政府2002年起造林政策的推行，使許多廢棄的耕地與農田轉變為造林地。其中，位於花蓮縣光復鄉的大農大富平地森林，周圍有許多以務農為主的聚落，是一個與人類社會為鄰的森林。平地森林造林後，對原有以農業為主的區域水文收支有何影響，是一個在學術與實務上的重要問題。本研究於2020年6月1日至2020年12月17日，以大農大富平地森林3種常見的闊葉樹—樟樹、光臘樹及台灣櫸共15棵樣樹為對象，測量樣樹的樹液流，以初步探討樹木的蒸散作用及其控制因子。樹液流的研究是使用Granier所提出的熱消散法，以本研究自製的樹液流熱消散系統，包括探針感應器與Arduino資料紀錄器，進行六個月的連續量測。

研究結果顯示，樟樹、光臘樹與台灣櫸的樹液流速分別介於0-216、0-344和0-139 cm3 m-2 s-1，且樹液流速與樹種及胸高直徑不具相關性。樹液流速與環境因子的迴歸分析結果顯示，樹液流速與大氣溫度、淨輻射量、飽和水蒸氣壓差與風速呈正相關；樹液流速與相對溼度則呈負相關。進一步的冗餘分析（Redundancy Analysis）結果則顯示，樹液流速的主要環境控制因子依序為飽和水蒸氣壓差、淨輻射量和相對溼度。

本研究以Penman-Monteith 估算潛勢蒸發散量（Potential evapotranspiration，PET），並與實際量測的樹液流速進行比較。結果顯示樟樹與光臘樹的樹液流速隨著PET上升而線性上升，台灣櫸的樹液流速則在達到一個PET閥值後趨緩上升。此結果暗示著，樟樹及光臘樹較台灣櫸能承受更高的水分散失逆境。
樹液流速的晝夜變化具遲滯現象，亦即在相同的環境條件下，上午的樹液流速與下午的樹液流速具有差異。樹液流速與VPD及大氣溫度為順時鐘遲滯軌跡，即上午的樹液流速高於下午的樹液流速；樹液流速與淨輻射量為逆時鐘遲滯軌跡，即下午的樹液流速高於上午的樹液流速。而以能綜合代表環境蒸發需求的PET與樹液流速進行遲滯分析，結果則為逆時鐘遲滯軌跡，說明樹液流速的遲滯現象不僅受環境因子，也受非環境因子影響。藉由計算遲滯軌跡內的面積，量化每日遲滯現象的程度，結果顯示6月至12月的遲滯現象程度減緩，且樹木的每日最大樹液流速與遲滯現象程度皆具正相關，其中以光臘樹的相關係數最高。

本研究量測的樹液流速範圍，是介於先前文獻所量測的數值範圍內。然而，本研究的樹液流速計算公式，皆是使用Granier提出的經驗公式，尚未進行樹種間的樹液流速公式校正。近年許多研究指出，Granier公式並不適用於某些樹種，因此此部分為本研究的量測不確定性，若可以進一步的進行公式校正，是有助於本研究獲得更準確的樹液流速資料。依據本研究的PET分析結果，顯示3個樹種的樹液流速反應具有差異，然而本研究無法驗證，樹液流速與非環境因子之間的關係。若能再進一步的量測樹種間的氣孔導度、木質部的導水率、水勢及樹幹的儲存水能力，將有助於釐清此差異。

The implementation of the government's afforestation policy in 2002 has turned many abandoned farmlands into plantations. Among them, Da-Nong-Da-Fu Plain Forest in Hualien County, Guangfu Township, is surrounded by many agricultural settlements. To what extent the hydrological system of the agricultural landscape will be influenced by the afforestation, remains an important scientific and practical question. In this study, sapflow of three common broadleaved tree species, Cinnamomum camphor, Zelkova serrata and Fraxinus griffithii, were investigated from June 1st to December 17th, 2020 for understanding transpiration and its controlling mechanisms in the Da-Nong-Da-Fu Plain Forest. Self-made heat dissipation sapflow measurement systems were employed, which consist of probes based on Granier's original design, and an Arduino-based controlling and logging system.

The results showed that, the sapflow rate of Cinnamomum camphora, Zelkova serrata and Fraxinus griffithii were between 0-216、0-344 and 0-139 cm3 m-2 s-1, respectively. The sapflow rate was not correlated with tree species and tree's breast height diameter. Sapflow rate was positively correlated with air temperature, net radiation, vapour pressure deficit, and wind speed; and was negatively correlated with relative humidity. Results of redundancy analysis further showed that the main controlling factors for sapflow rate were vapour pressure deficit, net radiation, and relative humidity.

The sapflow rate was analyzed against the potential evapotranspiration (PET) calculated by Penman-Monteith equation. The results showed that the sapflow rate of Cinnamomum camphora and Zelkova serrata increased linearly with the increase of PET, while the sapflow rate of Fraxinus griffithii only slowly increased after reaching a PET threshold. This result suggests that, Cinnamomum camphora and Zelkova serrata might overcome higher water stress than Fraxinus griffithii.

Hysteresis in the diurnal variation of sapflow rate, indicating that under the same environmental conditions, the sapflow rate in the morning is different from that in the afternoon. The sapflow rate and the VPD, air temperature displayed clockwise hysteresis loops, that is, the sapflow rate in the morning was higher than that in the afternoon.On the contrary, the sap flow rate and the net radiation displayed anti-clockwise hysteresis loops, that is, the sapflow rate in the afternoon was higher than that in the morning. Hysteresis analysis of sapflow rate against PET showed anti-clockwise hysteresis loops. As PET approximately represents the abiotic driving forces of transpiration, the hysteresis between sapflow rate and PET indicates a significant biological control in transpiration. By calculating the area within hysteresis loops, the extent of daily hysteresis was quantified. The results showed that the degree of hysteresis was decreasing from June to December, and the daily maximum sapflow rate was positively correlated with the degree of hysteresis, in which Zelkova serrata owned the highest correlation coefficient.

The sapflow rates measured in this study were within the ranges in the literature. However, the calculation of sapflow rate from the two-needle temperature difference was from the Granier's formula, which has recently been proven for incorrect for several tree species.This represents a potential measurement uncertainty of this study. The calibration of Granier's formula would be necessary for the local tree species. According to the different reaction patterns of sapflow rate to PET, a further investigation on the biological control of transpiration would be important. The hydraulic characteristics of tree species like the stomatal conductance, xylem hydraulic conductivity, water potential, and water storage capacity of tree trunks, could be focused on in the further research.

1. 前言 1
1.1 蒸散作用的重要性 2
1.2 蒸散作用的影響因子 4
1.3 蒸散作用的量測—樹液流速法 7
1.4 研究動機與目的 9

2.材料與方法 11
2.1 樹液流熱消散系統 11
2.1.1 探針感應器的製作 12
2.1.2 資料紀錄器（datalogger）的製作 16
2.1.3 樹液流熱消散系統的架設流程 20
2.1.4 樹液流熱消散系統的故障問題 22
2.1.5 樹液流熱消散系統的量測成果—樹液流速之計算 22
2.2 研究樣區 25
2.2.1 樣區介紹 25
2.2.2 氣象及環境因子 27
2.3 樣樹的基本資料 28
2.4 樹液流速的資料分析 30
2.4.1 樹液流速的數據處理 30
2.4.2 資料分析 32

3. 結果 33
3.1 15棵樣樹的樹液流速資料 33
3.2 15棵樣樹的樹液流速與樹種、胸高直徑的關係 35
3.3 樹液流速與環境因子的關係 38
3.4 樹液流速與潛勢蒸發散量的關係 44
3.5 樹液流速與環境因子的遲滯現象 46

4. 討論 53
4.1 熱消散法的限制與誤差 53
4.2 15樣樹的樹液流速與樹種、胸高直徑的關係 54
4.3 樹液流速的遲滯現象 57

5. 結論 61

6. 參考文獻 63

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