Latewood density and overall ring anatomy responses to temperature in Scots pine explained by carbohydrate diffusion and cellular kinetics

Our understanding of wood formation is poor. Key anatomical properties in conifer and ring-porous tree species that have not been explained include the overall anatomy of growth rings (with consistent transitions from low-density earlywood to high density latewood), strong relationships between latewood density and temperature (used for historical temperature reconstructions), the regulation of cell size, and overall growth-temperature relationships. We have developed a theoretical framework based on observations on Pinus sylvestris L. in northern Sweden. These observed anatomical properties emerge from our framework as a consequence of interactions in time and space between the production of new cells, the dynamics of developmental zones, and the distribution of carbohydrates across the developing wood. Here we find that the diffusion of carbohydrates is critical in determining the final ring anatomy, potentially overturning current understanding of how tree growth responds to environmental variability and transforming our interpretation of tree rings as proxies of past climates.