Temperature Regimes of the Active Layer and Seasonally Frozen Ground under a Forest-Steppe Mosaic, Mongolia

ABSTRACT Permafrost underlying forested north‐facing slopes and seasonally frozen ground underlying mountain steppes on south‐facing slopes co‐exist within a small mountain basin that represents the most general landscape type in northern central Mongolia. A 5‐year time series of hydro‐meteorological parameters on these slopes is presented in order to identify the factors controlling ground temperature regimes. A thick organic layer (0.2–0.4 m) beneath the forest on a north‐facing slope impedes the effects of summer air temperature on the ground, and the forest canopy strongly blocks downward shortwave radiation during summer. Active layer thickness was determined by summer warmth. The mountain steppe on a dry south‐facing slope receives a large amount of downward shortwave radiation compared to an adjacent forested slope, and therefore the surface temperature exceeds air temperature during summer, leading to a warm soil profile. In winter, snow cover was the main factor controlling interannual variations in the thickness of seasonally frozen ground. The onset of soil thawing in the forested area was later than in the mountain steppe, even though soil freezing began simultaneously in both areas. Overall, the forest cover keeps the ground cool and allows permafrost to persist in this region. Copyright © 2014 John Wiley & Sons, Ltd.