Increasing ENSO variability synchronizes tree growth in subtropical forests

Rising El Ni & ntilde;o-Southern Oscillation (ENSO) variability is expected to influence Earth's forest ecosystems, through changes in how coordinated annual tree growth is across large spatiotemporal scales. However, the mechanisms by which changes in ENSO variability affect tree growth in subtropical forests remains poorly understood. We use a newly built tree ring network collected from 4,028 trees at 144 forest locations across East Asian subtropical forests (EASF), to assess long-term influences of ENSO on the spatiotemporal variability in tree radial growth across China at subcontinental scales (similar to 2,000 km). Our results demonstrate a west-east dipole pattern of synchronized tree growth in EASF tree populations, with positive growth responses to El Nino in southeastern China, and negative growth responses in southwestern China, likely due to different patterns in moisture limitation. Specifically, the likely contrasting effects of ENSO on drought limitation along a longitudinal gradient resulted in trees that grew more in El Ni & ntilde;o years in eastern populations, but less in western populations. Our results also show that increasingly severe El Ni & ntilde;o/La Ni & ntilde;a years have caused a sharp rise in tree growth coherence over the past 150 years in these moisture-limited populations. Increasing ENSO variability, as is expected with climate change, may potentially further destabilize subtropical forest ecosystems by synchronizing tree growth to an unprecedented level, with unknown consequences for forest stability and resilience.