THE 1920S DROUGHT RECORDED BY TREE RINGS AND ...

412 ERYUAN LIANG ET AL.Figure 2. Correlation coefficients between eight new tree-ring width chronologies with monthlyprecipitation and monthly mean temperature at nearby meteorological stations (Table III). Blackcircles indicate positive correlations and empty circles indicate negative correlations. The shadingrepresents the data significance at the p < 0.05 level. The circle size shows the strength of correlation,in which the smallest circle denotes r ≤ 0.15 and the largest circle denotes r ≥ 0.50 with the intervalof 0.05. For calibrating periods see Table I.therefore, precipitation in the previous August–September and May–June of thegrowth year has a significant correlation to tree growth. In those years when theclimate was extremely dry, such as 1928 and 1929, cambial activity was so inhibitedthat a locally absent ring occurred. Several studies in the semi-arid and arid areasof northern China all revealed that precipitation in the early growing season inMay and June and soil water storage prior to tree growth is critical for tree growth(Liang et al., 2001; Liu and Ma, 1999; Zhang et al., 2003; Shao et al., 2005).A negative correlation between tree growth and temperature is also indicative ofmoisture limitation on tree growth in the study area (Liang et al., 2001; Shaoet al., 2005). The analysis suggests that these tree-ring chronologies are sensitiveto precipitation and are thus excellent records of past moisture variation. Togetherwith the published tree-ring chronologies, the tree-ring network described in thisstudy is an important resource for examining large-scale drought events in northernChina.2.5. CORRELATIONS AMONG THE TREE-RING CHRONOLOGIESMultiple analyses revealed the similarity in magnitude and trend of ring-widthvariation between the chronologies within the same regions (Figures 3 and 4). In