Quantification of uncertainties introduced by data-processing procedures of sap flow measurements using the cut-tree method on a large mature tree

Motivation: Sap flow sensors are crucial instruments to understand
whole-tree water use. The lack of direct calibration of the available
methods on large trees and the application of several data-processing
procedures may jeopardize our understanding of water uptake dynamics by
increasing the uncertainties around sensor-based estimates. We directly
compared the heat ratio method (HRM) sap flow measurements to water uptake
measured gravimetrically using the cut-tree method on a large mature aspen
tree to quantify those uncertainties for ten consecutive days. Dataset: In
this dataset, we provide sap flux density (ten-minutes intervals;
g.cm-2.hr-1; corrected for wounding and sapwood thermal diffusivity)
obtained from four HRM sap flow sensors installed at 2.5 m high on the
focus tree (20 m tall, 60 years old trembling aspen in the boreal
mixedwood region of Alberta) between July 18th and August 22nd 2017. We
present the code and data (weather data from neighboring weather station)
used to calculate whole-tree sap flux (L.hr-1) from each of the individual
sensors using different methods of radial integration of sap flux density
across the sapwood area estimated via different calculations, as well as
different zero-flow corrections used. The cut-tree procedure was applied
to the focus tree, and gravimetric measurements of water uptake
(ten-minutes intervals) were made using a recording scale. We directly
compared the different estimates of hourly, daily and cumulative sap flows
obtained with gravimetric measurement of water uptake. We present the code
providing the statistical analysis and results reported in the associated
publication (Merlin, M., Solarik, K.A., Landhäusser, S.M. Quantification
of uncertainties introduced by data-processing procedures of sap flow
measurements using the cut-tree method on a large mature tree. 2020.
Agricultural and Forest Meteorology,
http://dx.doi.org/10.1016/j.agrformet.2020.107926)

研究背景：树液流量传感器（sap flow sensors）是解析整树水分利用过程的关键仪器。当前现有树液流量测量方法缺乏针对大径级成熟树木的直接校准，且多种数据处理流程的应用会增大基于传感器的估算结果的不确定性，进而干扰学界对树木水分吸收动态的认知。为此，本研究针对一株成熟大径级颤杨，采用伐树称重法（cut-tree method）直接测定其水分吸收量，并与热比率法（Heat Ratio Method, HRM）的树液流量测量结果开展对比实验，以量化上述不确定性，实验连续开展十日。
数据集说明：本数据集包含2017年7月18日至8月22日期间，安装在加拿大阿尔伯塔省北方混交林区一株高20米、树龄60年的成熟颤杨树干2.5米高度处的4台热比率法树液流量传感器所采集的树液通量密度（sap flux density）数据，数据时间间隔为10分钟，单位为g·cm⁻²·hr⁻¹，已针对伤口损伤与边材热扩散率（sapwood thermal diffusivity）完成校正。
本数据集同时提供了配套代码与辅助数据（含邻近气象站的气象观测数据），可用于将单台传感器的树液通量密度（sap flux density），通过不同径向积分方法（基于不同边材面积计算方式）以及不同零流量校正（zero-flow corrections）方案，换算为整树树液通量（whole-tree sap flux）（单位为L·hr⁻¹）。
研究过程中对目标树木实施了伐树处理，并通过记录式称重秤以10分钟间隔获取了水分吸收量的重量测定数据。本研究直接对比了通过重量法测得的水分吸收量，与不同处理方法得到的小时、日及累积树液流量估算结果。
本数据集还附带了用于统计分析的代码，以及发表于相关学术期刊的分析结果：Merlin, M., Solarik, K.A., Landhäusser, S.M. 量化采用伐树称重法对大径级成熟树木树液流量测量数据进行处理时引入的不确定性. 2020, 《农业与森林气象学》, http://dx.doi.org/10.1016/j.agrformet.2020.107926