栽植距離對柳杉樹輪寬與氣候因子關係之影響

Abstract

樹輪寬記錄了林木的生長歷程。藉由樹木年代學(dendrochronology)的研究，可以瞭解林木與環境之間在時間與空間上的互動情況，如林木受競爭與氣候的影響等。本研究旨在探討溪頭地區之柳杉(Cryptomeria japonica)人造林，在不同起始栽植距離下，林木的氣候訊號表現有何差異。本研究比較負指數法(negative exponential curve)、Hugershoff curve法、三次平滑曲線法(cubic smoothing spline curve)等三種不同的生長趨勢移除(detrending)方法在擷取環境訊號上的差異，各趨勢移除方法皆分別建立標準年表(standard chronology)、殘差年表(residual chronology)、與自迴歸年表(ARSTAN chronology)。將以上輪寬年表與氣候因子分別以相關函數(correlation function)與反應函數(response function)分析，選用的氣候因子分別是溪頭地區的月平均最高溫(Tmax)、月平均溫(Tmean)、月平均最低溫(Tmin)、月降雨量等地域性因子，與NINO3.4指數。結果顯示：標準年表與氣候的反應較佳，三種趨勢移除方法則各有優劣。本研究中，與輪寬年表關係較好的氣候因子有：當年十月、十一月 (正相關)，前一年七月、八月(負相關) 之Tmean；當年七月、一月(負相關)，前一年七月、八月(負相關) 之Tmax；當年十、十一、十二月(正相關) 之Tmin；當年一、二月(正相關)，與前一年二月(正相關) 之降雨量。本研究也發現，林木之初始栽植距離較小者，與氣候因子間的關係較強，且林木生長前期的輪寬也與氣候因子的關係較強。由以上結果推導出，本研究區域的柳杉，在競爭作用強的環境下時，有較好的氣候訊號擷取能力。

Tree-ring widths record the growth history of trees. Dendrochronology is the study of the interactions between tree growth and environmental conditions across space and time, e.g. the influences of competition and climate. The main objective of this research is to understand the differences in climate signal expression among trees with different initial spacing in a Japanese cedars (Cryptomeria japonica) plantation in Xitou, central Taiwan. This study compared the differences of three detrending methods, namely, negative exponential curve, Hugershoff curve, and cubic smoothing spline curve, in extracting signals from tree-ring series. The standard chronology, residual chronology, and ARSTAN chronology were built for each of the three detrending methods. Correlation and response functions were calculated for the detrended tree-ring width chronologies and local monthly climatic records, which included monthly average maximum temperature (Tmax), monthly average mean temperature (Tmean), monthly average minimum temperature (Tmin), and monthly precipitation, as well as the NINO3.4 index. The results showed that the standard chronology had the best correlation and response function relationships with climate. All three detrending methods had both pros and cons. This study found that the ring width chronologies had good relationships with the following climatic factors: Current October and November (positive correlation) and previous July and August Tmean (negative correlation); current July and January, and previous July and August Tmax (negative correlation); current October, November, and December Tmin (positive correlation) and current January and February, and previous February precipitation (positive correlation). This study also found that trees with narrower initial spacing showed stronger relationships with climatic factors, and ring widths in early growth stage had better relationships with climatic factors. These results suggested that the Japanese cedars in the study area had better ability to capture the climatic signals when they are under strong competition condition.