Frequent locally absent rings indicate increased threats of extreme droughts to semi-arid Pinus tabuliformis forests in North China

•Locally absent rings can be the proxy to locate tipping points of forest systems.•Pinus tabuliformis suffered increasing locally absent rings since 2000s.•The highest locally absent ring frequency was at the driest distribution margin.•Loally absent ring frequency increased along with tree age and moisture deficit.•Locally absent ring risk would gradually increase in the future.