The Duality of Reforestation Impacts on Surface and Air Temperature

Evidence is mounting that temperate‐zone reforestation cools surface temperature ( T surf ), mitigating deleterious effects of climate warming. While T surf drives many biophysical processes, air temperature ( T a ) is an equally important target for climate mitigation and adaptation. Whether reductions in T surf translate to reductions in T a remains complex, fraught by several nonlinear and intertwined processes. In particular, forest canopy structure strongly affects near‐surface temperature gradients, complicating cross‐site comparison. Here the influence of reforestation on T a is assessed by targeting temperature metrics that are less sensitive to local canopy effects. Specifically, we consider the aerodynamic temperature ( T aero ), estimated using a novel procedure that does not rely on the assumptions of Monin‐Obukhov similarity theory, as well as the extrapolated temperature into the surface layer ( T extrap ). The approach is tested with flux tower data from a grass field, pine plantation, and mature hardwood stand co‐located in the Duke Forest (North Carolina, USA). During growing season daytime periods, T surf is 4–6 °C cooler, and T aero and near‐surface T extrap are 2–3 °C cooler, in the forests relative to the grassland. During the dormant season, daytime differences are smaller but still substantial. At night, differences in T aero are small, and near‐surface T extrap is warmer over forests than grasslands during the growing season (by 0.5 to 1 °C). Finally, the influence of land cover on T extrap at the interface between the surface and mixed layer is small. Overall, reforestation appears to provide a meaningful opportunity for adaption to warmer daytime T a in the southeastern United States, especially during the growing season.