西双版纳热带季节雨林水热通量

Inter-annual and seasonal variations of energy and water vapour fluxes above a tropical seasonal rain forest in Xishuangbanna,SW China

利用西双版纳热带季节雨林2003和2004年常规气象、生物量以及水热通量观测资料,对该林地两年内各能量分量的数值大小和变化规律、能量分配以及水量平衡特征等进行了分析研究。结果表明,2003和2004年净辐射总量分别为3516.4MJ/(m.2a)和3516.6MJ/(m.2a)。在能量分配过程中潜热通量占优势,2003年和2004年的总量分别是相应年份净辐射总量的46%和44%,显热通量则分别只有12%和11%。2003年和2004年林冠传导率均值分别为10.3mm/s和10.0mm/s,其中干热季期间的林冠传导率明显低于雾凉季和雨季。林冠传导率与叶面积指数和空气饱和水汽压差值之间分别呈极显著的正、负线性相关关系;它基本上不受土壤含水量的影响,只是当长期无雨或雨量很小导致土壤含水量低于0.15m3/m3时,林冠传导率才与土壤含水量间存在极显著的相关关系。西双版纳热带雨林2003和2004年的蒸散量分别是663mm和634mm,受浓雾和林冠传导率的综合影响,该森林生态系统干季蒸散量低于雨季,这是西双版纳热带季节雨林能够在水热极限条件下生存并良好发育的重要原因。

The values and variation characteristics of energy components, the relation of these energy components with net radiation and the characteristics of water balance in the forest were analyzed, based on the observation data of energy fluxes, meteorological parameters and biomass in a tropical seasonal rain forest in Xishuangbanna from January 2003 to December 2004. The results showed that annual net radiation was 3516.4 MJ/（ m^2 a） and 3516.6 MJ/（ m^2 a） in 2003 and 2004, respectively, of which 46% and 44% were used in latent heat flux, 12% and 11% were lost as sensible heat flux. Annual mean canopy surface conductance was 10.3 mm/s and 10.0 mm/s in 2003 and 2004, respectively. Moreover, canopy surface conductance was lower in dry-hot season than those in fog-cool and rainy season. Canopy surface conductance correlated significantly and positively with leaf area index, but negatively with water vapour pressure deficit. In general, canopy surface conductance was not affected directly by soil water content, but highly depended on soil moisture status when soil water content was below 0.15 m^3/m^3. Annual total evapotranspiration was 663 mm and 634 mm in 2003 and 2004, respectively. Influenced by heavy fog and canopy surface conduction, the evapotranspiration of this forest ecosystem in dry season was lower than that in the rainy season, which was considered as one of the most important reasons that tropical seasonal rain forest could survive and flourish in Xishuangbanna at limit of water and heat.