High-latitude vegetation can experience much higher surface temperatures (Tsurf, at radiative equilibrium) than the ambient air temperature (Tair). In snow-free seasons, Tsurf is closely linked to plant physiological and biochemical processes. We drove the dynamic ecosystem model LPJ-GUESS with reanalysis data ERA5-land Tsurf and 2-m Tair to understand regional responses to these two temperatures. We show that plant growth in the tundra is stimulated by warmer Tsurf in the summer months, but in the boreal forests, colder Tsurf in the non-summer months constrains leaf development and enzyme activity for the growing season. Tsurf drives higher primary productivity of tundra plant individuals, but in the boreal forests, productivity is co-influenced by less productive individuals and compensatory changes in vegetation structure (coverage and density). This study demonstrates the importance of forcing temperature in simulating high-latitude ecosystem processes and calls for using correct plant-experienced temperatures to reduce uncertainties in estimating responses and feedback to the climate.