Biophysical Impacts of Deforestation in Different Forest Types on Seasonal Warming in Northern Midlatitudes

The biophysical effects of forests on climate and climate change have been extensively studied by using climate models and satellite data at the global scale. However, the climatic effects of forests vary with specific forest types and locations, and the sign and magnitude of temperature responses resulting from biophysical impacts of temperate forests remain uncertain. In this study, we utilized site-based flux tower observations from the FLUXNET2015 and AmeriFlux datasets in North America and Europe, as well as a decomposed temperature metric, to investigate how distinct forest types influence seasonal changes in surface temperature (T_s). The results indicate that deciduous broadleaf forest (DBF) generally exhibits higher albedo than evergreen needleleaf forest (ENF) except in winter, while ENF is characterized by greater surface roughness and Bowen ratio. Although the larger albedo difference contributes more to T_s reduction at ENF sites than that at DBF sites, the dominant drivers of T_s changes are associated with surface turbulent fluxes, and these mechanisms vary with forest types and seasons. Specifically, deforestation at ENF sites leads to a consistent warming effect throughout the year due to reduced sensible heat flux. In contrast, at DBF sites, the warming effect from decreased sensible heat is partially offset by increased latent heat flux in winter and spring, whereas the warming effect of reduced latent heat flux becomes more pronounced in other seasons. These findings suggest that surface turbulent fluxes are the primary biophysical drivers of local T_s changes, and different forest types play a critical role in modulating seasonal energy exchange processes and temperature responses in the northern midlatitudes. Overall, our study provides insights on the mechanisms of how different temperate forest types influence seasonal T_s changes.