Beech latewood density as a proxy for temperature reconstruction.

Maximum latewood density of conifers is the most widely used annual-resolution summer temperature proxy. Regions with few conifers, however, remain underrepresented in global paleoclimate records. Here, we use x-ray micro-computed tomography (micro-CT) to show that latewood density measurements of European beech (Fagus sylvatica L.) in a temperate lowland forest exhibit a strong summer (May to September) temperature signal (r = 0.73; 1833 to 2022 CE). Complementary wood anatomical analyses using deep learning segmentation reveal that both vessel and fiber anatomy are key drivers of latewood density variability and its temperature sensitivity. By integrating these anatomical responses, x-ray micro-CT-based latewood density measurements generate a robust and temporally stable summer temperature signal. Our results highlight the untapped potential of broad-leaved tree species for density-based climate reconstructions in temperate regions and open previously unidentified avenues for high-resolution paleoclimatology beyond the use of conifers.