The comparison of long-term flux measurements from BOREAS against the surface fluxes in the global reanalysis from NCEP/NCAR and ECMWF show the large climate impact of the surface forcing from the boreal forests. In spring, frozen soils coupled with low evaporation and the low albedo of the coniferous forest lead to deep boundary layers. In summer evaporation is subject to stomatal control, and variations in evaporation are controlled not by soil moisture variations (as over grassland) but by the water content of the surface moss layer. The global forecast models need to be upgraded to represent realistically the seasonal cycle of these physical processes.