1 Physical Geography, 2012, 33, 5, pp. 1–XX. http://dx.doi.org/10.2747/0272-3646.33.5.1 Copyright © 2012 by Bellwether Publishing, Ltd. All rights reserved. TOPOGRAPHY-CONTROLLED SOIL WATER CONTENT AND THE COEXISTENCE OF FOREST AND STEPPE IN NORTHERN CHINA Hongyan Liu 1 Laboratory for Earth Surface Processes, Ministry of Education, and College of Urban and Environmental Sciences Peking University, Beijing, 100871 China Siyuan He Laboratory for Earth Surface Processes Peking University Beijing, 100871 China Oleg A. Anenkhonov Institute of General and Experimental Biology Russian Academy of Sciences, Siberian Branch Ulan-Ude 670047, Russia Guozheng Hu Laboratory for Earth Surface Processes Peking University Beijing, 100871 China Denis V. Sandanov and Nathalia K. Badmaeva Institute of General and Experimental Biology Russian Academy of Sciences, Siberian Branch Ulan-Ude 670047, Russia Abstract: The semi-arid forest-steppe ecotone in China is characterized by a patchy pat- tern of forest and steppe, with forest patches restricted to shady slopes. To address the effect of topography on forest distribution through regulation of available water, we calculated evaporation as a function of slope aspect and inclination. Field vegetation records from randomly selected sites with minimum slope inclination were used to test the simulated forest distribution. Seasonal and diurnal changes of surface soil temperature and mois- ture of shady and sunny slopes were recorded. Soil water content was measured during two growing seasons on both sunny and shady slopes with the same forest type at three sites located along the mean annual precipitation (MAP) gradient. Evaporation decreases with slope inclination on shady slopes, but increases with inclination on sunny slopes. The shady slope received 35% of the annual direct solar radiation received by the sunny slope when the slope inclination was 25°, and the contrast in annual direct solar radiation between the shady and sunny slopes further widens as slope inclination increases. Steeper shady slopes can support forests in dryer climates, with log-linear regression revealing a 1 Corresponding author; email: lhy@urban.pku.edu.cn [Authors: Please check that author afiliations have been indicated correctly in the new format]