臺灣中部武陵地區臺灣二葉松樹輪年內密度變化之季節氣候訊號

Abstract

在山區生態系統中，季節性乾濕變異對植物生長產生顯著影響。樹輪學提供了高時間解析度的氣候替代資料，其中樹輪年內密度變化 (Intra-annual Density Fluctuation，IADF) 被認為能敏感記錄生長季中的氣候變化。本研究以臺灣中部武陵地區的臺灣二葉松 (Pinus taiwanensis) 為對象，將IADF區分為四種類型，包含IADF-E、IADF-E+、IADF-L及IADF-L+，探討其與乾旱指標之關聯性，以評估IADF作為過往季節性氣候訊號指標的可行性。 本研究共挑選出45根樹芯樣本，建立樹輪寬度及密度資料，記錄並計算IADF穩定化出現頻率 (Stabilized frequency，Fstab)。使用環山與臺中氣象站氣候資料並計算SPI與SPEI指標，再以CRU TS 4.08、GPCC及CSIC SPEI等網格資料分析場域相關性。結果顯示：(1) 臺灣二葉松樹輪密度對最低氣溫最為敏感，樹輪寬度則無明顯相關性；(2) IADF-E的生成與春季短期乾旱有關；IADF-E+與春季至夏季長時段濕潤條件呈正相關；IADF-L則在夏季持續乾旱、秋季突降雨時最易形成；(3) 場域分析再次證實IADF-E+及IADF-L與上述氣候變化的關係，並指出IADF-E+可能對中國華南至臺灣初夏水氣路徑具高靈敏度。 綜合而言，本研究證實臺灣中部地區之臺灣二葉松IADF與季節性乾旱變異的關聯性，指出IADF能作為解析季節尺度乾濕變異的高時間解析度替代資訊。未來可擴展樣本區域，改善IADF判斷的準確度，並結合其他氣候資料，以提升對季節性氣候事件歷史重建的準確性，為森林資源管理與氣候適應策略提供科學依據。

The seasonal alternation between wet and dry conditions has a marked influence on plant growth in mountain ecosystems. Dendrochronology offers high-temporal-resolution climate proxy data, and intra-annual density fluctuations (IADF) within tree rings are regarded as sensitive recorders of climatic variation during the growing season. Focusing on Taiwan red pine (Pinus taiwanensis) in the Wuling area of central Taiwan, this study classified IADF into four types: IADF-E, IADF-E+, IADF-L, and IADF-L+. It examined the relationships between these types and drought indices to evaluate the feasibility of using IADF as indicators of seasonal climate signals. This study analyzed 45 increment cores, constructing ring width and density datasets, recording IADF values, and then calculated the stabilized frequency (Fstab) of each IADF type. Climate data from the Huanshan and Taichung meteorological stations were employed to derive SPI and SPEI; field correlations were further explored with gridded products such as CRU TS4.08, GPCC, and CSIC SPEI. The results revealed that (1) ring density in P. taiwanensis was highly sensitive to monthly mean of daily minimum temperature, whereas ring width showed no clear climatic relationship; (2) formation of IADF-E was linked to short-term spring drought; IADF-E+ was positively associated with prolonged wet conditions from spring to summer; IADF-L formed most readily when persistent summer drought was followed by abrupt autumn rainfall; and (3) spatial analyses confirmed the connections between IADF-E+/IADF-L and the climate patterns, indicating that IADF-E+ was particularly sensitive to summer moisture transport from South China to Taiwan. In summary, this study substantiates the strong association between IADF in P. taiwanensis and seasonal drought variability in central Taiwan, demonstrating that IADF constitutes a high-resolution proxy for deciphering hydro-climatic fluctuations at the seasonal scale. Future work that expands the sampling area, refines IADF identification, and integrates additional climate data will enhance the accuracy of historical reconstructions of seasonal climate events, supporting forest-resource management and climate-adaptation strategies.