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《Acta Phytoecologica Sinica》 2004-02
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FOG CHARACTERISTICS IN A TROPICAL SEASONAL RAIN FOREST IN XISHUANGBANNA, SOUTHWEST CHINA

LIU Wen_Jie 1,2 ZHANG Yi_Ping 1 LI Hong_Mei 1 and DUAN Wen_Ping 1 (1 Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China) (2 Research Center for Eco_environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China)  
Fog frequency and duration were measured between November 1998 and February 2003 in a seasonal rain forest in Xishuangbanna, Southwest China. The amount of fog and dew precipitation was measured daily using twelve bottle_funnel collectors set in a random pattern on the forest floor. Related microclimatic variables including air temperature, relative humidity, wind speed, solar radiation and rainfall were recorded by a meteorological observation system mounted on a 72 m tall meteorological tower in the study site. At night the fog occurred first at the top layer of the canopy, and then a thick fog penetrated the understory. Before fog occurred, the air temperature was greater at 0.5 m above the canopy than on the canopy surface but was lower after fog occurred. The number of fog days was much higher inside the rain forest (258 days/year) than in open areas (188 days/year). Fog frequency in the rain forest was 90% during the foggy season (November-February), slightly lower (78.7%) in the dry_hot season (March-April), and lowest (55.4%) in the rainy season (May-October). The number of fog days in each season was negatively correlated with the amount of rainfall. The onset of fog occurred on average at 2 300 and lifted at 1 100 hours during the foggy season. During the dry_hot season and rainy season, the fog occurred 0.7 and 2.3 hours later and lifted 0.8 and 2.2 hours earlier, respectively. Meanwhile, there was a negative correlation between the time of fog occurrence and lift. Average fog duration per day during the foggy season was 12.2 hours, and was 1.2 and 1.6 times longer than average fog duration of the dry_hot and rainy season, respectively. During the study period, the absolute amount of mean annual fog and dew precipitation was (89.4±13.5) mm (mean±SD), which was 4.9%±1.7% of the annual precipitation. Of the total annual amount of fog and dew precipitation, 85.9%±6.6% was collected during the foggy season and dry_hot season. The results suggest that fog, which both condenses water vapor into available precipitation in the forest and buffers temperature changes, plays an important role in the hydrology of the forest, especially during the foggy and dry_hot seasons. Therefore, horizontal precipitation (fog interception) needs to be included in calculations of the water balance in this forest. These results also demonstrate the importance of understanding the impacts of climate factors, and have important implications for ecologists and hydrologists interested in fog_inundated ecosystems.
【Fund】: 国家自然科学基金 ( 3 0 10 0 0 19);; 云南省应用基础研究基金 ( 2 0 0 1C0 0 2 3Q和 2 0 0 3C0 0 0 9Z);; 中国科学院知识创新工程重大项目(KZCX1_SW_0 1_0 1A)
【CateGory Index】: S718.5
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