溪頭孟宗竹林之竹桿年齡對蒸散量的影響

Effect of culm age on transpiration in a Moso bamboo forest, Xitou, Taiwan

林松駿(Song-Jun Lin)

指導教授 ： 久米朋宣

國立臺灣大學/生物資源暨農學院/森林環境暨資源學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201610179

摘要

近年來，竹林有迅速擴張並且取代原有林分的狀況，此情形可能造成當地植被蒸發散的改變進而對當地水文循環產生影響，但是竹林的蒸散特性到目前還沒被明確的瞭解。跟木本植物人工林相比，竹林具有年齡結構以及胸高直徑分布每年改變的特殊性，但沒有任何研究討論竹桿的老化如何影響竹子的蒸散。為了瞭解年齡結構對於林分規模蒸散量的影響，竹桿年齡對於竹子蒸散的影響為重要的研究環節之一。為了明確的瞭解竹桿年齡對於竹林蒸散量的影響，本研究在台灣大學溪頭實驗林進行孟宗竹林樹液流測量，總共選定34根竹子作為樹液流測量樣本，並且將竹子分為五個齡級 (2014年生、2013年生、2012年生、2012年以前生較年輕、2012年以前生較老)。本研究目的有以下四點：(1)呈現孟宗竹林四年間的林分結構以及胸高直徑分布的變化，(2)探討竹桿年齡及樹液流的關係，(3)推估每個齡級竹子的蒸散量以及對於林分總蒸散量的貢獻，(4)探討林分結構對於林分蒸散推估的影響。
研究結果顯示孟宗竹林連續四年的林分結構以及胸高直徑分布的變化，同時結果也顯示，在較老齡級的竹桿，樹液流明顯較其他年輕齡級的竹桿來的低，此外，在最年輕的齡級，竹子樹液流出現高峰值的時間較其他齡級來的早。在蒸散量推估的部分，林分年蒸散量推估大約300 (mm/year)，各年齡組蒸散量占總林分蒸散量的比例分別為，「2014年生」17.9%、「2013年生」24.3%、「2012年生」11.4%、「2012年以前生較年輕」38.1%以及「2012年以前生較老」8.4%。由於最老齡級竹桿的最慢的樹液流速，最老齡級的竹子也呈現了最低的林分蒸散貢獻量即使該組竹子仍在樣區內佔有可觀的數量。此外，我們也嘗試在林分蒸散量的推估中比較考慮年齡結構與否的差異，發現到如果我們不考慮年齡結構，林分蒸散量的推估質可能高估或低估。總體而言，本研究顯示，竹桿的老化會明顯影響竹子的樹液流流速，以及在基於樹液流測量的研究中，考慮竹林年齡結構是了解林分規模蒸散量不可或缺的一環。

關鍵字

樹液流 ； 蒸散 ； 竹桿年齡 ； 孟宗竹 ； 年齡結構 ； 胸高直徑分布

並列摘要

Bamboo forests have been expanding by replacing surrounding ecosystem recently, and the expansions of bamboo forests could alter local water cycling due to significantly large transpiration in bamboo forests. But the characteristics of bamboo forests are still not clearly understood. Although bamboo forests have different stand structure characteristics such as year-to-year variations in culm age structure from those of woody plantation, no studies have examined how the culm aging can affect bamboo transpiration. For better understanding stand-scale transpiration in bamboo forests, the research of the influence of culm age on transpiration is needed. To clarify the culm age effect on transpiration in bamboo forests, this study conducted sap flux measurements in a Moso bamboo forest in National Taiwan University (NTU) forest. Sap flux measurements were performed in total 34 individuals, which were separated into five age classes (ie, born 2014, born 2013, born 2012, before 2012 newer, and before 2012 older). This study aimed (1) to show the variations of the age structure and DBH distribution of the Moso bamboo forest for four years, (2) to quantify relationship between culm age and individual sap flux, (3) to estimate the stand transpiration and contribution of each age class transpiration to total stand transpiration and (4) to find the impact of age structure on the stand-scale transpiration estimates.
In this study, the distribution of DBH and age structure showed considerable year-to-year variations in the four years. As well, the results showed that culm age effected on the sap flux, that is, sap flux in older culms were significantly lower than that of younger age culms and the new culms showed earlier peak time than older culms. In the part of transpiration estimate, the annual transpiration of the study site is around 300 (mm/year) during July 2014 to June 2015 , and the contribution of each age class to total stand transpiration was 17.9%, 24.3%, 11.4%, 38.1%, and 8.4% for born 2014, born 2013, born 2012, before 2012 newer, and before 2012 older, respectively. Because of the lowest sap flux in the before 2012 older, the oldest group’s bamboos showed the lowest contribution in the study site despise the considerable occupation of culm number in the oldest group. Moreover, this study tested stand transpiration estimates with and without considering culm age structure. Consequently, the transpiration estimates in bamboo forests maybe under- or over-estimated if we do not consider the age structure. Overall, this study concluded that culm aging significantly affected bamboo transpiration and that consideration of culm age structure is needed to understand stand transpiration based on sap flux measurements.

並列關鍵字

sap flux ； transpiration ； culm age ； Moso bamboo ； age structure ； DBH distribution

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