Temporal and spatial distribution characteristics of thermal effects in a tropical seasonal rainforest in Xishuangbanna, southwest of China.

Based on observation data in the fog-cool and dry-hot seasons, the temporal and spatial distribution characteristics of air temperature and trunk surface temperature of tropical seasonal rainforest in Xishuangbanna were studied. It is found that air temperature and trunk surface temperature present obviously temporal and spatial differences influenced by local climate, forest structure and solar radiation variation in different sites and time. The trunk surface temperature, air temperature and daily air temperature difference all reach maximum near the forest canopy, which shows that the forest canopy possesses stronger thermal effect; moreover, it is significant in dry-hot season. Around the canopy, the directions of thermal transfer between the air and forest canopy surface are opposite in fog-cool and dry-hot season from 12:00 to 16:00. In fog-cool season, the air temperature is lower than canopy surface temperature, which makes heat transfer from canopy surface to air; while it is quite the contrary in the dry-hot season. The air temperature is almost higher in the morning and afternoon, but lower around the noon than canopy surface temperature at the height of the second canopy in the forest; moreover, the absolute values of temperature difference are bigger in the dry-hot season than those in the fog-cool season; near ground, the heat is often transferred from the canopy to the surrounding air, which indicates that temporal and spatial variability characteristics of heat transfer. There often exhibits phenomenon of trunk surface temperature and air temperature inversion in the tropical seasonal rain forest. The trunk surface is a hot source in the morning, while at noon the air turns to a hot source and there keeps heat equilibrium between the trunk surface and the air in the afternoon. Thermal effect of tropical seasonal rain forest is so complicated and multiform that makes thermal effect distribution diversification and induces microclimatic environment heterogeneity.