Importance of calibration in determining forest stand transpiration using the thermal dissipation method
Importance of calibration in determining forest stand transpiration using the thermal dissipation method
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DOI：
10.1016/j.agrformet.2021.108356
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发表时间：
2021-05
影响因子：
6.2
通讯作者：
N. Fujime;T. Kumagai;T. Egusa;H. Momiyama;Y. Uchiyama
中科院分区：
文献类型：
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作者：
N. Fujime;T. Kumagai;T. Egusa;H. Momiyama;Y. Uchiyama
森林蒸腾(Tr)是陆地生态系统的主要水文通量，它控制着流域水量平衡和地表能量平衡，可作为植被与大气交换效率的指标。热耗散法(TDM)用于测定单株树干的木质部液流密度(Fd)，是估算林分Tr(Tr_Stand)值最有力的工具之一。单株林木Tr值可以作为林分总边材面积(AS_STAND)和林分平均Fd(JS)的乘积来提升TOTRSTAND。本研究以日本雪松(Cryptomeria Japan onicaD.)Don)检查因错误估计AS_STAND/或JS而产生的错误INTR_STAND值。我们发现，对边材和心材中的树干水分活跃区进行简单的颜色识别，对准确估计林分的AS值几乎没有影响。然后我们考察了JS的错误估计的影响，这主要是由于Fd测量失败的结果。考虑到在以前的许多研究中已经确定了热示踪剂衍生的Fd值的不确定度，我们应用校准来提高TDM-Fd值的准确性，使用新鲜切割的日本雪松茎的边材段，并以负压作为驱动力来实验测定片段内的Fd值。校准实验表明，热示踪剂衍生的Fd值的校准转换方程得到的值与使用原始TDM方程测定的值显著不同，并且严重低估了Tr_Stand。Fd校正使−1年Tr_Stan值从229 mm增加到593 mm，而校正值与从流域尺度水量平衡观测得到的Tr_Stan值没有显著差异。新的TDM校准方程极大地改进了基于TDM的Tr标准估计，突出了本研究校准方法的重要性。
Forest transpiration (Tr) is the major hydrologic flux from terrestrial ecosystems; it dominates the catchment water budget and land surface energy balance and can be used as an index of exchange efficiency between vegetation and the atmosphere. The thermal dissipation method (TDM) is used to obtain the xylem sap flux density (Fd) of individual tree stems; it is among the most powerful tools for estimating forest standTr(Tr_stand) values. Individual treeTrvalues can be upscaled toTr_standas a product of stand total sapwood area (AS_stand) and stand meanFd(JS). In this study, we performed laboratory experiments using Japanese cedar (Cryptomeria japonicaD. Don) to examine errors inTr_standvalues generated by mis-estimation ofAS_standand/orJS. We found that simple color identification of the stem hydroactive zone in sapwood and heartwood had little effect on accurate estimation ofAS_standvalues. Then we examined the effects of mis-estimation ofJS, which is primarily the result ofFdmeasurement failures. Considering that uncertainties in heat-tracer-derivedFdvalues using the TDM have been identified in numerous previous studies, we applied calibration to improve the accuracy of TDM-Fdderivation using freshly cut sapwood segments of sample Japanese cedar stems and negative pressure as a driving force to determineFdwithin the segments experimentally. The calibration experiment revealed that the calibrated conversion equation for heat-tracer-derivedFdvalues resulted in values that differed significantly from those determined using the original TDM equation and significant underestimation ofTr_stand. TheFdcorrection increased the annualTr_standvalue from 229 to 593 mm year−1, while the corrected value was not significantly different from theTr_standvalue obtained from catchment-scale water budget observations. The novel TDM calibration equation improved TDM-basedTr_standestimates dramatically, highlighting the importance of this study's calibration method.