A long-term observation on the air temperature, relative humidity, and soil temperature in a mixed forest and its adjacent open site in Changbai Mountains of Northeast China

The influence of forest on air temperature and relative humidity is the basis of forest ecological function. Aimed to approach the microclimatic effect of forest, a three-year (2005-2007) micrometeorological observation was conducted on the diurnal and seasonal changes of air temperature and relative humidity in a broadleaved-Korean pine mixed forest and its adjacent open site in Changbai Mountains, Northeast China. As compared with open site, the air temperature in the near-ground surface in the forest was lower at daytime but higher at night, with a lower diurnal difference. There was a remarkable difference in the mean monthly air temperature in the near-ground surface between the forest and open site in growth season, but no obvious difference in non-growth season. The greatest difference appeared in July, which coincided with the appearance of the maximal leaf area index of the forest. The mean annual air temperature difference was lower in the forest than in open site, with a difference up to 6.3 °C. There also existed a remarkable difference in the soil temperature between the forest and open site. Throughout the observation years, the forest had a lower soil temperature than the open site when the soil temperature was above 0 °C, but was in adverse when the soil temperature was below 0 °C, with the difference of mean monthly soil temperature at 5 cm depth between forest and open site up to 5.3 °C in January, 2005. In growth season, the relative humidity in the forest and open site had a significant difference, especially during the peak growth season July-August, with the greatest difference up to 7.0 °C in July, 2006.