Biophysical climate impact of forests with different age classes in mid- and high-latitude North America

Forest age structures have been reported to be substantially influenced by natural and anthropogenic disturbances worldwide. However, related biophysical feedback to climate is not well understood. This study aims to investigate the biophysical impact of changes in forest age on surface temperature and illustrate the mechanisms underlying such temperature differences. To this end, we use data from five paired evergreen needleleaf forest (ENF) eddy covariance towers in North America. Results show that older ENF is 1.7 K cooler than younger ENF at annual scale. The latent and sensible heat fluxes of older forests dominate an average cooling effect of -1.9 K, which counteracts albedo-driven warming (+2.3 K). Additional warming effect is further offset by emissivity (-1.1 K) and incoming radiation (-0.5 K). Our results confirm that considering forest age may facilitate improved forest management to local climate mitigation and adaptation in future climate change.