Background:Forest canopies play a major role in biosphere—atmosphere interaction. Temperature is one of the principle controls over plant distribution and productivity, with large effects on physiological. We used a tropical rain forest stand located at Xishuangbanna, southwestern China (21°55′39″N, 101°15′55″E, elevation 750 m). The forest canopy tree height about 36 m. The stand has a stem densit of 964 trees ha-1(diameter ≥5cm) and a total basal area of 32.28 m² ha^-1. The forest structure at the study site can be divided into three general tree layers that are represented by different species.
Question: What are canopy leaf temperature distribution over space and time over a 36 m tall primary tropical rain forest in SW China ?
Methods: Canopy surface temperature was measured with two thermal cameras (Flir P25, accuracy ±2%, resolution 320×240 pixels, USA) mounted 3–5m above the canopies. these were rotated among sites. We scanned a defined part of the three layers with two thermal cameras from the tower from 8:00 to 19:00 (local time). Similarly exposed and sized canopy surface polygons were selected to track mean temperature. Wind speed (A100R, VECTOR, UK), air temperature and humidity (HMP45C, VAISALA, Finland), photosynthetically active radiation (LI190SB, LI-COR, USA), net radiation (CNR-1, KIPP&ZONEN, Netherlands), soil temperature (TCAV, CAMPBELL, USA) and soil moisture (CS616, CAMPBELL, USA), were all measured simultaneously. These factors were sampled in 0.5 Hz and the data were stored in the data loggers. 30 min averages were also calculated by the data loggers and stored.
Results/conclusions: The upper layer tree species Pometia tomentosa, showed the highest mean leaf temperature (31.8℃), which were 10.2℃ higher than that the lower layer tree species Mezzettipsis creaghii (21.6℃). Pometia tomentosa had the highest mean leaf to air temperature difference (⊿T_L-A) (6.4 K) followed by Barringtonia pendula (6.1 K), while Mezzettipsis creaghii had the lowest⊿T_L-A (1.9K). Our results illustrate the importance of tree species composition for the local climate. This study demonstrates mean canopy temperature can be partly explained by photo flux density.