宜蘭縣棲蘭山區台灣扁柏近50年偽輪的氣候意義初探

Abstract

樹輪氣候學研究，除了可以樹輪寬度與密度了解古氣候外，樹木異常結構－偽輪 (false ring)亦可反映氣候異常事件或森林生態受干擾。 本研究以中、高海拔台灣扁柏 (Chamaecyparis obtusa var. formosana) 易有偽輪的特性，瞭解棲蘭山地區的氣候變化。透過軟X射線方法量測8棵12根樹芯樹輪寬度與密度，經由交互定年得到樹輪參數年表及每年偽輪出現的比例。 由5種參數年表：全輪寬度、早材寬度、晚材寬度、最小密度及最大密度，經與氣候因子相關分析，大致顯示樹輪寬度對於溫度反應佳，樹輪密度對於降雨量敏感。偽輪位置出現於早材生長期間的比例多於出現於晚材。偽輪位於早材的年份氣候常呈現5月異常高溫、多雨或7月異常高溫。而偽輪出現在晚材位置的年份，10月多呈現異常低溫。台灣扁柏出現偽輪的年份，7-8月颱風侵襲較其它月份高。初步研究結果表示，台灣扁柏偽輪可作為重建古氣候上的有用參數。

The width and density of tree-ring is not only affect by climate, but the pathological structure, such as false ring, also reflect the change of climate. Ring growth and the presence of false rings were studied in Chamaecyparis obtusa var. formosana growing in the Mt. Chilan area. Five tree-ring parameters, including total ring width (RW), earlywood width (EW), latewood width (LW), maximum density (MaxD), minimum density (minD), were obtained by soft x-ray image-analysis method. The five tree ring chronologies and false ring proportion from 1960 to 2009 A.D. have been established by soft x-ray image-analysis method, cross dating and ARSTAN program. The correlations between the above five parameters and climate data from Ilan station indicate monthly mean temperature is more sensitive to tree-ring width than monthly precipitation. Most false rings were found in the earlywood. The year of coourence of false ring contrast to climate data of April-October at the same year, the results show: (1) The appearances of false ring in the earlywood are relative to the anomaly of high temperature or precipitation in May, or an abnormal high temperature in July. (2) The false rings in the latewood appear under an abnormal low temperature in October. (3) The false rings are most likely related to the typhoon events of July and August. Overall, false ring is an unique feature in tree ring and can be applied successfully in dendroclimatic studies.