Individual asynchrony promotes population-level tree growth stability

Community-level stability is widely considered to increase with species richness and asynchrony. However, it is not well understood to what extent population-level stability may be regulated by population size and within-population asynchrony among individuals. Using a large set of global tree-ring data, we quantified the effects of population size and within-population tree growth asynchrony on the temporal stability of population-level tree growth rate. We also examined the relationship between the global distributions of within-population tree growth asynchrony and population-level tree growth stability. The results showed that population-level tree growth stability asymptotically increased with population size and quickly levelled off at an average population size of 26. After population size was controlled, population-level tree growth stability increased with within-population tree growth asynchrony (R² = 0.54). Globally, population-level tree growth stability was 52% higher than individual-level tree growth stability on average. This percentage varied considerably across climate zones and was highest in the Tropical zone (84%) due to its highest within-population asynchrony, while lowest in the Dry zone (34%) due to its lowest asynchrony. Synthesis. Our results indicate that individual asynchrony plays a primary role in stabilizing population-level tree growth rate, followed by population size. This finding highlights the importance of individual-level differences in alleviating environmental stresses on forest growth.