Variation in Tree Growth Increases With Global Warming

Global warming is raising both climate and weather variability. However, how this tendency may destabilise forest ecosystems is poorly understood. Using a set of global tree-ring data, we calculated the 5-year variance and mean of tree growth rate over 1401-2010, and modelled the variance-mean relationship. We found that the global averaged variance increased much faster than the mean in the past century (+40.0% vs. +8.5%), and closely covaried with the accelerated global warming since the 1970s (r = 0.93). The exponent of tree-level variance-mean power law was higher in wetter habitats and less drought-resistant species, and has increased significantly under global warming, indicating an environment- and trait-dependent growth-safety tradeoff and a decreasing resistance to a warmer climate. Our study shows that global warming may have strongly destabilised tree growth and made forest dynamics less predictable, adding to the growing concern that global warming is jeopardising the functioning of forest ecosystems.