Non-summer hydrothermal conditions controlling tree growth in north subtropical China are closely related to AMO and PDO

Key messagePhase transitions of the AMO and PDO promote shifts in non-summer hydrothermal conditions, which further affect tree growth in north subtropical China.AbstractBased on tree-ring samples collected from Shiyan, Hubei Province, a region with superior hydrothermal conditions during summer, we produced a 188-year standardized tree-ring width (STD) chronology, and calculated the accumulated anomalies of the STD chronology (STDA) to obtain more significant, low-frequency periodic signals. The response analysis showed that the restrictive effect of climate on tree growth was mainly manifested through the positive influence of non-summer (previous September to current May) precipitation and the negative influence of the maximum temperature during the previous autumn and winter (September-December). Moisture conditions in the current April-May were particularly critical for early tree growth. The different growth stages represented in the STD chronology indicated that a wet-cold non-summer climate was more conducive to rapid tree growth. Power spectrum analysis results indicated that hydrothermal variations in this area may be influenced by the El Nino-Southern Oscillation (ENSO) and sunspot activity at high frequencies and by Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO) at low frequencies. Further analyses yielded that phase transitions of AMO and PDO promoted shifts in non-summer hydrothermal conditions, which further drove tree growth in the study area. At the same time, the partial correlation results emphasized that AMO mainly regulated precipitation variability, whereas PDO had a more pronounced effect on temperature variability. These insights will improve future decisions related to tree growth to cope with climate forcings based on regional hydrothermal evolution.