Characteristics and trend of soil temperature in subtropical evergreen broad-leaved forests in Mt. Ailaoshan

Soil temperature is an important factor affecting plant growth and soil respiration. We analyzed the long-term data of soil temperature in the open areas and interior forests observed at the Ailaoshan Station for Subtropical Forest Ecosystem Study(ASSFE). Compared with open areas, interior forests had a lower mean soil temperature(by 2.4 ℃), a lower mean maximum soil temperature(by 13.4 ℃) and a higher minimum soil temperature(by 3.4 ℃), which implies a strong canopy shading effect on soil temperature. The difference between soil temperature inside forests and in open areas was higher in dry seasons than in wet seasons. Soil temperature increased with a stronger trend in dry seasons than in wet seasons. Soil temperature of interior forests had a stronger rising trend(0.017 ℃/year) than in open areas(0.010 ℃/year). In conclusion, soil temperature is generally rising, while the difference of soil temperature and air temperature is decreasing, and so is the soil temperature difference between open areas and interior forests. Consequently, the distribution elevation of subtropical montane evergreen broad-leaved forest will be driven upward by the trend of warming, and carbon balance and soil respiration will be inevitably disturbed as a result of rising soil temperatures.