Abstract: Based on the micro climate observation data from 2008 to 2009, the diurnal and seasonal variations of photosynthetically active radiation (PAR) in the near surface layer of four introduced plant sites in Xishuangbanna Tropical Botanical Garden were analyzed. All the plant sites showed obvious diurnal and seasonal variations in PAR. The highest PAR appeared in rainy season, which reached 406.6 mol·m^-2·d^-1 in open field, while the lowest one appeared in fog cool season, which was 236.0 mol·m^-2·d^-1 in open field. In the sites with tall trees, including the Rain Forest Valley, Dipterocarp Garden, and Arboretum, the PAR was relatively lower. with the effects of solar elevation angle and canopy gap, there was a “jump up” for the PAR in rainy season. Spatially, the PAR appeared to be higher in the sites with  tall trees. Tempora
lly, rainy season had a higher PAR than other seasons. The PAR in the sites with tall trees and large shelters was less than 10% of that in open field, and the PAR ratio was only 1.6% in the Rain Forest Valley compared with the open field in fog cool season, which was the lowest among all the sites. However, this ratio reached 98.7% in dry  hot season in the Tropical Fruits Garden, which had little shading. Generally, the temporal and spatial heterogeneities of PAR existed in different plant sites, which could definitely affect the rhythm of the introduced plant species in Xishuangbanna Tropical Botanical Garden.

Key words: Forest landscape, Landscape changes, Landscape characteristics