The fog, especially predominant in low-lying areas during and after the thawing of frozen Arctic seas, stops sunshine from getting through to plants even during the long summer days. As evaporation is consequently low for most of the year, annual precipitation exceeds evaporation, and is sufficient to sustain the dense vegetation growth including large trees. This explains the striking difference in biomass per square metre between the Taiga and the Steppe biomes, (in warmer climates), where evapotranspiration exceeds precipitation, restricting vegetation to mostly grasses.