Different moisture regimes during the last 150 years inferred from a tree-ring δ18O network over the transitional zone of the Asian summer monsoon

•Tree-ring δ18O network indicates an east–west clustering pattern.•Regional variability of tree-ring δ18O is regulated by hydroclimatic changes.•Different patterns of tree-ring δ18O variability represent different moisture signals.•El Niño-Southern Oscillation modulates δ18Otree variability across southern China.