Abstract: Based on the data obtained from vertical gradient measurem ents of m icroclimatic elem ents of canopy gap in tropical secondary forest of Xishuangbanna in fog—cool and dry-hot season，the daytim e characteristics of temporal—spatial distribution and variation of trunk surface tem perature，air temperature，water vapor pressure and relative humidity in canopy gap were discussed．The data showed that gap edge had not only a rem arkable therm al effect，but also a significant water vapor effect．These effects resulted in environmental heterogeneity in canopy gap．The results provided a basis for further studying heat and water vapor transport，m icroclimatic form ation，biodiversity，and forest succession in canopy gap．

Key words: seed germination, germination rate, germination index, radicle growth, plumule growth, Artemisia halodendron.