Background

As sap flow research expands, new challenges such as fast sap flows or flows co-occurring with freeze/thaw cycles appear, which are not easily addressed with existing methods. In order to address these new challenges, sap flow methods capable of measuring bidirectional, high and slow sap flux densities (F_d, cm³ cm⁻² h⁻¹), thermal properties and stem water content with minimum sensitivity to stem temperature are required.

Purpose

In this study we assessed the performance of a new low-power ratio-based algorithm, the maximum heat ratio (MHR) method, and compare it with the widely known heat ratio (HR) method using a cut-tree study to test it under high flows using Eucalyptus grandis trees, and a freeze/thaw experiment using Acer saccharum trunks to test its response to fast changing stem temperatures that result in freeze/thaw cycles.

Results

Our results indicate that MHR and HR had a strong (R² = 0.90) linear relationship within a F_d range of 0–45 cm³ cm⁻² h⁻¹. Using the MHR algorithm, we were able to estimate wood thermal properties and water content, while extending the measuring range of HR to approximately 0–130 (cm³ cm⁻² h⁻¹). In our freeze/thaw experiment, the main discrepancy between MHR and HR was observed during freezing, where HR had consistently lower F_d (up to 10 cm³ cm⁻² h⁻¹), with respect to MHR. However, both algorithms identified similar zero flows.

Conclusion

Consequently, MHR can be an easy-to-implement alternative algorithm/method capable of handling extreme climatic conditions, which can also run simultaneously with HR.

中文翻译：

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最大热比：用于快速和慢速树液流测量的双向方法

背景

随着树液流研究的扩展，出现了新的挑战，例如快速树液流或与冷冻/解冻循环同时发生的流，这些挑战无法用现有方法轻松解决。为了应对这些新挑战，需要能够测量双向、高和慢树液通量密度（F _d，cm ³ cm ^-2  h ^-1）、热特性和茎水含量的汁液流方法，并且对茎温的敏感性最低.

目的

在这项研究中，我们评估了一种新的基于低功率比的算法，即最大热比 ( MHR ) 方法的性能，并使用割树研究将其与广为人知的热比 ( HR ) 方法进行比较，以在使用巨桉树的高流量，以及使用Acer saccharum树干的冷冻/解冻实验，以测试其对导致冷冻/解冻循环的快速变化的茎温度的响应。

结果

我们的结果表明MHR 和HR 在0-45 cm ³  cm ^-2  h ^-1 的F _d范围内具有很强的（R ² = 0.90）线性关系。使用 MHR 算法，我们能够估计木材的热性能和含水量，同时将 HR 的测量范围扩展到大约 0–130 (cm ³ cm ^-2  h ^-1 )。在我们的冻融实验中，在冷冻期间观察到 MHR 和 HR 之间的主要差异，其中 HR 始终较低的F _d（高达 10 cm ³  cm ^-2  h ^-1)，关于 MHR。然而，两种算法都识别出类似的零流量。

结论

因此，MHR 可以是一种易于实施的替代算法/方法，能够处理极端气候条件，也可以与 HR 同时运行。