Forest buffers soil temperature and postpones soil thaw as indicated by a three-year large-scale soil temperature monitoring in the forest-steppe ecotone in Inner Asia

Increases in soil temperature affect both soil biotic process and the soil hydrological cycle in the mid and high latitudes of the Northern Hemisphere. Using a three-year automatic record of soil temperature in paired forest and steppe plots along a temperature gradient from northern China to southern Siberia in Russia, collected from 2008–2011, we investigated how vegetation cover has impacted soil temperature at a regional scale, with focus on soil freezing/thawing timing. We found that there was a buffering effect of forests on soil temperature, as indicated by cooler soil temperatures in the warm season and warmer soil temperatures in the cold season. Forest soil thawed about 15 days later than steppe soil at the same site. At a regional scale, the onset date of soil freezing showed significant positive correlation with cold season soil temperature in both forest and steppe. The onset date of soil thawing was significantly negatively correlated with cold season mean daily soil temperature (DST) in the steppe, but showed no significant correlation in the forest. In terms of space-for-time-substitution, it could be implied that forest might face an increased likelihood of drought by impeding snowmelt infiltration, under the present warming trend in soil temperature.