Ring-width-index of five west african tree species, Aguima Catchment, Benin

Core samples were taken from a total of 191 trees with an increment borer (Suunto, Finland) with an inner diameter of 5 mm at the measured diameter at breast height (DBH = 130 cm height) from two perpendicular directions. In addition from each species at least one stem disc was taken. The samples were dried and transported to the dendrochronological laboratory of the University of Göttingen, Germany. Core samples were polished together with the stem discs consecutively with sandpaper up to a grain of 600 µm. Ring widths were measured with a digital measuring device (LINTAB, Rinntech, Heidelberg, Germany) to the nearest 0.01 mm. Individual tree-ring series were cross-dated visually and statistically and combined to a mean curve (chronology). Measures for the statistical cross-dating were the Student's T-value (Baillie and Pilcher, 1973) and the percentage of parallel run (p.p.r.) indicating the year-to-year agreement in the oscillation of two curves within the overlapping interval (Schweingruber, 1988, Fichtler et al., 2004). Tree-ring statistics were performed with the computer program TSAP (Time Series Analysis and Presentation, Rinntech, Heidelberg, Germany). This program also transforms raw ring curves into index curves by removing long-term growth trends using a 5-year moving average. The residuals of this procedure are normally distributed, which is a basic condition for the correlation with climate data (Cook and Briffa, 1990). […]

本研究采用内径为5mm的生长锥（increment borer，芬兰Suunto公司），在191株树木的胸径（Diameter at Breast Height, DBH，即高度130cm处的树干直径）位置，从两个垂直方向钻取树芯样本。此外，每一个树种至少采集一份茎盘样本。所有样本经干燥处理后，运送至德国哥廷根大学树木年代学（dendrochronology）实验室。将树芯样本与茎盘样本依次使用砂纸打磨，直至粒度达到600微米（µm）。使用产自德国海德堡Rinntech公司的LINTAB数字测量仪测定年轮宽度，测量精度可达0.01mm。对单株树木的年轮序列分别开展目视与统计交叉定年，并整合为平均曲线（年表，chronology）。统计交叉定年采用的指标包括Student's T值（Baillie与Pilcher，1973）以及平行百分率（percentage of parallel run, p.p.r.），该指标可反映重叠区间内两条曲线振荡的逐年吻合程度（Schweingruber，1988；Fichtler等，2004）。年轮统计分析使用德国海德堡Rinntech公司开发的TSAP软件（Time Series Analysis and Presentation，时间序列分析与展示）完成。该软件还可通过5年移动平均法去除长期生长趋势，将原始年轮曲线转换为指数曲线。此流程得到的残差符合正态分布，这是与气候数据开展相关性分析的基础条件（Cook与Briffa，1990）。[…]