Abstract: Based on the observation data of wind speed and wind direction at different heights on the observation tower (70 m) in the tropical seasonal rainforest of Xishuangbanna,this paper analyzed the annual,seasonal and diurnal characteristics of wind.The results showed that the wind speed above crown canopy was stronger than that under canopy,and the diurnal and vertical change under the canopy was not obvious.From the height of 30 m to 50 m,the vertical change of wind speed was most remarkable,but its annual change was not obvious.Above 50 m,the change trend was opposite.Dry-hot season (March-April) had the strongest wind speed,followed by rainy season (May-October) and foggy-cool season (November -next February).The wind speed at daytime was stronger than that at nighttime.At daytime,wind speed was in order of morning>afternoon>noon.Wind direction had obvious diurnal characteristics,i.e.,leaning southeast wind at daytime and leaning west wind at nighttime.At daytime,the change trend of zero-plane displacement (d) was in order of morning>noon>afternoon,and the annual change range in the afternoon was wider and lower than that in the morning and at noon.The change trend of roughness length (Z₀) at daytime was opposite to that of d.The d value in the afternoon was obviously higher than that in the morning and at noon.

Key words: photosynthesis, simultaneous gas exchange and chlorophyll fluorescence method, the curve-fitting method, instantaneous carbon isotope (¹³CO₂) discrimination method., mesophyll conductance