Barbour M M, Hunt J E, Walcroft A S, Rogers G N D, McSeveny T M, Whitehead D
Landcare Research, PO Box 69, Lincoln, New Zealand.
New Phytol. 2005 Feb;165(2):549-58. doi: 10.1111/j.1469-8137.2004.01257.x.
Here we develop and test a method to scale sap velocity measurements from individual trees to canopy transpiration (E(c)) in a low-productivity, old-growth rainforest dominated by the conifer Dacrydium cupressinum. Further, E(c) as a component of the ecosystem water balance is quantified in relation to forest floor evaporation rates and measurements of ecosystem evaporation using eddy covariance (E(eco)) in conditions when the canopy was dry and partly wet. Thermal dissipation probes were used to measure sap velocity of individual trees, and scaled to transpiration at the canopy level by dividing trees into classes based on sapwood density and canopy position (sheltered or exposed). When compared with ecosystem eddy covariance measurements, E(c) accounted for 51% of E(eco) on dry days, and 22% of E(eco) on wet days. Low transpiration rates, and significant contributions to E(eco) from wet canopy evaporation and understorey transpiration (35%) and forest floor evaporation (25%), were attributable to the unique characteristics of the forest: in particular, high rainfall, low leaf area index, low stomatal conductance and low productivity associated with severe nutrient limitation.
在此，我们开发并测试了一种方法，用于将针叶树扁柏主导的低生产力老龄热带雨林中个体树木的液流速度测量值扩展至冠层蒸腾量（E(c)）。此外，在冠层干燥和部分湿润的条件下，将E(c)作为生态系统水平衡的一个组成部分，结合林地蒸发速率以及使用涡度协方差法测量的生态系统蒸发量（E(eco)）进行了量化。利用热消散探针测量个体树木的液流速度，并根据边材密度和冠层位置（遮蔽或暴露）将树木分类，从而将其扩展至冠层水平的蒸腾量。与生态系统涡度协方差测量值相比，干燥日E(c)占E(eco)的51%，湿润日占22%。低蒸腾速率以及冠层湿润蒸发和林下蒸腾（35%）与林地蒸发（25%）对E(eco)的显著贡献，归因于该森林的独特特征：特别是高降雨量、低叶面积指数、低气孔导度以及与严重养分限制相关的低生产力。
