological niche analyses show various responses of the circumboreal and QTP larches under different climate scenarios, but both lineages are negatively impacted by warming climates. These findings have important conservation implications given the sensitivity of boreal forests in the face of global warming. Our work further emphasizes the importance of a solid phylogenetic framework for evolutionary and biogeographical inferences.